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Chief Editor: Prof. Dr. H. Parlar Institut für Lebensmitteltechnologie und Analytische Chemie TU München - 85350 Freising-Weihenstephan, Germany e-mail: [email protected]
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Prof. Dr. A. Görg Fachgebiet Proteomik TU München - 85350 Freising-Weihenstephan, Germany Prof. Dr. A. Piccolo Università di Napoli “Frederico II”, Dipto. Di Scienze Chimico-Agrarie Via Università 100, 80055 Portici (Napoli), Italy Prof. Dr. G. Schüürmann UFZ-Umweltforschungszentrum, Sektion Chemische Ökotoxikologie Leipzig-Halle GmbH, Permoserstr.15, 04318 Leipzig, Germany Environmental Chemistry:
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TSUNAMIS AMONG THE NATURAL DISASTERS Chris Tzanis, Katerina Theodorakopoulou, Panagiotis Theodorakopoulos and Costas Varotsos ORIGINAL PAPERS
CONTRIBUTION OF CARBONACEOUS AND IONIC COMPONENTS OF PM2.5 AEROSOLS IN THE URBAN AREA OF ATHENS Alexandra Bolbou, Heidi Bauer, Maria Ochsenkühn-Petropulu and Hans Puxbaum SHEAR STRENGTH MEASUREMENT OF MINERAL FILTER CAKES Birgul Benli, Ozgul Taspinar and Perviz Sayan
THE DIATOMS Odontella sinensis, Coscinodiscus wailesii AND Thalassiosira punctigera IN THE EUROPEAN ATLANTIC: RECENT INTRODUCTIONS OR OVERLOOKED IN THE PAST? Fernando Gómez and Sami Souissi
IMPACT OF IRRIGATION WITH UNCONVENTIONAL WATERS ON THE SOIL-PLANT SYSTEM: SOME EXPERIENCES WITH SUNFLOWER Marco Antonio Russo, Adalgisa Belligno and Vito Sardo TREATMENT OF DYE AQUEOUS SOLUTIONS USING A NOVEL AROMATIC POLYAMIDE ASYMMETRIC NANOFILTRATION MEMBRANE Xiaojing Ren, Tao Wang, Changwei Zhao, Songshan Du, Zhaokun Luan, Jun Wang and Deyin Hou AQUEOUS CADMIUM ION REMOVAL BY FUNCTIONALIZED SBA-15 MATERIALS Aijun Gu, Zhongchun Li, Zhaolian Ye and Li Jiang ASSESSMENT OF FLUOROQUINOLONES TOXICITY WITH APPLICATION TO Lemna minor Microbiotest Justyna Kolasińska, Magdalena Bielińska and Grzegorz Nałęcz-Jawecki MAMMALIAN SEX HORMONES INFLUENCE GERMINATION VELOCITY AND ENZYME ACTIVITIES IN GERMINATING MAIZE SEEDS Serkan Erdal, Rahmi Dumlupinar, Turgay Cakmak and Mucip Genisel
USING MULTIPLE REGRESSION ADSORPTION MODELS TO ESTIMATE Zn AND Cu ADSORPTIONS ONTO Fe OXIDES, Mn OXIDES, ORGANIC MATERIALS AND THEIR BLENDS IN SURFICIAL SEDIMENTS Shanshan Li, Qian Gao, Xiaoli Wang and Yu Li
SEASONAL REGIME SHIFT OF AN ALTERNATIVE-STATE LAKE XINGYUN, CHINA Yingcai Wang, Zhicong Wang, Weiju Wu, Mingming Hu, Zhen Wang, Aihua Xu, Genbao Li and Yongding Liu DEGRADATION OF 4-CHLOROPHENOL BY MODIFIED NATURAL ZEOLITES Stanislava Pavlíková, František Šeršeň, Karol Jesenák and Gabriel Čík THE EFFECTS OF HABITAT TYPE AND DIURNAL HARVEST ON ESSENTIAL OIL YIELD AND COMPOSITION OF Lavandula angustifolia Mill. Christos N. Hassiotis, Diamanto M. Lazari and Konstantinos E. Vlachonasios POSSIBLE TOXICITY AND TOLERANCE PATTERNS TOWARDS POST-EMERGENCE HERBICIDES IN MAIZE INBRED LINES Vesna Dragičević, Milena Simić, Lidija Stefanović and Slobodanka Sredojević PUMICE ADDITION EFFECT ON AVAILABLE WATER CAPACITIES OF SOILS Özcan Mehmet, Özhan Süleyman and Gökbulak Ferhat
RESPONSE OF YOUNG Brassica juncea PLANTS TO CADMIUM AND SELENIUM TREATMENT Matúš Peško, Katarína Kráľová and Elena Masarovičová NOTE
LEGISLATIVE FRAMEWORK OF INTEGRATED WATER RESOURCE MANAGEMENT IN TURKEY Aynur Aydın Coşkun
Chris Tzanis1*, Katerina Theodorakopoulou2, Panagiotis Theodorakopoulos3 and Costas Varotsos1
1 Climate Research Group, Division of Environmental Physics and Meteorology, Faculty of Physics, University of Athens, Panepistimiopolis Build. Phys. 5, 15784, Athens, Greece
2 Department of Geography, Harokopeio University of Athens, 17671, Athens, Greece 3 Department of Medicine, Laboratory of Social Medicine, University of Thrace, 68100, Alexandroupolis, Greece
ABSTRACT
The 26 December 2004, Sumatra-Andaman earthquake of magnitude 9.0 on the Richter scale triggered a massive tsunami in the Indian Ocean, which led to a widespread catastrophe. A comparison of tsunamis with the diverse kinds of natural and man-made disasters that are of utmost importance is herewith explored to show the necessity for the development and implementation of a special satellite monitoring of disasters, and especially tsunamis, under the general program of environmental monitoring. The adverse impacts of tsunamis to the public health are also examined.
KEYWORDS: Tsunami, natural disasters, environmental monitor-ing, health impacts
INTRODUCTION
Environmental catastrophes are conventionally defined as extreme, disastrous situations in the vital and economic activity of the population, caused by substantial unfavora-ble changes in the environment [1]. They can be provoked by human-made causes, by dangerous natural phenomena (e.g. tsunamis), and due to complex interrelated human- and nature-induced factors (e.g. the case of desertification). Tsunamis are practically water waves or seismic sea waves caused by large-scale sudden movement of the sea floor due to earthquakes, landslides, volcanic eruptions or man-made explosions. They usually have a period of 200–2000 s and a speed of 150–250 m/s in the open ocean with wavelengths up to 500 km [2]. As an example, the 26 December 2004 Sumatra-Andaman earthquake of Mw 9.0 triggered a mas-sive tsunami that devastated coastal areas throughout the Indian Ocean.
Disasters are theoretically defined as spasmodic changes in a system, which appear in the form of the system’s sudden response to gradual changes of the external conditions [1]. There are diverse kinds of natural disasters that are of ut-most importance, such as: earthquakes and tsunamis, floods, forest and grassland fires, tropical cyclones, drought, land slides, snow storms, ozone and climate changes, desertifi-
cation and deforestation, oil spills, etc [3-8]. According to the World Disasters Report, published by the International Federation of Red Cross and Red Crescent Societies (IFRC) in 2004, up to 300 million people were affected by natural disasters, conflicts, or a combination of both [9].
The kinds of disasters are generally singled out as the geophysical disasters (e.g. earthquakes, tsunamis, volcanic eruptions, mudflows, landslides and landslips, the climatic disasters (e.g. droughts, storms, tornadoes, severe frosts or heat periods), the hydrological disasters (e.g. river floods, fast seashore inundations, slow but large-scale variations of levels of lakes, inland seas), the biological disasters (e.g. bursts of various pests, epidemic outbreaks among humans or other living organisms), the anthropogenic disasters (e.g. the pollution of various natural media, deforestation, deser-tification, soil erosion and salination, fires) (e.g. [10]).
It is hardly possible to separate distinctly one kind of environmental disasters from another because some of them are of mixed origin (e.g. [11]).
For instance, tsunamis are simultaneously a geologi-cal (by the origin) and hydrological (regarding its conse-quences) phenomenon. Tsunamis differ from other earth-quake hazards since they can cause serious damage thou-sands of kilometers away from the causative faults. The earthquake of the West Coast on Northern Sumatra (meas-ured 9.0 on the Richter Scale) set off a series of other earth-quakes lasting 12 hours on the 26th of December (from 00:58 to 11:05 UTC), 2004 and led to a widespread catas-trophe, particularly in Sri Lanka, India, Maldives, Indone-sia and Thailand with damage also in Malaysia, Bangla-desh, Somalia and Seychelles.
Another example is the desertification, which may be caused by climatic, man-made or mixed activities [7]. Also, deforestation, which may lead to a local biological disas-ter, is human-induced. Finally, fires are more and more often caused not by natural phenomena but by human activi-ty, or are of mixed origin.
The main objective of this paper is to examine the re-cent tsunami event from the point of view of its disastrous impacts in comparison with other severe natural or man- made disasters occurred in the historical past. Additionally,
the significant role of remote sensing to natural disasters is pointed out, predicating its use as necessary mean for the prevention and adjustment of hazardous situations hence natural catastrophes.
GEOGRAPHICAL DISTRIBUTION OF DISASTER CONSEQUENCES
From the viewpoint of socio-economic consequences, the statistics on the calamities for individual states is of great importance. The list of countries having larger quan-tities of victims (2,000 persons and more) of a single disas-ter during the period 1968-1992 (from the IFRC for 1994) is most-revealing (Table 1):
TABLE 1 - Number of victims of a single disaster during the period 1968-1992 [1].
Ethiopia 48,465 Nicaragua 4,619 Bangladesh 40,536 Burundi 4,237 Cameroon 40,011 Peru 4,163 Somalia 21,697 Iran 3,315 Sudan 16,197 Columbia 2,970 China 12,682 Iraq 2,918 Mozambique 11,778 Lebanon 2,579 India 4,888 Philippines 2,131
The list in Table 1 comprises those states, which are
located in regions that are most often subjected to disas-ters. However, a number of countries, the situation of which is dangerous from the standpoint of potential natural calami-ties, have not been included in the list. Among these, there is Japan affected by earthquakes, tsunamis, tropical cyclones, volcanic eruptions, and the USA that are often subjected to earthquakes, river floods, tropical cyclones in the western, central and eastern parts of the country, respectively. These are two rich countries, which invest a lot of money into the monitoring of disasters and minimization of their conse-quences.
TSUNAMI-INDUCED DISASTERS IN THE HISTORY OF CIVILIZATION
Natural disasters and mankind
A retrospect to the historical past convinces that natu-ral disasters were the cause of many human calamities. Earthquakes and inundations, droughts and fires, and other unfavorable natural phenomena affected the man of the past to even more extent than at present, since the mankind was less experienced in foreseeing and had lower technical support for protection against disasters.
Natural disasters, which resulted in human death, the destruction (complete or partial) of settlements and cities, made agricultural activities difficult. Along with other causes, they could contribute to the destruction of whole cities, and even states. Forecasting, establishing the role of natural phenomena in producing unfavorable for people
natural situations, which would prevent or hamper their vital activity, is of undutiful interest for the present time as well.
This paper examines only some disasters - those which caused highest damage to man. Two large groups can be distinguished among these phenomena, which differ in their manifestation time period: short-term (occurring quickly) and long-term (extended in time).
Volcanic eruptions
Volcanic eruptions are related to one of the most de-structive types of natural disasters [12, 13]. The areas of volcanic activity have, since long ago, attracted people due to their rich soils, which are formed on volcanic rocks thrown out during eruptions. This is why there are generally lots of settlements on the lands surrounding volcanoes, and even cities appeared around many of them. The slopes of volcanic mountains have been used for a long time as farm-ing lands.
Lots of settlements and cities situated at the feet or in the environs of volcanoes were subjected to destructive effect of volcanic eruptions. Some of them were swept away by fire lava, and other were buried under the layer of ash, pumice, or lava. Thus, some cities disappeared from the earth, and new original volcanic landscapes appeared in-stead. People forgot with time about the location of buried settlements. The nature did its own work: the sun, wind and water changed the landscape appearance and it seemed as if it existed eternally.
Numerous legends, the epic poems of different people of the world say about the destructive force of oldest vol-canic eruptions, which was experienced by many ancient inhabitants of the planet.
The scientific geological and archaeological evidence on the history of volcanic eruption effect on people is still insufficient. For example, undoubtedly, the discovery which was made by the staff of the Department of Ancient History at the Cologne University is of great interest. While making archaeological investigations in the Rhine River basin on the FRG territory, they discovered early for this area hu-man settlements approximately 11,000 years old and buried under lava [14]. This was the time of the end of the last glaciation in Europe. The glacier had already receded to the north of Europe when a volcano erupted in the area of lake Laakherzee in the Neuwieder Hollow, where first tribes appeared. The lava layer spread over the Hollow and reached the depth of 15 m. The ash traces of this eruption (probably, rather intensive) have also been found on the territory of the present Poland. The information on the vol-cano eruption at the Rhine River and on its effect upon the Europe population is very little, which fact is not surpris-ing since it took place about 11,000 years ago.
Natural disasters of similar size, which occurred much later, in the civilized world, were erased from the memory of people. Thus, even in densely populated Italy, the loca-tion of two earlier well-known cities - Pompeii and Hercu-laneum was forgotten for a long time. In 79 A.D., an inten-
sive eruption of Vesuvius Volcano (to be more exact, its predecessor - Somma Volcano) took place in the vicinity of which the two cities were located. It lasted for quite a short period of time - not more than 48 hours. Both Pom-peii and Herculaneum disappeared. They were buried: Pom-peii under the layer of ash and pumice, and Herculaneum under the layer of dirt. Over 1,600 years passed, and only in the late 30ies in the XVIII century, Herculaneum was found as a result of excavations, lying under almost a 20-m layer of sediments. Pompeii was found later on. They have not been yet excavated completely, but even the work done has opened slightly the curtain of terrible tragedy experi-enced by these cities. The inhabitants of the Vesuvius envi-rons seem not to have guessed that this mountain was a volcano. It did not erupt until 79 A.D. according to the memoirs of Romans and Etruscans. Now, they would be a signal of the threatening disaster, but at that time, this fact escaped the attention of people. Devastations around Vesu-vius took place in the district having the radius up to 18 km on the area above 310 km2.
In other regions of the planet, volcanic eruptions cov-ered more extended areas, and the chief thing is that they were more destructive for the population of the surround-ing area. This particularly concerns some regions in Cen-tral America in which there are located individual volca-noes and the accumulations of active volcanoes. It is well-known that volcano eruptions disturbed the everyday life of ancient inhabitants of Central America. These tragic events were reflected in the legends of American Indians and in the fine art. The causes of the fall of the Central Ameri-ca ancient civilizations have not yet been completely found out, though volcanic eruptions could be one of them.
One of the best-known accumulations of Chalguapa archaeological monuments is situated in Salvador Repub-lic. Here, in the Rio Pas River, the remains of one of the major city-states of the ancient Maya were found. The exca-vations discovered lots of temples, original stepped pyra-mids and other constructions hidden under a thin soil layer covered partially by vegetation. It is noteworthy that ash and pumice were present everywhere in the sediments. They were thrown out during the Ilopango volcano eruption lo-cated 75 km far from the city of Chalguapa. The pumice layer of 2 m in depth was found around the volcano in the radius of up to 50 km. Ash was scattered over a longer distance: almost 80 km far from the volcano. Near the volcano, the depth of ash layers reached tens of meters. Two ash layers, 20 m and 50 m in depth, have been found at a distance from it. The emissions of glowing noxious gases, hot ash and tuff burned out everything around the volcano. For example, there were burned out forests and bushes, all settlements, and the city. The total area of burnt out land is estimated to be 3,000 km2. This is approxi-mately 10 times larger than that around Vesuvius after its eruption in 79 A.D.
Unlike the environs of Vesuvius, the layer of volcanic sediments around Ilopango volcano was not so deep since there were no powerful flows of dirt and lava here, though
the disaster was of larger scale and more destructive on the whole. It is not surprising that a vast territory became deserted. Judging by layers, the volcano eruption took place in three stages. Therefore, those who did not die, had enough time to escape. According to archaeological data, a considerable population income was observed, at that time, to the districts located northward of Chalguapa. As approx. estimated, the population could be 30,000 in the eruption area. The district became deserted afterwards for several hundreds of years - until the early V century A.D. [1].
The most destructive eruption for the population of ancient Maya, inhabiting in former times the territory of the present state Salvador, occurred in 260 century A.D. As a result, the city of Tseren perished, which was situated at a distance of 25 km to the northwest of Ilopango volca-no. Two volcanic eruptions can be distinguished among other large-scale volcanic eruptions, which took place in the subsequent time. One of them is related to 600 A.D., and the other to about 900-1000 A.D. The American archaeolo-gist P. Sheets [15] assumed that the aforementioned vol-cano eruptions had an effect on the development of Maya state in this region.
A powerful volcanic eruption, probably involved the downfall of the so-called Minoan period on Crete Island in the Mediterranean Sea, though at first sight, this state-ment might seem to be paradoxical, since neither active nor extinct volcanoes are present on the Island. Various hy-potheses explained this event by effects of tsunamis, earth-quakes or climatic changes that were caused by the vol-canic eruption of the Santorini volcano [16]. Volcanic ash beds as primary deposits of the Minoan eruption of the Santorini volcano between 1650-1450 B.C. were traced throughout the Aegean islands, in drill cores from the Mediterranean and the Black Seas, and in Anatolia [17]. In the 30-es of the XX century, the Greek archaeologist S. Marinatos [18, 19] expressed the hypothesis that the state on Crete was destroyed in 1500 XVI B.C. as a result of the eruption of Santorini volcano on Thera Island, which is much smaller in size than Crete and located at a distance of 120 km to the northeast of Crete. Depositions of vol-canic ash and pumice layers found during the excavations on Crete (mainly in Central and Eastern Crete, from Knosos to Zakros area) helped to prove this hypothesis. At the archaeological site of Amnissos on Crete, Marina-tos [18] found the floors of Minoan ruins to be covered by a thick layer of seaborne pumice from Thera, and he hy-pothesized that a destructive tsunami caused by the Thera eruption invaded the Aegean Sea coast of Crete. Earlier, Sir Arthur Evans [20] had suggested that Cretan palaces were abandoned due to repeated earthquake activity.
After these theories were proposed, both geologists and archaeologists started collecting evidence, and many scien-tists brought in question the correlation between the fall of the Minoan civilization with the volcanic eruption of Thera Island [21, 22].
Firstly, there is a big problem concerning the dating of the volcanic eruption. According to the technological-stylistic evolution of the ceramic shreds found in the pre-historic, buried by volcanic ash, site of Akrotiri in Thera Island, the volcanic eruption is dated around 1500 B.C. Nev-ertheless, radiocarbon dating attempted on organic materials from Akrotiri, corresponded to the calendar-year interval 1630-1530 B.C. [23, 24]. Radiocarbon data derived from carefully selected organic material from Late Minoan 1A and 1B contexts, suggested that the eruption of Thera/ Santorini most likely occurred in c. 1650-1620 B.C. [25]. Recently, radiocarbon dating performed on an olive tree buried alive in life position by the tephra in the island, constrained the eruption date to the range 1627-1600 B.C. with 95.4% probability [26].
Moreover, Hammer et al. [27] detected a high annual average H+ concentration in the acidity profile of the entire Dye 3 ice core of the South Greenland, and they concluded that the high acidity signature comes from the Thera erup-tion. They estimated the most accurate date to be 1645 ± 20 B.C., whereas studies from tree-rings records in the United States (American bristlecone pine), correlated the Thera eruption with a 1628-1626 B.C. frost-ring event [28, 29].
There is also evidence from many archaeological sites in Crete (Zakros, Amnissos, Nirou Chani, Pseira etc) that pumice and ash depositions were found in earlier layers than the phase of destruction of these sites, and most of the abandoned and destroyed sites in Crete had traces of fire [30]. So, many archaeologists correlated the decline of the Minoan state with some socio-economic changes, invasions of Mycenaeans, climatic changes occurred after the erup-tion, earthquake activity, or/and the combination of all the above-mentioned parameters. More evidence is needed in order to determine the exact reason of this fall.
The reliability of such an event allows us to believe in the reality of events, which were the basis of the myth of Atlantis, which is well-known in the Mediterranean Sea area, in Ancient Greece. Marinatos [19] related this mythi-cal catastrophe of Atlantis to the possibility of large-scale volcano eruption on Thera Island. The later excavations on this island and geological investigations confirmed the correctness of this hypothesis [31]. The fact that the Crete civilization stopped existing unexpectedly in the mid-XVI B.C. was known in the earlier time due to investigations made by archaeologist A. Evans [32]. He managed to prove that approx. in 1520 B.C. the eruption of Santorini volca-no occurred on Thera Island. Archaeological investiga-tions showed that a buried city, Akrotiri - the prehistoric Pompei- is situated under volcanic rocks on this island. The depth of the ash and pumice layer above the remains of the city exceeds 10 m [32].
Geological investigations enabled obtaining infor-mation on the latest geological history of the island, fact that allowed us to estimate the natural situation in a new fashion [19, 31]. There is now a huge volcanic crater hav-
ing the diameter of about 11 km. The volcano itself as a mountain does not exist since it was destroyed during the eruptions and explosions. It is widely known among vol-canologists that the Minoan Thera eruption characterized by a sequence of 4 distinctive volcanic phases, started with strong Plinian activity and ended with collapse of the vol-canic cone [33, 34]. The explosive eruption in the Plinian phase ejected huge amounts of volcanic aerosol and tephra into the atmosphere [35]. Westerly to northwesterly winds spread the ejections over the eastern Mediterranean region. The eruption of the last phase collapsed the Stronghyle volcano [36], leading to formation of the pre-sent shape of the Santorini caldera.
It has been stated that the airborne tephra accumulat-ed over Minoan settlements on Rhodes [37], Kos [34] and Crete [38]. Moreover, the discovery of the Thera tephra in deep-sea sediment cores from the Eastern Mediterranean [39] and in lacustrine sediments of Western Turkey [35] gave evidence that the main transfer of volcanic ejections took place eastward. Guichard et al. [40] reported the dis-covery of tephra from this Minoan event in laminated sedi-ments of the Black Sea. This finding provided constraints on the distribution of debris from the eruption. They estimated a minimum fallout area of 2 x 10 km2 extending from the Black Sea in the north to the southeastern Mediterranean Sea.
Studies of numerical simulation of the Minoan tsu-nami revealed that the Aegean Sea coast of Western Tur-key and Crete was subjected to tsunamis with wave heights exceeding 5 m. The highest water level (~21 m) in the model is found to the south of Ios Island and it appears that the Minoan harbor of Amnissos was attacked by waves with an elevation exceeding 10 m. The fallout of tephra in the troposphere was preceded by the invasion of tsunamis and the duration between the arrival of tsunamis and the ash-fall was probably very short. The ejections probably reached over the eastern Mediterranean within a few days, whereas a train of tsunami waves is numerically inferred to have arrived at the Aegean shore of western Turkey about 2.5 h after the caldera’s collapse. This indicates that the time scale of the Minoan tectono-volcanic event is on the order of 24 h.
Trenching methods on the coasts of Didim and Fethye (Western Turkey) revealed the traces of tsunami invasion. Sediment layers composed of fine to medium sand grains with marine fossils were found to intercalate in the non-marine sediments of coastal sequences. Additionally, in the archaeological site of Gouves (15 km east of Knossos) in Crete [38], it was found a floor covered by a thin veneer of carbonate sand, composed of unsorted grains of skeletal fragments of marine origin and an overlying 10-20 cm thick pumice layer. It is interpreted that the sand layer was depos-ited during sea water flooding in Late Minoan period.
Most of the great calamities are explained by volcanic eruptions in the historical past. However, the total number of victims and the scale of devastation as a consequence
of them are much smaller than those from earthquakes, in-undations, or hurricanes. Nevertheless, volcanic eruptions, rather frequent in the historical past, involved some cen-ters of large-scale disasters, which were followed by a great number of victims and the devastation of vast territories (Table 2). The effect of volcanic eruptions on climate has been studied quite thoroughly [12].
TABLE 2 - Largest volcano eruptions in the history of mankind (the number of lives lost as result of eruptions and their consequences is ≥ 5,000) [1].
Year Country Volcano lost
lives Number of victims
1586 Indonesia Kelut 10,000 1631 Italy Vesuvius 18,000 1669 Italy Etna 10,000 1783 Indonesia Paradajan 9,340 1792 Japan Unzen 15,190 1815 Indonesia Tambor 92,000 1883 Indonesia Krakatau 36,420 1902 Martinique
(France) Montpellier 29,000
(30,000) 1902 Guatemala Santa Maria 6,000 1919 Indonesia Kelut 5,110 (5,000) 1985 Columbia Nevado del
Ruis 22,000 (23,000)
Earthquakes
Earthquakes cause considerable devastations of densely populated regions of the Earth, the death and ruin of many thousands of people. Documentary evidence about the most ancient of them, which caused human death, can be found in the Chine catalogue of earthquakes that was compiled during 3 thousand years. Other countries have no similar chronicles about earthquakes, which covered a long time period. However, the echoes of large-scale disasters were imprinted upon the memory of people, were reflected in legends and myths, fact which requires special scientific interpretation. Maybe, the Bible stories on terrible disasters of the past caused by underground shocks are based on real facts.
In some regions of the Earth, man was subjected to simultaneous influence of several natural forces. It is obvi-ous that different natural interacting forces are much more difficult to withstand. On the coasts of some seas (in tec-tonically active areas), man is often met with two forces: earthquake and inundation of coast. Tectonic motions lead to uprise or sinking of some coastal parts; in the latter case, the parts of land were flooded by seawater. Such a phe-nomenon, in particular, was observed on the coasts of Black and Mediterranean Seas. Some parts of their coasts proved to be under water very soon, sometimes, as a result of tec-tonic sinking, especially in the periods of their own marine transgressions. The cities and settlements sank to the sea bottom together with them. One of such parts is near Na-ples. Here, in the Poccuoli district, at the depth of about 7 m, the remains of a Roman imperial palace were found at the place of the former ancient Roman city Baya, which sank to the depth of 14 m [41].
In the early 1980es, the ruins of flooded cities were discovered, including ports, at the coast of India. How did they turn out to be at the sea bottom? The specialists of National Oceanographic Institute in the city Goa and those of Archaeological Department, State Tamilnad University, in particular, tried to answer this question. The drowned cities are at different depths - from 10 to 130 m. Some of them are mentioned in ancient Indian books. Thus, in par-ticular, Bet-Dvorak is mentioned in the “Makhabharat”. In 1983, its remains were found at the State Gujarat coast. The biggest flooded city was discovered at the Madras coast, 1 km far from the coast. It is supposed to be the city Caveripatinam, a major old Indian commercial center and port in the past. Much is not clear as to why the cities earli-er situated at the India coast proved to be at the sea bottom. The ancient sources, for example, inform that Cav-erpatinam was unexpectedly flooded by a gigantic tidal wave. It should be emphasized that the coast of India expe-riences periodical flooding by oceanic waves, particularly by tsunamis, due to underwater earthquake. However, after water recess from the coastline, cities are restored and remain on the land. The aforementioned cities turned out to be flooded, most probably, as a result of coast sinking. Deep geological processes could cause different motions of the coast parts and, hence, cities are found at different depths and distances from the coast. It would be possible to establish the true cause of cities` destruction with the help of future underwater investigations.
Earthquakes involve flooding of many ancient settle-ments and cities, which were located at the coast of the Mediterranean Sea. A small city of Tsavtat is situated at the Adriatic coast of Yugoslavia. The local inhabitants and specialists-archaeologists noticed that some structures in the city, for instance, roads and aqueducts, built by ancient Romans, suddenly break at the coast. The city looks like continuing at the bay bottom. According to fishermen, one can see, sometimes, the walls of underwater structures through the water depth. The outstanding British archae-ologist Arthur John Evans, in particular, who discovered Minoan civilization on Crete, knew of this fact. More than 100 years ago Evans visited Tsavtat [32]. A strong convic-tion grew up in him that a drowned city is located at the Tsavtat Bay bottom. It was, most probably and according to Evans, the ancient Roman city Epidavr. The city was believed to disappear from the Earth’s surface, but the information about it remained: its name and location was mentioned in historical sources - Greek manuscripts. The name of the city can also be read on vases. The Yugosla-vian Epidavr was founded as a Greek colony by the emi-grants from the city of the same name, which was situated not far from Corinth in Greece. The city is also known to exist for a long time period. It changed from a Greek colo-ny to a Roman city. With the fall of Roman Empire, Epi-davr perished. It is believed to have been ruined by barbari-ans in the middle of the VI century A.D. A new settle-ment ap-peared later on its place, which has become the present Tsavtat.
According to other sources, Epidavr was under water not due to the destructions made by man during wars as it turns out. A small group of archaeologists headed by Falcone-Barker in the 50s of the XX century carried out the first serious underwater investigations and discovered the city for science. There were found walls, columns, streets, which continued some roads of the modern Tsavtat. Some historical sources, as well as chronicles, indicated that Epidavr was ruined during the earthquake. According to one of the chronicles, the earthquake occurred in 365 A.D., covering an extended territory in Italy, Ger-many and Illiria (on the territory of Yugoslavia). During this disaster, a large part of the coast together with the city sank and was buried under water. The city’s ruins, to be more exact, turned out to be at the depth of about 20 m. Thus, the city, the center of marine communications with a population of 40,000, was destroyed.
The ruins of one more ancient city found, Apollonia, aroused great interest of archaeologists and geographers. This city has long ago perished, and there is small settle-ment Apollonia on its place, or more exactly, in the vi-cinity of it, lying among the ruins, at the coast of Libya. The Cambridge University expedition found numerous flooded city structures [42]. Apollonia was founded in the VII B.C. It was built as a city-port to link Kirena, the capital of Kirenaika, located at a distance of 20 miles, with Greece. The city structures under water are found at a distance of up to 400 m from the coast. The city became a Roman colony in the 90es B.C. Judging by the coastal structures, it proved to be drowned in the VI A.D. The flooded port structures evidence that, in the Roman period, sea level did not only rise but it also temporarily fell. This is, in particular, indicated by bottom deepening operations to clear the canal (passage) between islands for ships coming to the city. The geological investigations have shown that Apollonia turned out to be flooded due to tec-tonic descent of the coast part and subsequent inundation of the district. The land parts drowned together with the city are at the depth of not more than 2 m.
Most of the settlements suffered from tsunamis in the past. One of the largest calamities took place in 1833 dur-ing the Krakatau eruption. At the same time, the earthquake produced a huge wave, which reached the nearby densely populated coasts on Java and Sumatra Islands, and led to the death of about 30,000 persons, devastating the coastal areas. In Europe, the greatest disaster occurred in 1755 at
the coast of Portugal. Tsunami with the center near the coast came down to Lisbon, the capital of the country. According to rough estimations, it resulted in the death of 50-70 thou-sand of the citizens, ruining the city [1].
The 26th December 2004 earthquake of Mw 9.0 is the second largest earthquake ever to have been recorded. As mentioned above, it generated a tsunami, which affected several Asian countries. In India, the Andaman & Nicobar group of islands, and coastal states of Tamil Nadu, An-dhra Pradesh and Kerala were severely affected [43]. The 26 December 2004 Indian Ocean tsunami propagated with a maximum strength perpendicular to the Sumatra trench and a minimum parallel to it [44], but this effect is not observed in the tsunami induced seismic signal [45]. Ac-cording to Yuan et al. [45], two mechanisms can possibly explain the observed large tsunami induced seismic sig-nals. Sea level changes will cause changes of gravitational effect to seismometers and/or tilt of island and coastal area. Both effects are likely to exist simultaneously but the latter seems to be the dominant mechanism.
Sea level changes
People were drawn long since to the coast of seas and oceans when settling. Many settlements, which later be-came big cities, appeared at their coasts, particularly in the convenient bays and gulfs of Mediterranean, Baltic, Black, and North Seas. In the states, which had an outlet to the sea, there were favorable conditions for developing trade, fishing, navigation, and naval art. The sea has played an important role in the development of many powers, among which are Phoenicia, Ancient Greece, Turkey, Spain, Great Britain, or Russia. However, the effect of sea is not only positive but it also has the negative side for the states hav-ing an access to sea. Seacoasts, including densely populat-ed ones, were always subjected to the impact of sea events. Disasters often occurred on the low coasts, which caused damage to population and, sometimes, to the vital activity and economy of a country on the whole (Table 3).
Seacoasts were periodically flooded for a short time during storms, as well as a result of tsunami development. Besides, the coastal areas were dried up or flooded due to slow fluctuations of sea level, its transgressions or regres-
TABLE 3 – Biggest floods of seacoasts in the history of mankind with ≥35,000 victims [1].
Year Country, location Flood cause Number of victims 365 East Mediterranean Tsunami 50
1099 England, Holland Cyclone 100 1164 Germany (north-west) Cyclone 100 1200 Holland (Frisland) Cyclone 100 1212 Holland (north) Cyclone 306 1421 Holland (Frisland) Cyclone 100 1737 India (Gangesdelta) Cyclone 300 1755 Portugal (Lisbon) Tsunami and earthquake 60 1864 India (Calcutta) cyclone 50
sions. It has been a long time since the low coasts in many densely populated regions of the Earth were subjected to disastrous sea floods of various origins. Some of them ap-peared owing to the rise of seawater during monsoons. Together with southwest monsoons, strongest air currents moving to the coast of India and Pakistan, a sharp rise of the level of coastal water and coast flooding took place.
Specific features and consequences of several outstanding geological disasters Earthquakes
Earthquakes are one of the most terrible natural phe-nomena. How to avoid catastrophic consequences of earth-quakes? The most important thing that should be done is to avoid large-scale construction in seismic zones and with the account for the known historical experiences (for example, in Ashkhabad, in Armenia) it would be expedient to trans-fer cities in other safe places. Nevertheless, many places, where one tenth of our planet’s population is concentrated, are located exactly in seismic zones. Among 100 largest cities of the world (where one tenth of our planet’s popu-lation is concentrated), 70% of them may be exposed to underground shocks up to 6 numbers (Mercalli scale) once in 50 years (Fig. 1). In 25 % of these cities, shocks of 8 num-bers are quite possible [46].
Recently, Varotsos et al. [47] in a monograph reported the current understanding of the Seismic Electric Signals (SES), the study of which started almost 25 years ago in Greece. SES are low frequency (≤ 1Hz) transient electric signals that are recorded at certain sites (sensitive sites) of the Earth’s surface, several hours to a few months before earthquakes (e.g. [48-55]). In particular, this monograph presents the recent experimental results (field measurements as well as laboratory ones) that are closely related with the physical understanding of the SES transmission and/or generation. For example, the recent field measurements showing measurable time difference between the SES elec-tric field and the time derivative of the magnetic field are also included. In addition, the theoretical understanding of the SES transmission through a strongly inhomogeneous medium like the Earth is also given. Natural explanations of the SES physical properties, e.g., their “low frequency” nature, the existence of sensitive (and non-sensitive) sites, the selectivity effect, the way of determining the epicenter from the ratio of the two SES components, the difference between the SES polarization and that of magneto-telluric variations, the criteria to distinguish SES from noise etc., are also provided. In Varotsos et al. [56], the recent ad-vances on the
FIGURE 1 - Risk for the biggest 100 cities due to earthquakes, volcanic eruptions, tsunamis, storms and cyclones [1]. 1 a,b – 100 largest urban agglomerations (1985) (a) including 50 of the most developing (1985 – 2000) (b) ; 2 – zone of risk due to earthquakes (with the intensity of /VI numbers on modified Mercalli scale once in 50 years); 3 – areas of active volcanism; 4 –seashores prone to tsunami; 5 - zones of regu-lar development of tropical cyclones and storms (with the intensity of /8 numbers on Beaufort scale); 6 – zones of regular development of extra-tropical (winter) storms (with the intensity on Beaufort scale).
analysis of the SES data are finally presented. Not only does this provide additional modern tools for discriminat-ing true SES from noise, but it also enables the estimation of the time-window of the impending main shock with accuracy of the order of a few days. The latter is achieved only if the analysis is made in the frame of a new time domain, which has been suggested in 2006 by Varotsos and coworkers [47] and treated in a series of publications (see references therein). This time domain, which sheds light on SES characteristics (e.g., “universality”, strong “memory”) that were hitherto unknown, can be under-stood as a natural development of the proposal of Varotsos et al. in the early 80s that the emission of precursory electric signals can be explained on the basis of critical phenomena [48, 49].
Volcanic eruptions
By their scale and extent of impact on ecosystems and mankind as a whole, volcanic eruptions rank considerably below both earthquakes and floods, because they rarely occur. But, on the other hand, they belong to the most terri-ble and destructive natural disasters. Everyone of such dis-asters occurring in densely populated regions may result in
many victims [57] and considerable material damage. In the 20th century, only due to eruption of two volcanoes (Montpelee in 1902, Martinique Island and Ruiz in 1985, Columbia), 28 and 25 thousand persons were killed, re-spectively.
On a global scale, this phenomenon is not among the most destructive ones both by the number of killed or wounded persons, and by material damage. This is testi-fied by volcanic eruption data for the period from 1900 up to 1995 (Table 4) [57]. During this period, 76,960 persons were killed. Certainly, as compared to other disasters, these figures are far lower. The same is true for the number of evacuated and wounded persons. For example, during the period from 1985 to 1995, inclusive this number (with due account for the number of catastrophes with more than 1000 evacuated persons) made up 1.31 million persons.
As well as some other natural phenomena, volcanic eruptions are sometimes destructive not only in their direct, but also in indirect consequences. Quite often, earthquakes provoke activation of other dangerous phenomena, which turn out to be disastrous for population (Table 5) [58]. For
TABLE 4 - Several outstanding volcanic calamities starting from 1000 A.D. with the number of perished of 300 and more persons [1].
Volcano Country Year Ultimate cause of death Pyroclastic
flows Lava flow Flow of fragmen-
tal rocks Death
because of starvation Tsunami
Merapi Indonesia 1006 1000 100000 Kelut - 1586 Vesuvius Italy 1631 18000* Etna 1669 10000* Merapi Indonesia 1672 300* Awu 1711 3200 Oshima Japan 1741 1480 Cotopaxi Ecuador 1741 1000 Makian Indonesia 1760 Papandayan 1772 2960 Laki Iceland 1783 9340 Asama Japan 1783 1150 Unzen 1792 15190 Mayon Philippines 1814 1200 Tambora Indonesia 1815 12000 Galunggung 1822 4000 80000 Nevado del Ruiz Columbia 1845 1000 Awu 1846 3000 Cotopaxi Ecuador 1877 1000 Krakatau Indonesia 1883 Awu 1892 1530 Sufriere St. Vincent St. Vincent 1902 1560 MonPelee Martinique 1902 29000 St. Maria Guatemala 1902 6000 Taal 1911 1330 Kelut Indonesia 1919 5110 Merapi 1951 1300 Lamington New Guinea 1951 2940 36420 Khaibok-Khaibok Philippines 1951 500 Agung St. Helens Indonesia 1963 1900 El Chichon USA 1980 60 >22000 Nevado Mexico 1982 >2000 Del Ruiz Columbia 1985
Comment: ∗together with mud-rock flows TABLE 5 - Human victims caused by volcanic eruptions, 1600 – 1986 [1].
Ultimate cause of death 1600 - 1899 1900 - 1986 Pyroclastic flows and avalanches Mud-rock flows (lahars) and floods Tephra and impact bombs fall Tsunami Diseases, starvation etc Lava flows Gases and acid rains Other or unknown Volcanic total Annual average
18,200 (9.8 %) 8,300 (4.5 %) 8,000 (4.3 %)
43,600 (24.4 %) 92,100 (49.4 %)
900 (0.5 %)
15,100 (8.1 %) 186,200 (100 %)
620
36,800 (48.4 %) 28,400 (37.4 %)
3,000 (4.0 %) 400 (0.5 %)
3,200 (4.2 %) 100 (0.1 %)
1,900 (2.5 %) 2,200 (2.5 %)
76,000 (100 %) 880
example, in the course of Nevado del Ruiz volcano erup-tion in Columbia in 1985, 25 thousand people were killed not directly because of volcanic emissions, but of mud-rock flow. The latter originated due to melting of glaciers and snow at the top of the volcano.
Tsunamis - Public health effects
According to the NOAA (National Oceanic and At-mospheric Administration) earthquake database, at least, 31 events have been found in the Indian Ocean in terms of tsunami event since 1900 [59]. Some more recent tsunami events, along with the magnitude of the earthquake by which they were generated, are presented in Table 6.
TABLE 6 – Recent tsunami events (NOAA / PMEL / Center for Tsunami Research).
Date Location / Earthquake magnitude
Oct 7, 2009 Vanuatu (Mw 7.6) and Santa Cruz Islands (Mw 7.8) Sep. 29, 2009 Samoa (Mw 8) Aug. 10, 2009 Andaman Islands (Mw 7.7) Jul. 15, 2009 New Zealand (Mw 7.8) Nov. 14, 2007 Northern Chile (Mw 7.7) Sep. 12, 2007 Sumatra (Mw 8.4) Aug. 15, 2007 Peru (Mw 8) Apr. 1, 2007 Solomon Islands (Mw 8.1) Jan. 13, 2007 Kuril Islands, Russia (Mw 8.2) Nov. 15, 2006 Kuril Islands, Russia (Mw 8.1) Jul. 17, 2006 South Java (Mw 7.7) Mar. 28, 2005 Indonesia (Mw 8.7) Dec. 26, 2004 Indonesia (Sumatra) (Mw 9) Sep. 25, 2003 Hokkaido (Mw 8.3) Jun. 23, 2001 Peru (Mw 8.4) Jan. 13, 2001 El Salvador (Mw 7.6) Nov. 26, 1999 Vanuatu (Mw 7.5) Jul. 17, 1998 Papua New Guinea (Mw 7) Jun. 10, 1996 Andreanov (Mw 7.9)
On 17 July 2006, an Mw 7.7 earthquake (as calculated
by the United States Geological Survey-USGS) occurred south of Java, Indonesia. Waves, 2-7 m high, travelling as far as 2 km inland, followed the earthquake. At least 23,000 people did eventually evacuate the coast, either afraid that more tsunamis were coming or because their
homes had been destroyed. The WHO Regional Office for South-East Asia reported that approximately 668 people died, 65 were missing, and 9299 were in-treatment because of the disaster, while the number of internally displaced persons was estimated at 5172. Some of the diseases re-ported are gastritis, diarrhea, Thypus abdominalis, mea-sles, hepatitis and malaria.
An Mw 8.1 earthquake (USGS) took place on 1 April 2007, near the island of Gizo, in the Solomon Islands. At least, 52 people were reported to have been killed and 60 reported missing when a tsunami triggered by the earth-quake struck the Solomon Islands, wiping out 13 or more villages. Thousands were left homeless, and damages were estimated in millions. It was reported that an outbreak of measles and diarrhea emerged among the survivors.
A tsunami hit Samoa and American Samoa following an Mw 8.0 earthquake in the south of the main Samoan Island chain on September 29, 2009. Villages, houses, buildings, and communication lines were damaged as sea water surged inland. According to the WHO Regional Of-fice for the Western Pacific, the main health conditions they encountered were upper and lower respiratory tract infec-tions, infected wounds, scabies, chronic illnesses and psy-chosocial issues. The official casualties count as of 9 Octo-ber was 138 dead, 310 injured and 6 missing people.
The tsunami that struck 11 countries in South Asia on the morning of December 26, 2004, resulted in a natural disaster of apocalyptic proportions. The devastation wrought by the tsunami was catastrophic - more than 150,000 people dead, tens of thousands of people missing, thousands of miles of destroyed coastline, and loss of livelihood for mil-lions of distraught survivors. The clinical and epidemiologic profile of this disaster is similar to that of a cyclone or hurri-cane with resultant flooding.
The WHO has highlighted that in the aftermath of the tsunami, infectious disease outbreaks will add to the heavy toll of the disaster itself, possibly even doubling the number of casualties.
Flooding is the most common type of natural disaster worldwide, accounting for an estimated 40% of all natural disasters [60]. There are multiple environmental conse-quences of flooding that can directly affect public health.
Water sources, for example, can be contaminated with fae-cal materials or toxic chemicals. Nevertheless, in the past 3 decades, epidemics of water-borne diseases, such as chol-era and shigella dysentery, have been uncommon after floods [61]. In the summer of 1993, 75% of countries in Missouri USA were flooded [62]. An increase in upper respiratory tract infections and sporadic outbreaks of diseases, such as leptospirosis, was observed but it was not widespread.
The experience in the USA needs to be seen in con-trast to the aftermath of flooding in the developing world. Flooding in Ecuador (1983), Khartoum, Sudan and Bang-ladesh (1988) was followed by outbreak of malaria, hepa-titis A, gastrointestinal infections and diarrhoeal diseases.
Earthquakes have minor impacts to the outbreak of in-fectious diseases, as the cause of immediate death continues to be primarily by traumatic injuries [63]. However, there are some examples of certain infectious diseases following earthquakes and volcanic eruptions. The loss of potable water in Philippines led to increases in gastrointestinal ill-ness, the bad hygiene conditions to outbreak of hepatitis in Columbia etc [62].
Displaced population in camp settings are at high risk of infectious diseases due to a large array of risk factors acting synergistically: overcrowding, inadequate shelter, poor sanitation, malnutrition, inadequate quantity/quality of water, poor personal hygiene etc [64]. Death rates of over 60 times the baseline have been recorded in displaced peo-ple, with over 3 quarters of these deaths caused by com-municable diseases, like respiratory infections, malaria, tuberculosis, HIV, measles, meningitis, diarrhoeal diseases [65].
Although the tsunami catastrophe was unusually vast, it was a classic natural disaster. The causes of death were drowning and blunt trauma, and the injuries among the survivors arise from complications of near drowning and trauma. Wound infections and, in unvaccinated populations, tetanus presented a major problem in this disaster [66]. Public health surveillance in Thailand gave evidence for an increase in diarrhoeal diseases after the tidal wave that was quickly stabilized. No cholera and malaria outbreak nor measles have been reported in any of the tsunami-affected areas, due to the prompt international aid efforts to provide large quantities of fresh water, vector control and vaccines. Acute respiratory infections appeared to be the most com-mon complaint at makeshift outpatient clinics.
The public health impact of the tsunami in South Asia can potentially be immense, comprising high rates of com-municable diseases and high excess mortality rates, but these are the consequence of the refugee camp settings and large displaced populations rather than the tidal wave itself. The threat of post-disaster infectious disease outbreaks should be neither overrated nor underestimated. The prompt international aid response minimized the danger of outbreak of infectious diseases, and preventive measurements proved
to be essential for their control. A summary of the main public health interventions to minimize infectious dis-eases is shown in Table 7.
TABLE 7 - Public health interventions - infectious diseases [64].
Preventive measure Impact on spread of Site planning Acute respiratory infections, diarrhoeal
diseases Good sanitation Diarrhoeal diseases, vector-borne diseases Clean water Diarrhoeal diseases, typhoid fever Adequate nutrition Measles, tuberculosis, acute respiratory
infections Vaccination Measles, meningitis, Japanese encephali-
tis, influenza, diphtheria Vector control Malaria, dengue, Japanese encephalitis Personal protection Malaria, dengue Insecticide- treated nets Malaria Personal hygiene Louse-borne diseases: typhus, trench
fever, relapsing fever Health education Sexually transmitted infections,
HIV/AIDS, diarrhoeal diseases Case management Cholera, shigellosis, tuberculosis, acute
PERSPECTIVES OF DISASTERS MONITOR-ING - THE ROLE OF REMOTE SENSING
Remote sensing and hazardous terrain mapping can play key roles in the management and mitigation of natu-ral disasters. To improve the efficiency of remote sensing in disaster management, it is proposed to combine remote sensing and geographical information system (GIS). If we know nothing about an event, remote sensing may provide some spectrum information of objects. If we have some data in advance, we can choose suitable sensors to target the object in due place and time; remote sensing and GIS can be much more effective if combined with the compo-nents of a disaster system [67].
The main stages that are important for the manage-ment and prevention of natural disasters are [68]:
(1) Pre-disaster. Maps showing the distribution of geohaz-ards and their relative severities can be used to mini-mize the danger to people and infrastructure. For this
stage, geomorphological mapping based on stereoscopic aerial photography has been widely used for many years (e.g. [69-71]. A new development is mapping based on spectral responses and digital elevation models (DEMs) [72, 73]. Furthermore, early warnings of dis-asters caused by slope instability, seismic activity or volcanic eruption should be feasible within a few years, using constellations of radar satellites to detect ground
deformation [74].
(2) Event crisis. With the onset of a disaster, medium- resolution (15-250 m pixel) satellite imagery (e.g. Landsat or MODIS) is useful for assessing the regional extent and relative severities of the various impacts.
(3) Post disaster .Geomorphological and geo-ecological mapping, based on the interpretation of aerial photog-
raphy or spectral and DEM data from satellites, can assist disaster recovery by highlighting locations with essential resources (e.g. water, wood fuel) and mate-rials for reconstruction, such as timber and sand-gravel or clay deposits [68]. GIS and remote sensing have already been widely used
in monitoring, predicting, early warning, loss assessment, rescue activities, and aid crisis management for natural disasters.
Different kinds of disasters call for different satellite systems and the idea of an all-purpose disaster monitoring satellite system is in some ways naïve. Tsunamis, volcanic eruptions, earthquakes, and sea level rise call for different types of satellite remote sensing systems. There is also a difference between, on the one hand, trying to develop a warning system in advance of a disaster and, on the other hand, monitoring the situation in the wake of a disaster. The first aspect is excruciatingly difficult. Tsunamis happen very rarely and the danger is of giving too many false alarms and discrediting one’s technology. The problem with the tsunami of 26 Dec 2004 was not the problem of foreseeing it, at least, as far as the Indian subcontinent was concerned; it was noticed some hours before it hit the Indian subconti-nent (though, of course, the time before it hit south Thai-land was quite short). But there was no way of communi-cating a warning to people on the ground who were in dan-ger of being swamped by it. On the other hand, monitoring the effects of a disaster, once it has happened, is well within the reach of present satellite remote sensing.
The remote sensing of natural hazards appears to be headed towards an increase in microsatellites, increased pixel resolutions, increased repeat times, and an increase in the integration of satellites [75]. In this respect, new satel-lites and constellations of satellites with passive and active sensors have been launched in the very last years, such as DMC, CartoSat-2, Rapid Eye, Pleiades, EROS C, SAR-Lupe, COSMO-SkyMed and TerraSAR-X.
For instance, the Disaster Monitoring Constellation (DMC) is a small constellation of remote sensing satel-lites, built by UK-based Surrey Satellite Technology Ltd (SSTL) and operated for the Algerian, Nigerian, Turkish, British and Chinese governments by DMC International Imaging [76]. The DMC satellites provide daily coverage of the Earth at a spatial resolution comparable to that of Landsat TM [77], and were specifically designed to sup-port the logistics of disaster relief. The individual DMC satellites are AlSAT-1, BilSAT, NigeriaSAT-1, UK-DMC (first generation), Beijing-1, UK-DMC2, Deimos-1 and NigeriaSAT-2 (second generation). Each satellite can pro-vide 32-m resolution imaging (UK-DMC2 and Deimos-1 provide 22-m resolution imaging) in three spectral bands (near-infrared, red, and green) with an extremely wide im-aging swath of 600 km on the ground. The first spacecraft, AlSAT-1, was launched in November 2002. The DMC has monitored the effects and aftermath of the Indian Ocean Tsunami (December 2004), Hurricane Katrina (August
2005), and many other floods, fires and disasters. Each partner country gives five per cent of its capacity to free daily imaging of disaster areas for aid agencies through Reuters AlertNet in the beginning. UK-DMC provides data through RESPOND, an ESA funded project focused on delivering maps to aid agencies. The group as a whole is also signed up to the International Charter "Space and Ma-jor Disasters".
The International Charter “Space and Major Disasters” established in October 2000, provides a unified system of space data acquisition and delivery to those affected by natural and man-made disasters through Authorized Users. Presently, ten agencies viz., European Space Agency (ESA); Centre National d'Etudes Spatiales (CNES), France; Ca-nadian Space Agency (CSA); Indian Space Research Or-ganisation (ISRO); National Oceanic and Atmospheric Administration (NOAA), USA; Argentina's Comisión Nacional de Actividades Espaciales (CONAE); Japan Aerospace Exploration Agency (JAXA); United States Geological Survey (USGS); DMC International Imaging (DMC), England, and China National Space Administration (CNSA) are members of the Charter. Each member agency has committed resources, in terms of satellite data and its analysis, to support the assessment of the impact of disasters on human life and property. The space resources of the member agencies are ERS, ENVISAT, SPOT, For-mosat, RADARSAT, IRS, POES, GOES, SAC-C, ALOS, Landsat, Quickbird, GeoEye-1, AlSAT-1, Nigeri-aSAT, BilSAT-1, UK-DMC, TopSat and FY, SJ, ZY satellite series.
These advances in satellites, sensors, and data distribu-tion should significantly improve our ability to assess and predict natural hazards over the next years.
The U.S. National Tsunami Hazard Mitigation Program (NTHMP) [78] is a State/Federal partnership created to reduce tsunami hazards along U.S. coastlines. The National Oceanographic and Atmospheric Administration, the United States Geological Survey, the Federal Emergency Man-agement Agency, and the 28 U.S. Coastal States Territo-ries, and Commonwealths are working together to assess tsunami hazard, facilitate communication of hazard infor-mation, improve early detection of tsunamigenic earth-quakes, reduce false tsunami alarms, and support tsunami mitigation efforts for at-risk communities. Primary goals of NTHMP are to: 1) raise awareness of the affected popu-lation; 2) develop integrated tsunami maps and models that can be used to develop improved warning guidance and evacuation maps; 3) improve tsunami warning systems; 4) incorporate tsunami planning into state and federal multi-hazard programs. The successful implementation of the NTHMP 2009 – 2013 Strategic Plan will result in the fol-lowing outcomes: 1) reduction of loss of life and property damage from tsunami, 2) successful execution of NTHMP tsunami mapping, modeling, mitigation, planning and education efforts, 3) tsunami inundation maps that sup-port informed decision making in tsunami-threatened
communities, 4) tsunami evacuation maps that support effective preparedness and response, 5) a culture of tsuna-mi preparedness and response, 6) establishment of more tsunami resilient communities, 7) effective and reliable warning dissemination to people at risk, 8) understandable and effective Tsunami Warning Center products.
Since 1952, Japan has been developing its Pacific tsu-nami warning system. Around Japan, there is a network of 300 seismic sensors, including 80 on the seabed, which record seismic activity and water pressure around the clock. Tsunamis are predicted based on the location, strength, and depth below the surface of a quake.
Some poor Asian countries have no tsunami warning system. The sudden and enormous loss of 300,000 lives and property in the December 26, 2004 tsunami affected numerous countries across different continents [79].
Remote sensing has been widely used in the December 26, 2004 tsunami’s detection, mapping, monitoring, dam-age assessment, and crisis management, and would play a large role in an effective warning system due to its “wide and insightful eyesight” in observing similar catastrophic disasters.
Remote Sensing technology and Geographic Infor-mation System helped to locate the site for tsunami warn-ing towers in Thailand giving a clear broad view and specific location within a short time. Both high and low resolution satellite images with Geographic Information system (GIS) and Global Positioning System (GPS) were applied to locate suitable position of Tsunami Warning Tower. Tsunami Warning Tower can reduce disaster impact if warning is issued promptly, however, the help of Tsunami Warning Tower depends largely on commu-nity’s awareness and strict response to warnings [80].
In particular, the direct monitoring of tsunamis is pos-sible via tide gauge stations located at shorelines of conti-nents and islands [81]. More recent detection equipment in-cludes ocean bottom pressure gauges [82]. Satellite altime-try can be used to observe tsunamis only if the satellites pass over the relevant region at the time of tsunami [83, 84]. GPS detections of ionospheric disturbances, created by tsunami-induced acoustic waves, are perhaps very prom-ising for tsunami monitoring [85].
Nowadays, it is of no doubt that a special satellite moni-toring of disasters is required. However, the plans for de-veloping satellite remote sensing did not include the rele-vant section before the last decade. Such problems should have been tackled under the general programme of envi-ronmental monitoring, such as the international Earth Ob-serving System (EOS) programme on observations of the Earth from space, the basic goal of which was a complex study of the environment and natural resources [1, 86]. By 1991, under the aegis of NASA, a full-scale EOS program was prepared, which was planned to be performed in the next 5-7 years [86]. It was planned to launch in 1999 the
first EOS satellite called “Terra” which was actually launched on 18 December 1999 (the related conceptual aspects of the problems of global changes and instru-mentation developments were discussed earlier [87]).
The introduction of the EOS Research Plan contains a historical outline of the development of environmental and natural-resources remote sensing observations, as well as the World Climate Research Programme (WCRP) and In-ternational Geosphere-Biosphere Programme (IGBP). From 1985 on, the US National Research Council has prepared a series of reports, which included substantiation of the strat-egy for observational systems in the context of priorities of environmental change studies. In this context, the NASA Earth System Science Committee set up, in 1988, the pro-gram of long-term observations of the environment charac-teristics on a global scale. It has been emphasized that com-plex observations are necessary for solving the key envi-ronmental problems and substantiating the models of the Earth system, as well as development of information sys-tems (data archives) providing information accessibility.
EOS has been a part of the US Global Change Re-search Programme (USGCRP), the four key components of which are the studies of [86]: 1) climate variability on a seasonal-to-interannual time scale; 2) climate variability on a decadal-to-centenary scale; 3) changes in total ozone, ul-traviolet radiation and chemical processes in the atmosphere; 4) changes in land surface properties and the dynamics of continental and marine ecosystems. Monitoring of the val-ues and processes at the atmosphere, extra-atmospheric solar radiation, land, ocean, cryosphere is of key importance for implementing the EOS programme.
As to the atmospheric part, the EOS data contain in-formation on processes from cloud systems to regional and global spatial scales. In the context of the climate change problem, particular emphasis is placed on studying the cloud-climate feedbacks, as well as aerosol-cloud-climate interactions. Analysis of the data on greenhouse gases and chemical processes in the atmosphere open the possibili-ties for more adequate understanding of the processes of tropospheric ozone formation with consideration, in particu-lar, for biomass burning and processes on the land surface [88-92]. The stratospheric data enable better understanding of the processes of ozone layer formation and ozone impact on climate [93-106]. Monitoring of volcanic eruption consequences (first of all, stratospheric aerosol changes) is of importance for climate studies [107-112]. Global monitoring of air pollution enables to investigate questions about air-quality changes and the transboundary transport of pollutants and their linkage to climate change [113-122]. Observations of ocean are used for obtaining the data on physical and biological processes in the World Ocean, including the general circulation, bio-productivity and their role in gas ex-change between the ocean and the atmosphere (this particularly refers to carbon dioxide). Observations of the dynamics of land ecosystems and hydrological process-es open the perspectives for obtaining the global infor-
mation on vegetation cover and its characteristics and, hence, the dynamics of land biosphere. New glaciological information plays an important role in solving “cryosphere and climate” problems, as well as in understanding the ocean level variability.
As a follow-on to the EOS missions, the Earth System-atic Missions (ESM) program continues to advance the understanding of the climate system and climate change. The ESM program includes missions from the former Earth Observing System (EOS) and the future Earth Science Decadal Survey (ESDS) missions. The Decadal Survey is a first-ever comprehensive survey of all Earth sciences that could benefit from space-borne observations. The study is requested and supported by NASA, NOAA, and USGS. For the next decade, the decadal survey identified 15 new space missions for NASA and 3 missions for NOAA (in-cluding 1 joint mission with NASA).
One of the important aspects of NASA's Earth science programme, in general, is to develop a scientific understand-ing of Earth's system and its response to natural or human-induced changes, and to improve prediction of natural haz-ards.
Each year, the U.S. government spends billions of dol-lars to assist regions impacted by natural disasters world-wide, such as severe thunderstorms, tornadoes, hurricanes, tsunamis, blizzards, floods, landslides, volcanic events, wildfires, and earthquakes. Decision makers need access to the most accurate and timely information available to help them plan their response to these natural disasters. Correct forecasts and predictions of natural phenomena are vitally important to allow for proper evacuation and damage miti-gation strategies. To reduce the overall impact of natural disasters on society, and to aid evacuation and recovery efforts, NASA works collaboratively with the Federal Emer-gency Management Agency (FEMA), the National Oceanic and Atmospheric Administration (NOAA), the U.S. De-partment of Agriculture (USDA), and the U.S. Geological Survey (USGS). NASA Earth science data are being incor-porated into an improved decision support system (DSS) created by FEMA to meet the requirements of planners, early warning systems and first responders, and to contrib-ute to impact assessments, risk communication, mitigation, and implementation of relief efforts. NASA’s Earth science data and models provide important input into these deci-sion support systems that help improve their accuracy and predictive capabilities. As data from additional Earth ob-servation satellites and surface measurement systems are integrated into predictive models over the next years, the accuracy and reliability of the forecasts issued will con-tinue to improve, as will their usefulness for disaster man-agement applications.
The Moderate Resolution Imaging Spectroradiometer (MODIS) Land Rapid Response System is an example of how NASA data make an immediate difference in planning for, and responding to, disasters. This system is designed to
serve the need for quick access to data from the MODIS instrument onboard the Terra and Aqua satellites, whenever and wherever disaster strikes around the world. In cases where damage is widespread - e.g., major floods and tsu-namis - MODIS can obtain an image of the area after the disaster, and it can be compared to an image of the same area obtained before the disaster occurred to see how the landscape has changed.
EOS and NASA science missions which include sev-eral mission/system concepts devoted primarily to disaster management, or that have disaster management as an area of application, are the following: TOPEX/Poseidon (Ocean Topography Experiment), GOES I – M (Geostationary Operational Environmental Satellite, I-M Series), QuikSCAT (Quick Scatterometer), Terra, SRTM (Shuttle Radar Topography Mission), CHAMP (Challenging Mini-Satellite Payload for Geo-scientific Research and Applica-tions program), Jason-1, GRACE (Gravity Recovery and Climate Experiment), ICESat (Ice, Clouds, and Land Eleva-tion Satellite), CloudSat, Aqua, GPM (Global Precipitation Measurement), Landsat 7, LDCM (Landsat Data Continui-ty Mission), NOAA/POES (Polar-Orbiting Environmental Satellites), OSTM (Ocean Surface Topography Mission), Sea-Winds (ADEOS II), SAGE III (Stratospheric Aerosol and Gas Experiment), TRMM (Tropical Rainfall Measur-ing Mission), and NPOESS that will be launched in 2014.
The future missions that have been recommended in the National Research Council Earth Science Decadal Survey in 2007 regarding the natural disasters management are the Deformation, Ecosystem Structure and Dynamics of Ice (DESDynI) and the Soil Moisture Active-Passive (SMAP) that will launch from 2010–2013, the Geostationary Coastal and Air Pollution Events (GEO-CAPE) and the Hyperspec-tral Infrared Imager (HyspIRI) that will launch from 2013–2016, and the Gravity Recovery and Climate Experiment (GRACE-II), the 3D-Winds (Demo), the Lidar Surface Topography (LIST) and the Precision and All-Weather Temperature and Humidity (PATH) that will launch from 2016–2020.
It should be mentioned here that, according to the cur-rent literature, the character of the geophysical catastrophic events is of nonlinear nature. On this point is based the modeling efforts of the pre-driving causes in order to esti-mate the magnitude and the location of the specific disas-trous event. Catastrophic events share characteristic nonlin-ear behaviors that are often generated by cross-scale inter-actions and feedbacks among system elements [123]. Also, natural hazards, such as earthquakes, forest fires, and land-slides, often follow a power-law (fractal) frequency-size distribution [124]. For instance, the Earth’s crust exhibits nonlinear, critical behavior in several ways. First, earth-quakes occur over a wide range of sizes with a frequency-size distribution characterized by a power law. This obser-vation, known as the Gutenberg-Richter law, is the most fundamental rule of seismology. Seismicity also exhibits temporal correlations that have self-similar properties [56].
The crust also exhibits nonlinear critical behavior in the way that magma makes its way through the crust and is released as volcanic eruptions. The frequency-size distri-bution of volcanic eruptions appears to follow a power-law distribution analogous to the Gutenberg-Richter distribu-tion in terms of the volume of material released [125].
The tsunami wave is an example of a nonlinear sur-face wave that arises following underwater earthquakes or underwater volcano eruptions [126]. "Coherent structures" also arise in giant earth ocean waves like tsunamis [127]. The generation and propagation of tsunami waves is an extremely complex process. The propagation of tsunamis (particularly the Indian Ocean tsunami of December 2004) from the deep sea, where nonlinearity and dispersion are small to the coastline and where these parameters become significant, has been examined in various studies (e.g. [128, 129] and references therein). The wave propagation away from the source can be investigated by shallow water mod-els which may or may not take into account nonlinear ef-fects and frequency dispersion [130]. Such models include the Korteweg-de Vries equation [131] for unidirectional propagation, nonlinear shallow-water equations and Bous-sinesq-type models [132-134]. The reliable estimate of the extension of the flooding zone is a key problem of the tsunami prevention and mitigation.
Despite all these efforts, tsunamis and natural disasters will always be a threat to society. In this respect, the wide-spread catastrophe of the 26th of December 2004 empha-sized the need to reduce false warnings, improve commu-nication and coordination between states and the warning centers and incorporate tsunami efforts into existing and future all-hazard mitigation programs. Although significant progress in all stages of tsunami research has been achieved in recent years, there are still several important issues that need to be addressed. GIS and remote sensing could be implemented into every task from forecasting, monitoring, and early warning to assessing, regulating, and intervening, and this would considerably relieve the impact of a tsunami hazard.
CONCLUSIONS
With the occasion of the 26 December 2004 Sumatra-Andaman earthquake and the induced great tsunami, the considered-above results indicate the growing importance of the problems on natural and anthropogenic disasters. An illustration of such a situation is the implementation of various projects and programmes concerning natural disas-ters, such as the “Natural Catastrophes and Developing Countries” (CAT) project started in the International Insti-tute of Applied Systems Analysis (Laxenburg, Austria), funded by the World Bank (WB) [1]. The long-term goal of this project was the substantiation of the scenarios, which can realistically demonstrate the effect of disasters on dif-ferent branches of the economy, and open the possibilities of minimizing the destructive effects of natural calamities.
On the other hand, it has allowed the WB and other inter-national creditors to render more effectively the required financial help to the states, which suffered from disasters. Under the CAT Project, it was planned to develop the scenarios, which would produce the bases for assessing direct and indirect material losses as a result of natural ca-tastrophes in developing countries, which required finding out the factors especially strongly affecting the conditions of socio-economic development when tsunamis, floods, earthquakes and other disasters occur. The methodology of CAT Project included two key components: 1) analysis of critically important factors which determine the progress of a developing country and its liability to the effect of natu-ral calamities, 2) simulated “shocks” due to natural disasters affecting the results of macroeconomic modeling. The first results evidenced that even rough estimations of losses can be the basis for useful macroeconomic analysis of the con-sequences of natural disasters. The project developed a modeling technique to integrate direct estimated costs of natural disasters to economic planning models for develop-ing countries. The modeling work created a platform to help interested parties evaluate tools for financing the cost of post-disaster reconstruction.
Also, summing up the discussion above, the problem of environmental safety should be one of the main issues as far as the general program of environmental monitoring is concerned. In this connection, a special care is necessary concerning the systematic examination of the problems of natural and anthropogenic disasters. Special consideration should be undertaken with respect to the problem on tsu-namis. Fortunately, the last major event and its disastrous consequences were imprinted upon the memory of people.
ACKNOWLEDGEMENTS
We express our gratitude to the anonymous reviewers and the editor for their essential contribution to the refine-ment of this paper.
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Received: October 26, 2009 Revised: December 22, 2009 Accepted: January 07, 2010 CORRESPONDING AUTHOR
Chris Tzanis Climate Research Group Division of Environmental Physics and Meteorology Faculty of Physics, University of Athens University Campus, Bldg Phys 5 15784 Athens GREECE E-mail: [email protected]
Alexandra Bolbou1, 2, Heidi Bauer2, Maria Ochsenkühn-Petropulu1* and Hans Puxbaum 2
1 Laboratory of Inorganic and Analytical Chemistry, School of Chemical Engineering, National Technical University of Athens, Iroon Polytechniou 9, 157 73 Athens, Greece
2 Institute for Chemical Analytics and Technology, University of Technology of Vienna, Getreidemarkt 9, 1060 Vienna, Austria
ABSTRACT
This study aims to investigate the different carbona-ceous components as well as the major ionic compounds in PM2.5 aerosols and their correlation in the urban area of Athens. Sampling was carried out during a two-months period in wintertime at two urban sites, with the use of a Gent Stacked filter unit collecting coarse (PM10-2.5) and fine (PM2.5) fractions of particulate matter. Further analy-sis was focused on the fine fraction due to its potential harmful impact on human health. The chemical composi-tion of ambient aerosols was investigated by different ana-lytical methods. Concentrations of Total Carbon (TC), Ele-mental or Black Carbon (EC or BC) and Organic Carbon (OC), as well as concentrations of 8 major water-soluble ions (Na+, NH4
+, K+, Mg2+, Ca2+, Cl- , NO3- , SO4
2-) were measured in a total of 39 samples.
Ions contributed approximately 36% to the total PM2.5 mass concentration. Among ions, NH4
+, NO3-, and SO4
2- were found in higher concentrations. Carbonaceous mate-rial (CM) accounted for 48-54% of PM2.5 at the monitor-ing sites. Speciation of carbon content into EC and OC was carried out with a thermal and a thermal-optical method, and an assessment of possible emission sources was per-formed using a statistical evaluation.
KEYWORDS: PM2.5 aerosols; carbonaceous species; organic, elemental, inor-ganic and total carbon; ion chromatography; urban area
INTRODUCTION
Throughout the last decades, there has been a growing interest in atmospheric aerosols research as they appear to have effects on health and climate. Aerosol constituents may have allergenic, carcinogenic or mutagenic properties, which presumably cause concern over public health risks. As for climate impact, optical and physical properties of aerosol particles, i.e. particle size, light absorption or scat-tering etc., reduce visibility, change atmosphere’s tempera-
ture, cause radiative forcing and change cloud properties [1, 2]. Therefore, the chemical composition of atmospheric aerosols needs to be identified and quantified, providing relevant information about the emission sources.
Particles size plays an important role to their impact and thus, numerous studies have focused on the analysis of the inhalable PM10 fraction and the respirable PM2.5 frac-tion, as well as the coarse fraction PM10-2.5. However, there is limited information for eastern Mediterranean sites in Europe [3].
Aerosol components consist of a large number of sub-stances, such as acids, organic compounds, metals and soil or mineral dust particles. Airborne particulate matter derives from various natural (e.g. vegetative debris, forest wild fires etc.) and anthropogenic (e.g. vehicle exhausts, industrial activities, domestic heating etc.) sources and can be either of primary or secondary origin. Primary constituents are directly released into the atmosphere, such as elemental carbon and mineral dust, while secondary particles, such as nitrate and sulfate, are formed through oxidation and pho-tochemical reactions within the atmosphere, known as gas–to–particle conversion mechanisms [4, 5].
Carbonaceous material (CM) comprises a major com-ponent of ambient aerosol samples in urban areas. Carbon content is estimated through the measurement of total car-bon (TC), but increased attention is paid to the analysis of its different components: Elemental Carbon (EC), Organic Matter (OM) and Carbonate Carbon (CC). EC or BC (Black Carbon) are two operational definitions for the same term, depending on the method for its determination (thermal or optical, respectively). EC is produced by incomplete com-bustion of carbonaceous material. EC is non-volatile in ambient conditions, and it is known for its light-absorbing properties. OM is composed of Organic Carbon (OC), which can be of primary or secondary origin and it contains a large number of compounds, many of them still unidenti-fied. CC (usually in the form of CaCO3) levels are general-ly low in ambient aerosol samples and, especially in PM2.5 fraction, CC concentrations are often negligible [4, 6-9]. Intercomparison studies have shown good agreement in TC concentrations determined with different thermal
methods, while the results of OC/EC split are often con-tradictory through different analytical methods. The pres-ence of “brown” carbon originating in biomass smoke is a misleading factor for the real evaluation of EC. Various methods - thermal, oxidative, thermo-optical ones - with or without the use of optical correction, have been tested for the determination of EC. However, the provided data often differ substantially and are hardly comparable, hence there is still no method universally accepted [6, 10, 11].
Limited data are available for the levels of carbona-ceous material and its components, as only a few studies have addressed (directly or indirectly) the levels of EC and OC in Athens [12-15]. In the present study, carbonaceous material and ions are determined in a series of PM2.5 am-bient samples collected during a two-months period in wintertime from two urban sites of Athens. Water-soluble ions were determined with ion chromatography (IC). Car-bon content was determined through different methods and the obtained results were compared. TC was determined with a thermal combustion method [6-8], EC was deter-mined with a two-step thermal “Cachier method” [T2S in ref. 11] and a thermal method with optical correction (thermo-optical method, TOM / method #9b in ref. 12), CC was also quantified with the combustion method for TC after a thermal pretreatment step and with the TOM. OC was determined with the thermo-optical method (TOM) and indirectly calculated by subtracting EC and CC from TC as they were obtained from the thermal method. In a lim-ited number of samples, BC was evaluated with a home-made photometric device [6-8, 11].
In this study, OC and EC concentrations are presented as they were obtained from two different methods and it was attempted to evaluate these concentrations based on local parameters and influences. An assessment of emission sources based on correlation matrices between the differ-ent components and factor analysis of components` load-ings are presented with the aim of apportioning the main emission sources.
MATERIALS AND METHODS
Sampling
The Athens Basin is characterized by a complex to-pography in an area of about 450 km2. The basin is sur-rounded on three sides by mountains and the Saronic Gulf to the south. The population of Athens exceeds four mil-lion (more than one third of the Greek population).
Two identical low-volume Gent Stacked (SFU) sam-plers [16] were placed in two central sites in the urban area of Athens:
Site A (Mets) is densely populated, mostly affected by domestic facilities. The sampler was placed in ‘Trivonianou’ street on a roof, at a height of approximately 15 m.
Site B (Patission) is traffic-dominated, and many ad-ministrative and commercial facilities are carried out on a
daily basis. The sampler was placed near ‘Patission’ street on the 5th floor of the old building of the National Tech-nical University of Athens, at a height of approximately 20 m from the street level.
The distance between the two sampling sites is ap-proximately 3 km and their exact locations are shown in Fig. 1.
FIGURE 1 - Map of Athens showing the sampling sites (A and B).
The sampling period lasted between 5th February and
1st April 2009, with a frequency of 2-3 samples per week from each site. The sampling flow-rate was the same for both samplers 16.7 L min-1 and size-fractionated particles were collected on two types of filters used in sequential filtration; PM10-2.5 particles were collected on Nucleopore polycarbonate filters (Ø 47 mm, pore size 8 µm, Whatman) and PM2.5 particles on quartz-fiber filters (Ø 47 mm, pore size 0.45 µm, Millipore AQFA). A total of 39 pairs (coarse and fine fraction) of samples were gathered from both sites. Both types of filters were used for monitoring PM mass concentrations, but only quartz fiber filters (fine frac-tion) were further analyzed for their carbon and ion con-tents. The meteorological data were provided by the Min-istry of Environment.
Weighing and sample preparation
All filters were protected in plastic filter holders be-fore and after sampling. Particle mass concentrations were determined gravimetrically using an electronic microbal-ance with a resolution of 10-6 g. Prior to weighing, filters were conditioned in the balance room maintained at tem-perature 20±1 oC and relative humidity 50±5 %. For analy-sis of ions and carbon species, discs of 10 and 12 mm Ø were stamped out of the quartz fiber filters with steel ring
punches. A filter factor was used to recalculate the results from each analysis and adjust them to the total surface of the filter.
Analytical Methods Determination of TC, EC, CC and OC with thermal methods
Total carbon (TC) was determined with a thermal com-bustion method [6-8], with NDIR (Non-Dispersive Infra-Red) detection for the CO2 measurement. Filter discs were burned in a vertical oven at 1000 oC in an oxygen stream, and the evolved CO2 was detected with two NDIR detec-tors in series (both Maihak SIFOR 200 with two different measurement ranges). Solid tartaric acid standards (Merck) were used for the calibration, corresponding to 1–200 mg C. The detection limit was 4.1 µg/cm2 (corresponding to air concentration 2.2 µg/m3), calculated as three-fold standard deviation of the blank quartz filter.
CC was determined with a two-step combustion method [8]. Filter discs (10mm Ø) were preheated at 460 °C, so that OC and EC were removed, but CC remained on the filters. This pretreatment was followed by combustion at 1000 °C and CC was quantified as TC as the only constit-uent remaining on the filter.
EC was determined with a two-step combustion method [Cachier method, T2S in ref. 11]. During the first step, the samples were kept for 2 h at 340 oC in a muffle oven (AHT Austria, with controller RKC REX-C900) in a flow of pure oxygen (1.3 L min-1, O2 purity 4.8) for 2 h. The pur-pose of this pretreatment is to oxidize organic compounds to CO2, leaving EC and CC on the substrate. An excess of oxygen should avoid charring phenomena. EC is then quan-tified in a subsequent combustion at 1000 oC as described above for TC. OC was calculated as the difference be-tween TC and (EC+CC). The detection limit of EC by the thermal method was 0.45 µg/cm2 (corresponding to air concentration 0.24 µg/m3), calculated as three-fold standard deviation of the blank quartz filter.
Determination of OC, EC and CC with a thermal–optical method (TOM) with linear temperature program
Thermal–optical analysis was performed with the use of a simultaneous laser transmission measurement and NDIR detection of the CO2 [6-8]. The separation of OC and EC is possible due to the different thermal stabilities of these carbonaceous fractions. A sample disc of the quartz fibre filter (12 mm Ø) was placed in a horizontal furnace FROK 200/50/1000 (AHT Austria) at room tem-perature in a stream of oxygen, and then heated to 800 oC with a linear ramp of 20 oC min-1. A manganese oxide cata-lyst heated to 700 oC converts all the carbonaceous gases to CO2, which is measured continuously using an NDIR ana-lyser (Maihak UNOR 6N). During the heating procedure, the transmittance of a laser beam (wavelength 632.8 nm) through the filter disc is recorded. In the beginning of the heating process, filter transmission decreases because of the charring of organic material. Then, as elemental carbon is removed, filter transmission increases again until all car-bon has been removed. The OC/EC split is set when the
transmittance reaches the same value as in the beginning of the analysis. The change of the transmittance gives in-formation about charring phenomena which can lead to in-creased blackness of the filter, and also about the tempera-ture range of the burn-off of the EC, allowing identifica-tion of EC in the TLT (Temperature Laser Transmission)-plot. CC is the last peak evolving from the decarboxyla-tion of carbonates at temperatures higher than 550 °C.
Determination of BC
BC was furthermore determined with a non-destructive optical method by the use of a home-made photometric device (obtained from Aerosol Research at LBL, designed by Novakov) operating according to the aethalometer prin-ciple. Since the specific attenuation cross section was not determined, a default value of 19 m2 g-1 was used. The linear range of the BC determination is limited at approxi-mately 18 mg BC cm-2. Filters transported to and from the sampler, but not used for sampling, were available as field blanks [6, 8].
Determination of ions
The cations Na+, NH4+, K+, Mg2+, and Ca2+ were deter-
mined by isocratic cation chromatography. Discs of 10 mm Ø punched from loaded filters were taken as aliquots and extracted ultrasonically in 12 mM methane sulfonic acid (MSA), which was also used as the chromatographic elu-ent. Filter blanks were treated in the same way as the sam-ples. The determination was performed using a Dionex CS 12A cation-exchange column and a CG 12A guard col-umn. The system is fitted with a CSRS Ultra II 4 mm auto-regenerated suppressor and a Dionex QIC conductivity detector with SRS controller. Quantification was carried out using Chromeleon® 6.6 software. Calibration was per-formed by the direct injection of aqueous standard solu-tions made from 1000 mg L-1 parent solution (Aristar® Na+, NH4
2 - were determined by isocratic anion chromatography (Dionex AS12A, electro-chemical suppression, sodium carbonate/bicarbonate eluent, eluent flow 1.5 ml min-1). Filter discs of 10 mm Ø were taken as sample and blank aliquots, and extracted ultra-sonically in ultra-pure Milli-Q water. Calibration was car-ried out with aqueous standard solutions made from 1000 mg L-1 parent solutions (CertiPUR®, chloride, nitrate, and sulfate standards, Merck). The limit of detection (LOD), defined as three-fold standard deviation (3s) of multiple injections of a standard at concentrations close to the lower limit of determination, are 0.010 µg ml-1 for all ana-lysed cations. As for anions, the limits of detection were 0.03 µg ml-1 for chloride and 0.02 µg ml-1 for the others [8]. Detected concentrations of the ions were generally above detection limits for all ions, except for Mg in a few samples.
Evaluation of data
Statistical treatment (i.e. Pearson correlation matrices and factor analysis) of the experimental data was achieved
with the use of “Systat 12” (SPSS Inc., Chicago, USA) soft-ware package.
RESULTS AND DISCUSSION
PM mass concentrations
PM2.5 mass concentrations at both sites during the sampling period (Feb. – March 2009) ranged from 10.0 to 31.2 µg/m3, with mean values 20.7 ±5.6 µg/m3 at site A and 16.0 ±4.4 µg/m3 at site B. PM2.5 and PM10-2.5 mass con-centrations are presented in Fig. 2. The average PM10 con-centrations, calculated from the sum of the two fractions (PM2.5 + PM10-2.5) were 38.2 and 32.5 µg/m3 in sites A and B, respectively, and ranged from 19.6 to 98.3 µg/m3. The PM2.5/PM10 ratio was 0.57(±0.15) on average and the mean PM10-2.5/PM2.5 ratio 0.85, which is close to ratios previously reported [17] indicating that in the urban area the fine fraction is enriched toward the coarse one. Earlier PM2.5 concentrations reported for Athens sites were found to be 28.8 µg/m3 (Nov.2005-March 2006), 31.6 µg/m3 (March 2004), and 25.3 µg/m3 (June-July 2003) [12, 18, 19].
PM2.5 mean concentrations during the sampling period were below the EU annual average guideline level of 25 µg/m3 [20]. The daily PM10 threshold limit value is 50 µg/m3, not to be exceeded more than 35 days/calendar year (9.6%). During the sampling period of this study, the PM10 concen-trations were higher than this limit at 4 of 39 sampling days (16%). For one of these four times (1/4/2009), the exceed-ing of the limit is explained by an African dust transport episode in the region [21].
Athens is characterized by mild winters and the meteor-ological conditions were typical for the city, with relatively high temperatures (daily mean: 10.1 oC, min: 4.2 oC, max: 17.6 oC), moderate relative humidity (daily mean: 60.5%, min: 36.8%, max: 79.7%) and moderate wind speed (daily mean: 3.0 km/h, min:1.4 km/h, max:4.8 km/h). PM2.5 con-centrations are generally higher during winter due to lower atmospheric dispersive conditions, and carbonaceous spe-cies are expected to be elevated in comparison with other seasons of the year due to particular anthropogenic activ-ities, e.g. space heating, that enhance their emissions. [22-24].
Ionic content
Contributions of ionic content to the PM2.5 mass con-centration were on average similar at both sites: 35.7±8.4% (min: 18.7%, max: 50.9%) in site A and 37.5±6.2% (min: 27.0%, max: 47.2%) in site B. Table 1 shows the mean values of cations and anions of the two sampling sites obtained by Ion Chromatography (IC). Among cations, NH4
+ (>1 µg/m3) was found in highest concentrations and Mg2+ (~0.1 µg/m3) in lowest concentrations, at both sites. Sulphate dominated among anions, followed by nitrate. Concentrations of NH4
+, SO42- and NO3
- are similar to those measured from November 2005 to March 2006 in a coastal industrial area of Attica [18] and for the investi-gated time period in the centre of Athens [25]. Cations except for Ca2+ are comparable with that ones measured in the centre of Athens in March 2004 [19].
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PM10 (site A) PM2.5 (site A)
PM10 (site B) PM2.5 (site B)
FIGURE 2 - Temporal variation of PM2.5 and PM10-2.5 mass concentrations in February – March 2009. The dotted (50 µg/m3) and black (25 µg/m3) horizontal lines show the EU guideline values for PM10 and PM2.5, respectively.
Thermal determination of TC has been long-established and investigated in inter-comparison studies, showing good
agreement through different combustion methods [10, 11]. The mean concentrations of TC for the total of the PM2.5 samples (n=39) are demonstrated in Table 2 and Fig. 3 showing the temporal variation of TC concentrations at both sites along with the daily mean temperature and wind speed. The data indicate a slight trend of increasing TC con-centration with the decrease of temperature and wind speed. TC values varied between 4.0-11.1 µg/m3, with mean con-centrations 7.6±1.9 µg/m3 at site A and 6.5±1.8 µg/m3 in site B. Mean values of TC have been found to range be-tween 2 -8 µg/m3 in European cities, hence the observed con-centrations fall well into this range [12]. In a previous study, TC content in total suspended particles (TSP) was de-termined with the same method with concentrations rang-ing from 11.1 to 20.8 µg/m3, at four urban sites in north-western Greece [26].
TABLE 2 - Carbonaceous data from the thermal and the thermo-optical method for the total of the PM2.5 samples.
TC (µg/m3) EC (µg/m3) OC (µg/m3) OC/EC OM (µg/m3) CM (µg/m3) OM/CM Thermal Method (TM) n=39
Average value 7.1 1.8 5.2 3.1 7.3 9.0 0.8 Standard devia-
tion 1.95 0.58 1.47 0.73 2.05 2.52 0.03
Minimum value 4.03 0.92 3.00 1.96 4.20 5.16 0.73 Maximum value 11.05 3.23 8.45 5.39 11.84 14.43 0.88
Thermal –Optical Method (TOM) n=36 / BC by Optical Method (n=30) Average value 2.6 / 2.86 4.4 1.8 6.1 8.7 0.7
Standard devia-tion 0.95 / 0.91 1.16 0.48 1.62 2.42 0.05
Minimum value 1.15 / 1.42 2.78 1.09 3.89 5.04 0.60 Maximum value 4.91 / 4.56 6.50 3.54 9.10 13.50 0.83
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TC (µg/m3) -site B
Mean temperature (oC)
Wind speed (km/h)
FIGURE 3 - Temporal variation of TC concentrations in PM2.5 samples at sites A and B, including the daily mean temperature and wind speed.
In the PM2.5 filters of this study, Carbonate Carbon (CC) values were extremely low and in most samples negligible (<1-2 %), hence this constituent of carbon is not taken into consideration for further calculations.
The typical problem with the determination of carbo-
naceous aerosols is the discrimination of Elemental (EC) and Organic Carbon (OC). Inter-comparison studies have compared the results from different techniques and demonstrated fairly good agreement between the methods applied in the current study. An uncertainty range has been designed through a factor between 0.75-1.25, in order to en-compass biases and uncertainties associated with EC determinations [27]. The two methods that were used for the determination of OC and EC concentrations provided results that differed by a factor of 1.2. More particularly, EC concentrations at site A (n=21) measured with the ther-mal method varied between 0.9-3.2 µg/m3 with an average of 1.9±0.6 µg/m3, while with the thermo-optical method (TOM) they varied between 1.5-4.9 µg/m3 with an average of 2.8 ±0.95 µg/m3. Likewise, EC concentrations at site B (n=18) measured with the thermal method varied between
1.0-2.8 µg/m3 with an average of 1.6±0.5 µg/m3, while with the thermo-optical method they varied between 1.2-4.0 µg/m3 with an average of 2.3±0.9 µg/m3. The clearly higher ratios of EC/TC determined with the TOM in rela-tion to those of the thermal method are shown in Fig. 4. EC or BC was also determined with an optical method for an indicative number of samples (n=30) from the two sites, resulting in similar concentrations with the corresponding values of EC by TOM. The following equation presents the relationship between black carbon and transmission: BC [µg m-2] = - (100/19)* ln (I/I0), where I and I0 refer to the intensity of the light for each sample and for reference samples, respectively [7, 8]. BC mean concentration was found to be 2.9±0.9 µg/m3 and ranged from 1.4 to 4.6 µg/m3. The basic premise for the measurements of BC with this optical method is that BC is the only light-absorbing sub-stance in the atmospheric aerosol. However, last decade, several studies have proven that the use of optical meth-ods for the determination of BC leads to overestimated values due to the presence of “brown carbon” which is ap-preciably light-absorbing from long to short wavelengths [7].
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EC/TC by Thermo-OpticalMethodTC/PM2.5
FIGURE 4 - Temporal variation of EC/TC and TC/PM2.5 ratios measured by the thermal and thermo-optical method at sites A and B.
FIGURE 5 - Comparison of EC (or BC) concentrations obtained by the three used methods (S1-S39 = number of samples).
Taking into account the above, concentrations of BC
were used mainly for comparison purposes. Figure 5 shows the concentrations of EC for the total of the PM2.5 samples, according to the three used methods for the determination of this component.
Average data from both sampling sites for carbon analy-sis are gathered and presented in Table 2. Contributions of carbonaceous material (CM) to the PM2.5 mass concentra-tion were 49.1±13.7% (min: 22.5%, max: 74.6%) at site A, and 53.3±13.4% (min: 27.7%, max: 87.3%) at side B. CM is the arithmetical expression of carbonaceous con-tent, resulting from the sum of EC and organic material (OM). OM is obtained from OC values multiplied by a factor of 1.4. This conversion has been suggested in order to include other elements, except for carbon, to the composi-tion of organic compounds, and 1.4 is a reasonable esti-mate of this adjustment for urban aerosols [12, 28].
According to a previous study on carbon levels in cen-tral Athens during summertime 2003, the mean EC concen-tration was 1.6 µg/m3 and mean OM 8 µg/m3, while mean OC/EC was 3.9 [12]. Thus, we conclude that carbon and mass concentrations now are significantly lower than the ones reported for Athens in 1990 [15].
During sampling and analysis procedures, there are various artefacts that may affect the different parameters of the methods and, consequently, the final results of EC and OC fractions. The semi-volatile nature of some or-ganic compounds and the absorption of gas-phase organic compounds are indicative of the complexity of the matter during sampling [11, 22, 28]. Additionally, during analy-sis, several factors may contribute to positive or negative artefacts to the measurements of the real concentration of each component. Some of these factors are the presence of
oxygen-containing minerals, the presence of active inor-ganic salts (such as ammonium sulphate) as well as Na and K that can catalyze the combustion of EC, or the evolution of light-absorbing organic material (usually in biomass smoke), i.e. ‘brown’ carbon, that leads to overestimation of EC. Moreover, some organic gases can be absorbed on quartz filters with more than a single mono-layer and thus, they may appear in more than one thermal fraction, caus-ing misleading measurements [7, 12, 22]. Taking into con-sideration these facts, the differences in the results from the two methods are attributed to the different temperature programmes followed by each method, the presence of inorganic salts as will be discussed further below, and the artefacts caused by some organic compounds that affect the interpretation of the optical transmission in TOM.
A statistical evaluation of the ions and the carbon concentrations (TC, EC, OC) obtained from the thermal method using correlation matrix and factor analysis allowed an estimation of the chemical compounds present on PM2.5 aerosols, and an explanation of their origin and the possible emission sources. The data from the thermal method were used as this method was the one calibrated and validated with standard samples (tartaric acid).
The resulting correlations between the components are presented in Tables 3 and 4. The Pearson correlation coefficients between the analyzed components revealed the formation of some inorganic salts, common in the two moni-toring sites. NH4
+ is an important neutralizing agent of sulphuric and nitric acid. SO2 is assumed to derive from domestic fuel oil rich in S content, while NOx are pro-duced mostly from vehicle emissions. Stable correlations are observed for both sites between NH4
+ with NO3- and
SO42-, indicating the formation of inorganic salts NH4NO3,
NH4HSO4 and (NH4)2SO4. The particulate-phase ammonium nitrate is attributed to the reaction between gas-phase am-monia and nitric acid. Na+ is expectedly correlated with Cl-, as NaCl likely originated from sea sprays. Strong correlation between K+ and Mg2+ enhances the assumption of marine influences, while a less intense correlation be-tween Ca2+ and Mg2+ indicates the possible contribution of mineral sources. Ca2+ and Mg2+ concentrations are also
connected to Cl-, revealing the formation of Ca(Cl)2 and Mg(Cl)2. The formations of these salts in the atmosphere could be explained by the reactions of CaCO3 and MgCO3 with HCl. A possible production of HCl may derive from the reaction of NaCl with HNO3 and/or H2SO4. Calcium occurrence in aerosols may be enhanced by karstic erosion phenomena that occasionally occur in the region [17- 19].
TABLE 3 - Pearson Correlation matrix from the total of the PM2.5 samples (n=39) from sites A and B.
The factor analysis yielded four independent factors
that had eigenvalues greater than unity. For the evaluation of the loadings and a tentative identification of the sources, component loadings higher than 0.4 were taken into ac-count (Table 4). Traffic-related emissions, soil dust, sea salts, emissions from industrial facilities, domestic heating and cooking have been addressed as main sources of pollu-tants in the urban and greater area of Athens [12, 15, 29, 30]. Road traffic and vehicle emissions (including diesel and gasoline exhausts, fuel evaporation, resuspension of road dust) have certainly impacts on EC, OM, NO3
- and SO4
2- concentrations. NH3 and, by extension, NH4+ is
assumed to derive mostly from motorcycles, which repre-sent an im-portant part of the road traffic composition in Athens [31]. These components are the major contribu-tors (factor 1) accounting for 37.2%, according to factor analysis. Measurements of black smoke in Athens have shown indirectly the noteworthy contribution of elemental carbon to aerosols, confirming the dominance of com-bustion-related sources [29, 32]. Central heating processes also enhance the emissions of TC and SO4
2-. High loadings of Na+, K+, Mg2+, Ca2+ and Cl- present in factor 2 reveal marine influences and some crustal sources.
In reference with OC/EC variance, much depends on the used analytical method. OC/EC ratios stemming from biomass burning can vary between 2.5-10 and OC/EC ratios resulted from tunnel experiments (focused on fossil fuel sources) and ranged between 0.4-1.2 [27]. A carbon iso-tope analysis would be a more appropriate method to estimate contributions of fossil fuel combustion (where
essentially no 14C should be present) and ‘modern’ carbon to total carbon mass [27, 28]. The above presented results (Table 2) with mean OC/EC ratios 3.1 by the thermal method and 1.8 by the thermo-optical method confirm the presence of OC-dominated sources which may be space heating and emissions from 2-stroke engines (motorbikes and engines).
TABLE 4 - Results from factor loadings
analysis for the total of the PM2.5 samples (n=39).
This study showed that levels of PM2.5 mass concen-tration in the urban area of Athens were generally lower than the suggested guidelines by EU for 2010. The con-tent of water-soluble ions and carbonaceous material con-stituted over 80% of the PM2.5 mass in winter. The EC and OC concentrations were measured with two different meth-ods and the obtained results were compared. A factor analy-sis revealed four factors attributed to urban emissions, min-eral dust, sea spray and ammonium sulfate. Among the local sources, road traffic and heating systems are regarded as the main anthropogenic emission sources contributing to the air pollution.
ACKNOWLEDGEMENTS
This work was supported by the EU’s Students Ex-change Programme “Erasmus/Socrates” between the NTUA and the TUV and was presented at the 6th ‘Instrumental Methods of Analysis’ Conference (IMA 2009) held in Athens, Greece, 4-8 October 2009. The authors would like to thank Dr. Klaus-Michael Ochsenkühn and Mr. Michael Paraskevas for their contribution to the sampling process and the statistical evaluation of the data.
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[27] Gelenscer A., May B., Simpson D., Sanchez-Ochoa A., Kasper Giebl A., Puxbaum H., Caseiro Al., Pio C. and Legrand M. (2007) Source apportionment of PM2.5 organic aerosol over Europe: Primary/secondary, natural/ anthropo-genic, and fossil biogenic origin. Journal of Geophysical Re-search 112: D23S04
[28] Turpin B J., Saxena P. and Andrews E. (2000) Measuring and simulating particulate organics in the atmosphere: problems and prospects. Atmos. Environ. 34:2983-3013
[29] Chaloulakou A. Kassomenos P., Spyrellis N., Demokritou P. and Koutrakis P. (2003) Measurements of PM10 and PM2.5 particle concentrations in Athens, Greece. Atmos. Environ. 37: 649-660
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[31] Ahlvik P., Eggleston H.S., Gorissen N., Hassel D., Hickman A.J., Joumard R., Ntziachristos L., Rijkeboer R., Samaras Z. and Zierock K.H. (1997). COPERT II: Computer Programme to Calculate Emissions from Road Transport. European Envi-ronment Agency, European Topic Centre on Air Emission
[32] Viana M., Chi X., Maenhaut W., Querol X., Alastuey A., Mikuska P. and Vecera Z. (2006) Organic and elemental car-bon concentrations in carbonaceous aerosols during summer and winter samling campaigns in Barcelona, Spain Atmos. Environ. 40:2180-2193
Received: March 29, 2010 Accepted: April 16, 2010 CORRESPONDING AUTHOR
Maria Ochsenkühn-Petropulu Laboratory of Inorganic and Analytical Chemistry School of Chemical Engineering National Technical University of Athens Iroon Polytechniou 9 157 73 Athens GREECE E-mail: [email protected]
SHEAR STRENGTH MEASUREMENT OF MINERAL FILTER CAKES
Birgul Benli1, Ozgul Taspinar1* and Perviz Sayan2
1 Istanbul Technical University, Chemical Engineering Department, 34469, Maslak, Istanbul, Turkey 2 Marmara University, Chemical Engineering Dept., Goztepe, Istanbul, Turkey
ABSTRACT
The shear strength of filter cakes of dolomite and quartz minerals was measured using a uni-axial test appa-ratus which was designed in the laboratory. For this aim a uni-axial button pressing machine used in textile industry was modified and used to measure the shear strength of dolomite and quartz pressure filter cakes with satisfying results. The results obtained with this machine were com-pared and found as in good agreement with the results of industrial devices, Fisher test apparatus and Universal Sand Strength Machine.
Among very versatile application fields, shear strength is especially important in two major areas: Soil mechanics and design of a reliable bulk solids handling. There is sub-stantial knowledge of literature on the powder and soil mechanics, especially on the tensile, compression and shear strength theory and testing of different materials. But the knowledge on the measuring of the shear strength of the wet consolidated very fine grained minerals, especially filter cakes are limited [1-5]. The shear strength can be general-ly defined as the movement of the particles, which is a slip between two surfaces. This idealized slip plane is made up of substantial particle rolling, sliding and slipping in the zone shown as a surface.
A simple representation of an idealized shear strength experiment is given in Figure 1 after Dartevelle [6].
Contrary to the tensile strength, the studies on the measuring and standardization on the shear strength of consolidated wet powder beds and filter cakes are rela-tively new and still continuing. Although there are several dynamic models on the pressure filtration of fine suspen-
sions, Shirato et al. [7], Tiller and Cooper [8] and Wake-man [9]; the studies on the consolidation step and the measuring of the strength of the filter cakes are limited. Among the very recent studies, Reichmann and Thomas [10, 11] have designed, constructed and tested a so-called Press-Shear Cell to identify the compression, permeation and flow behavior of fine particle suspensions. They have proposed a new dynamic expression model considering the time and local variations of material properties inside the cake during constant pressure expression. They have used the new test apparatus for in-situ simulation of the expres-sion operation and rheological testing of a compressed cake. The apparatus combines the compression-permeability cell with a high performance ring shear cell.
FIGURE 1 - The idealized experiment: granular medium within two rough plates, the bottom one is immobile, while the top one can move in order to generate a shear stress (S) within the medium. The whole medium is under a load N [6].
Filter cakes are formed with collecting very fine grained
minerals one over the other. Therefore, the shear strength of mineral filter cakes is influenced by the particle size, shape, packing fracture and surface tension as well as the applied pressure, length of time for consolidating before testing, and the saturation degree [12-14]. Similar to ten-sile strength, shear strength of mineral filter cakes are de-pendent especially on the saturation degree, S which is the quantity of liquid retained within a filter cake [3, 4, 15, 16]. The shear strength is also dependent on the capillary pressure as in the Eq.1:
Here, PK is the capillary pressure and is a function of the porosity of the cake, ε; surface tension of the mineral suspension, γ; contact angle, δ; particle shape, f and parti-cle size, x as in the following equation:
PK = [((1-ε)/ε) γ cos δ 6f]/x (2)
Schubert [3] and Pietsch and Rumpf [17] have meas-ured the tensile strength of the different material’s agglom-erates and filter cakes and given the following relation be-tween the tensile strength and particle size, x; porosity, ε and the adhesion forces, H:
εε
σ−
×=1
2xH (3)
The adhesion forces of two particles are determined by the characteristics of the liquid bridge between them. And it is a function of the relative distance between the particles, a/x; central angle of the liquid bridges, β; the contact angles, δ and as well as the surface tension, γ. In recent studies, Ozcan and co-workers [13] correlated and obtained similar relation for the shear strength of the filter cakes, τ as in Eq.4.
τ = S * Pk = [S * ((1-ε)/ε) γ cos δ 6f]/x1.6 (4)
Shear Strength Measuring Devices:
Shear tests are commonly considered in three groups [18]: 1. Unconfined compression (Unconsolidated-undrained or U test) 2. Direct shear and direct simple shear tests (shear box or vane shear test) 3. Confined compression or tri-axial tests.
Apart from using common shear strength test devices, the selection of shear strength device for filter cakes is essentially important. Filter cakes are consolidated samples and their measurements can be made up with confined compression test apparatus. The shear loading is very small during the tests with filter cakes because they are very duc-tile. Therefore, the selection of the appropriate device for the tests is important. The device should measure both very
smaller loading such as 10 or 20 g and larger loading such as 5000 g or 25000 g with the same sensitivity. For larger shear loading measurements there are lots of choices such as Instron devices, etc. But in a small loading it was nec-essary to design a new apparatus for laboratory measure-ments.
For this aim a new test apparatus named as BOS (com-posing of the first capital letters of the names of the re-searchers, B: Benli, O: Ozgul, S: Sayan) was developed by modification of a textile button pressing machine by our team in the laboratory. Detailed explanation of the new device, experimental procedure and calculations are given in the following pages.
First application of the small loading apparatus for the measurement of the shear strength of filter cakes is the Fischer test device and used by Barthelmes [1, 2] and Ozcan et al [19] in their previous studies. Schematic rep-resentation of this device is given in Figure 2. Suitable test specimen of this device is the filter cake having 10 mm height and 46 mm diameter. The sample is put in the filter cake container and hence it is in between the fixed shear punch and the container. The movable shear punch is then forwarded via hydraulic cylinder which is moved manual-ly by crank driver.
The loading configuration used in the present study for the apparatus BOS is the same as Fischer test device and it is illustrated in Figure 3. A cylindrical or disk shape filter cake of diameter, Dc and height, hc is placed onto a crosshead. To prevent movement on the crosshead, the sample is fixed by its upper part. A transverse central load, F is applied onto the filter cake via a hydraulic press until the sample is broken into two parts. The contact region is assumed as frictionless. Because the applied force, F; the diameter, Dc and the height, hc of the cake are measured directly, the shear strength is then calculated as follows [1, 12, 19];
cc hDF*
=τ (5)
FIGURE 2 - Fischer test apparatus used in the shear strength measurements of filter cakes in previous studies [12, 19].
FIGURE 3 - Loading configuration used in both Fischer test device and the new designed apparatus BOS: a) Sketch of a filter cake-loaded shear strength measurement, showing the geometry of the crossheads and the position of a filter cake which is drawn in cross lined, b) Height measuring points on a filter cake (five dotted circles).
The diameter of the filter cake, Dc is calculated by an
arithmetic mean value of two different measurements of the diameter in x and y directions. The height of the filter cake, hc is calculated using five points of measuring which is shown in Figure 3 (b) by a hyper geometric mean value as follows;
2DD
D yxc
+= (6)
( )13
h3hh sidemiddlec
∑+= (7)
In this formula the “3” is the hyper geometric standard-ization factor and it was obtained empirically with statis-tical methods [12, 20]. The applied force, F to cut the sam-ple increases slowly and reaches to a maximum at the point where the sample is broken into two parts and then goes down to zero. The maximum value of this applied force is recorded and used in the Eq.5 to calculate the shear strength. Eqs. 5, 6 and 7 were also used in the present study to calculate the shear strength with the new designed appa-ratus, BOS.
Another shear strength measuring apparatus can be seen in Figure 4. The apparatus in this figure is the Uni-versal Sand Strength Machine, USSM and used only for dry consolidated cylindrical shaped samples with standard dimensions, 50mm diameter and 50mm height. This highly accurate machine consists of three major parts: Frame, pendulum weight and pusher arm. The pusher arm is moti-vated by means of a small hand wheel which, through a gear box, rotates a pinion engaged in a rack on the quadrant. The pendulum weight swings on ball bearings and can be
FIGURE 4 - Universal Sand Strength Machine.
moved by the pusher arm, via a test specimen, from a vertical position, through 90°, to a horizontal position, with a consequent increase of load on the test specimen. A magnetic rider is moved up a calibrated scale by the pendu-lum weight and indicates the point at which specimen col-lapse occurs. The machine is calibrated in psi for 2 inch diameter x 2 inch height standard sand specimens. Vari-ous accessories may be easily attached to perform differ-ent tests such as compression, shear, tensile, transverse, deformation and splitting strength [21].
Problems in Measurements Preparation Process of Powder Bed/Pre-consolidation:
It is difficult to obtain the reproducible data during the shear strength measurements due to the possibility of the formation of the small cracks in powder bed during the preparation process. The measurement value obtained from any device is largely dependent on the preparation proce-dure in this testing method. Several studies are still con-tinuing on the effects of applied filtration pressure, i.e. pre-
consolidation, applied normal stress, pre-shear and shear procedures, dry frictional and wet viscoplastic behavior of compressed, drained/undrained powder beds on the shear strength of powder beds and filter cakes [10, 11]. To avoid the formation of cracks and channeling in the filter cakes, several precautions were applied during the cake prepara-tion process in the present study. These precautions and preparation procedures are given detailed in the following pages.
The aim of the present study is to measure the shear strength of the pressure filter cakes of quartz and dolomite with a laboratory designed apparatus, BOS and compare the results with industrial devices.
MATERIALS AND METHODS
Fine grained dolomite and quartz minerals have been used in the experiments to obtain filter cakes. The average particle size and the sources of these minerals are given in Table 1.
TABLE 1 - The average particle size
and the sources of the mineral samples.
Mineral Ave. particle size, µm Source Dolomite 16 Kale Maden/Turkey Quartz 15 Kale Maden/Turkey
Filter Cake Preparation: Pre-consolidation and Consolidation Procedures
The preparation of the filter cakes from the suspen-sions having approximately 20 % volume concentration of solids was consisted of two steps: Cake formation (Pre-consolidation) and Consolidation. To avoid the crack for-mation in the filter cake some precautions have been taken in the study:
1. The suspension was mixed continuously and rigor-ously to avoid settling in a separate container and trans-ferred very quickly into the filtration cell.
2. The suspension was filtered with 2 bar pressure in each experiment and from the watching window it is fol-lowed just before to dryness. The cake was not dried com-pletely to avoid channeling and crack formation (Pre-consolidation step).
3. A very thin and glazy paper was put just over the cake to avoid the sticking of the cake to the metal disc compression helping tool on which the compressed air was employed (Consolidation step).
The filter cakes were obtained in a laboratory pres-sure filter unit purchased from Bokela-Germany which was also used in the previous studies [13, 14]. The cakes obtained from the apparatus are in the disc form and have approximately 10 mm height and 50 mm diameter. The height of the cakes is measured using an electronic com-pass in five points as shown in Figure 3b.
Cake formation (Pre-consolidation)
The first step is the application of the filtration in which the filter cake was formed by applying 2 bar air pressure for 2- 5 minutes on the top of the suspension in the filter cell.
Consolidation
In the second step, the formed cake was covered with a metal disc in the same filtration cell and the cell was closed with its tap. Then the pressurized air at 2, 4, and 6 bars was fed through the air line which is at the top of the filtration unit (see Refs. 1, 13, 14) into the cell for 20 minutes. Hence the cake was consolidated. At the end of 20 minutes, the air was stopped, the tap of the cell was opened, and the cake was taken out from the bottom part of the filtration unit, Filtratest. The cakes obtained at these conditions were fully saturated with water (S = 100 %). In order to obtain partially saturated cakes, these cakes were dried for a definite time at the open atmosphere in the labora-tory.
Details of the New Designed Apparatus: BOS
A button pressing machine used in textile industry is so modified by our team in the laboratory that it is possi-ble to use it with a high satisfaction as a shear strength measuring device for filter cakes. As mentioned before, the name of the apparatus is BOS. It is also a confined com-pression uni-axial shear force-loading device, which con-sists of a uni-axial load piston and a sensitive hydraulic pressure control unit. The apparatus is composed of four main parts:
1. The uni-axial press which composed of a hydraulical-ly moving cylinder (piston) and a fixed and a movable shear jaw
2. The hydraulic pressure control unit consists of a pres-sure regulator, an on-off control button, pipes, and two cylindrical hydraulic oil containers, two needle valves on the outlets of these containers, a hydraulically mov-ing arm and a hydraulic cylinder (piston). The hydrau-lic piston applies a constant compression and suction rate on the movable upper shearing jaw. The bottom shearing jaw is put on the electronic balance and fixed. The filter cake sample is placed on this fixed bottom jaw and it is cut between the two jaws with the downward action of the upper jaw.
3. A computer connectable electronic balance
4. A computer and a software named Filtratest purchased from Bokela-Germany. The software is essentially used for measuring the filtration rate with Filtratest appa-ratus [13, 14].
The apparatus has connected to the computer via the electronic balance interface which measures the force ap-plied during the shear tests. The Filtratest program was used to record this force. The detailed schematic representation of the equipment of the apparatus BOS is given in Figure 5.
FIGURE 5 - Schematic of the equipment of the apparatus BOS.
The best advantage of the apparatus, BOS to the
Fischer device and Universal Sand Strength Machine is the sensitive hydraulic pressure control unit, instead of handy control. With this unit the strainer or revolving lifter rate is hydraulically adjusted with air pressure. The 15-16 bar pressurized air coming from the main compressor of the laboratory building has decreased to 3-4 bars via a pres-sure regulator. Then the air line was connected to an on-off control unit. The air is separated two parts from this point and fed two different cylindrical containers which contain hydraulic oil for compression and suction. The pipes coming from the cylinders have the oil inside and the oil pressure in the pipes is adjusted again with needle valves. The outlet streams of the containers were connected to the compression line (bottom line) and to the suction line (upper line) of the main hydraulic piston. Hence the movement of the metal arm of the piston connected to this main hydraulic cylinder moves with a constant rate. This eliminates the personal errors in the measurement. Since mineral filter cakes are very ductile, their shear strength is very small. Therefore, the rate of the upper movable jaw for shearing must be slow and carefully controlled.
The second advantage of the apparatus BOS is its con-
nection to a computer through an electronic balance to record the applied force for reducing personal errors dur-ing measurements. The controlling and recording of the applied force is very important for obtaining reproducible measurements.
A third advantage of the device should probably be in
its price. It should be much cheaper to modify such a press into shearing test apparatus than a test device sold in the industrial markets. It is also very easy to use the apparatus in the laboratory conditions.
Shear Strength Measurements with the Apparatus BOS
The measurement of the shear strength of these cakes were then made using the apparatus BOS. The apparatus is suitable for holding samples, which have a uniform cylin-drical shape with 50 mm diameter. And, the maximum height of filter cakes can be up to 50 mm. The photog-raphy of the apparatus BOS is also shown in Figure 6.
BOS apparatus was used as connected to two different devices for measuring the applied force for comparison and also for high loadings. Fig.6 shows the apparatus connected to:
1. Electronic balance and
2. Mark-10 Digital torque indicator
The axial-load applying part of the device consists of a fixed frame and a hydraulic cylinder (a vertical bar). It is connected to the crosshead, upper shearing jaw which can be either raised or lowered by compressed air obtained from the compressor with a sensitive pressure control. By using the sensitive hydraulic pressure control unit, the constant loading rate of displacement can be achieved as 8.4 mm/min (0.14 mm/s). The speed of the displacement can be changed manually by adjusting the needle valves. The filter cake specimen is put between the bottom jaw and the sample holder and fixed; then it is cut in between two jaws by the downward action of the upper movable jaw. The upper and bottom jaws, filter cake and the sam-ple holder (filter cake container) are shown in Figure 7.
The test data is given as the applied shear force (meas-ured as weight) versus the displacement time using the Filtratest software. As it is mentioned before, the software is the same used by Filtratest apparatus to obtain the fil-tration rate of pressure filtration of the mineral slurries. In the case of filtration rate measurements, the weight of the
FIGURE 6 - BOS shear strength measuring apparatus using with (a) Electronic balance, (b) Mark-10 Digital torque indicator.
FIGURE 7 - The movable upper jaw, the fixed bottom jaw and the sample holder (filter cake container) of the device, BOS.
filtered liquid is measured and recorded by the electronic balance with time and then transferred to the computer to obtain the t/V-V graphs [13, 14]. Similarly the force applied on the cake specimen for shearing the sample is measured as weight and recorded by the balance in time because the bottom jaw is put on the balance. The filter cake is put on this jaw and forced to be cut by the upper jaw’s down-ward motion. The applied force for shearing the filter cake specimen increases in time and reaches to a maximum near the cut point of the sample. When the sample is cut be-tween two jaws, the Force-Time curve gives a maximum
and then goes down. The weight, recorded at this maxi-mum point was taken as the shear force used in the shear strength calculations as already given in Eq.5:
cc h*DFτ = (5)
In this apparatus, BOS, a digital force/ torque indica-tor with S- shaped sensor (MARK-10) can also be used as an external axial-load measuring device instead of the electronic balance. With this digital indicator, the measur-
ing range of BOS is increased up to 25 kg while the meas-uring range of the electronic balance is only up to 3 kg. In the case of torque indicator, the force is measured direct-ly, not as the weight.
In all the measurements, the electronic balance was used for recording the shear force if otherwise cited.
RESULTS AND DISCUSSION
Investigation of the Effect of Speed of Upper Moving Jaw on the Shear Strength Measurement:
To determine the changes in the shear strength of the filter cakes (dolomite cakes were used in these measure-ments) with the speed of the jaw, experiments have been done with the five different speeds of upper jaw. The results are given graphically in Figure 8.
As it is seen in Fig. 8, the shear strength has a maxi-mum value approximately at the speed of 0,12mm/s and then decreases slightly. Both slow and fast speed of the jaw has given lower shear strength values. In all the following experiments therefore, the speed is taken as 0,12mm/s as the speed of upper jaw.
The Control of the Reproducibility of the Shear Strength Measurements with the Apparatus, BOS
Filter cakes are formed via the collection of very fine mineral particles one over the other. Therefore, the filter cake does not have a uniform structure. In addition to that,
the shear strength of mineral filter cakes are influenced by the particle size, shape, packing fracture and surface ten-sion as well as the applied pressure, length of time for consolidating before testing, and the saturation degree [1-3, 7]. From all mentioned reasons, filter cakes can not be formed repeatedly at the same properties, although they are under the same physical conditions. The control of the reproducibility of the shear strength measurement is done in the following way:
First a filter cake is filtered and compressed with a defined pressure as described in the previous pages in the “Methods” section. After that, the prepared filter cake was divided into two equal parts. Each part of the filter cake was then used as a specimen in the shear strength meas-urement for controlling. The results of these measure-ments are given in Table 2.
In Table 2, both samples 1-2 and samples 3-4 are half parts of the same filter cakes at saturation degree around 96 % for dolomite and 0 % for quartz cakes. The dimen-sions of the cake samples were also given in the table. The two dolomite samples have reached the same shear strength value, 22.3 kN/m2. Similar results were obtained with quartz samples: one half of the same cake’s shear strength was 7.2 kN/m2 and the other’s was 7.2 kN/m2. It is very clear from these findings that the apparatus BOS gives reproducible results. According to these results, it is pos-sible to say that the apparatus BOS can be used conven-iently as a shear strength measuring device.
0
5000
10000
15000
20000
25000
0.05 0.12 0.14 0.18 2.00
Speed of upper screw jack, mm/s
Shea
r Str
engt
h, N
/m2
FIGURE 8 - The effect of speed of upper jaw on the shear strength measurement
TABLE 2 - The results of reproducibility controlling experiments of the shear strength measuring apparatus, BOS.
The Comparison of the Shear Strength Results of the Appa-ratus BOS with the Other Industrial Devices: Comparison with Fischer Test Apparatus
Fisher test apparatus is an industrial device for meas-uring force answers of different materials and it was used for shear strength measurements of different mineral filter cakes in the previous studies of Ozcan and co-workers [1]. The schematic representation of the device is shown in Figure 1. It operates with the same principle as BOS and detailed explanation was already given in the previ-ous pages in the Introduction section.
Several experiments have been done to measure the shear strength of the filter cakes of dolomite and quartz using the apparatus BOS. And the results were then com-pared with the results of Fischer test device for several minerals’ filter cakes given in the previous studies [1]. Ex-periments were performed at the seven different saturation degrees under three different pressures. The results are given graphically in the Figures 9 and 10. These figures clearly show that the shear strength of the cakes increases with the increase of the compression pressure in all of the satura-tion values. The relation between the shear strength and the saturation is similar to the Schubert’s relation between tensile strength and saturation [4]. According to the Fig-ures 9 and 10 and the Schubert’s conclusion, the relation can be separated into three regions for the two different minerals dolomite and quartz and for all pressures (2, 4 and 6 bars):
Region 1: 0 ≤ S < 0.3: The bridging region in which the shear strength increases with the saturation.
Region 2: 0.3 < S < 0.8: The transition region in which the shear strength has a minimum value around S= 0.4- 0.6.
Region 3: 0.8 < S < 1: Capillary region in which the shear strength has a maximum value.
The same tendency of the shear strength-saturation curve can also be seen in the previous study of Ozcan et al. [1] in which the Fischer test device was used for meas-
FIGURE 9 - The change of the shear strength of dolomite with saturation degree at different pressures (measured with BOS).
FIGURE 10 - The change of the shear strength of of quartz
with saturation degree at different pressures (BOS measured).
FIGURE 11 - The shear strength changes of different size calcite, TiO2 and glass sphere filter cakes at 15 bar obtained with Fischer test apparatus [1].
urements. For different sized calcite, glass spheres and TiO2 minerals the results obtained at 15 bar using the Fischer test device are graphically given in Figure 11.
It is more clearly seen from the comparison of the Figures 8 and 9 with Fig. 10 that, even with different min-erals at different pressures and with different devices, the results gave the same shaped curve with three different regions. The shear strength of any mineral gives a maxi-mum around the capillary region, S = 90 % and a minimum around the transition region, S = 40-50 % measured either with BOS or with Fischer test device even at different pressures. From these comparisons it is possible to say, that the results of the apparatus BOS are in good agree-ment with the results of Fischer test device.
Comparison with Universal Sand Strength Machine:
To compare the performance of BOS apparatus, the tests were repeated with using Universal Sand Strength Machine. This apparatus measures standard samples with dimensions, 50 mm diameter and 50 mm height. The prepared filter cake samples however were approximately 10 mm high. Therefore, some supports were put as plat-form under the 10 mm high filter cakes to increase the total height up to 50 mm. The results of the measurements
of dolomite filter cakes compressed at 6 bars and 96 % saturation degree are given in Table 3.
TABLE 3 - Shear strength of dolomite filter cakes at 96 % satura-tion and 6 bar compression pressure measured with apparatus BOS and Universal Sand Strength Machine (USSM).
Type of Apparatus Dimensions of filter cake Shear Strength, kN/m2
As it is seen in Table 3, the shear strength values of
the samples of dolomite filter cakes obtained with both of the devices are very close to each other. Each half of the same cake gave the same shear strength value of 22.3 kN/m2 as mentioned before with the apparatus, BOS. The Univer-sal Sand Strength Machine, USSM also gave the shear strength values 22.4 and 22.2 kN/m2 for the two equal parts of the same dolomite filter cake. These values are also very close to the results obtained with BOS. From these findings it is strongly possible to say that the appa-ratus BOS can be used as a shear strength measuring device for compressed filter cakes.
Some Measuring Results with the Torque Indicator Connect-ed to BOS:
In the case of high loadings, especially for very fine grained mineral filter cakes, the upper limit of the elec-tronic balance (max. 3 kg) used as connected to the BOS to measure the applied force was not sufficient. In such cases it is better to use the torque indicator. To make compari-sons, different fractions of the same quartz mineral filter cakes’ shear strengths were measured by using both the electronic balance and the S-shaped sensor Mark-10 digi-tal torque indicator. Although it is possible to measure the coarser fractions cakes’ shear strength with a high sensi-tivity with electronic balance, for fine fractions, i.e. 6 and 10 microns of the same mineral the torque indicator was necessary for measurements. The results obtained with the electronic balance for coarser fractions and the torque indi-cator for fine fractions of the same quartz mineral are given in Table 4.
TABLE 4 - Shear strength measuring results of different quartz fractions’ filter cakes using electronic balance and torque indicator in connection with the apparatus BOS (at 6 bar compression pres-sure).
Particle size, µ
Shear Strength, kN/m2 Measuring device (S = 0 %) (S = 70-80
As it is seen in the Table 4, the shear strength of fine
fractions, i.e. 6 and 10 micron quartz filter cakes are al-most higher than 35.0 kN/m2. Because the maximum meas-
uring value with the electronic balance is around 30.0 kN/m2 (maximum loading is 3 kg) it is better to use the torque indi-cator up to 25 kg loading which is the maximum measur-ing value of the device. Especially finely ground filter cakes compressed at high pressures have very high shear strength values compared to the coarser ones [1, 2, 13]. It was therefore necessary to use the torque indicator in the case of the finely ground particles’ filter cakes which are consolidated at high pressures instead of the electronic balance connected with the apparatus BOS.
The results of the study can be concluded as follows: The laboratory designed apparatus; BOS for measuring the shear strength of the compressed filter cakes has given very satisfying and reproducible results. These results are in good agreement with the results of industrial test de-vices, Fischer and Universal Sand Strength Machine. The apparatus BOS was designed with the modification of a textile button pressing machine by attaching the jaws for shearing the cakes, a hydraulic piston for controlling the speed of the upper jaw, an electronic balance connected to a computer and the Filtratest program for recording the force applied on the filter cake. Instead of the electronic balance, computer and the program; a torque indicator can be used directly to record the applied force for shearing the cakes especially for high loadings.
CONCLUSION
The laboratory designed apparatus; BOS for measur-ing the shear strength of the compressed filter cakes has given very satisfying and reproducible results. These results are in good agreement with the results of industrial test devices, Fischer and Universal Sand Strength Ma-chine. The apparatus BOS was designed with the modifi-cation of a textile button pressing machine by attaching the jaws for shearing the cakes, a hydraulic piston for controlling the speed of the upper jaw, an electronic bal-ance connected to a computer and the Filtratest program for recording the force applied on the filter cake.
NOMENCLATURE
S: Saturation degree, % τ: Shear strength, N/m2 PK: Capillary pressure, bar ε: Porosity of the cake γ: Surface tension of the mineral suspension, dyn/cm δ: Contact angle f: Particle shape x: Particle size, H: Adhesion forces σ: Tensile strength, N/m2 Dc: The diameter of the filter cake, mm hc: The height of the cake, mm
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THE DIATOMS Odontella sinensis, Coscinodiscus wailesii
and Thalassiosira punctigera IN THE EUROPEAN ATLANTIC: RECENT INTRODUCTIONS OR OVERLOOKED IN THE PAST?
Fernando Gómez1,2,3,4* and Sami Souissi1,3,4
1 Université Lille Nord de France, 59000 Lille, France 2 ULCO, LOG, 62930 Wimereux, France
3 CNRS, UMR 8187, 62930 Wimereux, France 4 USTL, LOG, 62930 Wimereux, France
ABSTRACT
The diatoms Odontella sinensis, Coscinodiscus wailesii and Thalassiosira punctigera are the most com-mon examples of non-indigenous phytoplankton species in the European Seas. We investigated their seasonal and interannual distributions at two fixed stations in the northeast English Channel (1998-2005). The climate condi-tions along our 8-y time series and those during the first historical outbreaks in Europe were reconstructed. Odon-tella sinensis was preferentially found in late summer and early autumn, especially after 2003. A change in the cli-mate in 1903 may have favoured the development of O. sinensis that until then had gone unnoticed due to the low sample coverage. Coscinodiscus wailesii was preferential-ly found in winter and early spring, with a maximum in April 2001 (720 cells L-1). This coincided with exception-ally high precipitation rates, river discharges and a cold winter (negative phase of the North Atlantic Oscillation). Thalassiosira punctigera was sporadically found between autumn and early spring, with a peak in mid-December 2005 after abnormal autumn weather. The blooms of C. wailesii and T. punctigera in 1977-79 coincided with the arrival of the ‘Great Salinity Anomaly’ into the English Channel, negative NAO phase and higher river discharges. In addition to an introduction from sub-arctic waters, these two diatom species may remain as residual populations under ‘normal’ hydro-climatic conditions, misidentified, overlooked in the past and favoured after atypical climate periods. The consideration for these diatoms being la-belled as introduced or non-native species is questionable.
The impacts of global climate change on earth’s eco-systems are the subject of an increasing number of studies. Biological invasions are being recognized as an important element of global change, following the observation of increasingly spectacular developments of alien species in various regions of the world [1]. It has become obvious that human activities are responsible for massive move-ments of species, i.e. ballast waters, between the different oceans of the world [2]. The local plankton communities may be altered as well as their invasibility by exotic spe-cies from other regions [3, 4].
The climate variability may determinate the adapta-tion success of the introduced plankton species. The North Atlantic Oscillation (NAO) is responsible for much of the variability of weather in the North Atlantic region, affect-ing wind speed and wind direction changes, variations in temperature and moisture distribution and the intensity, number and track of storms. In years of high (positive) NAO winter index (December through March), the strengthened westerlies bring warmer, maritime air over northwest Europe causing a rise in temperature, mild winters, cool summers and frequent precipitation. In years of low (negative) NAO winter index, the effect of the westerlies is suppressed caus-ing the temperature to be more extreme in summer and winter leading to heatwaves, deep freezes and reduced pre-cipitation [5]. A link between the NAO and the distribution of phytoplankton [6-9] and other marine organisms have been described [10].
Numerous studies have documented the establishment of non-indigenous phytoplankton in the European waters (see references in [3]). Three centric diatoms, Odontella sinensis (Greville) Grunow, Coscinodiscus wailesii Gran et Angst and Thalassiosira punctigera (Castracane) Hasle are the most common examples in the literature. Odontella sinensis was described from material collected at Hong Kong Bay [11]. In Europe, it was first noted after prolif-eration in the North Sea in 1903, being since then a com-mon member of the diatom assemblage [12, 13]. This is
the first example of introduced phytoplankton species in the literature, presumablely carried by ballast waters, from the Red Sea or Indian Ocean [12].
Coscinodiscus wailesii and Thalassiosira punctigera have a much later start than Odontella sinensis. Coscino-discus wailesii is a giant diatom, considered as a new spe-cies from the coasts of the British Columbia [14]. In winter 1977, a high phytoplankton bloom associated with exten-sive mucus provoked the clogging of fishing nets in the southern English Channel [15, 16]. The organism respon-sible for this phenomenon was identified for several years as the giant diatom Coscinodiscus nobilis Grunow [17, 18]. It was reported for many years in other regions of the Eu-ropean Atlantic [19-22] and identified by R. Simonsen as C. wailesii (cited in [19]).
In addition to C. wailesii, another diatom identified as Thalassiosira angstii (Gran) Makarova was cited as a new-comer off Plymouth in 1978 [23]. Kat reported the prolif-eration of this diatom since March 1981 along the Dutch coasts [24]. Rincé and Paulmier also cited its presence in the English Channel since 1978 [19], and Hasle in the Skagerrak since 1979 [25]. This diatom began to receive in-creased attention and Hasle proposed that T. angstii be identified as a synonym of T. punctigera, a species of prob-lematic identification described under different names [25]. It was abundant in the English Channel in the years 1980-1981, but declined in later years [26]. Odontella sinensis, C. wailesii and T. punctigera are the most famous exam-ples of non-indigenous phytoplankton species in the Euro-pean Seas [3, 4].
The analysis of the phytoplankton seasonal and inter-annual variability would greatly aid in the detection of the arrival and the interpretation of future movements of the plankton species. The Strait of Dover, the maritime corri-dor between the English Channel and the North Sea, is a key area for the study of the distribution of plankton spe-cies in the European Atlantic. This region is under the in-fluence of the Seine River, the main supplier of freshwa-ter into the English Channel, which discharges contribute significantly to the nutrient load transported northward along the French coasts through the ‘coastal flow’. The French national SOMLIT (Service d’Observation en Milieu LITtoral) monitoring program was established off Bo-lougne-sur-Mer (NE English Channel) in November 1997. We examined the evolution of Odontella sinensis, Coscinodiscus wailesii and Thalassiosira punctifera along an 8-y time series in order to establish their seasonal and interannual variability. In addition, we reconstructed the climate-environmental conditions when the first outbreaks of these species were reported in Europe. The combination of these data aims to elucidate between two hypothesis for the biogeographical origin of these species: 1) human-induced introduction (i.e., ballast waters, imported oys-ters), or 2) these species were already present as minor component of the phytoplankton, they were overlooked in the past, or they are now receiving attention after an
anomalous set of climate conditions triggered the prolif-erations.
MATERIALS AND METHODS
Overall, 158 cruises were carried out on board the R/V Sepia II from November 1997 to December 2005 off Bou-logne-sur-Mer (NE English Channel) (Fig. 1). Two fixed stations were sampled during the high tide. One station was located 2 km offshore (50°40.75’; 1°31.17’ E; 21 m depth) and influenced by ‘coastal flow’ and the other station was 8 km offshore (50°40.75’N; 1°24.60’E, 50 m depth). The sampling frequency was planned to be biweekly, but cruises were sometimes cancelled or restricted to the close to shore station due to meteorological constraints. Sea-water samples were collected with a Niskin bottle at the surface and at one meter above the bottom. Lugol-fixed samples of 25 or 50 mL were settled in composite settling chambers. The entire chamber was scanned at 200× magnification with an IX71 inverted Olympus microscope and specimens were photographed at 400× magnification. The sample analysis of the 8-y time series was carried out with the same meth-odology and by the same observer.
FIGURE 1 - Map of the English Channel.
Sampling stations indicated by solid circles. Continuous records of air temperature, precipitation,
wind strength and direction (0-360°) were provided by the French Meteorological Agency (Météo-France Boulogne-sur-Mer) from a meteorological station located at Boulogne-sur-Mer (50°44’N, 1°36’E, altitude 73 m). These data are re-presented as average values per season. North Atlantic Oscil-lation winter index, hereafter abbreviated as -NAOw-, was downloaded from the National Center for Atmospheric Re-search website (http://www.cgd.ucar.edu/cas/jhurrell/indices. html). Daily river discharges of the Seine measured at Poses dam are obtained from the GIP Seine-Aval (http://seine-aval.crihan.fr/).
In proximity to the Strait of Dover, the strong winds enhanced the northward current from the English Channel into the North Sea. The mean wind direction along the 8-y time series was 179° (southerly winds). This dominant wind direction is altered by westerlies (values closer to ~210°) with moist Atlantic air and the north - or south - easterlies (values closer to ~150°) from the continent with extreme temperatures. As a general trend, this 8-y time series study revealed two main periods: 1998-2000 was predominated by a moderate or high positive NAOw, (i.e. mild winters, strong winds and high autumnal precipitation), a transition period in 2001 and by a neutral, NAOw ~0, in 2002-2005 (i.e. reduction of wind strength and higher weather variabil-ity, extreme winter and summer temperatures) (Fig. 2).
1998-2000 NAO positive phase and 2001 transition period. The 1998-2000 period was characterized by mild winters, abundant precipitation, especially in autumn and stronger winds with an important westerly component (Fig. 2). The NAOw in 2000 showed the highest positive value of the 8-y time series (2.80). The general trend for a high positive NAOw are strengthened westerlies that bring war-mer, maritime air over northwest Europe causing a rise in temperature. After scarce precipitation in winter, the spring of 2000 showed the highest rainfall along the 8-y time series (Fig. 2F). The autumn of 2000 resulted showed the high-est mean wind strength (7.38 m s-1) with the highest com-ponent of westerlies (199°) for that season along the 8-y time series (Fig. 2M,N,O,P). The blowing of the maritime
wind in autumn 2000 was associated with the highest au-tumnal precipitation values as compared to any other year (Fig. 2N).
In contrast to the previous year, 2001 is illustrated by the lowest (negative) NAOw (-1.89) since 1996 (-3.78). The lowest winter temperatures (4.91 °C), lowest wind strength and direction (158°) for the 1998-2005 period were recorded in 2001 (Fig. 2A,C,D). The highest precipitations were re-corded in autumn 2000 and continued to the winter of 2001, with values higher than those of any other winters (Fig. 2B). These precipitation rates were associated with the norther-ly and easterly wind events. In March 2001, the discharge of the Seine River resulted in the highest peak water level (2280 m3 s-1) over the last six decades (Fig. 3). The lowest April mean temperatures for the 1998-2005 period were re-corded in 2001 (8.22 °C). Along with these factors, the water column mixing and river runoff were expected to increase the nutrient stock for the spring diatom bloom in 2001.
2002-2005 neutral NAO phase. Higher autumnal rain-fall was recorded throughout the 1998-2000 period and was associated with higher wind strength and westerlies. In contrast, the autumn seasons of the 2002-2005 period were drier and the wind strength was reduced about 30-40% with a lower contribution of westerlies (Fig. 2N-P). In the period 2002-2005, the values of NAOw were neutral (index ~0). A moderate positive NAOw (0.76) in 2002 constituted the only exception. It showed the strongest winter winds (7.76 m s-1) along the 8-y time series, along with an important contri-bution of westerlies. The maritime air contributed to an in-creased temperature, resulting in the one of the mildest winters (6.7 °C) in 2002 (Fig. 2A-D).
FIGURE 2 - 1998-2005 variations in monthly means of air temperature (°C) (A,E,I,M), daily precipitation (mm) (B,F,J,N), wind speed (m s-1) (C,G,K,O) and wind direction expressed as degrees (0-360°) with respect to the north (D,H,L,P) in winter, spring, summer and autumn of the period 1998-2005 at Boulogne-sur-Mer. The NAO winter indices are indicated in the upper panels.
FIGURE 3 - Temporal evolution of freshwater discharges of the Seine River at Poses Dam. Source: http://seine-aval.crihan.fr/webGIPSA/; and the NAO winter index (December-March). Source: http://www.cgd.ucar.edu/cas/jhurrell/indices.html
The summer and autumn in 2002 and 2003 was rep-
resented by more stable weather conditions, lowered wind strength and decreased westerly winds (Fig. 2I-P). The summer of 2003 was the warmest recorded during the 8-y time series (Fig. 2I). In contrast, the autumn of 2003 demonstrated the second coldest temperatures (9.27 °C) and was the driest for the 1998-2005 period (Fig. 2M). The summer of 2004 incurred a higher wind strength and in-cidence of westerlies since 2001 (Fig. 2K,L). The highest mean autumn temperatures (10.97 °C), and the weakest mean winds for the 1998-2005 were recorded in 2005 (Fig. 2M-P). Under the stable weather, the Seine River had the lowest discharges in summer-autumn of 2003 and 2005 (Fig. 3).
Odontella sinensis
In the northeast English Channel the genus Odontella C.A. Agardh was represented by O. aurita (Lyngbye) C.A. Agardh, O. mobiliensis (J.W. Bailey) Grunow, O. regia (M. Schültze) R. Simonsen, O. rhombus (Ehrenberg) Kützing and O. sinensis. The last taxon is identified by its large size 100-250 µm (apical axis) and the flat or slightly con-cave valve face between processes (Fig. 4A-C). Odontella sinensis and O. regia may be confused with each other.
Although O. sinensis may be occasionally encountered throughout the entire year, it tended to reach higher abun-dances in early autumn. The species was not recorded in the years 2000 and 2002. Offshore (8 km), the abundance was lower than the more onshore station (2 km). Inshore, the abundance was higher on the surface, whereas in the offshore station the abundance tended to be slightly higher
in deeper waters (50 m depth) (Fig. 5A-B). The interannual distribution of O. sinensis showed two peaks in October 2003 (3200 cells L-1) and September 2004 (8000 cells L-1). The warmest summer temperatures for the 1998-2005 peri-od were recorded in 2003 (Fig. 2I). In contrast, the autumn of 2003 was the second coldest and the driest (Fig. 2M). These abnormal and contrasting weather phenomena seem to favour the peak of O. sinensis (Fig. 5A-B). In 2004, an unusual peak in abundance appeared in spring and early summer, with the greatest in September 2004. The lowest spring wind strength and precipitation for the 1998-2005 period were recorded in 2004 (Fig. 2F-G). The unusually calm conditions for spring 2004 seemed to favour the small peak of abundance. The calm spring was followed by a summer with the greatest wind strength since 2001, contrib-uted by the westerlies (Fig. 2C-D). The anomalous mete-orological conditions in the warmer seasons since 2003 may have favoured the proliferation of a priori warm-water species such as O. sinensis (Fig. 5A-B).
Coscinodiscus wailesii
This large, centric diatom (180-450 µm in valve diame-ter) had a rectangular outline in girdle view and the valves are flattened with a concentric depression. The valvar sur-face had hexagonal areolae with a sharp radial disposition and a hyaline central area (Fig. 4D-F). Coscinodiscus wailesii is occasionally recorded from late autumn to late spring, with peaks in winter and early spring. Inshore, the abundance was slightly higher on the surface. The highest abundance was recorded in April 2001 (720 cells L-1). The abundance decreased since 2003, and was not detected in 2004 at all (Fig. 5C-D).
This diatom is smaller in size than the previously men-tioned taxa (40-100 µm in diameter). The most distinctive characteristic is the ring of strutted processes (fultoportulae)
FIGURE 5 - Temporal distribution of the abundance (cells ×103 L-1) of Odontella sinensis (A, B), Coscinodiscus wailesii (C, D) and Thalassi-osira punctigera (E, F) in the NE English Channel (1998-2005). Left and right panels for offshore and onshore stations, respectively.
on the margin of the valve that has short external tubes and a convex valve surface. It tended to appear as single cells or short colonies connected by a thin thread (Fig. 4G-I). The abundance rarely exceeded 150 cells L-1 and it was even less in offshore waters. It is difficult to establish a trend on the distribution of T. punctigera because the records are dis-persed and can be found throughout the entire year, except in the summer. The highest abundance (3200 cells L-1) was recorded in mid-December 2005 (Fig. 5E-F). The autumn of 2005, especially October, was the warmest of the 8-y time series (Fig. 2M). For example, the mean daily air tem-perature was 18.4 °C on October 30th and decreased to 2.9 °C on November 25th. The anomalous conditions pro-longed the warm summer conditions until November when a drastic decrease in temperature was associated with a peak of T. punctigera.
DISCUSSION
Odontella sinensis
This diatom was described in an early study on marine plankton from the warm coast of southern China in Hong Kong Bay [11]. The distribution of O. sinensis along the 8-y time series in the NE English Channel revealed higher abun-dances since 2003. The summers and autumns of the peri-od 2001-2005 (negative or neutral NAOw) showed lower wind strength when compared to the 1998-2000 period. According to the literature, the summer of 2003 incurred a heat wave in August and was the warmest during the past 500 years [27]. Calmer conditions and higher temperatures, especially since 2003, seem to favour the occurrence of O. sinensis. However, the thermal stratification (stabilization) did not favour the nutrient inputs required for the prolifer-ation of large diatoms such as O. sinensis. In 2003, there was a drastic transition between an exceptionally warm summer and extremely cold autumn. In October 2003, the first autumnal storms may have enriched the still warm waters, favouring the short bloom of O. sinensis (Fig. 5A-B). The intense wind strength in the summer of 2004 may have been responsible of the largest abundance of O. sinen-sis in September. The summer conditions extended to late October in 2005 (Fig. 2N). Under these unusually stable conditions in autumn, the development of O. sinensis was delayed until the beginning of November, which was later than usual and resulted in a smaller abundance (800 cells L-1) in comparison to previous years (Fig. 5B).
Odontella sinensis was cited for the first time in Europe in 1903 [12]. However, Boalch [26, p. 232] reported “Odon-tella sinensis which came to Europe from the Far East in 1889 and spread throughout European water (Ostenfeld, 1908) and is now an important constituent of the winter and spring diatom flora”. We are unable to find the source of the earlier citation from 1889, but in our sampling region, O. sinensis tended to appear in late summer and autumn. Dur-ing the nineteenth century most of the world’s taxonomic expertise and sampling effort was concentrated along the
northern European coasts. Before 1903, especially in 1889, the sample coverage was low and it is not unusual that any diatom would be first cited in the North Sea before any other regions of the world [12].
Most of the large diatom species were first described
from the European coasts. The pioneer study of Greville in 1866 reported numerous new species, such as O. sinensis, later found to be common in Europe [11]. However, the dia-toms described from locations outside Europe should not be considered of exotic origin due to the scarce sampling cov-erage. For example, Skeletonema costatum (Greville) Cleve has been traditionally cited as one of the most common blooming diatoms in the estuarine and coastal European waters. As O. sinensis, S. costatum was first described in Hong Kong Bay, and it was not considered a non-indigenous species in Europe. Odontella regia, quite similar to O. sinen-sis, was described from the North Sea. In Chinese waters, O. regia is a common blooming species [28]. Due to the polymorphism of O. sinensis [29], O. sinensis may have been misidentified with O. regia before 1903. It is risky to consider O. sinensis as an introduced or non-indigenous species in European waters because presumably it went unnoticed before 1903. Recent studies have shown that the cosmopolitan diatom Skeletonema costatum sensu lato is composed of several morphologically and genetically dis-tinct species [30]. Molecular methods have not been ap-plied to investigate the genetic characteristics of the popu-lations of O. sinensis, C. wailesii and T. punctigera in dif-ferent world regions.
An environmental factor, such as a climate drift, may
have triggered the proliferation of, until then, minor mem-bers of the phytoplankton assemblage. In 1903, after 3 years of negative NAOw, the highest positive index (3.89) in 126 years (since the first index in 1864 and 1989) was re-corded. It was in that year that a 12-y period of positive NAO phase began and O. sinensis became widely dis-tributed throughout European waters. In our study, it was difficult to establish a relation between the distribution of O. sinensis and the positive or negative NAOw due to a higher proliferation that coincided with neutral values, NAOw ~0. The NAOw is based on the atmospheric pres-sure recorded between December and March [5]. Conse-quently the NAOw is not a good descriptor for the climate conditions of the summer and early autumn periods when diatoms, such as O. sinensis, proliferated. The NAOw would be more useful for the phytoplankton that proliferated in winter and early spring (i.e. C. wailesii). Along our 8-y time series, O. sinensis proliferated in warm periods, especially after mixing events (nutrient inputs). This scenario may be similar to a harbour in a tropical region with warm waters and high nutrient inputs (type locality of O. sinensis). The climate conditions before 1903 may have been unfavoura-ble for O. sinensis, being undetected due to the scarce sample coverage or misidentified with O. regia. The exotic origin of the early description of O. sinensis should not provoke the thought that it was a non-indigenous species.
Coscinodiscus wailesii is a world-wide distributed spe-cies, known from all the ocean regions. The populations in the subarctic waters [31] are connected with the boreal waters of the Pacific and Atlantic Oceans. It is a common blooming species at both sides of the temperate-boreal North Pacific [32, 33] and the tropical Pacific [34-36] and cited at both sides of the temperate South Pacific [37, 38]. It is found mutually on either side of the South Atlantic [39, 40]. In the North Atlantic, it is cited from the Carib-bean Sea [41] and the North American Atlantic coasts [42- 44], with a massive bloom reported off Florida [45]. The blooms of C. wailesii seem to be more frequent in cold coastal waters with frequent freshwater inputs [33, 46]. The world-wide distribution of C. wailesii is contrary to the theory that it is a non-indigenous species in any location.
According to the literature, C. wailesii was first rec-orded in Europe in 1977. The records of large Coscino-discus species in Europe are usually assigned to the spe-cies C. asteromphalus Ehrenberg, C. centralis Ehrenberg, and C. concinnus W. Smith, which are morphologically similar and may cause identification problems [20]. Stud-ies based on clonal cultures have reported a high variabil-ity in the valve morphology of C. concinnus, which also include other forms comparable to C. granii Gough [47]. In addition, C. wailesii demonstrated a high intraspecific variability during clonal culturing methods [48]. Most of the giant Coscinodiscus species, easily collectable by net sampling in coastal-estuarine waters, were described in the earlier diatom studies along the nineteenth century. How-ever, C. wailesii was described relatively late, in 1931, along the shores of British Columbia [14]. The original description, published in a local journal of a Marine Station from the Pacific coast may have gone unnoticed by European re-searchers. Unless since 1972, the Helgoland phytoplankton time-series, German North Sea, reported a large Coscino-discus identified as C. wailesii. Wiltshire and Dürselen [49] reported “For this species, data in the electronic database were changed later - but not from all size classes. Examples: March 1972 Coscinodiscus sp. size class 400 µm was changed to C. wailesii later; May 1987 Coscinodiscus sp. size class 270 µm was changed to C. wailesii later”.
Coscinodiscus nobilis renamed as C. wailesii? The re-sponsible agent for the large blooms of phytoplankton in the winter of 1977 in the English Channel was identified as C. nobilis for several years [17, 18]. In later years, R. Si-monsen (cited in [19]) stated that the responsible diatom for the plankton bloom in 1977 was C. wailesii instead of C. nobilis. The latter was described from the brackish waters of the Caspian Sea [50] and has been cited from the arctic [51], boreal (Okhotsk, Japan, China Seas) and tropical wa-ters (Indonesia, Madagascar, Gulf of Guinea) (see refer-ences in [52]). Cleve-Euler considered it as a form of C. concinnus (=C. concinnus f. nobilis (Grunow) Cleve-Euler) [53]. Coscinodiscus wailesii and C. nobilis are similar in shape, size, the lack of a central rosette and the number of areolae in 10 µm. The valve is flat in C. wailesii and
flat or slightly convex in C. nobilis [34, 54]. Baars [54] from a culture of C. concinnus observed two morphotypes, the normal voluminous form and a flatter form with a few inter-calary bands. Baars observed that the absence or presence of a hyaline area and intercalary bands are not diagnostic crite-ria for the species separation [54].
Since the 1960s, C. nobilis and C. concinnus have been cited as separated species in the estuaries of Brittany, Eng-lish Channel [55]. The studies on the morphology of C. wailesii over the last three decades have been numerous, re-vealing a high intraclonal morphological variability [48], whereas no study of C. nobilis has been published. Before the 1980s, the records of C. nobilis were numerous with the latest being completed in 1968 and 1971 [52, 56]. After the blooms in late 1970s, the citations of C. wailesii have been numerous, whereas C. nobilis has disappeared from the literature. Coscinodiscus wailesii is a common blooming species around Japan and China [32, 35, 46]. However be-fore 1931, C. nobilis (also described as C. cylindricus Mangin) was the giant diatom found in these regions [57-59]. A comparative morphological study of both taxa is necessary to discard the hypothesis that C. wailesii is a syno-nym of C. nobilis. A study from material collected in the type locality of C. nobilis could solve these doubts. How-ever, the current environmental conditions of the Caspian Sea are far from those in the nineteenth century [50].
Blooms in 1977-1983: Coscinodiscus wailesii or C. no-bilis began to receive attention after the intense blooms in the winter of 1977. A set of climate-environmental factors triggered the population of C. wailesii as a true newcomer species and/or expanded the local populations of C. nobi-lis from the estuaries of Brittany into the English Chan-nel. Cold, eutrophic waters with high freshwater runoffs characterize the type localities of both species, the coasts of the British Columbia and the Caspian Sea. Both C. wailesii and C. nobilis, are giant, non-buoyant, diatoms requiring high nutrient inputs (silicate) and water column mixing to proliferate.
In 1968, an incursion of fresh, cold polar waters, ‘Great Salinity Anomaly’, via the Denmark Strait propagated into the North Atlantic and arrived at the English Channel in 1977, the North Sea in 1978, apparently returned to the Icelandic region in 1982 [60]. After a positive NAO phase occurred from 1972, negative NAO phase was recorded in 1977 (-2.14) and 1979 (-2.25). The winter discharges of the Seine River were unusually low in the 1971-1976 period, whereas in the period 1977-1983 was recorded very high winter discharges (Fig. 3). The exceptional climate condi-tions in the period 1977-1979 favoured the C. wailesii blooms.
Blooms in 2001: The highest abundance in this study (720 cells L-1) was recorded in April 2001. This observa-tion coincided with a bloom associated with mucus produc-tion in the northern Bay of Biscay [61]. In 2001, a very low (negative) value of the NAOw (-1.89) occurred. In March 2001, the highest peak (2280 m3 s-1) of freshwater dis-
charges from the Seine River over the past six decades occurred (Fig. 3). The transition between a high positive NAOw in 2000 (high autumnal precipitation) and a nega-tive NAOw in 2001 (the coldest and rainiest winter, high mixing) favoured the highest abundance of C. wailesii during the early spring of 2001.
Rincé and Paulmier [19] suggested the introduction of
C. wailesii by ballast water transport or through the impor-tation of Japanese oysters. In contrast, two hypotheses for the biogeographical origin of the new blooming species in 1977 are proposed: 1) Coscinodiscus wailesii, known from polar waters and the Atlantic coasts of North America [42], was transported by currents into the European Atlantic, where the bloom was favoured by the ‘Great Salinity Anomaly’, cold temperatures and freshwater inputs from 1977-1979; or 2) the local populations, previously misi-dentified with congeneric species, such as C. concinnus or C. nobilis, bloomed and expanded under the exceptional favourable conditions in 1977-1979.
Thalassiosira punctigera
Thalassiosira punctigera is a medium-size diatom (~50 µm in diameter), inefficiently retained by net sam-pling where its delicate processes are easily damaged, thus making identification difficult during routine analysis. Ac-cording to Hasle [25], T. punctigera is an extremely variable species with regard to size and valve structure and may be confused with other species. This taxon, initially described as Ethmodiscus punctiger Castracane, has been further des-cribed as other species such as Coscinodiscus verecundus Mann, Coscinodiscus angstii Gran in Gran and Angst (= Thalassiosira angstii (Gran) Makarova) and Thalassiosira japonica Kiselev. Thalassiosira licea Fryxell and T. lun-diana Fryxell are closely related species (see references in [25]). Hasle entitled her article “a widely distributed ma-rine planktonic diatom” that discussed the cosmopolitan character of T. punctigera [25].
The proliferation of C. wailesii after the extreme con-
ditions seen in 1977-1979 increased the interest in the new diatoms. Kat [24] revealed that T. punctigera (as T. ang-stii) was favoured by the freshwater inputs. Coscinodiscus wailesii and T. angstii were described from the same study and region [14]. Consequently both taxa may be favoured by similar climatic conditions. After the dry 1971-1976 period, the high precipitation during 1977-1983 favoured the development of T. punctigera. In the present study, the highest abundance of T. punctifera was recorded after a drastic decrease in temperature during the abnormal autumn in 2005. Minor components of the phytoplankton assemblage may have gone unnoticed for long periods due to the low abundance and/or difficult identification. During the abnormal hydro-climatic conditions, i.e. 1977-1979 or late 2005, the usual diatom assemblage may pos-sibly have been altered, while rare species, such as T. punctifera, were allowed to proliferate. The non-indigenous character of T. punctigera was highly questionable.
CONCLUSIONS
The consideration of introduced species implies that: 1) it colonizes a new region where it was not previously present; (2) the extension of its range is linked, directly or indirectly, to human activity; (3) there is a geographical dis-continuity between its native area and the new area (re-mote dispersal). This means that the marginal dispersal, occasional advances or withdrawals of a species at the frontiers of its native range linked to climatic episodes is not taken into consideration [2]. The diatoms, O. sinensis, C. wailesii and T. punctigera, did not achieve any of these conditions to be considered as non-native species in Europe. Odontella sinensis may have gone unnoticed due to the scarce sample coverage and the unfavourable conditions before 1903 or it was simply confused with O. regia. Thalassiosira punctigera, a minor component of the diatom assemblage, may have been easily confused with other congeneric species, which proliferated under the extreme climate conditions from 1977-1979. Coscinodis-cus wailesii, known from the sub-arctic waters and the north-western Atlantic may have been transported by currents into the European Atlantic and bloomed due to the ‘Great Salinity Anomaly’ and the climate in 1977-1979. Conversely, the local populations, previously misi-dentified with other Cos-cinodiscus species, such as C. concinnus or C. nobilis, bloomed and expanded during the 1977-1979 period. In any case, this constituted a marginal dispersal linked to climatic episodes and it is not the intro-duction of exotic flora. It is questionable to consider these diatoms as introduced or non-native species in the Euro-pean Seas. The lack of ex-perts in taxonomy of phyto-plankton in the monitoring programs makes it difficult to evaluate future changes in marine biodiversity.
ACKNOWLEDGEMENTS
Samples were collected within the context of the SOM-LIT program on board R/V Sepia II (INSU-CNRS). We thank N. Degros, E. Lecuyer, D. Devreker and G. Flamme for their help in sample collection. This is a contribution to Seine-Aval program (projects CLIMAT and BIODISEINE). We thank the GIP Seine-Aval (http://seine-aval.crihan.fr/) for providing daily data on Seine River discharges.
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Received: September 21, 2009 Revised: December 21, 2009 Accepted: January 29, 2010 CORRESPONDING AUTHOR
Fernando Gómez Université Lille Nord de France Laboratoire d´Océanologie et Géosciences CNRS UMR 8187, MREN-ULCO 32 Av. Foch, 62930 Wimereux FRANCE E-mail: [email protected]
IMPACT OF IRRIGATION WITH UNCONVENTIONAL WATERS ON THE SOIL-PLANT SYSTEM: SOME EXPERIENCES WITH SUNFLOWER
Marco Antonio Russo1*, Adalgisa Belligno1 and Vito Sardo2
1Department of Agrochemistry, University of Catania, via Santa Sofia 98, 95130 Catania, Italy bDepartment of Agricultural Engineering, University of Catania, via Santa Sofia 98, 95130 Catania, Italy
ABSTRACT
A research was conducted on lysimeter-grown sun-flower plants (Helianthus annuus L.), irrigated with sea-water diluted to 1/6 and 1/3; two crop cycles were grown in two successive years while in the intermediate season rain-fed winter wheat was grown. Treatments included two salinity levels plus a control with freshwater and two leaching fractions (approximately 20 % and 33 %).
The results largely confirmed earlier data on mecha-nisms developed by plants to alleviate salt stress, such as the changes in relative content of inorganic and organic components, all aimed at balancing the osmotic potential and the nutritional disorders. Also the evaluation of some parameters including the K/Na ratio as well as the proline and sorbitol relative content as indicators of plant stress level was done. The research showed the need to revise available guidelines for the estimation of plant tolerance to salinity, since it was once again shown that those exist-ing grossly underestimate it.
The results from treatments with different leaching fractions showed the inadequacy of the approach general-ly adopted in determining leaching requirement, since higher volumes of applied saline water resulted in a higher saline content in soil-saturated extract due to the soil col-loid adsorption.
Results showed also that in a typical Mediterranean cli-mate, where winter precipitations average is about 500 mm, there is a potential for sustainably using brackish waters for irrigation, provided that an efficient drainage system is available.
The ever more acute shortage of good quality water has prompted a vast amount of research aimed at assessing the effects and the sustainability of the irrigation with non-conventional waters.
New salt-tolerant plant varieties are explored, toler-ance thresholds are revised, the environmental impacts are accurately assessed; however, the necessary integrated ap-proach required by all the ecology-related issues is rarely adopted [1].
In fact, while it is important to know in detail plant re-sponse and adaptation mechanisms to saline conditions as well as the impact of saline waters on soil fertility, it is of paramount interest to explore the combined response of crops and soils to irrigation with saline waters and the sub-sequent leaching on dependence of winter rains.
The present research investigated the effects of the use of highly saline water for the irrigation of two cycles of sunflower (Helianthus annuus, cv. Katharina) with an in-termediate cycle of rain-fed durum wheat (Triticum durum, cv. Ofanto) with the aim of exploring the response of the plants and the soil to the various saline treatments and, therefore, refers to plant response to irrigation with saline water and salt balance in the soil as affected by precipita-tions during three consecutive growth cycles.
Since salinity depending on seawater addition deter-mines effects different from those of other salinity sources, while seawater is a widely available resource, it was se-lected for the research and the effects of two different con-centrations were observed.
The purpose of the research was two-fold: 1) analyz-ing in some depth plant response in terms of biomass and yield production and of chemical components variation as an adaptation to salinity, and 2) studying the salinity fluc-tuations in the soil as affected by leaching fractions and rainfall.
Both purposes derived from the awareness that exist-ing guidelines for the prediction of yield reduction due to salinity and the determination of leaching requirements, worked out in times of abundant freshwater availability, are only an approximation, needing a refinement as accu-rate as possible.
MATERIALS AND METHODS
Experiments were conducted in 1-m3 lysimeters filled with a sandy loam soil which is characterized in Table 1.
TABLE 1 - Physical-chemical characteristics of soil (0-30 cm depth) during the experimental period.
Sand % 57.80 Silt % 16.60
Clay % 25.60 C % 0.95 N ‰ 1.15
Ca total % 2.00 Ca active ‰ 0.80
The treatments included three levels of salinity and two
leaching fractions, as reported below, with three replica-tions, thus reaching a total of 18 lysimeters. The details of the treatments are reported in Table 2.
“LF 1” indicates those treatments where irrigation water was applied in excess, since an amount correspond-ing to 100% potential evapotranspiration (PET, as deter-mined by averaging data resulting from a class A evaporime-ter, and those resulting from the Hargreaves-Samani equa-tion) was applied throughout the two sunflower cycles,
even in those stages when plant requirements were well below the maximum. The difference between PET and the real plant evapotranspiration, corresponding to about 20% of the irrigation volume, was drained and constituted “Leaching fraction 1”. In the treatments labelled as “LF 2”, 20% more water was applied than in LF1: water drained in the three treatments labeled LF1 averaged 110 mm, whereas in LF2, it averaged 220 mm.
Plants were fertilized with nitrogen-phosphorus-potassium (NPK 11, 22, 16) and irrigated by means of an automatic drip system with six drippers per lysimeter, ap-plying identical amounts of water to all of them at the rate of 2 L/h. The drippers were arranged in a way that the ratio of those applying freshwater to those applying seawater was 6 to 0 in the freshwater treatment, 5 to 1 in the 1/6 seawater treatment, and 4 to 2 in the 1/3 seawater treat-ment. The characteristics of fresh water as well as the com-position of sea water and solutions (1/6 and 1/3) used for irrigation are presented in Table 3.
Twelve sunflower plants of the cultivar Katharina per lysimeter were planted in April and harvested in July, in a 100-days cycle. A second cycle with the same plant densi-ty was planted in June (of the next year) and harvested in September, with a duration of 120 days.
In the winter season, between the two sunflower cy-cles, durum wheat of the cultivar Ofanto was planted in November with a seed density of 20 g/lysimeter and the plants were harvested in May.
Precipitations in the period between the two sunflower cycles, from July to June, totalled 305 mm.
The following sets of analyses were conducted on second cycle, and the plants were harvested in September. • biometric analysis: plant fresh and dry weight; N total,
P total, K, Na, Ca, and Cl in the leaves [2].
For Cl analysis, 0.5 g were incubated in 5 ml of distil-lated water for 30 min at 60 °C and, after centrifugation, the supernatants were collected. This procedure was re-peated three times. Cl was determined by the mercuric thio-cyanate method using a reagent kit from Hach (DR/2000 direct reading spectophotometer).
• spectrophotometric determinations in the leaves: chlo-rophyll, extracted by addition of aqueous acetone (80 %), according to Arnon [3]
total proteins, extracted by addition of 5 ml of 10 % trichloroacetic acid in acetone containing 0.07 % β-mercaptoethanol, according to Ashraf and Harris [4]
proline, extracted with 3 % sulphosalicylic acid. Ex-tracts (2 ml) were held for 1 h in boiling water by add-ing 2 ml ninhydrin and 2 ml glacial acetic acid, after which cold toluene (4 ml) was added [5]
• gaschromatographic determinations in the leaves: glucose, sucrose, fructose, sorbitol, citric, malic and succinic acid. Sugar and organic acid contents, extracted by addition of aqueous ethanol (80 %), according to Bates et al. [6].
At the end of every cycle, the electrical conductivity of soil saturation extract was analyzed.
The results were statistically proven by means of a one-way analysis of variance (ANOVA), using Tukey`s test to compare the means. Different letters indicate significant differences at P≤ 0.05.
RESULTS
Only the most valid and verified data are presented within this paper.
In Table 4, the evolution of soil salinity is presented, showing its fluctuations in dependence of the irrigation with saline water during the two cropping cycles, and the influence of rainwater leaching between them.
Table 5 includes the reduction of dry weight of above-ground biomass in the saline treatments as compared to the control.
Chlorophyll a and b percentages in fresh matter showed a steady and consistent decrease parallel to salinity in all the treatments (Table 5), so that their ratio remained fairly constant.
The final content of inorganic components, in terms of percentage of dry matter, followed the expected pattern, with an obvious steady increase of Na and Cl in treatments
TABLE 4 - Fluctuations in soil electric conductivity (EC) (dS m-1) with different salinity.
TABLE 5 - Dry weight and content of chlorophyll a and b (mg 1000 g-1 fresh matter) in sunflower (cv. Katharina) leaves (g m-2) with different salinities.
dry weight 481.52 a 233.84 b 187.85 c 599.12 a 512.46 b 335.58 c chlorophyll a 9.23 a 7.62 b 6.22 c 9.65 a 8.41 b 7.23 c chlorophyll b 5.87 a 3.83 b 2.63 c 3.66 a 3.35 b 2.79 c
Mean values followed by different letters are significantly different at P≤ 0.05; fw = fresh water (control)
TABLE 6 - Content of elements (% dry matter) in sunflower (cv. Katharina) leaves with different salinities.
N 0.92 a 0.85 b 0.86 b 0.93 a 0.89 a 0.77 b P 0.62 a 0.40 b 0.32 c 0.86 a 0.33 b 0.29 c K 3.49 a 3.17 b 2.06 c 3.61 a 3.42 b 2.62 c Ca 3.92 c 4.66 b 5.63 a 3.71 b 4.79 a 4.90 a Na 0.33 c 0.54 b 0.69 a 0.16 c 0.34 b 0.75 a Cl 0.26 c 0.81 b 1.27 a 0.29 c 0.66 b 1.14 a
K/Na 10.57 a 5.87 b 2.98 c 22.56 a 10.06 b 4.03 c Significance of the letters and abbreviations as in Table 5.
TABLE 7 - Contents of sorbitol, carbohydrates and organic acids (mg 100 g-1 dry matter), total protein (% dry matter) and proline (µmol g-1 fresh matter) in sunflower (cv. Katharina) leaves with different salinities.
sorbitol 1.23 c 2.03 b 2.35 a 2.35 c 2.85 b 4.25 a fructose 79.57 c 146.0 b 186.16 a 90.17 b 152.47 a 150.45 a glucose 135.55 b 136.55 b 238.92 a 134.25 b 163.65 a 167.15 a sucrose 19.05 c 37.15 b 50.14 a 31.25 b 39.25 b 56.84 a
succinic acid 5.18 b 6.20 a 5.33 b 5.96 ab 6.54 a 5.62 b malic acid 3.46 a 2.66 b 3.21 a 5.09 a 4.67 b 5.15 a citric acid 214.02 a 226.48 a 159.42 b 262.88 a 169.85 c 234.30 b
total protein 17.94 a 15.31 b 15.63 b 16.63 a 12.69 b 16.60 a proline 0.46 b 3.13 a 3.03 a 0.49 c 1.10 b 3.37 a
Significance of the letters and abbreviations as in Table 5.
1/6 and 1/3; Ca and K too showed the usual opposite pat-tern, since the percentage of the former resulted increas-ing with salinity while the opposite was true for the latter; as a consequence, also the K/Na ratio was considerably de-creasing. Phosphorus final content showed a close inverse relationship to soil salinity in all the treatments while, contrary to it, the nitrogen percentage was hardly affected (Table 6).
The organic component percentages (Table 7) were significantly affected by the treatments, which showed a remarkable and consistent increase with salinity. Proline response was also (consistent, thus) confirming the results of earlier researches [7-8].
DISCUSSION
The results, while in part confirming well-known evi-dence, highlighted also a few points of interest.
Soil salinity: From the diagram in Fig. 1, based on da-ta in Table 4, the leaching action of winter precipitations (305 mm) between the two sunflower cycles can be ap-preciated, opposite to the negative effect of the higher quantity of salts applied through the larger amounts of saline water in the treatments labeled LF2; in the latter case, in fact, the higher amount of applied water (approxi-mately 33 % LF) resulted in considerably higher values of EC, compared to the treatments LF1 1/6 and LF1 1/3, were a leaching fraction of about 20 % was applied (lumped data for the two cycles are reported in the diagram).
FIGURE 1- Salinity evolution in the soil.
Although it is traditionally suggested that the leach-ing requirement is increasing with increasing water salini-ty [9], it is perhaps not sufficiently acknowledged 1) that this recommendation only applies to very permeable soils, where a prompt and very efficient salt drainage is secured, otherwise a salt accumulation in the presence of even small amounts of colloids inescapably occurs, and 2) that there is no point in adding excess saline water beyond that strictly required to leach the salts to a deep soil horizon [10].
The conclusion is that encouraging soil leaching through rain water to the possible extent (e.g. by means of “water harvesting”) is to be recommended [11]. Leaching with saline water is to be confined to those conditions where a very efficient natural and/or artificial drainage can be ob-tained. In this case, only those limited water amounts barely sufficient to leach down accumulated salts should be added.
Biomass yield: Inhibition of growth due to salt stress has been universally observed, even in tolerant plants. The early response to salt stress is a considerable decrease in root, shoot, and leaf growth biomass [12]. The reduction in above-ground biomass dry weight was considerably less than shown in the literature [13]. It is easy to appreciate the much steeper slope of reduction reported in the literature and the absence of the so-called “threshold” in our results. Such a sharp difference can hardly be explained with the variation in the response of the specific cultivars.
Inorganic components: There is a clear evidence that salinity alters transport of ions and their content in plants [14]. Ion uptake and compartmentation are crucial for plant grown under saline conditions when ion homeostasis is critical. Plants, whether glycophytes or halophytes, cannot tolerate large amounts of salt in the cytoplasm, therefore, under saline conditions they either restrict the excess salts in the vacuole or compartmentalize ions in different tis-sues to facilitate their metabolic functions [15].
Plant response evidenced a reaction to salinity depend-ing on the need to poise the lower osmotic potential and the unbalanced ion absorption: K+ absorption was decreased due to membrane carriers’ inability to distinguish it from Na+ [16], while the increased uptake of Cl- and Na+ is re-sponsible for the nutritional unbalance [17]. Salinity im-poses on plant tissues ion-specific stresses resulting from
altered K+/Na+ ratio [18]. In a previous study [19] on sun-flower subject to sea water treatments, an increase of Na+ and Cl- was observed as direct consequence of their higher uptake and translocation due to the higher salt concentra-tion in the soil.
The salt stress to the plant is attenuated by the Ca2+ ions, which respond as a signal of stress [20] and membrane polarity and osmoregulation [21], and are useful to stabilize membranes [22] and increase membrane permeability as well as to contrast Na+ toxicity by regulating the transport of K+ and Na+ through the plasmatic membrane [23]. Externally supplied Ca2+ reduces the toxic effects of NaCl, presumably by facilitating higher K+/Na+ selectivi-ty; the plants, thus, regulate the expression and activity of K+ and Na+ transporters and of H+ pumps that generate the driving force for transport. High salinity also triggers increased cytosolic Ca2+ that is transported from the apo-plast and in-tracellular compartments [15].
In fact, it was observed that in two cultivars of Vigna unguiculata, respectively, sensitive and tolerant to salinity, the increased content in K+ and Ca2+ paralleled the reduc-tion of Na+ content in the salt-tolerant cultivar, thus giving evidence of the plant`s ability to exclude, at least in part, Na+ ions uptake [24].
The involvement of Ca2+ in salt tolerance has already been shown by [25] who have observed an induction of a Ca2+-binding protein in salt-stressed Arabidopsis. Moreo-ver, after salinization, an increase of mRNA levels of a Ca2+-ATPase and of a Ca2+-dependent protein kinase have been observed in tomato [26] and mungbean [27].
In the literature, it is reported that under conditions of sodium excess, if the Ca2+/ K+ ratio is about 3:1, membrane permeability is not impaired [28] since the ratio K+/ Na+ is less unbalanced [29] and, accordingly, this parameter can be assumed as an indicator of plant adaptability [18].
The reduction in N observed in saline treatments and, more evident, in those with LF2, is easily explained by both the leaching action of irrigation water and the well-known antagonism between NO3
- and Cl- ions. In fact, the two ions, although with a different ionic radius, have a quite similar hydration radius, and since chlorine has a higher chemical potential, it has also a higher absorption rate.
The K+/Na+ ratio evidences an unbalanced condition and can be, therefore, considered to be an indicator of plant tolerance to salt stress; also the enhanced Ca2+ content de-
nounces the plant ability to contrast salinity, due to the well-known antagonism between Ca2+ and Na+.
The reduction in nitrogen uptake with salinity can be explained with the antagonism between NO3
- and Cl- as well as with the modified membrane ATPase due to the excess of sodium in the rhizosphere.
Organic components: The reduced nitrogen uptake in-fluences the protein metabolism, disturbing the synthesis of structural proteins. In general, protein content is differ-ently affected by salinity: at lower levels of NaCl, it in-creases, whereas higher salt concentrations cause it to de-cline in both root and shoot [30]. Opposite to that, proline synthesis, parallel to Ca2+ content [31], was enhanced by salinity, thus confirming its role in plant defence against salinity as well as its possible use as a salt stress indicator.
The increase in proline content may play a role as osmoregulator [32], allowing sunflower to minimize the in-hibitory effects of Cl- and Na+ against N metabolism. In fact, while some authors consider the increases of proline content observed under stress conditions as an index of the damage, the increase of this osmo-compatible compound might be a mechanism used by the plant to oppose to Na+ excess. Many plants accumulate proline as a non-toxic and protective osmoregulator under saline conditions. An in-crease in Na+ and Cl- contents favors proline accumulation but decreases both the activity of proline dehydrogenase (a catabolic enzyme of proline) and the total and water-soluble Ca2+ contents [15]. Proline accumulation has been shown to be fast in Pancratium maritimum L. [30], and it is thought to function in salt stress adaptation, through protection of plant tissues against osmotic stress and/or acting as an enzyme protector.
Carbon organization was strongly influenced by salin-ity, with a relative increase in glucose, fructose and sucrose (Table 8): such data reveal the plant reaction to salt stress through the osmo-regulating activity of carbohydrates [33, 34].
Also sorbitol accumulation in leaves is an indicator of plant response to alleviate salt stress.
The decline in productivity observed for many plant species subjected to excess salinity is often associated with the reduction in photosynthesis capacity [35]. Reduc-tion in chlorophyll concentrations is probably due to the inhibitory effect of the accumulated ions of various salts on the biosynthesis of the different chlorophyll fractions.
Salinity affects the strength of the forces bringing the com-plex pigment protein-liquid, in the chloroplast structure.
Salinity reduces the chlorophyll content in salt- suscep-tible plants and increases in salt-tolerant plants.
The nearly constant chlorophyll a/b ratio (data not shown) concurs to support the relative plant ability to pre-vent the unbalancing effect of salinity observed in typically salt-sensitive plants.
CONCLUSIONS
The results largely confirm earlier data on mecha-nisms developed by plants to contrast salt stress, such as the changes in relative content of inorganic and organic components, all aimed at balancing the osmotic potential and the nutritional disorders. Also the possibility of as-suming some parameters, including the K+/Na+ ratio, the proline and sorbitol relative content as indicators of plant stress level was confirmed.
The research showed the need to revise available guidelines for the estimation of plant tolerance to salinity, since it was once again shown that those existing grossly underestimate it.
Also the generally recommended methods for estimat-ing leaching requirement are demonstrated to be inadequate for a sustainable use of saline waters in irrigation, since the critical coupling of excess water proportionally to salt con-tent, as generally suggested, leads to unnecessarily high amounts of water and salt application to the soil.
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Received: September 24, 2009 Revised: November 30, 2009; February 18, 2010 Accepted: February 19, 2010 CORRESPONDING AUTHOR
Marco Antonio Russo Dipartimento di Scienze Agronomiche, Agrochimiche e delle Produzioni Animali Università degli Studi di Catania via Santa Sofia 98 Università degli Studi di Catania 95130 Catania ITALY Phone: +39 095 7580202 Fax: +39 0977141581 E-mail: [email protected]
USING A NOVEL AROMATIC POLYAMIDE ASYMMETRIC NANOFILTRATION MEMBRANE
Xiaojing Ren1, Tao Wang1,2, Changwei Zhao1*, Songshan Du1, Zhaokun Luan1, Jun Wang1 and Deyin Hou1
1State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P.O. Box 2871, Beijing100085, China
2College of Chemical Engineering, Xiangtan University, Xiangtan 411105, China
ABSTRACT
The textile industry produces enormous quantities of dye wastewater, containing high salt and organic concen-trations, which are therefore difficult to be treated. In this work, an asymmetric Poly(m-phenylene isophthalamide) (PMIA) nanofiltration membrane was prepared by phase inversion method in order to reduce the quantity of the disposed water and, at the same time, to reuse the treated water. The morphology of the resulting membrane was characterized by scanning electron microscopy (SEM) as well as atomic force microscopy (AFM), and the molecular weight cut-off of the membrane was estimated using differ-ent polyethylene glycol (PEG) solutions. The asymmetric membrane was also evaluated for the removal of three different anionic dyes (acid, direct and reactive dyes). The effects of various parameters, such as pressure, pH, feed temperature and the presence of salt were evaluated. It was observed that the rejections of three dyes were all above 95% under 0.7 MPa at 25 oC. Long-term operating experi-ments showed that the membranes with a 900 Da cut-off could be used to concentrate 100 mg/L saline direct blue 71 solution with a high flux (＞50 L/m2·h), a high dye rejection (＞96%) and a salt retention lower than 6%. The newly developed nanofiltration membrane is suitable for the treatment of dye effluents.
It is a well-established fact that dyehouse effluents dis-charged without appropriate treatment bring about a num-ber of serious environmental problems. The textile dyes contain organic components which are usually non-bio-degradable and have ecosystem actions on rivers [1]. There are three groups of textile dyes depending on their state in
solution and on their charge: group N: neutral dyes such as disperse, vat and sulphur dyes which are not soluble in water; group C: cationic dyes like basic dyes and group A: anionic dyes that is to say acid, direct and reactive dyes which are soluble in water.
Because membrane process can act as a purely physi-cal barrier to specific components without either the deg-radation of the components or the addition of chemicals, they are different from the conventional treatment technolo-gies, such as coagulation, biological, adsorption, oxidation, ion-exchange and electrochemical methodologies [2-4]. However, among all types of membrane operations, nano-filtration (NF), due to its different mechanisms of reten-tion allows to concentrate and reject soluble and ionic dyes, such as acid, basic, direct and reactive dyes [5-7], while water and NaCl can pass through the membrane. In addi-tion, NF can also be used to eliminate coloured pollutants from wastewaters without applying very high pressures needed by reverse osmosis (RO), making this use as one of the most important applications of this membrane tech-nology [8].
Nowadays, most commercially available NF mem-branes can only be used under 45-50 oC [9, 10]. Such a re-quirement means extra capital and operating cost when deal-ing effluents from a textile bleaching and dyeing indus-try whose temperatures can range between 40-95 oC [11, 12]. Besides, as the dominant ingredient of ultra-thin dense layer for commercial composite NF/RO membranes, poly-amides are all formed through interfacial polymerization [13, 14]. There is an urgent need to develop simple tech-nologies to fabricate high-temperature resistant NF mem-branes in a single step, an area with few publications [15].
Poly(m-phenylene isophthalamide) (PMIA) is one of the most important aromatic polyamides and has been widely used because of its high thermal resistivity com-bined with excellent mechanical properties [16, 17]. Fur-thermore, it is possible to develop PMIA NF membranes by means of phase inversion method. By far, no literature is found using PMIA as material to prepare NF mem-branes through phase inversion method.
In this study, synthetic dye wastewater was treated using a novel asymmetrical PMIA nanofiltration membrane prepared by phase inversion technique. The membrane per-formance was tested at different operating variables. The final aim is to reduce the quantity of the disposed dye waste-water and, at the same time, to reuse the dyes as well as the treated water.
MATERIALS AND METHODS
Materials
Acid Red 14, Reactive Blue 19 and Direct Blue 71 pur-chased from Liaoning Liangang Pigment and Dyestuff Chemicals Co., Ltd (China), were used to make synthetic dyeing wastewater without further purification. The main characteristics of the used dyes are shown in Table 1. Syn-thetic dye solutions were prepared by dissolving dyes in distilled water at a concentration of 100 mg/L without add-ing any auxiliary compounds [18]. Addition of NaOH and HCl to the solution was used to set the pH.
TABLE 1 - Characteristics of the dyes.
Dye Symbol M.W.
(Da) Structure Charge
Acid
Red 14 AR14 502 Monoazo -2
Reactive
Blue 19 RB19 627 Anthraquinone -2
Direct
Blue 71 DB71 1030 Polyazo -4
For the synthesis of NF membranes, commercial poly
(m-phenylene isophthalamide) (PMIA) from Yantai Spandex Co. Ltd. (China) was received in fibre form, and its chemi-cal structure is shown in Fig. 1. The polymer was dried for at least 5 h at 100 oC before being used in preparing poly-mer solution. N,N’-dimethylacetamide (DMAC) (analyti-cal grade) and lithium chloride (LiCl) (analytical grade) used as solvent and cosolvent, were purchased from Tianjin Fuchen Chemicals Reagent Factory (China). Acetone, sodi-um chloride (NaCl) and polyethylene glycol (PEG) series with different molecular weights were supplied from Si-nopharm Chemical Reagent Co., Ltd (China) and used without further purification.
N
H
N
H
O O n
FIGURE 1 - Chemical structure of PMIA used in this study.
Formation of aromatic polyamide asymmetric NF membranes
Different weight percents of PMIA were dissolved in a mixture of DMAC, LiCl and acetone to form a casting dope, and then filtered and de-aerated. Subsequently, the polymer solution was cast on a horizontal glass plate. After exposing in the oven at 140 oC for a certain time, the nas-cent membranes were immersed in a water-bath to form the asymmetric membrane structure. The membranes used for NF experiments were washed with flowing tap water for at least 12 h and wet-stored.
Membrane characterization
The morphology of the asymmetric membranes was observed with a scanning electron microscope (SEM, JSM-6301F, JEOL). The samples were cryogenically fractured in liquid nitrogen, and then sputter coated with a thin gold film prior to SEM observation. The roughness of the in-vestigated membrane surfaces was evaluated by Atomic Force Microscopy (AFM), Nanoscope III (Digital Instru-ments, VEECO Metrology Group). The colour density shows the vertical profiles of the membrane with the bright regions being the high peaks and the dark regions the val-leys and pores.
The molecular weight cut-off (MWCO) of the prepared membrane was measured using a PEG series (400, 600, 800, 1,000, 1,500 Da). The observed retentions of the dyes and salts were measured under different pressures (0.3-0.9 MPa), pH values (3-11) and temperatures (25-65 oC). The concentrations of dye solutions were analyzed by UV-VIS spectrophotometry (DR 5000, HACH, U.S.A) at the wave-length of the maximum absorption of each dye. The con-centrations were determined by conductivity (DDSJ-308A, China) for the salt solution and by Total Organic Carbon (Liquitoc, Elementar, Germany) for the single PEG solu-tions.
The water flux was measured using a small-scale membrane evaluation module shown in Fig. 2, which can offer an effective membrane area of 21.2 cm2. Each membrane was subjected to pressure at 1.0 MPa for 30 min before the permeation experiment, and then meas-
ured under 0.7 MPa at 25±1 oC. All the experiments were conducted three times to obtain the results presented in this study (average values with a variation of ±5%).
RESULTS AND DISCUSSION
The microscopic structure of NF membrane
Fouling is a common phenomenon in membrane pro-cesses. It decreases the membrane flux and reduces the membrane separation efficiency. Fouling increases with an in-creased roughness of the membrane surface which can easy adsorb and accumulate inorganic and organic pollutants. Therefore, one would like to produce a mem-brane having a smooth surface [19]. Atomic force microsco-py (AFM) might be a useful tool to estimate the average surface roughness of virgin membrane samples, which is a criterion to evaluate the affinity to fouling.
The AFM surface study of the PMIA NF membrane is shown in Fig. 3. It can be seen that the membrane pre-pared shows a very flat surface, where a mean roughness in 1×1 µm area is 0.689 nm. The flat surface characteristics of the membrane can decrease the tendency of membrane fouling. The pore diameter of the PMIA NF membrane measured by nitrogen adsorption-desorption is concentrated on 18 nm (Fig. 4).
FIGURE 3 - AFM image of the membrane surface for the PMIA NF membrane.
0 20 40 60 80 1000.000
0.002
0.004
0.006
0.008
0.010
dV(d
)(cc
/nm
/g)
Pore Diameter (nm)
FIGURE 4 - Pore size distribution of PMIA NF membrane. The SEM images (Fig. 5) confirm the results of the
AFM studies. The top layer of the resulting PMIA NF mem-brane is uniform, dense and smooth, which covers totally the open porous sponge-like sub-layer. In the cross-section im-age of the membrane (Fig. 5(a)), we can see that the surface layer is very thin which is responsible for the membranes high water permeability.
(a) (b)
FIGURE 5 - SEM photograph of the PMIA NF membrane: (a) cross section (×1,000) and (b) surface texture (×10,000).
FIGURE 6 - PEG retention as a function of molecular weight of PEG.
The molecular weight cut-off of NF membrane
The molecular weight cut-off of the self-made NF membranes was measured by filtration of various PEG solu-tions with molecular weight ranging from 400 to 1500 Da. The results are given in Fig. 6. It can be seen that the MWCO for the membranes prepared are around 900 Da and higher than the molecular weight of the AR14 and RB19 (Table 1), so the sieving retention mechanism will be limited, particularly for these two dyes.
Application to the treatment of dye solutions Dye retention
The permeate flux and rejection of three dyes as a function of pressure are presented in Fig. 7. We can see that the rejections of three dyes are all over 95% in the pressure range studied of 0.3–0.9 MPa. The high reten-tion (～100%) for DB71 can be ascribed to the high mo-lecular weight (1030 Da) and the number of sulfonate groups (four groups). The retentions for AR14 and RB19 were lower than that for DB71 because of their lower mo-lecular weight and, in particular, lower charge density (two sulfonate groups). In this case, the sieving mechanism is slightly less important and dye retention takes place by an ionic exclusion mechanism [20].
75
80
85
90
95
100
0.3 0.4 0.5 0.6 0.7 0.8 0.920
40
60
80
100
120
Flux of DB71 Flux of AR14 Flux of RB19 Rejection of DB71 Rejection of AR14 Rejection of RB19
Flux(L
/m2 . h
)
Pressure (MPa)
Rej
ectio
n(%
)
FIGURE 7 - Flux and observed dye rejection as a function of ap-plied pressure for the separation of three dyes ([dye] =100 mg/L, Temp.:25 oC).
The effect of pressure on permeate flux shows an al-
most linear relationship. However, the flux obtained from three dye solutions varied, depending on the chemical and physical properties of the dyes used. The major factors affecting the flux of the membrane seemed to be the mo-lecular size and surface charge of the dyes. Generally speak-ing, when dyes (such as AR14 and RB19) with low molecu-lar weight and surface negative charge were used, they easi-ly attached to the membrane surface, and even get into the pores of the NF membrane, blocking the pores, and reduc-ing the flow of the water, and then causing the water
flux to decrease. On the other hand, when dyes (such as DB71) with large molecular size were used, the na-nometer pores are much smaller than the dyes, so it is less possible for the dyes to get into the pores of the membrane, not inducing such flux decline as that of low-molecular weight dyes.
From Fig. 7, we can see that although the flux of the solutions of RB19 was lower than the solutions of DB71 and AR14, it also reached 35 L/m2.h at 0.7 MPa. Thus, it can be conclusively said from this result that the NF PA membrane with MWCO 900 is suitable to efficiently re-move three different anion dyes out of their aqueous solu-tion.
Effect of pH
In this part of the study, permeate flux and retentions of dyes were evaluated at different pH values. The results are shown in Table 2. It can be seen that there is no obvi-ous change on the retentions or permeate flux of DB71 and RB19 in the studied pH range. However, the perme-ate flux of AR14 is very sensitive to pH. Acid red 14 is an anionic dye with two sulfonate groups. This dye can be used for dyeing and printing wool, acetate and nylon at pH between 2.5-4. It was observed from Table 2 that when
decreasing the pH from 7 to 3, the permeate flux decreases by more than 20%. This decline has been attributed to the strong adsorptive property of AR14 for the polyamide membrane under acid conditions, which leads to the foul-ing of the membrane [21].
The membrane temperature resistance
Further experiments were conducted to test the tem-perature resistance of the membrane prepared using the same concentration of dye solution (100 mg/L) but at differ-ent operating temperatures. A well-known commercial na-nofiltration membrane (NF270) was purchased from Film-Tec Corporation (USA) and used as a reference because this membrane is also an aromatic polyamide nanofiltration membrane. The results are shown in Fig. 8.
It can be seen that the AR14 rejection by self-made NF membrane remains higher than 97%, and was always about 8% higher than that of NF270 when temperature increases from 25 to 65 oC. The slight decrease of rejec-tion (＜1%) is ascribed to the increase of diffusivity of the dye molecules at higher temperature. The membrane pre-pared shows excellent thermal stability, and has exces-sively useful potential in the treatment of hot dye effluents.
TABLE 2 - Effect of pH on the permeability and the dye retention.
Dye
pH=3 pH=7 pH=11
J
(L/m2·h)
R
(%)
J
(L/m2·h)
R
(%)
J
(L/m2·h)
R
(%)
AR14 36.74 99.56 50.65 98.09 56.31 95.07
RB19 39.59 96.41 41.54 95.47 43.24 94.30
DB71 53.00 99.46 55.59 98.93 56.74 98.82
Test conditions: [dye] =100 mg/L, Temp.:25 oC, Pressure: 0.7 MPa.
20 30 40 50 60 7080
85
90
95
100
Rejection of PMIA Rejection of NF270
Rej
ectio
n (%
)
Temperature ( oC)
FIGURE 8 - Observed rejection of AR14 as a function of feed tem-perature ([dye] = 100 mg/L, Pressure : 0.7MPa).
Effect of salt on the dye retention
As already mentioned, the coloured effluents of the tex-tile industry are saline ones. Further experiments were con-ducted to test the separation performance of PMIA mem-brane in the presence of salts. A direct dye (DB71) with a high molecular weight and an acid dye (AR14) with a low molecular weight were chosen since they are widely used to colour wool and nylon fibers, and the process requires large amounts of salt and causes serious environmental problems. The dye concentrations were set at 100 mg/L and concentrations of salt were set at 170 mM. The results are presented in Fig. 9.
AR14 without CaCl2 AR14 with CaCl2 DB71 without NaCl DB71 with NaCl
Rejection(%)
Pressure(MPa)
FIGURE 9 - Observed rejection of AR14 and DB71 as a function of applied pressure ([dye] = 100 mg/L, [salt] = 170 mM, Temp.: 25 oC).
It can be seen that the presence of salt in dye solution
decreases the selectivity of the membrane. AR14 rejection is observed to be notably lowered in the presence of CaCl2 while the downward tendency of DB71 rejection is not obvi-ous in the presence of NaCl. The reason is that salt addition leads to a large increase in ionic strength, the membrane charges are shielded and the Donnan effect is considera-bly reduced, especially for divalent cations like CaCl2. Under these conditions, dye rejection is controlled essen-tially by a sizing effect. Moreover, Schaep et al. [22] found that the efficiency of dye rejection generally could be worse in the presence of salts, and this became particularly notice-able for low molecular weight dyes. AR14 is an anionic dye like DB71 but it has a lower molecular weight and is less charged (only two sulfonate groups against four for DB71), and this made it more sensitive to the pres-ence of salt.
Effect of time on the permeability and the dye retention
Fig. 10 shows the flux and dye rejection as a function of running time. The coloured solution with salt (DB71 with NaCl) was recycled to the feed tank at the pressure of 0.7 MPa.
0
20
40
60
80
100
0 400 800 1200 160020
30
40
50
60
70
Flux Rejection of DB71 Rejection of NaClFl
ux(L
/m2 . h
)
Time (min)
Rej
ectio
n (%
)
FIGURE 10 - Flux and observed rejection of DB71 in presence of NaCl as a function of time ([dye] =100mg/L, [NaCl] =340 mM, Temp.: 25 oC).
It is observed that the rejection of dye increases a lit-
tle (from 95.2 to 96.6%) as the operating time extended. This phenomenon was attributed to the fact that the dye accumulates on membrane surface when increasing oper-ating time. The gel layer formed by the rejected dyes may increase the surface charge density of the membrane, which results in the increase of dye rejection. However, the gel layer formed may be much loose due to the smooth mem-brane surface, so no flux decrease is observed during 24 h. The rejection of NaCl is very low (＜6%). Thus, the mem-brane fouling is less important, and makes it suitable for the dye wastewater treatment and desalination-purification process for the raw product of dyes.
CONCLUSION
The present work demonstrated the feasibility of us-ing poly(m-phenylene isophthalamide) (PMIA) as mem-brane material to prepare a nanofiltration membrane by means of phase inversion method. Both scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirmed a much smoother membrane surface which could decrease the tendency of membrane surface fouling. The evaluation of the salt effect showed that the presence of salt generally decreases membrane retention for the dyes, especially for low-molecular weight dyes. This phenomenon is due to less important effect of the ionic exclusion mecha-nism than the sieving mechanism. Long-term operating experiments showed that the membranes with a 900 Da cut-off can concentrate direct blue 71 (MW 1030 Da) with a high flux (＞50 L/m2.h), a high dye rejection (＞96%) and a salt retention lower than 6%. Even after 24 h of oper-ation, the flux and retention are almost constant and the membrane fouling is negligible.
ACKNOWLEDGEMENTS
This work was supported by the National “863” Re-search project for High Technology Development (Grant no. 2007AA06Z339), National Natural Science Founda-tion of China (no. 50708109) and the National Key Tech-nologies R&D Program (Grant no. 2006BAD01B02-02, Grant no. 2006BAJ08B00).
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Received: November 02, 2009 Revised: February 22, 2010; March 12, 2010 Accepted: March 30, 2010 CORRESPONDING AUTHOR
Changwei Zhao State Key Laboratory of Environmental Aquatic Chemistry Research Center for Eco-Environmental Sciences Chinese Academy of Sciences P.O. Box 2871 Beijing100085 PR CHINA Phone: +86-10-62849198 E-mail: [email protected]
AQUEOUS CADMIUM ION REMOVAL BY FUNCTIONALIZED SBA-15 MATERIALS
Aijun Gu*, Zhongchun Li, Zhaolian Ye and Li Jiang
School of Chemistry and Chemical Engineering, Jiangsu Teachers University of Technology, Changzhou 213001, P. R. China
ABSTRACT
Mesoporous silica material SBA-15 with highly or-dered pore structure was synthesized via a hydrothermal method. The as-synthesized mesoporous materials were functionalized with 3-mercaptopropyltrimethoxysilane and 3-aminopropyltrimethoxysilane to graft the groups of SH and NH2, respectively. Structures of the materials were characterized by means of X-ray diffraction (XRD), Fou-rier transform infrared spectroscopy (FT-IR), nitrogen ad-sorption-desorption and thermogravimetric analysis (TGA). The results of adsorption experiments showed that both of the modified mesoporous adsorbents exhibited excellent ability to remove cadmium ions from aqueous solution, while the adsorption ability was affected by contact time, pH and initial concentration of cadmium ions. The adsorp-tion isotherm mechanism followed Langmuir model very well. The maximum adsorptive capacity of SH-SBA-15 is bigger than that of NH2-SBA-15 under the same conditions.
KEYWORDS: mesoporous material; SBA-15; adsorption; cadmium ion
INTRODUCTION
Cadmium, one of the most toxic metals, is a serious risk to human health and ecological systems. A wide varie-ty of techniques have been applied to remove cadmium ions from water, such as adsorption, precipitation, ion ex-change, coagulation, reverse osmosis and electrochemical operation [1-3]. However, there are some limitations for these measures, like low removal capacity, low selectivi-ty, high operating and energy costs. Since Feng [4] used thiolated MCM-41 to remove mercury from solution, peo-ple have paid considerable attention to those mesoporous silica materials due to their large specific surface area, highly ordered pore structure, tunable pore size and well-modified surface properties [5-8]. The mesoporous adsor-bents may be one of the promising materials for improv-ing the efficiency of heavy metal ion removal.
In recent years, some studies on the cadmium ions re-moval by hybrid mesoporous materials have been carried
out. The functional groups mainly included thiol [9-12], amino [13, 14], iminodiacetic [15] and imidazole [16]. For instance, Perez-Quintanilla et al. [10] used the mesoporous silica SBA-15 modified with 2-mercaptopyrimidine to ad-sorb Cd2+ from aqueous media. Heidari et al. [13] investi-gated the removal of Ni2+, Cd2+ and Pb2+ ions from aqueous solution by using the nano-particles of amino functionalized MCM-41. In 2007, Lam and co-workers [14] reported the selective adsorption of Ni2+ and Cd2+ from binary compo-nents` solutions using mesoporous NH2-MCM-41 adsorbent. Gao et al. [15] utilized iminodiacetic acid-modified SBA-15 to separate cadmium from aqueous solution. These stud-ies indicated that the mesoporous materials modified by thiol or amino groups showed a wonderful adsorption per-formance for the cadmium ions. However, comparison of the adsorption of SBA-15 functionalized by thiol and amino groups for removing cadmium ions has been reported scarcely.
In this work, mesoporous SBA-15 materials modified by thiol and amino groups were prepared by a post-graft method and characterized by XRD, FT-IR, nitrogen ad-sorption-desorption and TGA. The contact time, pH value and cadmium ion concentrations were investigated by a series of adsorption experiments. The adsorption capacity of the modified SBA-15 materials was compared.
MATERIALS AND METHODS
Materials
Surfactant Pluronic P123 (PEO20PPO70PEO20) was used as the structure directing agent and tetraethoxysilane (TEOS) was employed as the silica source. The organo-alkoxysilanes selected as functional groups were 3-mer-captopropyltrimethoxysilane (MPTMS) and 3-aminopropyl-tri-methoxysilane (APTMS). These reagents were all pur-chased from Aldrich. Cadmium nitrate, dry toluene, ethanol, nitric acid and sodium hydroxide were supplied by Aladdin. All the reagents used were at least of analytical grade.
Adsorbents synthesis
The mesoporous SBA-15 was synthesized by the pro-cedure of Zhao [17]. Thiol-modified SBA-15 (labeled as SH-SBA-15) and amino-modified SBA-15 (labeled as
NH2-SBA-15) samples were prepared by the post-grafting method. SBA-15 aliquots (4 g) were dehydrated at 120 °C in vacuum, and then stirred in 100 ml of dry toluene con-taining 5 ml of either MPTMS or APTMS under refluxing conditions for 6 h. Subsequently, samples were washed out with toluene. Finally, the products were dried at 80 °C under vacuum.
Cadmium ion adsorption experiment
Batch processes were carried out to study the adsorp-tion of Cd2+ from aqueous solutions onto the modified SBA-15 materials. Approximately 50 mg of SH-SBA-15 or NH2-SBA-15 was added to 50 ml of cadmium nitrate aque-ous solution with different concentrations (20~200 mg·L-1). The pH value (1-7) of the solution was adjusted by adding a small amount of nitric acid or sodium hydroxide. The solution was stirred for a particular time at 30 °C. The solu-tion was then filtered and the filtrates were measured for the cadmium ion concentrations by inductively coupled plasma, atomic emission spectrometry (ICP-AES, Perkin-Elmer Optima 2100). The amount of Cd2+ qe (mg·g-1) adsorbed by the modified SBA-15 was determined through the fol-lowing equations:
0( ) /e eq C C V m= −
where C0 (mg·L-1) and Ce (mg·L-1) are the initial and final concentrations of Cd2+ in the solution, respectively; V (L) is the volume of cadmium nitrate solution and m (g) is the weight of the adsorbent.
Characterization
Small-angle X-ray diffraction (XRD) patterns were obtained on a Rigaku Diffractometer (D/ Max 2000) using Cu Kα radiation (λ = 1.5418 Å). Infrared spectra were re-corded on an IR 200 (Thermo Nicolet) FT-IR spectropho-tometer in the region of 4000~400 cm-1 using KBr pellets. N2 adsorption-desorption isotherms were measured at 77 K by a Micromeritics Tristar 3000 instrument. The specific sur-face area was calculated by employing the Brunauer-Emmett-Teller (BET) method. The pore volume and pore size distributions were obtained from the Barrett-Joyner-Halenda (BJH) model. The thermogravimetric analysis (TGA) was performed on a SDT Q600 V8.2 instrument under nitrogen from room temperature to 800 °C with a heating rate of 10 °C/min.
RESULTS AND DISCUSSION
XRD analysis
The XRD patterns for mesoporous silica are plotted in Fig. 1. All the diffractograms exhibit the characteristic peak (1 0 0) corresponding to the pore family denoting their mesoscopic order. The XRD patterns of pure SBA-15 display well-ordered hexagonal mesophase structure with a very sharp (1 0 0) peak at 0.92 and two weaker peaks at 1.56
and 1.70 assignable to (1 1 0) and (2 0 0), respectively. For SH-SBA-15 and NH2-SBA-15 samples, there is a gradual decrease in the peak intensities and a light shift towards higher angle for the (1 0 0) peak. It suggests that the modi-fied materials maintain the mesoporous structure well after functionalization. However, the pore sizes of modified me-soporous silica materials tend to reduce because of the attachment of the organic functional groups in the mesopore channels.
1 2 3 4 5 6 7 8
Inte
nsity
(a.u
.)
2θ (°)
NH2-SBA-15
SH-SBA-15
SBA-15
FIGURE 1 - XRD patterns of SBA-15, SH-SBA-15 and NH2-SBA-15 samples.
4000 3500 3000 2500 2000 1500 1000 500
-CH2-
Wavenumber / cm-1
SH-SBA-15
NH2-SBA-15
SBA-15-CH2-
S-H
N-H
FIGURE 2 - FT-IR spectra of SBA-15, SH-SBA-15 and NH2-SBA-15 samples.
FT-IR analysis
The organic functional groups bonded to the SBA-15 through reaction with surface silanol groups could be de-tected from the IR spectra. The FT-IR spectra of pure SBA-15 sample and modified SBA-15 samples are illustrated in Fig. 2. The broad absorption band of the SBA-15 sample at 3460cm-1 is assigned to SiOH groups. Compared to the SBA-15, some new adsorption bands appear at the IR spec-tra of the thiol-functionalized materials. For the SH-SBA-15 sample, the clear feature observed at 2935 cm-1 can be attributed to stretching of CH2 groups. At the same time, a new band of 2550 cm-1 due to a weak S-H vibration can be seen from the spectra. For the NH2-SBA-15 sample, new features can also be found at 2935 cm-1 and 1560 cm-1,
which can be assigned to C-H and S-H stretches of APTMS, respectively [18]. These results could confirm the success-ful functionalization of SBA-15 with SH and NH2 groups.
Nitrogen adsorption-desorption
The nitrogen adsorption-desorption isotherms for the mesoporous silica samples are described in Fig. 3. SBA-15 sample represents the typical Type IV isotherms with a H2 hysteresis loop and steep adsorption-desorption step that indicate a well-ordered array of pores consistent with the XRD profile [17]. The type IV isotherm shapes are pre-served well for both of the modified SBA-15, which sug-gests that the pore structure has been maintained after func-tionalization. However, the inflection position shifts slightly toward lower relative pressures, and the hysteresis loop de-creases with functionalization, indicative of a reduction in pore size and uniformity of mesopore structure.
0.0 0.2 0.4 0.6 0.8 1.00
100
200
300
400
500
600
Vol
ume
Abs
orbe
d / m
3 ⋅g-1
Relative pressure
SBA-15 SH-SBA-15 NH2-SBA-15
FIGURE 3 - Nitrogen adsorption-desorption isotherms of SBA-15, SH-SBA-15 and NH2-SBA-15 samples.
0 2 4 6 8 10 12 14
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
dV/d
D /
cm3 ⋅
g-1⋅n
m-1
Pore diameter / nm
SBA-15 SH-SBA-15 NH2-SBA-15
FIGURE 4 - Pore size distribution of SBA-15, SH-SBA-15 and NH2-SBA-15 samples.
TABLE 1 - Textural feature of SBA-15, SH-SBA-15 and NH2-SBA-15 samples.
Sample Surface area （m2·g-1）
Pore volume （cm3·g-1）
Pore size （nm）
SBA-15 684 0.983 6.4
SH-SBA-15 280 0.495 5.2 NH2-SBA-15 212 0.482 4.9
The mean pore size, pore volume and surface area calculated from the BJH and BET models are shown in Fig. 4 and Table 1. It is obvious that the functionalization has a dramatic effect on the textural feature of mesoporous silica. In the case of NH2-SBA-15, the surface area drops from 684 m2·g-1 to 212 m2·g-1 and the pore volume de-clines from 0.983 cm3·g-1 to 0.482 cm3·g-1. Amino func-tionalization reduces the textural property of SBA-15 more than the thiol treatment. These textural results confirm that the grafted species are located inside the mesopores and not only on the outer surface.
TGA analysis
Thermogravimetric analysis (TGA) is commonly used to identify the number of organic moieties grafted on the mesoporous materials. Fig.5 shows the TGA results for all mesoporous materials. For the SBA-15 (Fig. 5a), a 11.64 wt.% loss below 100 °C is apparently due to sur-face dehydration. Then, there is a slight weight loss with increasing temperature, which results from the dehydrox-ylation [19]. For the SH-SBA-15 (Fig. 5b), a slight weight loss (about 2%) below 100 °C is due to the loss of ab-sorbed water. A major weight loss (16.9%) above 300 °C could be attributed to the decomposition and total loss of the mercaptopropyl groups from the materials. For the NH2-SBA-15 (Fig. 5c), a 10 wt.% loss below 120 °C is also due to the adsorbed water removal. A weight loss (about 5%) at the temperatures 120-450 °C can be at-tributed to structural rearrangement of the incorporated aminopropyl groups [19]. A weight loss of 10% above 450 °C is due to the breakdown of aminopropyl groups grafted on the SBA-15. According to the results of TGA, the number of organic groups could be calculated. That is, the SH-SBA-15 and NH2-SBA-15 contain 2.87 mmol of thiolpropyl groups and 1.33 mmol of aminopropyl groups per gram of adsorbent, respectively.
0 200 400 600 80070
75
80
85
90
95
100
Wei
ght R
ate
/ %
Temperature / °C
a
b
c
FIGURE 5 – Thermogravimetric analysis of (a) SBA-15, (b) SH-SBA-15 and (c) NH2-SBA-15.
The effect of contact time on aqueous cadmium ion uptake can be seen from Fig. 6. The experimental results indicate that the pure SBA-15 adsorbs only little cadmium from the solution. It suggests that the surface silanol groups of the pure SBA-15 have poor affinity for Cd2+ adsorption whereas the modified SBA-15 materials are able to adsorb more metal ions. As seen, the adsorption quantities of cad-mium increase quickly in the early stages of the process. After 30-40 min, the adsorption reaches an equilibrium. Hereby, a stirring time of 60 min can be selected as the subsequent adsorption equilibrium time. As the adsorp-tion curves of the modified SBA-15 showed, SH-SBA-15 can adsorb more cadmium than NH2-SBA-15. These results demonstrate that the chemical moieties grafted on the SBA-15 are responsible for cadmium adsorptions [20].
0 20 40 60 80 100 1200
10
20
30
40
50
60
70
80
90
100
q e /
mg⋅
g-1
Time / min
SH-SBA-15 NH2-SBA-15 SBA-15
FIGURE 6 - Effect of the contact time on cadmium adsorption (T = 303 K, pH = 5, initial Cd2+ concentration = 100 mg·L-1).
1 2 3 4 5 6 70
20
40
60
80
100
SH-SBA-15 NH2-SBA-15q e
/ m
g⋅g-1
pH
FIGURE 7 - Effect of pH on cadmium adsorption (T = 303 K, Time = 1 h, initial Cd2+ concentration = 100 mg·L-1).
The effect of the pH value on the Cd2+ uptake was al-
so experimented and the results are shown in Fig. 7. The Cd2+ removal efficiency of SH-SBA-15 increases as the solution pH ranges from 1 to 5, then it remains almost changeless with further increase in pH. The adsorption performance of NH2-SBA-15 is similar to SH-SBA-15 ex-cept the inflexion of pH value (pH = 4). At pH 1, the cad-mium adsorption capacities of SH-SBA-15 and NH2-SBA-
15 are only 23.5 mg·g-1 and 13.4 mg·g-1, respectively. It is mainly due to the protonation of the sulfur atom in SH group or nitrogen in NH2 group, which diminish the ability of NH2 and SH groups to chelate with cadmium in aqueous solutions. When pH value is below 7, the form of cadmium in aqueous solution exists as Cd2+, which is favorable for the cadmium adsorption. When pH is above 8.3 which is calcu-lated from concentration product (5.3×10-15) of Cd(OH)2, precipitation of the cadmium hydroxide would begin [21]. The optimum pH value for the removal of cadmium from aqueous solution is about 5.
The adsorption isotherms are usually used to explore the adsorption characteristics of the adsorbent materials. Fig.8 shows the equilibrium adsorption isotherms for NH2-SBA-15 and SH-SBA-15 adsorbing cadmium. Each equilibrium adsorption experiment has been carried out by stirring 50 mg of adsorbent within 50 ml of aqueous solu-tions including initial cadmium concentrations ranging from 10 to 200 mg·L-1. The isotherms reveal that both of the modified mesoporous materials perform well at low cadmium concentration. And then, the adsorptions gradu-ally reach a saturation constant value when aqueous cad-mium concentrations continuously increase. It seems that the adsorption behavior corresponds to the Langmuir iso-therm model. Here, Langmuir model is selected to fit the adsorption data. The mathematical expression is:
max / (1 )e e eq q b C b C= ⋅ ⋅ + ⋅
where qe is the amount of cadmium adsorbed on ad-sorbent at equilibrium (mg·g-1); qmax and b are the pa-rameters of Langmuir model; qmax is the maximum ad-sorption capacity (mg·g-1), and b is the adsorption coeffi-cient; Ce is the residual cadmium concentration in solu-tion at equilibrium (mg·L-1).
0 20 40 60 80 100 120 1400
20
40
60
80
100
SH-SBA-15 NH2-SBA-15q e
/ m
g⋅g-1
Ce / mg⋅L-1
FIGURE 8 - Fitted Langmuir isotherms for adsorption of Cd2+ by the adsorbents (T = 303 K, Time = 2 h).
TABLE 2 - Fitting parameters of Langmuir isotherm models.
Fig. 8 exhibits the isotherm curves fitted by Langmuir
model, and Table 2 displays all the parameters calculated from the model. The plots show that there is a good fit between the model and experimental data. The calculated maximum adsorption capacity of SH-SBA-15 (103.2 mg·g-1) is significantly bigger than that of NH2-SBA-15 (62.3 mg·g-1). The SH group attracts to Cd2+ more than the NH2 group because of its stronger activity. At the same time, the amount of adsorbed metal ions is also related to the number of the functional groups grafted on the SBA-15. The better retention performance of SH-SBA-15 over NH2-SBA-15 is corresponding to the amounts of SH (2.87mmol·g-1) and NH2 (1.33mmol·g-1) groups in the synthesized materials.
Table 3 shows the maximum Cd2+ adsorption capacity (qmax) of different modified mesoporous materials, which is used to compare our results with those reported in the pub-lished literature. The Cd2+ adsorption capacity of modified mesoporous materials varies with the different functional groups and material supports. From the data of qmax, it can be concluded that the adsorption capacity of the materials we obtained is superior to most of adsorbents reported in literature. Especially, the adsorbents modified by thiol
groups synthesized in this work exhibit promising proper-ties for cadmium removal from aqueous solution. In addi-tion, the adsorbed cadmium ions can be recovered from the modified mesoporous materials by a simple acid wash. The regenerated adsorbents could be reused without much loss of performance [6].
Considering the potential application of the modified mesoporous materials to environmental problems, an elec-troplating wastewater sample was used to estimate the com-petitive adsorption. The competitive adsorption data of Cd2+, Ni2+, Zn2+ and Cu2+ ions on SH-SBA-15 and NH2-SBA-15 materials are summarized in Table 4. The adsorption capac-ity of the synthesized adsorbents declined resulting from the effect of other metal ions existing in the wastewater. The adsorbents affinity for different metal ions decreased in the order: Cu2+ > Cd2+ > Ni2+ ≥ Zn2+. Some researchers [20, 23] attempted to utilize the HSAB principle to explain the inequitable affinity for different metal ions. Despite some shortcomings, such as antinomy about borderline acids and bases, HSAB provides a good interpretative approach of the different adsorption capacities at present.
TABLE 3 - Comparison of Cd2+ adsorption capacity on the modified mesoporous materials.
TABLE 4 – Competitive adsorption of metal ions by the synthesized adsorbents.
Adsorbent Cd2+ (mmol·g-1)
Ni2+
(mmol·g-1) Zn2+
(mmol·g-1) Cu2+
(mmol·g-1) SH-SBA-15 0.82 0.04 0.03 0.93 NH2-SBA-15 0.45 0.17 0.11 0.52 Experimental conditions: T = 303 K, pH = 5, 0.05 g adsorbent, 50 ml electroplating solution, stirring time 2 h.
CONCLUSIONS
The mesoporous silica materials SBA-15 functional-ized with NH2 or SH groups have been synthesized by post-graft method to adsorb cadmium ions from aqueous solution. XRD, FT-IR and nitrogen adsorption-desorption analyses suggest successful functionalization (group addi-tions). Adsorption of cadmium ions by the modified SBA-15 samples is well-fitted to Langmuir isotherm model. The optimum pH value for the removal of cadmium by func-
tionalized SBA-15 is about 5. The adsorption equilibrium time ranges from 30 to 40 min. The maximum adsorption capacity of SH-SBA-15 is significantly stronger than that of NH2-SBA-15.
ACKNOWLEDGMENTS
This research was supported by the Natural Science Foundation of Jiangsu (No. BK2009106), the Natural Sci-ence Foundation of the Jiangsu Higher Education Institu-tions of China (No. 08KJB150007), and the Natural Sci-ence Foundation of Jiangsu Teachers University of Tech-nology (No. KYY08040).
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[22] da Silva L.C.C., dos Santos, L.B.O., Abate, G., Cosentino, I.C., Fantini, M.C.A., Masini, J.C. and Matos, J.R.(2008) Ad-sorption of Pb2+, Cu2+ and Cd2+ in FDU-1 silica and FDU-1 silica modified with humic acid. Micropor Mesopor Mat, 110, 250-259.
[23] Liu A.M., Hidajat K., Kawi S. and Zhao D.Y. (2000) A new class of hybrid mesoporous materials with functionalized or-ganic monolayers for selective adsorption of heavy metal ions. Chem. Commun., 13, 1145-1146.
Received: November 02, 2009 Revised: January 04, 2010 Accepted: February 26, 2010
Aijun Gu School of Chemistry and Chemical Engineering Jiangsu Teachers University of Technology Changzhou 213001 P. R. CHINA Phone: +86-519-86999823 Fax: +86-519-86999825 E-mail: [email protected]
ASSESSMENT OF FLUOROQUINOLONES TOXICITY WITH APPLICATION TO Lemna minor MICROBIOTEST
Justyna Kolasińska*, Magdalena Bielińska and Grzegorz Nałęcz-Jawecki
Department of Environmental Health Sciences, Medical University of Warsaw, 1 Banacha St., 02-097 Warsaw, Poland
ABSTRACT
Fluoroquinolones have been used as antibacterial agents for almost 20 years. Despite their common usage in human and veterinary medicine, their fate and effects on freshwa-ters are still unknown. The duckweed Lemna minor is generally used as a model organism for higher water plants. The test was conducted according to standard ISO protocol with some modifications. The number and area of L. minor fronds was measured as a biomass parameter. Additionally, chlorosis was assessed. The scans of the microplates with L. minor were analyzed by a special computer program. In this way the microbiotest with L. minor was quick and sim-ple to do from the set up of the test to reading and analysis.
Eight fluoroquinolones were assessed: ciprofloxacin, enoxacin, fleroxacin, lomefloxacin, nalidixic acid, norflox-acin, ofloxacin and pefloxacin. The most toxic substances proved to be ciprofloxacin and ofloxacin. The ciprofloxacin EC50, EC20 and EC10 values calculated for frond numbers are 243 µg L-1, 64 µg L-1and 47 µg L-1. The same parame-ters applied to frond area are 57 µg L-1, 28 µg L-1 and 18 µg L-1. The EC value calculated for frond area shows that it is a more sensitive parameter for assessing the toxicity than frond numbers for the most toxic substances: ciprofloxacin and ofloxacin.
Fluoroquinolones are very commonly used as effective medicines, e.g. in urinary tract and respiratory tract bacteri-al infections and gastrointestinal infections. They are will-ingly widely used because of good kinetics and rare side effects. They have quite a wide range of antibacterial ac-tion. They are effective against most aerobic Gram-negative bacteria, including those resistant to β-lactam antibiotics and aminoglycosides [1, 2]. They are used as first-line drugs in infections caused by Salmonella spp., Shigella spp., Le-gionella spp., Camphylobacter jejuni and P. aeruginosa [1, 2].
They are used in animals [3] and humans [4] as well as in fish breeding ponds. They stimulate fish growth with a very simple mechanism by eliminating bacterial infec-tions in fish [5].
Fluoroquinolones are still emitted into the surface wa-ter [6]. They come from hospital sewage and farm animal waste. Hospital wastewater containing medicines and me-tabolites is discharged into rivers [4, 7]. Animal manure goes to fields and than is filtered to natural water [3].
The presence of medicines in the environment is so serious that it requires official regulations for safety as-sessment [8, 9].
There is not enough data to predict the long-term im-pact of the presence of fluoroquinolones on the environ-ment. It is known that they cause bacterial resistance in the natural environment of a lake or a river [3]. Therefore, fluoroquinolones cause both negative and positive effects, but we do not know the long-term effects on the entire eco-system. It is important to find out more about the impact of this group of medicines on the environment [5, 10].
The duckweed L. minor plays an important role in aquatic ecosystems. It is an important food resource for many fish and birds (notably ducks). It grows to create a thick carpet over still water-bodies, shading out other water plant species – particularly algae – below and eliminating the competition [11].
L. minor is a model organism for a higher water plant willingly used in the microbiotests because of its small size and the possibility to use ISO and OECD standards [12, 13]. There are multiple toxicity endpoint indicators using the duckweed, such as frond number, plant number, root num-ber, root length, frond area, biomass, dry mass, chloro-phyll content and chlorosis [14].
It is a very useful species for biomonitoring [5, 10, 15, 16] including ecotoxicity evaluation of municipal and food industry wastewaters in bioassay [17]. The Lemna growth inhibition test is a very useful tool in pharmaceu-ticals’ toxicity evaluation in wastewater, and even surface water [18]. The removal rates of chromium, copper, lead, and zinc from aqueous solutions using L. minor show the biosorption abilities of the species [19], and prove to be able to manage a wide range of biomonitoring usage.
The aim of this study was to assess the toxicity of fluoroquinolones by application to the Lemna minor mi-crobiotest.
MATERIALS AND METHODS
The toxicity of 8 quinolones purchased from Sigma was assessed: ciprofloxacin hydrochloride (CAS No. 85721-33-1), enoxacin (CAS No. 74011-58-8), fleroxacin (CAS No. 79660-72-3), ofloxacin (CAS No. 82419-36-1), pefloxacin mesylate (CAS No. 70458-95-6), norfloxacin (CAS No. 70458-96-7), lomefloxacin hydrochloride (CAS No. 98079-52-8), nalidixic acid sodium salt (CAS No. 3374-05-8).
The microbiotest was conducted according to ISO standards [12] with some modifications [18, 20, 21]. The 6-well microplates were used with 10 ml capacity per well. It started from one plant with 3-4 fronds per one well. Each of the 8 quinolones was tested in a separate micro-plate with 1 control well and 5 wells with various concen-trations of the test substance. The range of the concentra-tions for each fluoroquinolone was determined during the preliminary range finding test. The next dilution was twice as low as the previous one. There was a separate control microplate for each experimental series.
After 6 days [18], the frond number, frond area and chlorosis were assessed. The microplates were digitalized with a flat scanner (HP), and the pictures were analyzed for assessment of the frond number, frond area and chlorosis. The frond number was counted using freeware Image Tool [18]. The area of fronds was assessed using the Lemna Program, created especially for this aim (freeware by R. Krej). The Lemna Program uses bitmap pictures of a high resolution, distinguishing different colors e.g. green, yel-low and others from the RGB scale and counting pixels [17]. In this way, the results are more repeatable and relia-ble than hand measurements. Chlorosis was estimated by observing the color of the plants and assessment of the extent of the changes. The green fronds were definitely green. The small changes are signified by the yellow color only in the coastal zone of the fronds. The partial chlorosis occurred when yellow stains appeared on the frond area. The total chlorosis was noticed when the fronds turned completely to yellow or white (Table 1).
EC50, EC20, EC10 values were counted on the basis of the growth inhibition rate IR that had been calculated on the basis of the growth rate R. Toxicity units (TU50, TU20, TU10) are the reciprocal values of EC, and they were counted to better show the test results (Figs. 1 and 2).
RESULTS
Seven of the 8 tested antibiotics are second generation quinolones called classical fluoroquinolones. The introduc-tion of the fluorine atom to the carbon skeleton significantly increases the antibacterial activity of these substances. They
are effective against most aerobic Gram-negative bacteria, including those resistant to β-lactam antibiotics and ami-noglycosides. The 8th substance applied was nalidixic acid as a first generation quinolone.
The most toxic substance was ciprofloxacin. It had a
strong influence on the growth of L. minor. The values of EC50, EC20 and EC10 calculated for frond numbers are 243, 64 and 47 µg L-1, respectively. The same parameters applied to frond area are 57, 28 and 18 µg L-1. The value of EC50 for ciprofloxacin calculated for the frond area is three times lower than those for the frond numbers. The values of EC20 and EC10 for frond area are more than twice as low as those noted for frond numbers. These results are presented in Figs. 1 and 2 as toxicity units (TU). Ciprof-loxacin caused chlorosis in a low concentration of 50 µg L-1 (Table 1). The values TU and observed chlorosis show the toxic effect of ciprofloxacin in a concentration 10 times lower than the other fluoroquinolones. It was not found for the others in such a low concentration.
0
500
1000
1500
2000
2500
CIPFLONFLOOFLOPENOX LO
MFRXNAL
TU
TU50TU20TU10
FIGURE 1 – The toxicity of tested antibiotics to L.minor. Endpoint – frond number after 6 days of exposure. Toxicity units (TU50, TU20, TU10) are the reciprocal of EC. The abbreviations of the substances’ names are the same as in Tab. 1.
0
1000
2000
3000
4000
5000
6000
7000
CIPFLONFLOO
FLOPENOX LO
MFRXNAL
TU
TU50
TU20
TU10
FIGURE 2 – The toxicity of tested antibiotics to L.minor. Endpoint – frond area after 6 days of exposure. Toxicity units (TU50, TU20, TU10) are the reciprocal of EC. The abbreviations of the substances’ names are the same as in Tab. 1.
The toxicity of norfloxacin and ofloxacin, on the basis
of TU50, for frond numbers was similar (Fig. 1). The toxici-ty of these substances was 2.5-fold lower than that of ciprof-loxacin. The values of TU20 and TU10 for frond numbers show that there were differences in the toxicity of norfloxa-cin and ofloxacin, despite the similar level of toxicity on the basis of TU50. Thus, ofloxacin was a more active toxin than norfloxacin. The values of TU50, TU20, TU10 calculated for frond area confirmed the higher toxicity of ofloxacin with regard to norfloxacin. The observed chlorosis proved the higher toxicity of ofloxacin compared to norfloxacin (Table 1).
Ofloxacin TU50 counted for frond area is over twice as high as for frond numbers.
Other toxic substances proved to be pefloxacin, enoxa-cin, lomefloxacin and fleroxacin. There was no difference between the toxicity of lomefloxacin and fleroxacin on the basis of TU50 for frond numbers. Lomefloxacin was more toxic than fleroxacin on the basis of TU20 and TU10, de-spite the fact that these substances had similar toxicity on the basis of TU50 (Fig. 1). The noted chlorosis underlined this result.
The least toxic substance was nalidixic acid, the only tested first generation quinolone. It showed toxicity in con-centrations about 100 times higher than the other sub-stances (Figs. 1 and 2, Table 1). It inhibited the growth of L. minor at the lowest level of its toxicity range, and it caused total chlorosis in its highest concentration.
All tested antibiotics caused white bleaching of fronds, especially new fronds. The degree of chlorosis depended on the compound (Table 1). For ciprofloxacin, chlorosis was evident in the 50 µg L-1 treatment, close to the EC50 value based on the frond area. For lomefloxacin, chlorosis was observed at all concentrations tested.
DISCUSSION
The results show that ciprofloxacin is the most toxic of all the tested substances. It is 2 to 20-fold more toxic
than the other fluoroquinolones. The value of EC50, which equals 243 µg L-1 for frond number, is similar to those obtained by Robinson et al. [5] in the static renewal test in 1-L beakers of L. minor (EC50 equals 203 µg L-1). In our study, two quantitative endpoints measuring the inhibition of growth of the duckweed based on the calculation of the frond number and frond area were applied. Chlorosis was estimated qualitatively by observing the color of the plants. The frond area is a 4-fold more sensitive endpoint than the frond number, with EC50 243 and 57 µg L-1, respectively. Chlorosis was observed at a concentration of 50 µg L-1, which means that the duckweed grew, even with a lower level of pigments. The results were contrary to the find-ings for Lemna gibba by Brain et al. [22], who discovered that the level of chlorophylls was a 2-fold less sensitive endpoint than the number of fronds. Moreover, L. gibba was less sensitive to ciprofloxacin with EC50 values of 697 and 1279 µg L-1, for the frond number and chlorophyll a, respectively [23].
In our study, the second most toxic substances were ofloxacin and norfloxacin. Concerning the frond number, their EC50 value was 2.5-fold lower than that of ciproflox-acin. However, when the frond area was taken into account, norfloxacin was much less toxic than ofloxacin and ciprofloxacin. This indicates that for this type of fluoro-quinolone fronds were not only more numerous, but also larger. The EC50 values for L. minor in this study are low-er than the results of Brain et al. [22] who, for L. gibba, reported EC50 values of 653 and 1146 µg L-1 for ofloxa-cin and norfloxacin, respectively. On the other hand, Brain et al. [22] and Robinson et al. [5] found that lomef-loxacin was the most toxic fluoroquinolone (e.g. EC50 equals 106 µg L-1 in Robinson et al. [5]), while in our studies this antibiotic is 10 times less toxic than ciprof-loxacin. This discrepancy was caused by different test protocols. Lomefloxacin has a short half-life in aqueous media. The above-mentioned authors used static renewal tests and the concentration of the tested compound was stable during the seven days. In this study, the medium was not renewed and the duckweed was exposed to the decreas-ing concentration of lomefloxacin.
The differences between EC50 and EC20 or EC10 show that sometimes it is not sufficient to assess exactly the toxicity on the basis of EC50 alone. EC20 and EC10 values are proposed as alternatives to LOEC and NOEC values. The ratio EC50 to EC20 and EC10 indicates the range of acute changes caused by the tested sample. The ratio close to two indicates a strong, acute toxicity, as in the case of norfloxacin, compared to the ratio of four for ofloxacin. The first injury symptoms caused by ofloxacin were found to occur in the 125 µg L-1 treatment, while in the case of norfloxacin at concentrations 2-fold higher, the EC50 values were in reverse order. These results are similar to those by Brain et al. [22], who found that the ratio EC50 to EC10 varied from 5 to 14 in the case of norfloxacin and lomefloxacin, respectively.
The values of EC10 and EC25 were taken into account in probabilistic ecological hazard assessment with the us-age of L. gibba and fluoroquinolones [23]. They are more useful in evaluating pharmaceutical effects on higher aquatic plants.
Using EC, additionally calculated for the frond area, shows that it is a more sensitive parameter to assess tox-icity than frond numbers for the most toxic substances: ciprofloxacin and ofloxacin. The basic parameter is, of course, the frond number but others, such as frond area, should also be measured [12, 13]. Practically, the frond area could be useful to assess toxicity of the most toxic substances as a more sensitive parameter.
Quinolones as a group caused chlorosis of L. minor. The results are similar to those by Brain et al. [22], who reported a very distinct white bleaching of new fronds. When chlorosis is used as an additional parameter [12, 13], it confirms the results. The theory that chloroplasts come from prokaryotes allows to suggest that their toxic sensi-tivity is similar to cyanobacteria. This way, fluoroquin-olones toxicity tested on duckweed is nearly as high as that observed in M. aeruginosa. In the Robinson et al. study [5], the values of EC50 for ciprofloxacin, ofloxacin and lomefloxacin counted for M. aeruginosa were 17, 21 and 186 µg L-1, respectively.
This study showed that the most toxic fluoroqinolone was ciprofloxacin with a toxicity 2-fold higher than the other substances tested. The toxicity threshold EC20 was as low as 20 µg L-1. The value is similar to the concentra-tions detected in hospital wastewaters of Vietnam up to 44 µg L-1 [4]. Thus, the fluoroquinolone antibiotics may cause toxic effects on duckweed populations.
It seems to be important to conduct the laboratory-field experiment to confirm laboratory results and to discover the real toxicity of fluoroquinolones in the environment. In this way, it would be possible to find out more about the connections and impact that fluoroquinolones have on the environment. Extensive knowledge can protect nature better for younger and future generations.
REFERENCES
[1] Hryniewicz, W. and Mészaros, J. (2001) Antybiotyki w pro-filaktyce i leczeniu zakażeń. Wydawnictwo Lekarskie PZWL.
[2] Ball, P. (2000) Quinolone generations: natural history or nat-ural selection? J Antimicrob Chemotherapy 46, 17-24.
[3] Hirsch, R., Ternes, T., Haberer, K. and Kratz K.L. (1999) Occurrence of antibiotics in the aquatic environment. Sci To-tal Enviorn 225, 109-118.
[4] Duong, H.A., Pham, N.H., Nguyen, H.T., Hoang, T.T., Pham, H.V., Pham, V.C., Berg, M., Giger, W. and Alder, A.C. (2008) Occurrence, fate and antibiotic resistance of fluoroquinolone antibacterials in hospital wastewaters in Hanoi, Vietnam. Chemosphere 72, 968-973.
[5] Robinson, A.A., Belden, J.B. and Lydy, M.J. (2005) Toxicity of fluoroquinolone antibiotics to aquatic organisms. Environ Toxicol Chem 24, 423-430.
[6] Picó, Y. and Andreau, V. (2007) Fluoroquinolones in soil: risks and challenges. Anal Bioanal Chem 387, 1287-1299.
[7] Daughton, C.G. and Ternes, T.A. (1999) Pharmaceuticals and personal care products in the environment: agents of subtle change? Environ Health Prospect 107, 907-938.
[8] Breton, R. and Boxall, A. (2003) Pharmaceuticals and per-sonal care products in the environment: Regulatory drivers and research needs. QSAR Combinatorial Sci 22, 399-409.
[9] European Medicines Agency (EMEA) (2006) Pre-authorization Evaluation of Medicines for Human Use. Guideline on the en-vironmental risk assessment of medicinal product for human use. EMEA/CHMP/SWP/4447/00 London 01.06.2006.
[10] Mohan, B.S. and Hosetti, B.B. (1999) Aquatic Plants for Toxicity Assessment. Environ Res Section A 81, 259-274.
[11] Leng, R.A., Stambolie, J.H. and Bell, R. (1995) Duckweed – a potential high-protein feed resource for domestic animals and fish. Livestock Res Rural Development 7. http:// www. lrrd.org/lrrd7/1/3.htm. Download 2nd Nov 2009.
[12] ISO/DIS 20079 (2006) Water quality – determination of tox-ic effect of water constituents and waste water to duckweed (Lemna minor). Duckweed growth inhibition test. Draft in-ternational standard.
[13] OECD (Organization for Economic Cooperation and Devel-opment) (2006) OECD Guidelines for the testing of chemi-cals. Lemna sp. Growth Inhibition Test.
[14] Blaise, C. and Férard, J.F. (2005) Small-scale Freshwater Toxicity Investigations 1, 271-298.
[15] Naumann, B., Eberius, M. and Appenroth, K.J. (2007) Growth rate based dose-response relationships and EC-values of ten heavy metals using the duckweed growth inhibition test (ISO 20079) with Lemna minor L. clone ST. J Plant Physiol 164, 1656-1664.
[16] Pomati, F., Netting, A.G., Calamari, D. and Neilan, B.A. (2004) Effects of erythromycin, tetracycline and ibuprofen on the growth of Synechocystis sp. and Lemna minor. Aquat Toxicol 67, 387-396.
[17] Ostra, M., Beklova, M., Stoupalova, M. and Ostry, M. (2009) Ecotoxicity evaluation in municipal and food industry wastewaters. Fresenius Environ Bull 18, 1674-80.
[18] Kaza, M. (2008) The application of microplate test with aquatic plant Lemna minor in toxicity assessment of selected pharmaceuticals and environmental samples. PhD Disserta-tion. Medical University of Warsaw.
[19] Elmaci, A., Özengin, N. and Yonar, T. (2009) Removal of chromium (III), copper (II), lead (II) and zinc (II) using Lem-na minor L. Fresenius Environ Bull 18, 538-42.
[20] Kaza, M., Mankiewicz-Boczek, J., Izydorczyk, K. and Sawicki, J. (2007) Toxicity assessment of water samples from rivers in central Poland using the battery of microbi-otests – a pilot study. Polish J Environ Studies 16, 81-89.
[21] Kaza, M., Nałęcz-Jawecki, G. and Sawicki, J. (2007) The toxicity of selected pharmaceuticals to the aquatic plant Lem-na minor. Fresenius Environ Bull 16, 524-531.
[22] Brain, R.A., Johnson, D.J., Richards, S.M., Sanderson, H., Sibley, P.K. and Solomon, K.R. (2004) Effects of 25 phar-maceutical compounds to Lemna gibba using a seven-day static-renewal test. Environ Toxicol Chem 23,371-82.
[23] Brain, R.A., Sanderson, H., Sibley, P.K. and Solomon, K.R. (2006) Probabilistic ecological hazard assessment: Evaluat-ing pharmaceutical effects on aquatic higher plants as an ex-ample. Ecotoxicol Environ Saf 64, 128-135.
Received: December 17, 2009 Revised: March 25, 2010 Accepted: March 25, 2010 CORRESPONDING AUTHOR
Justyna Kolasińska Medical University of Warsaw Department of Environmental Health Sciences 1 Banacha St. 02-097 Warsaw POLAND Phone: +48 225720740 E-mail: [email protected]
GERMINATION VELOCITY AND ENZYME ACTIVITIES IN GERMINATING MAIZE SEEDS
Serkan Erdal*,1, Rahmi Dumlupinar1, Turgay Cakmak1 and Mucip Genisel2
1Department of Biology, Science Faculty, Ataturk University, Erzurum, 25240, Turkey 2 Department of Biology, Faculty of Science and Art, Agri Ibrahim Cecen University, 04100, Agri, Turkey
ABSTRACT
Effects of mammalian sex hormones (progesterone and β-estradiol) on growth parameters (percentage of germina-tion, root and shoot length) and activity of selected en-zymes (α-amylase, superoxide dismutase, peroxidase, cata-lase and polyphenoloxidase) in germinating maize were studied. Maize seeds were germinated on Petri dishes in the solutions of steroids (concentrations: 10-4, 10-6, 10-9, 10-12, 10-15 M). Steroids in all tested concentrations significantly increased root and coleoptyle lengths as well as percent-age of germination of maize in comparison to control. The highest germination ratio, root and coleoptyle lengths were recorded at 10-9 M and 10-12 M of both progesterone and β-estradiol. Likewise, progesterone and β-estradiol in all tested concentrations stimulated the activities of superoxide dis-mutase (SOD), peroxidase (POX), catalase (CAT), poly-phenol oxidase (PPO) and α-amylase. The highest activi-ties of these enzymes were determined in endosperm of seeds under the influence of progesterone and β-estradiol at concentrations with the highest root and coleoptyle lengths as well as percentage of germination.
KEYWORDS: amylase, antioxidant enzymes, growth, maize, mammalian sex hormones.
INTRODUCTION
All organisms are always in need of steroid compo-nents to maintain their vital functions. These components, lipophilic ones with low molecular weight and derived from isoprenoid, play important roles as regulatory molecules in many physiological processes, such as development and re-production in higher eukaryotes [1]. In early studies, many analytical tools, such as radio immunoassay, thin-layer chromatography, and gas chromatography were used to detect steroids [2]. Recently, more sensitive tools, such as ultra-performance liquid chromatography combined with mass spectrometry and ultra-performance liquid chroma-
tography-electrospray tandem mass spectrometry in a posi-tive mode have been used [1]. Using these tools, many ster-oid components, their quantifications, biosynthetic pathways and physiological functions have been determined [1, 3-9].
Mammalian sex hormones are a group of steroids. These steroids are naturally present in plants, but their con-tents change depending on plant species, tissue and phase of development. Because of their significance in numer-ous critical processes in animals and plants, many researches have been performed on the effects of these steroids in plants since 1926 when these hormones were firstly detected in plants [10, 11]. In later studies, these steroids (estrone, progesterone, and androstenedione) were detected, iden-tified and isolated from the plants [1, 2, 12-14]. But, alt-hough many studies, such as specific binding sites and changes in element concentrations, have been made in order to elucidate the effect mechanism of these steroids, it is still unclear [1, 2, 15, 16].
Although effects of these steroids on various stages of plant development from germination to flowering have been investigated, only a few studies have been published about their effects on seed germination and seedling growth as well as enzyme activities [2, 8, 17-20]. It is known that seed germination, one of the most critical phases of plant life, is a very complex process [21]. Germination, which begins with the imbibition of water, is affected by many exogenous and endogenous factors [22-24]. One of the exogenous factors is represented by the mammalian steroids. Previous stud-ies demonstrated that these steroids stimulated seed ger-mination [25-28]. For example, Martínez-Honduvilla et al. [25] who studied biochemical changes in Pinus pinea seeds showed that these steroid hormones stimulated seed germi-nation, percentage germination, and root and shoot lengths. Some researches reported that the steroids significantly accelerated seed germination and growth in wheat [26, 27]. Pea embryos were stimulated by 1mg/ml estrone [28-30]. Iino et al. [14] reported that progesterone of 0.01-1 µM caused distinct hypocotyls elongation. Estrone and 17β-estradiol showed growth-stimulating effects in pea [31]. Similarly, it was reported that seed germination, growth and development were stimulated by phytoestrogens and
animal estrogens [31-34]. But, these reports are inadequate in terms of a number of studies and the investigated param-eters. Furthermore, to best of our knowledge, there is no report on the effect of mammalian sex hormones on ger-mination in maize seeds, and on the activities of polyphe-nol oxidase.
Because effects on biochemical and early growth pa-rameters in germinating seeds of these steroids have been studied poorly, we aimed to investigate the effects of seed soaking with progesterone and estradiol on germination, growth and activity of selected enzymes in maize, and to determine the optimal hormone concentrations by study-ing a wide range between10-4 and 10-15M.
MATERIALS AND METHODS
Plant culture and steroid treatment
Maize seeds (Zea mays L.) were immersed in 1% sodi-um hypochlorite solution for 20 min at room temperature [35], and rinsed four times in sterile distilled water. All further manipulations were carried out under sterile con-ditions. At first, the steroids (progesterone and β-estra- diol) were dissolved in a small volume of methanol (about 2 or 3ml for 1 L solutions) [36], and then diluted in water in order to obtain the following concentrations: 10-4, 10-6, 10-9, 10-12 and 10-15M. Seeds were soaked in prepared solu-tions about 6 h [37] and moved on Petri dishes with filter papers moistened with 10 ml distilled water (10 seeds per dish). Seeds were soaked in pure water, including a small volume of methanol (about 2 or 3 ml for 1 L distilled wa-ter). They were identified as control group. All seeds were germinated in the dark at 25 °C. The germinated seeds were counted at 1st, 3rd and 5th day in order to determine percent-age of germination. Root and coleoptyle length was also measured at 1st, 3nd and 5th day. Steroids used in this work were obtained from Sigma-Aldrich Co., St. Louis, MO, USA.
α-Amylase activity
For determining the α-amylase activity, endosperms of seeds were cut out at the end of the 1st, 3rd and 5th day. Crude extracts of these seeds were prepared according to Juliano and Varner [38]. Activity of α-amylase was spec-trophotometrically measured according to de Morais and Takaki [39]. One unit of enzyme was considered to be the quantity that causes an alteration of 0.1 in absorbance.
Activity of antioxidant enzymes
Activity of the following antioxidant enzymes was measured: catalase (CAT), peroxidase (POX) and polyphe-nol oxidase (PPO). Endosperms of seeds were cut out at the end of 5-days germination period. Endosperms were homo-genized in cold phosphate buffer (0.1M, pH 7.0), the ho-mogenate was centrifuged for 15 min at 12,000 g, and the enzyme activities in the obtained supernatant were measured spectrophotometrically.
The SOD activity was estimated according to the method of Agarwal and Pandey [40]. One unit of enzyme activity was taken as that amount of enzyme, which re-duced the absorbance reading to 50 % in comparison with tubes lacking the enzyme. The CAT activity was measured by monitoring the decrease in absorbance at 240 nm in 50 mM phosphate buffer (pH 7.5) containing 20 mM H2O2. One unit of CAT activity was defined as the amount of enzyme that used 1 µmol H2O2/min [41]. The POX activi-ty was measured by monitoring the increase in absorbance at 470 nm in 50 mM phosphate buffer (pH 5.5) containing 1 mM guaiacol and 0.5 mM H2O2
[42]. One unit of POX activity was defined as the amount of enzyme that caused an increase in absorbance of 0.01/min. The PPO activity was measured by monitoring the increase in absorbance at 420 nm in 200 mM phosphate buffer (pH 7) containing 25 mM catechol. One unit of PPO activity was defined as the amount of enzyme that caused an increase in absorbance of 0.001/min [43].
Statistical analysis
Each experiment was carried out in duplicate and re-peated at least three times. Analysis of variance was con-ducted using one-way ANOVA test (SPSS 13.0 for Mi-crosoft Windows software). P ≤0.05 was considered to be significant. Error bars represent means ±SD.
RESULTS AND DISCUSSION
At all the concentrations tested, progesterone and β-estradiol significantly (p<0.05) increased the germination rate of maize seeds during 5 days as compared to control. The best ameliorative effect of these steroids on germina-tion was observed at 10-9 M for progesterone and 10-12 M for β-estradiol (Fig. 1). At the end of the 1st and 3rd day, the germination rates were determined as 85 and 98% for 10-9M of progesterone-treated seeds and 83 and 96% for 10-12M of β-estradiol-treated seeds, respectively, whereas germination rate in the control seeds were only 61 and 79%. Besides, 100% germination was observed in the control and steroid-treated seeds at the end of 5th day. These results were in agreement with those reported by previous studies. But, the optimal concentrations (10-9 and 10-12M) obtained in the present study were lower than values reported for optimal concentrations of the steroids (estrone, estradiol, androstenedione, and testosterone) by previous researchers [8, 26, 27, 31-34]. They showed that the optimal concentrations of the steroids for germination in wheat seeds were in the range of 10-6 -10-8M. Similarly, Martinez et al. [25] claimed that Pinus pinea seeds ex-posed to estrone, β-estradiol and testosterone showed a higher growth rate and germination degree compared to their respective controls. On the other hand, some research-ers reported that these steroids applied at higher concentra-tions negatively affected the growth and development. For example, Iino et al. [14] informed that 0.01-1µM of pro-gesterone treatment weakly stimulated hypocotyle elonga-
tion, but at higher concentrations of progesterone the growth was inhibited. Similarly, Gioelli [44] observed that low concentrations of estradiol stimulated the growth by 100% in carrots; but, high doses inhibited. Contrary to these findings, Janeczko and Flek [45] reported that even high concentrations, such as 10-5-10-6M, of both male and fe-male steroid hormones stimulated the generative develop-ment of winter wheat. Similarly, Janeczko et al. [46] ob-served that 1 µM levels of progesterone, estrone and 17β-estradiol stimulated flowering, but androsterone and andros-tenedione did not stimulate. According to these data, it can be said that although mammalian sex hormones positively affect the seed germination at low concentrations, their effects may vary from one plant species to another at high concentrations.
FIGURE 1 - Effect of seed soaking with progesterone and β-estradiol on germination of maize estimated at 1st, 3rd and 5th day of culture (0 = control group).
Root and coleoptyle lengths are shown in Figs. 2 and
3, respectively. Progesterone and β-estradiol significantly stimulated the root and coleoptyle elongation with regard to control. This result is in agreement with those reported by other investigators [26, 27, 31-34]. They reported that the maximum root and coleoptyle lenghts were achieved with steroid concentrations in the range 10-6 - 10-10M; however, the optimal steroid concentrations in the present
study were found to be 10-9 and 10-12 M for progesterone and β-estradiol, respectively. The maximum root lengths were 0.141, 1.93 and 4.87 cm for progesterone-treated seeds as well as 0.127, 1.8 and 4.99 cm for β-estradiol-treated seeds at the end of 1st, 3rd and 5th days, respective-ly. The maximum coleoptyle lengths were recorded as 1.25 and 2.35 cm for progesterone-treated seeds and 1.25 and 2.3 cm for β-estradiol-treated seeds at the end of the 3rd and 5th day, respectively. In control seeds, root lengths were measured as 0.111, 1.54 and 4.11 cm at the end of the 1st, 3rd and 5th days, whereas shoot lengths were 0.98 and 1.92 cm at the end of the 3rd and 5th day, respectively. Parallel to germination velocity, root and shoot lengths were augmented by treatment of mammalian steroids.
Plant seeds accumulate storage materials, such as car-bohydrates and proteins, in cotyledons or endosperms [47]. Germinating embryos supply the necessary energy from the degradation of these storage materials existing in the en-dosperm [48]. To maintain respiratory metabolism and ger-mination, readily utilizable respiratory carbohydrates (solu-ble sugars) must be supplied constantly. However, the amount of readily utilizable soluble sugar is usually very
FIGURE 2 - Effect of seed soaking with progesterone and β-estradiol on root length of maize measured at 1st, 3rd and 5th day of culture.
FIGURE 3 - Effect of seed soaking with progesterone and β-estradiol on coleoptyle length of maize measured at 3rd and 5th day of culture.
limited, with starch being the main reserve carbohydrate in plant seeds [49-51]. Germination triggers the produc-tion of enzymes, which hydrolyze starch into oligosaccha-rides [52]. α-Amylase is considered to play a major role in degradation of reserve carbohydrates to soluble sugars dur-ing germination [53-54]. Therefore, induction of α-amylase is essential to maintain active respiratory metabolism, which allows germination of plant seeds. In the present study, it was found that at all the concentrations tested, progester-one and β-estradiol resulted in a statistically significant increment in α-amylase activity on 1st, 3rd and 5th days. These results are in accordance to those reported by pre-vious researchers. They informed that α-amylase enzyme activities in wheat were enhanced by estrone and 17α-hydroxy progesterone [27]. But, the optimal steroid con-centrations determined in the present study were lower than the optimal values, which were informed to be 10-6 -10-8 M by these investigators. Herein, the maximum α-amylase activities were achieved with 10-12 M of proges-terone and 10-9 M of β-estradiol. At the end of the 1st, 3rd
and 5th days, increases in α-amylase activity were 14, 13, 12.5% in the 10-12 M of progesterone-treated seeds and 19, 18.8 and 17.8% in the 10-9 M of β-estradiol-treated
seeds comparing to control, respectively. Concerning these findings, it is possible to say that the applications of the mammalian sex steroids might accelerate seed germination by resulting in the stimulation of α-amylase activity. On account of the fact that the mechanism of action of these steroids is still unclear, either they might be directly related to the increase in α-amylase activity or they might stimu-late physiologically active compounds, such as plant hor-mones. This assumption is supported by previous research-ers. In 1969, Kopcewicz [55] believed that mammalian steroids can stimulate the synthesis of gibberellins. Simi-larly, Dogra and Thukral [26] informed that steroids may also increase the metabolism of plants by synthesizing more nucleic acid, proteins and enzymes.
FIGURE 4 - α-amylase activity in endosperm of maize seeds at 1nd, 3rd and 5th day of germination - impact of progesterone and β-stradiol
Reactive oxygen species (ROS) are synthesized at very
high rates in the cells, even under optimal conditions. Plants have evolved mechanisms to scavenge toxic and reactive species by antioxidant compounds and by enzymatic anti-oxidant systems [56-57]. The disruptions in the electron transport system contribute to the production of ROS, such as O.
FIGURE 5 - Activity of antioxidant enzymes in endosperm of maize seeds treated with progesterone and β-estradiol at 5th day of culture.
matic ROS scavenging systems [58]. SOD transforms su-peroxide to H2O2 by acting as the first line of defence against ROS. H2O2 is metabolized to H2O by peroxidase (POX) and catalase (CAT) [59]. Furthermore, the effects of these hormones on PPO activity in germinating seeds were studied for the first time in the present study. Gener-ally, PPO catalyzes the oxidation of phenolic compounds to quinones [60]. Therefore, it is crucial for plants to maintain the activities of these enzymes in order to accommodate these oxidative conditions. In the present study, it was noted that at all the concentrations tested, progesterone and β-estradiol enhanced PPO, SOD, POX and CAT activities in comparison with control (Fig. 5), and maximum activi-ties for all enzymes were achieved at 10-9 - 10-12 M con-centrations for both. The highest SOD activities were meas-ured to be 44 and 50 U/g for progesterone and β-estradiol at the end of 5th day, respectively, whereas SOD activity was only 26 U/g in control seeds. POX and CAT activities were 214 and 13 U/g in control seeds, but were 339 and 25 U/g for progesterone-treated seeds and 718 and 35 U/g for β-estradiol-treated seeds, respectively. The PPO activi-ty was 718 U/g for progesterone-treated seeds, 860 U/g for β-estradiol-treated seeds, and 496 U/g for control seeds. Similar results were also reported by Dogra and Kaur [27]. They showed that CAT and POX activities were increased by estrone and 17α-hydroxy progesterone. However, the optimal concentrations (10-6 and 10-8M) reported by them were higher than the optimal values herein, 10 -9 and 10-12 M. Considering these results, it can be said that these steroids may control ROS production by regulating the antioxidant enzyme activities. Increasing antioxidant activity might evolve the plant resistance. Thus, increase in plant growth and development might be attributed to increasing plant resistance.
The obtained results showed that the steroids (proges-terone and β-estradiol) applied via seed soaking stimulated seed germination and seedling growth in maize plants which is accompanied by changes in activity of important enzymes. In spite of the fact that these results are in harmony with previous studies, our recorded optimal concentrations (10-9 and 10-12 M) were lower than those (10-6 and 10-8 M) in the previous studies. Because varying steroid concentrations might affect the results, 10-11 - 10-13 M levels for proges-terone and 10-8 - 10-10 M levels for β-estradiol were tested, and optimal concentrations were found to be 10-12 M for progesterone and 10-9 M for β-estradiol.
CONCLUSIONS
Considering the results, we propose that these steroids may be used in agricultural studies, particularly where seed germination and post-germination growth are required. These steroids are more effective than plant hormones such as indole-3-acetic acid and gibberellic acid. Martinez et al. [25] reported that in Pinus pinea seeds exposed to estrone, β-estradiol and testosterone as well as indole acetic acid and gibberellic acid, the highest growth rate and germina-
tion degree was recorded for the steroids. Besides, it is known that the usage of hormones in agricultural breeding can cause some chronically health problems in humans and also the other creatures which eat the products obtained by using these hormones. But, applying of these hormones in the lowest possible concentrations (such as 10-12 M) may decrease or prevent negative effects in breeding of the agricultural plants, animals and also, indirectly, human beings. That is why we think that the determination of the most optimal concentrations of each steroid is very im-portant. Moreover, the most optimal concentration of each steroid may vary from one plant species to another. So, it is necessary to search for various crop species separately.
On the other hand, it has been well-known that there are some plant species (e.g orchids) which have germina-tion difficulty. We think that the usage of these steroids may benefit the solution of this problem.
ACKNOWLEDGEMENTS
This work was supported by Grant from the Research Funds appropriated to Atatürk University, Erzurum, Tur-key (2008-104). The authors thank Mesut Taskin for his invaluable helps on preparing this manuscript.
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Received: December 14, 2009 Revised: March 02, 2010 Accepted: March 30, 2010 CORRESPONDING AUTHOR
Serkan Erdal Department of Biology Faculty of Science Atatürk University Erzurum 25240 TURKEY Phone: +90 442 231 4206 Fax: +90 442 236 0948 E-mail: [email protected]
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