AbstractPersistent organic pollutants such as polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are environmental contaminants that have widespread distribution and pose a serious threat to aquatic ecosystems. We conducted a study to quantify the distribution, patterns, and transport of PCDDs and PCDFs along the Pilica River in central Poland under different hydrological conditions to estimate the loads of these compounds and understand their fate in aquatic systems. Water samples were collected at five sampling points along the river that represent a range of hydrological conditions including flooding and stable and low water flows. Reduced river water flow was associated with lower average total and toxic equivalent (TEQ) concentrations of PCDDs plus PCDFs: 33.6 pg L−1 and 4.21 pg TEQ L−1 for flooding; 28.3 pg L−1 and 3.6 pg TEQ L−1 for stable flow; 18.4 pg L−1 and 1.0 pg TEQ L−1 for low-water flow. Similar results were observed for daily loadings of total and TEQ concentrations: the highest values were observed during flooding (331.1–839.4 mg d−1 and 27.8–110.7 mg TEQ d−1), medium under stable hydrological conditions (55.8–121.0 mg d−1 and 7.7–15.3 mg TEQ d−1), and the lowest values during low water flow (30.9 and 40.3 mg d−1 and 1.4–2.4 mg TEQ d−1). The results demonstrate that diffuse sources of pollution play a key role during periods of high water flow (i.e., flooding season), whereas point sources of pollution, including municipal and industrial wastewater treatment plant discharges, mainly determine the PCDD and PCDF concentrations seen during low water periods.
The Role of Hydrology in the Polychlorinated Dibenzo-p-dioxin and Dibenzofuran Distributions in a Lowland River
Magdalena Urbaniak,* Edyta Kiedrzyńska, Marcin Kiedrzyński, Marek Zieliński, and Adam Grochowalski
One of the major problems faced by river catch-ments and coastal marine ecosystems is the export of micropollutants to rivers and coastal zones accelerated
by human-related activities (Kannan et al., 2003; Hilscherova et al., 2003; Koh et al., 2004; Sapozhnikova et al., 2005; Urbaniak et al., 2010a). Of the various substances transported through river water, highly toxic halogenated aromatic hydrocarbons known as persistent organic pollutants (POPs) pose a serious threat to aquatic ecosystems, two examples being polychlori-nated dibenzo-p-dioxins (PCDDs) and polychlorinated diben-zofurans (PCDFs). Their long-range atmospheric transport and deposition on the catchment surface, long life in the environ-ment, as well as their ability to accumulate in soils, sediments, and aquatic and terrestrial food chains make them a long-term threat to both the environment and humans.
Although many worldwide studies have addressed the occurrence of PCDDs and PCDFs in river waters of the United States ( Jobb et al., 1990; Lohmann et al., 2000; Suarez et al., 2006), Europe (Rappe et al., 1989; Kutz et al., 1990; Gotz et al., 1994; Castro-Jiménez et al., 2008), and Asia (Maystrenko et al., 1998; Kim et al., 2002; Kakimoto et al., 2006; Liu et al., 2008; Chi et al., 2011; Minomo et al., 2011; Thuan et al., 2011; Nie et al., 2013), very few data exist about their presence in Polish water bodies (Urbaniak et al., 2012b, 2014a, 2014b). Because these compounds have great environmental significance, greater knowledge is required of the levels, distribution, patterns, and loads of PCDDs and PCDFs in Polish rivers.
The Pilica River, the longest left-hand tributary of the Vistula River, with a total length of 342 km and a total catchment area of 9 258 km2, is one of the most significant rivers in Poland. Eleven towns are located along its length, the largest four being Tomaszów Mazowiecki, with 65,375 inhabitants and strong textile, ceramics, machinery, metal, and leather industries; Warka, with 11,035 inhabitants and strong brewery and fruit
M. Urbaniak and E. Kiedrzyńska, European Regional Centre for Ecohydrology, Polish Academy of Sciences, Tylna 3, 90-364 Lodz, Poland, and Dep. of Applied Ecology, Faculty of Biology and Environmental Protection, Univ. of Lodz, Banacha 12/16, 90-237 Lodz, Poland; M. Kiedrzyński, Dep. of Geobotany and Plant Ecology, Faculty of Biology and Environmental Protection, Univ. of Lodz, 12/16 Banacha, 90-237 Lodz, Poland; M. Zieliński, Nofer Institute of Occupational Medicine, Teresy 8, 91-348 Lodz, Poland; and A. Grochowalski, Dep. of Chemical Engineering and Technology, Kracow Univ. of Technology, Warszawska 24, 31-155 Cracow, Poland. Assigned to Associate Editor Wei Zheng.
and vegetable industries; Białobrzegi, with 7328 inhabitants; and Nowe Miasto, with 3885 inhabitants (Urbaniak et al., 2012a, 2014a). Other than the urban areas, more than half of the Pilica catchment area (60%) is composed of agricultural land, which, together with various point sources of pollution, supplies nutrients, micropollutants, and other contaminants to the river and the Sulejów Reservoir located in its middle section (Kiedrzyńska et al., 2014b; Urbaniak et al., 2012a).
The Pilica River and the Sulejów Reservoir have acted as the base for a number of projects aimed to improve water quality by reducing the pollutant loads transported along the river to the reservoir. The river and its catchment is the UNESCO Global Reference Site in Ecohydrology and the Long-Term Socio-Ecological platform of the LTER-Europe Network and, since 2000, has been one of the UNESCO–UNEP demonstration projects developed within the framework of the UNESCO’s IHP Ecohydrology Program (Wagner-Łotkowska et al., 2004; Wagner et al., 2009). The Sulejów Reservoir itself is a part of the Polish National Long-Term Ecosystem Research Network and a European LTER site (Mirtl et al., 2009) and acts as a monitoring and research site for the Life + EnvEurope Project LIFE08 ENV/IT/000339 and Life + EKOROB Project LIFE08 ENV/PL/000519 (Izydorczyk et al., 2013).
Unfortunately, although a wealth of valuable data has been acquired by the long-time monitoring within these projects, information concerning the levels of PCDD and PCDF pollution in the area remains scarce. Nevertheless, initial studies from 2006 examined the concentration of dioxin-like polychlorinated biphenyls (DL-PCBs) in Pilica River sediments (Urbaniak et al., 2012a), and later studies focused on PCDD and PCDF sediment analyses of the Sulejów Reservoir (Urbaniak et al., 2010b, 2014b) as well as point sources of pollution in its catchment (Kiedrzyńska et al., 2014b; Urbaniak et al., 2014a). Despite this, no study has yet attempted to identify the relationship between the hydrology of the Pilica River and its water quality with respect to PCDD and PCDF levels. To address this gap, the aim of the present study was to quantify the distribution, patterns, and transport of PCDDs and PCDFs along the Pilica River continuum under a range of hydrological conditions to estimate the loads of analyzed compounds in particular river sections.
Materials and MethodsSubcatchments Land Cover Calculations
The boundaries of the Pilica River catchment and differential subcatchments were extracted from the National Hydrographic Map of Poland (Table 1; Fig. 1). The map CORINE-2006 was
used to obtain the information on the subcatchment land cover. Land cover cartographic analysis was performed using the GIS format in ArcMap 9.2 software (ESRI Inc.).
Sample CollectionThree sets of water samples were collected from the Pilica
River:1. During flooding in the spring of 2010 (on the first day of
the flood peak; during the flood hydrograph rising stage), the water level exceeded the flood alarm level of 230 cm in Sulejów and 280 cm in Spała (second and fourth sampling points, respectively) and the average water flow for all sampling points was 177.28 m3 s−1.
2. During stable water flow in the summer of 2010, the water level was below the warning status of 180 cm in Sulejów and 220 cm in Spała (second and fourth sampling points, respectively) and the average water flow for all sampling points was 41.24 m3 s−1.
3. During low water flow in the summer of 2012, the average water flow for all sampling points was 20.71 m3 s−1.
The samples were taken from five stations located along the river continuum, including one point situated above (second sampling point) and another below (third sampling point) the Sulejów Reservoir. All samples were taken from bridges located in the particular river sections. A Teflon sampler was used to take three to five samples from the mainstream of the river at each sampling point, and then the collected water was transferred into 40.0-L Teflon containers to obtain one representative well-mixed sample. Following this, a 5.0-L subsample was transferred into amber containers and transported to the laboratory in a car refrigerator at a temperature of 4°C. Further analysis of PCDDs and PCDFs was performed using the unfiltered water because the suspended particulate matter constituted <1% of the water volume and, according to the USEPA (1994b), such samples do not require filtration.
Polychlorinated Dibenzo-p-dioxin and Dibenzofuran Analysis
All analytical work was performed in the accredited Laboratory for Trace Organic Analyses at the Cracow University of Technology, Cracow, Poland, according to methods described earlier by Urbaniak et al. (2014a).
Water samples of 2.0 L of were spiked with 60.0 pg of 17 13C-labeled PCDDs and PCDFs (NK-LCS-G and WP-LCS, respectively, obtained from Wellington Laboratories) and liquid–liquid extracted with toluene. The toluene extract was placed in the bottom of a sealed polyethylene semipermeable
Table 1. Characteristics of the six Pilica River subcatchments’ land cover between individual monitoring profiles (calculated from CORINE-2006).
Type of land coverSubcatchment 1
(between river source and first sampling point)
Subcatchment 2(between first and
second sampling points)
Subcatchment 3(between second and third sampling points)
Subcatchment 4(between third and
fourth sampling points)
Subcatchment 5(between fourth and fifth sampling points)
membrane tube of 80.0-mm wall thickness and cleaned overnight with 100 mL of hexane. The hexane dialysate was cleaned on a silica gel column coated with 44.0% H2SO4 and alumina according to USEPA (1994b). The final extract was spiked with 20.0 mL of precision and recovery solution (ISS mix of 200 ng mL−1 of 13C12–1,2,3,4-TCDD and 13C12–1,2,3,7,8,9-HxCDD; USEPA, 1994b) prepared in nonane and evaporated to 20.0 mL in a gentle stream of N2.
Determination of the 17 PCDDs and PCDFs was performed by isotope dilution gas chromatography–tandem mass spectrometry (ID-GC/MS-MS) on a Thermo Scientific GCQ-1100/Trace2000 system equipped with Xcalibur data acquisition and analysis software. Separation was performed on a 30.0 m by 0.250-mm i.d. DB5MS J&W capillary column with 25-mm film and a DB17 30.0 m by 0.250-mm i.d. DB5MS J&W capillary column with 25-mm film. A sample of 2.50-mL volume was injected into a split/splitless (SSL) injector at 260°C. The GC oven was programmed as follows: an initial temperature of 130°C was held for 3 min, then the temperature was ramped by 50°C min−1 to 180°C, and then again by 2°C min−1 to 270°C. Finally, the temperature was ramped by 20°C min−1 to 300°C and held for 5 min. The resulting uncertainty was expressed as extended measurement uncertainty for k = 2 at a confidence level of 95%.
To achieve high quality results, an HP 6890 N HRGC–HRMS (Agilent Technologies) equipped with a DB5-MS
column (60 m by 0.25-mm i.d., film thickness of 0.25 mm) was used to test selected samples in the splitless injection mode. This was coupled to a high-resolution mass spectrometer (AutoSpec Ultima) using perfluorokerosene as a calibration reference, according to a method described earlier by Urbaniak et al. (2014b).
Quality Assurance/Quality ControlThe Laboratory for Trace Organic Analyses at the Cracow
University of Technology, Cracow, Poland, is involved in the Circuit Interlaboratories for Dioxins organized by the interuniversity consortium Chemistry for the Environment in collaboration with LabService Analytica S.r.l. All analytical methods used in this study were properly validated and the laboratory has successfully passed accreditation procedure no. AB 749. The HRGC/HRMS method was properly validated on the basis of internal reference materials; the analytical laboratory itself has also passed the accreditation procedure.
Quantification was performed by the internal standard method using certified calibration standards. Each analytical batch contained a method blank, a matrix spike, and replicate samples. A reagent blank was used to assess artifacts, the precision was verified by duplicate analyses, and recoveries were estimated using samples spiked with PCDDs and PCDFs.
Fig. 1. Location of river water sampling points along the Pilica River continuum on the basis of Pilica River subcatchments and its land cover.
Journal of Environmental Quality
Sample spikes were used to further confirm accuracy. Recoveries and detection levels throughout the analytical procedure are presented in Table 2. Moreover, all glassware and bottles used in the field and laboratory were cleaned with detergent, rinsed with ultrapure water, and then heated at 450°C overnight. Before use, the glassware was rinsed with acetone and hexane. The Teflon containers used in the field were also cleaned with detergent, rinsed with ultrapure water, and then with acetone and hexane.
Analysis of Polychlorinated Dibenzo-p-dioxin and Dibenzofuran Loads
To calculate the daily loads of PCDDs and PCDFs, the daily average outflows of the Pilica River (m3 d−1) measured at three water gauge stations, at Sampling Points 2, 3, and 4, were multiplied by the total PCDD, PCDF, and TEQ concentrations (pg L−1). The obtained loads are reported in milligrams of total PCDDs, PCDFs, or TEQ per day.
StatisticsStatistica 8.0 for Windows (Statsoft) was used for all statistical
analyses. The non-parametric Mann–Whitney U test was used to detect differences in the PCDD and PCDF concentrations at a given sampling point between high, stable, and low water flow periods. The degree of error for chemical analysis was assumed to be negligible. Significance was determined based on a probability level of p > 0.05.
Results and DiscussionDistribution of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans along the Pilica River Continuum in Relation to Hydrological Conditions
Water is one of the key intermediaries in the transfer of PCDDs and PCDFs from air to sediments and therefore plays an important role in their environmental fate. The PCDDs and PCDFs enter the river ecosystems through a number of pathways including industrial and municipal wastewater discharges, atmospheric deposition, and soil runoff, mainly from the agricultural land (Liu et al., 2008; Nie et al., 2013). In the case of the Pilica River, 60% of the total catchment area is covered by agricultural land (Table 1), which contributes high levels of water and soil runoff containing fertilizers, pesticides, and organic contaminants, as well as pollutants from the atmosphere. Point sources of pollution such as wastewater treatment plants add further micropollutants and other contaminants into the Pilica River (Urbaniak et al., 2012a, 2014a; Kiedrzyńska et al., 2014a, 2014b). In addition, the hydrology and meteorology of the river itself and its catchment may also influence the observed levels and distribution of pollutants along the river continuum.
Our findings show that the total concentrations of 17 2,3,7,8-substituted PCDDs and PCDFs in the water samples collected during the period of spring flooding in 2010 were heterogeneous, with values ranging from 21.6 to 47.9 pg L−1 (Table 3). Lower concentrations were found during stable water flow in summer 2010 (15.5–38.9 pg L−1), and the lowest were obtained during low water flow in summer 2012, with minimum and maximum concentrations of 15.0 and 21.3 pg L−1, respectively. The average total concentrations of PCDDs + PCDFs, calculated for all sampling points, fell as the river water flow rate decreased: 33.6, 28.3, and 18.4 pg L−1 being recorded for flooding and stable and low water flow periods, respectively (Table 3).
This fall in average total PCDD + PCDF concentrations was mainly due to the average PCDF concentration decreasing from 24.0 pg L−1 during flooding to 21.0 pg L−1 for stable flow and then to 11.3 pg L−1 during low water flow. The average PCDD concentrations for all sampling points also fell together with the flow rate, being 9.5 pg L−1 during flooding, 7.4 pg L−1 at stable flow, and 7.2 pg L−1 at low flow. A similar situation was observed for TEQ concentrations, with the highest values noted for the flooding period (4.2 pg TEQ L−1), less during stable hydrological conditions (3.6 pg TEQ L−1), and the lowest during low water flow (1.0 pg TEQ L−1) (Table 3). Significant differences were found between flooding and stable flow conditions at Points 2 and 5, between flooding and low water conditions at Points 1, 2, and 5, as well as between samples collected under stable and low flow conditions at Points 1, 4, and 5 (Table 4).
Distribution and Sources during Spring FloodingFloods are characterized by the resuspension of deeper layers
of sediments, leading to an increased micropollutant load. During spring floods, the highest suspended particulate matter and nutrient concentrations were observed in the Pilica River at the hydrograph rising limb (Wagner and Zalewski, 2000; Wagner-Łotkowska, 2001). The concentrations started falling before the river entered the hydrograph falling limb phase and continued decreasing during the decline in water discharge. Consequently, the pollutant load transported with the same water volume was higher during the flood hydrograph rising stage (condensing stage) than during the falling stage (dilution stage). This was confirmed by Kiedrzyńska et al. (2008a), who noted that 42% of the suspended sediment load was transported in the Pilica during floods, observed during 38% of the study time, and 58% of the suspended sediment load was transported during low water discharges, occurring 62% of the study time, between 2002 and 2004. Taken together with the present study, these results suggest that floods are responsible for the transport of a great amount of pollutants, including PCDDs and PCDFs, derived from the resuspension and mobilization of micropollutants accumulated in the deeper layers of river sediments (Urbaniak et al., 2014a; Kiedrzyńska et al., 2008a, 2008b).
Because wet and dry atmospheric deposition are two routes by which PCDDs and PCDFs can move from atmospheric emission sources to terrestrial and aquatic ecosystems, it seems reasonable to consider their role as sources of PCDDs and PCDFs in the Pilica River catchments. Because domestic burning is estimated to contribute about 60% of the total PCDD + PCDF emissions to the atmosphere in the United States, the emission of PCDDs
Table 2. Limits of detection (LOD) and recoveries of the analytical procedure.
or PCDFs by domestic heating, as well as their deposition on the catchment surface and surface runoff, may increase the final PCDD + PCDF concentration in the environment and its water ecosystems (USEPA, 1994a). Duinker and Bouchertall (1989) reported that while low-chlorinated congeners are dominant in filtered air, higher chlorinated forms are adsorbed to particulates, which can then be removed from the atmosphere by capturing aerosols in raindrops. This has the added effect of the water ecosystem being boosted with higher chlorinated compounds. In a study by Liu et al. (2008) conducted in the Xijiang River catchment, the highest PCDD and PCDF concentrations were found to occur in the wet season and the lowest in the dry season. Ren et al. (2007) noted that the average deposition fluxes of all 2,3,7,8-substituted PCDD and PCDF congeners was almost
four times higher in the rainy season than the dry season: 1900 and 500 pg m−2 d−1, respectively, and that strong correlation coefficients of up to 0.89 existed between PCDD and PCDF congener concentration, the amount of precipitation, and the number of rainy days.
Intensive rainfall results in the scouring of the soil and matter from the river catchment (Kiedrzyńska et al., 2008a, 2008b), further increasing the levels of organic contaminants present in the river water (Kowalewska et al., 2003; Urbaniak et al., 2010a, 2012b). Hence, diffuse sources of pollution related mostly to agricultural and urban runoff play an important role in the contamination of the river during intensive periods of rainfall and their consequent floods. It should be emphasized that in our study, the flooding samples were collected during May, i.e., at the beginning of the vegetation season, shortly after fertilization of the surrounding agricultural areas in the Pilica River floodplain. Hence, the prevailing high water level may become a source of fertilizers and pesticides, which are frequently used at the beginning of the growing season and are considered to be a source of PCDDs and PCDFs. Similar results were found by a seasonal analysis of PCDDs, PCDFs, and DL-PCBs in the water of the Ayse River in Japan by Minomo et al. (2011).
Our findings indicate that the highest concentrations of these compounds (identified in May) to be caused by runoff water contaminated by pesticides and herbicides from the catchment fields, and this was confirmed by Kakimoto et al. (2006). In
Table 3. The concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in Pilica River water samples from five sampling points at three sampling periods.
‡ Average values calculated for five sampling points.
Table 4. The results of statistical analysis of polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) concentrations using the Mann–Whitney U test. Minus signs denote no statistical significance; plus signs denote statistical significance at p ≤ 0.05.
addition, Dumortier et al. (2012) and Elskens et al. (2013) reported that commonly used fertilizers are contaminated with PCDDs and PCDFs. These observations, taken together with the growth of the Pilica River drainage area (Table 1), account for the higher total and TEQ concentrations found in the samples collected from Points 4 and 5 in the downstream section of the river: the drainage area at Point 5 (total drainage area of 9076.6 km2) was almost twice that recorded for Point 3 (4991.5 km2) (Table 1).
As well as the size of the drainage area, other characteristics of the particular subcatchments can influence the increased values noted in the downstream part of the river. Many studies have linked catchment size (Kannan et al., 2008) and degree of land use with the degree of contamination of the water ecosystems, pointing to the analysis of the catchment land cover as a practical tool for testing water quality (Comeleo et al., 1996; Black et al., 2000; Paul et al., 2002; Strayer et al., 2003, Kiedrzyńska et al., 2014a, 2014b). Hence, the highest total and TEQ values were found in the subcatchment located between the fourth and fifth sampling points—the one with the largest urban and agricultural land areas (Table 1). Increased concentrations of PCDDs and PCDFs were also observed at the second sampling point, which corresponds to the second largest subcatchment, with a very high proportion of agricultural land (62%) (Table 1).
Distribution and Sources during Stable and Low Water FlowThe samples collected during stable and low flow rates showed
a pattern different from that at flooding, with total and TEQ concentrations decreasing along the first three sampling points and then increasing at the fourth and fifth sites. There are three possible reasons for this.
First, self-purification of the river takes place at its upper section (Points 1 and 2) due to PCDD and PCDF retention and biodegradation by floodplain macrophytes and natural willow communities (Beurskens and Stortelder, 1995; Vervaeke et al., 2003; Field and Sierra-Alvarez, 2008; Kiedrzyńska et al., 2008b, Skłodowski et al., 2014). Willow is known to exert a positive influence on the remediation of soil and sediments, e.g., Vervaeke et al. (2003) noted a 57% reduction of aromatic compounds and mineral oils during 1.5 yr of willow (Salix viminalis L.) cultivation. A 98.56% reduction of soil hydrocarbons by Salix ´rubens (Schrank) and 98.65% by Salix triandra (L.) within 36 mo was reported by da Cunha et al. (2012). Similarly, our previous study demonstrated a 49% reduction in the PCB TEQ concentration along a 40-km stretch of the Pilica River between Points 1 and 2, which was covered by approximately 30 ha of natural willow communities (Skłodowski et al., 2014). In addition, the decreasing concentrations of PCDDs and PCDFs observed across this subcatchment may be associated with the fact that the highest proportion of forests is found within it, accounting for 46% of its total area (Table 1) (Comeleo et al., 1996; Black et al., 2000; Paul et al., 2002; Strayer et al., 2003).
Second, excellent conditions for the sedimentation and deposition of pollutants are created by the burial of PCDDs and PCDFs in the Sulejów Reservoir due to reduced flow velocity and increased amounts of flocculent settling in reservoirs. Urbaniak et al. (2012a) reported a 79% reduction of total PCBs and TEQ concentrations below the dam. Urbaniak et al. (2014b) in turn noted decreases of PCDD and PCDF TEQs in bottom
sediments along a gradient from the middle sections to the dam walls of three shallow lowland reservoirs, including the Sulejów Reservoir, which demonstrates the role of the reservoir as a trap for micropollutants. Other studies worldwide have confirmed the purifying character of reservoirs (Kentzer et al., 2010; Chi et al., 2011; Li et al., 2011; Ran et al., 2013)
Third, it can be seen at Points 4 and 5 that the largest cities and wastewater treatment plants within the Pilica catchment also exert an influence (Fig. 1). Urbaniak et al. (2014a) reported that the largest wastewater treatment plants within the Pilica River catchment are located in its middle to lower part. These discharge up to 1920.28 and 59.09 mg of the total PCDD, PCDF, DL-PCBs, and TEQ concentrations to the Pilica River each day, while smaller wastewater treatment plants located upstream deliver up to 176.6 and 4.6 mg d−1 of the total PCDDs, PCDFs, DL-PCBs, and TEQ concentrations. These figures, together with the lower river water volume occurring at low water flow, confirm the higher contribution made by treated wastewater in the Pilica River. They also clearly indicate that the largest wastewater treatment plants have a greater impact on the quality of the Pilica River.
Isomer Distribution of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans in the Pilica River in Relation to Hydrological Conditions
The seven 2,3,7,8-subsituted PCDD congeners and 10 2,3,7,8-subsituted PCDF congeners analyzed in the water samples from the Pilica River are depicted in Table 3, and their respective percentage contents are illustrated in Table 5. It is interesting that in all the analyzed samples, the PCDD concentration was only half to a third of the PCDF concentration. The lowest mean ratio of PCDDs to PCDFs was noted for samples collected during stable water flow (0.35) and the highest for samples taken during low water flow (0.64). The samples taken during the flooding season showed a mean ratio of 0.45 (Table 5). When these results are compared with those in Table 6, they reveal a similar trend to those noted by Maystrenko et al. (1998) for the rivers of the Republic of Bashkortostan and by Nie et al. (2013) for the Yangtze River. However, other researchers reported an opposite tendency. According to Thuan et al. (2011), the presence of higher concentrations of PCDF than PCDD may be related to pentachlorophenol (PCP) and Na-PCP inputs because the contamination of these products in Poland is estimated as 200 mg TEQ kg−1 for PCP and 0.05 mg TEQ kg−1 for Na-PCP (Kołsut, 2002).
The total amount of PCP produced in Poland is estimated to 3000 Mg, but it is not known how much is imported (Kołsut, 2002). However, although PCP and Na-PCP are thought not to be produced in the area of the Pilica River catchment, it does not mean that they were not used in the area. Lewandowski et al. (2014) and Kobusińska et al. (2014) noted contamination with PCP in the bottom sediment of the mouth section of the Vistula River (the Pilica River receiver) and the Gulf of Gdańsk. In addition, PCDD congeners are less water soluble than PCDFs, reflected in their octanol–water partition coefficient (KOW) (Shiu et al., 1988). Thuan et al. (2011) demonstrated that water samples characterized by small amounts of suspended
Journal of Environmental Quality
particulates, such as groundwater, contain higher percentages of dissolved PCDFs than PCDD homologs.
All seven PCDD congeners were detected in samples collected during the flooding and stable water stages, whereas only 1,2,3,4,7,8-HxCDD, 1,2,3,6,7,8-HxCDD, and 1,2,3,4,6,7,8,9-octachlorinated dibenzo-p-dioxin (OCDD) were observed in samples from the low water flow period, the concentrations of the other congeners being below the detection limit (Tables 3 and 5). The highest OCDD concentrations, 7.1 and 6.9 pg L−1, were noted during the low water stage at Points 2 and 5, respectively, which contributed 36.4 and 32.4% of the total PCDDs and PCDFs. The OCDD concentrations were several times lower during flooding and stable water, ranging from 0.6 to 3.1 pg L−1, with their contribution to the total PCDD + PCDF content varying between 2.9 and 10.2% (Tables 3 and 5).
According to our earlier studies examining the contamination and spatial distribution of PCDDs and PCDFs in the sediments of the Sulejów Reservoir, located in the middle section of the Pilica River, OCDD makes a strong contribution, as much as 90%, to the total PCDD and PCDF content (Urbaniak et al., 2010b, 2014b). As a similar situation was observed for untreated and treated wastewater, the high OCDD concentrations and their contribution to the total PCDD + PCDF levels in the water samples collected at low water flow may be attributable to the output from the wastewater treatment plants located in Koniecpol and Tomaszow Mazowiecki. This was confirmed by the high concentrations of total P observed in river water samples taken from Koniecpol (238.0 mg L−1) and Tomaszów Mazowiecki (322.0 mg L−1) compared with a maximum concentration of 181.0 mg L−1 recorded at the other Pilica River sampling sites.
Moreover, Urbaniak et al. (2014a) reported lower average OCDD levels in the outlet from the 17 wastewater treatment
plants located in the Pilica River catchment during the flooding period: the levels did not exceed 15.3%, compared with 62.8% during stable hydrological conditions. Similar results have been observed by Rappe et al. (1989), Jobb et al. (1990), and Chen et al. (2008), who reported that OCDD and octachlorinated dibenzofuran (OCDF) predominate as an effect of domestic and industrial wastewater inflow. Hence, it is reasonable to attribute the higher concentrations of OCDD in the Pilica River found during low water flow to the impact of wastewater.
In the case of PCDFs, the contribution of individual congeners to the total PCDD + PCDF content was more diversified, ranging from below the limit of detection to 22.6%. Similarly to the PCDDs, all 10 congeners were detected in samples collected during the flooding and stable water flow periods, while 2,3,4,7,8-PeCDF, 2,3,4,7,8-PeCDF, 1,2,3,4,7,8-HxCDF, 1,2,3,6,7,8-HxCDF, 2,3,4,6,7,8-HxCDF, and 1,2,3,4,7,8,9-HpCDF were not detected at any sampling site during low water flow (Table 5). An interesting trend was observed for the TCDF contribution, which increased slightly from the first sampling period to the second and then increased further to reach the highest levels in samples taken during low water flow (Table 5). However, the source of this congener in the Pilica River has not yet been identified.
Relatively similar total PCDD and PCDF congener contents were observed in samples collected during periods of high and stable water flow. This may confirm that the analyzed compounds were scoured from the surface of the Pilica River catchment following their dilution by intensive rains during the flooding season. According to Urbaniak et al. (2014a), the purified wastewater and the river water are almost identical in this regard, with a correlation of 0.98.
Table 5. Congener patterns of 2,3,7,8-dibenzo-p-dioxin (PCDD) and -dibenzofurans (PCDF) in Pilica River water samples from five sampling points at three sampling periods.
Polychlorinated Dibenzo-p-dioxin and Dibenzofuran Loads in the Pilica River in Relation to Hydrological Conditions
The annual loads of total PCDD + PCDF concentrations at Points 2, 3, and 4 were found to range between 331.1 and
839.4, 55.8 and 121.0, and 30.9 and 40.3 mg d−1 during flooding and stable and low water flows, respectively (Table 7). During flooding, the highest load was noted at Point 2, whereas during stable and low water flow, the highest loads were noted at Point 4 (Table 7). The PCDD and PCDF loads were found to be highest
Table 6. Polychlorinated dibenzo-p-dioxin (PCDD), polychlorinated dibenzofuran (PCDF) and their toxicity equivalent (TEQ) concentrations in river water reported worldwide.
Country River Sampling point Date of collection PCDDs PCDFs Total TEQ References
—————— pg L−1 ——————Japan Ayase River Ayase-shin bridge 2004–2005 190–4700† 0.26–7.0 Minomo et al. (2011)
Nose River Uranose bridge 2002–2004 326.7‡ 10.97‡ 0.29‡ Kakimoto et al. (2006)Kawashara bridge 2002 71 2.5 0.11
Yachiteramae bridge 2002 360 11 0.49Tsubata River Kawashiri bridge 2003 470 23 0.57 Kakimoto et al. (2006)
Suminoe bridge 2004 130 6.3 0.23Morimoto River lower reaches of the river 2003 660 37 1.01 Kakimoto et al. (2006)
Ohmiya River Tenu bridge 2003 160 13 0.24 Kakimoto et al. (2006)31 Japanese rivers na§ na 44.23 4.73 1.4 Kim et al. (2002)
China Xijiang River Gaoyao Hydrological Station (downstream
section of river)
2005–2006 16.16–66.25 0.29–1.26 0.012–0.075 Liu et al. (2008)
Yangtze River Three Gorge Reservoir 2004–2005 0.00–9.77 0.00–69 0.0008–0.317 Chen et al. (2008)Yangtze River 11 sampling points along
river2010 14.25‡ 20.09‡ 2.34‡ Nie et al. (2013)
Taiwan 3 largest reservoirs in Taiwan
na na 0.399–133.7† 0.007–0.265 Thuan et al. (2011)
Republic of Bashkortostan (Russia)
Belaja River on border with Tatarstan Republic
1994–1997 24.4 40 4.9 Maystrenko et al. (1998)
Uruzan River in Ural Mountains 1994–1997 9.7 18.8 2.6 Maystrenko et al. (1998)Ai River in Ural Mountains 1994–1997 15.1 34.9 5.2 Maystrenko et al. (1998)
Ufa River in Ural Mountains 1994–1997 10.8 18.4 2.9 Maystrenko et al. (1998)Sakmara River on border with Orenburg
region1994–1997 10.7 19.1 2.3 Maystrenko et al. (1998)
Zilair River below city of Zilair 1994–1997 18.4 17.7 2.3Suren River on border with Orenburg
region1994–1997 7.1 14.6 2.7 Maystrenko et al. (1998)
Poland Sokolowka River 5 sampling points along small urban river
2008 0.00–9.17 0.00–3.37 0.00–0.88 Urbaniak et al. (2012a)
Germany River Elbe na na 222–706† 3.04–8.05 Kutz et al. (1990)River Elbe na na 86.40–276.70† Gotz et al. (1994)
France River Vene outlet to Thau Lagoon 2005 2.22 0.55 0.053 Castro-Jiménez et al. (2008)Sweden Eman River na na 1.35–3.24† 0.042–0.085 Rappe et al. (1989)United States Houston Ship
Channel37 sampling points along
channel2002–2003 81.64–161.25 5.25–7.24 0.32–0.63 Suarez et al. (2006)
Hudson River na 1998 38.55† 0.24¶ Lohmann et al. (2000)Raritan Bay na 1998 17.79† 0.14¶ Lohmann et al. (2000)
† Sum of PCDDs and PCDFs.
‡ Average value.
§ na, not analyzed.
¶ International TEQ (I-TEQ).
Journal of Environmental Quality
during periods of flooding, with the respective values at Points 2, 3, and 4 being 89.2, 83.2, and 63.7% lower during stable flow (nine-, six-, and threefold lower), and 96.3, 90.6, and 87.9% lower (27-, 10-, and eightfold lower) during low flow (Table 7).
A similar pattern was found between the values obtained for PCDD and PCDF loads and those for total loads, with the highest values being noted at Point 2 during flooding and at Point 4 under stable and low water flow. Moreover, in all the cases, the PCDF loads were found to be between two and five times higher than the PCDD loads (Table 7).
Again, similar trends were observed for TEQ loads and total PCDD + PCDF loads, with the highest values being measured during flooding (27.8–11.7 mg TEQ d−1) and the lowest during low water flow (1.4–2.4 mg TEQ d−1). During stable hydrological conditions, the loads were found to be intermediate between those observed during the flooding and low water flow stages. Compared with flooding, the respective TEQ loads at Points 2, 3, and 4 were 89.9, 72.3, and 66.4% lower (10-, four-, and threefold lower) during stable water flow and 98.2, 91.0, and 97.0% lower (55-, 11-, and 32-fold lower) during low water flow (Table 7).
The identified loads are several times lower than those seen in other studies, e.g., Liu et al. (2008) calculated the loading of PCDDs + PCDFs in the Xijiang River as 21,205.5 mg d−1 and the TEQ loading at 71.2 mg TEQ d−1. Ko and Baker (2004) reported the PCB loads from the Susquehanna River to the Chesapeake Bay to be as high as 208.2 g d−1. The main reason for such comparatively low PCDD and PCDF loads in the Pilica River is its smaller catchment area: because the Xijiang River is 2214 km long with a catchment area of 353,000 km2, it is more than six times the length of the Pilica, with a catchment more than 38 times larger. The Susquehanna River catchment is about eight times larger, and the river transports >1 million Mg of sediment annually (USGS, 2003). In contrast, the Pilica River transports 33,054 Mg of total suspended sediment load every 3 yr (about 11,000 Mg yr−1) (Kiedrzyńska et al., 2008a)—90 times less than the Susquehanna River.
Worldwide Polychlorinated Dibenzo-p-dioxin and Dibenzofuran Concentrations and Thresholds in Freshwater
The PCDD and PCDF concentrations seen in the Pilica River are comparable to those reported in the Bashkortostan in Russia, the Hudson River in the United States, and the Xijiang River in China. In all these rivers, however, these values are several times lower than those seen in Japanese rivers and higher than those observed in Taiwan and Sweden (Table 6). However, a simple comparison between the values noted in the Pilica
River and other rivers is extremely difficult due to differences in river length, catchment size, and land cover, as well as the geomorphological and meteorological conditions occurring in a given catchment. Together with the industrial and agricultural activity in the given region, these factors exert a strong influence on the levels and ultimate fate of PCDDs and PCDFs.
To compare the quality of the Pilica River water with those of other worldwide water bodies, existing national thresholds can be applied, e.g., the Japanese environmental quality standard for river water of 1.0 pg TEQ L−1 (Minomo et al., 2011); the USEPA maximum contaminant level for dioxin (TCDD) of 30.0 pg L−1 (http://water.epa.gov/drink/contaminants/); the Canadian threshold for ambient water of 10.0 pg L−1 of TCDD (Environment Canada, 1990); and the California limit of 1.0 pg L−1 (Office of Environmental Health Hazard Assessment, 2010). Although almost all the Pilica River samples were found to exceed the Japanese environmental quality standard for river water and the California limit of 1.0 pg L−1, none of the tested samples were above the limits established by the USEPA or the Canadian Environmental Protection Act.
Potential for Improvement of River Water Quality with Regard to Polychlorinated Dibenzo-p-dioxins and Dibenzofurans
As the climate warms, the risk of significant floods as a result of anthropogenic changes in the water cycle in catchments grows (Milly et al., 2002; Zalewski, 2011; Kiedrzyńska et al., 2015). A good example is provided by climate scenarios for the South Baltic Sea catchment, which includes Poland. It is predicted that river flow will decrease by about 50% in summer and increase by up to 70% in winter (Helsinki Commission, 2007). Because water is one of the main mediums responsible for the export of pollutants from catchments, greater occurrences of prolonged summer droughts interrupted by extreme floods will alter the transport of pollutants into freshwater areas and degrade their quality.
Such a problem was observed in the present study. Despite the fact that the obtained values were mostly low, extremely high PCDD + PCDF loads, 55 times higher than seen under stable water flow conditions, occurred during flooding, mainly as a result of pollutant runoff from the catchment. Hence, it is essential to reduce the input of PCDDs and PCDFs from diffuse sources. The first stage in this process has to be to enhance their retention within the catchment by optimization of agricultural practices, reforestation, and creation of ecotone buffering zones. These approaches not only enable the retention of pollutants within the catchment—the “filtering and buffering” role of soils for POPs has been considered on a catchment scale (Gocht and
Table 7. Loads of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), PCDFs + PCDFs and toxic equivalents (TEQ) at five sampling points located along the Pilica River during three sampling periods. Loads were not determined due to lack of data for the Pilica water discharge at Sampling Points 1 and 5.
ParameterFlooding Stable water flow Low water flow
Grathwohl, 2004)—but also promote their biodegradation by soil–plant–microorganism consortia (Urbaniak, 2013).
Another promising tool is the use of constructed wetlands. They were first used for wastewater treatment in the 1950s; however, in recent years, they have been widely used for urban and agricultural runoff treatment. Several studies have proven that constructed wetlands can mitigate the pesticide pollution derived from various agricultural nonpoint sources (Schulz, 2004; Scholz and Lee, 2005; Budd et al., 2009). Schulz and Peall (2001) stated the effectiveness of constructed wetlands in retaining agricultural pesticide pollution to be 89% during runoff.
Closer to the river, a floodplain can be used as a tool to reduce the excess load of such micropollutants (Lair et al., 2009) because it can absorb and retain sediment and micropollutants such as PCDDs and PCDFs during stable and high-flow conditions (Kiedrzyńska et al., 2015; Skłodowski et al., 2014). Because the largest pollutant loads are usually transported by rivers during the rising water stages of floods, their redirection to floodplain areas during the initial stages of a flood would diminish the load transported along the river. The declining levels of PCDDs and PCDFs in river water occur not only via their retention and immobilization in floodplain sediments but also as an effect of bioremediation processes. Some naturally occurring plants in the floodplain zones, such as willow communities, promote the loss of POPs from the soil and sediments via rhizoremediation (de Cárcer et al., 2007; Slater et al., 2011; Urbaniak, 2013). These processes were investigated further in a previous study (Skołodowski et al., 2014) as well as in the present study (see above). Hence, wetlands and floodplains can be considered tools for reducing the concentrations of PCDDs and PCDFs transported along the river continuum (Kiedrzyńska et al., 2008a, 2008b; Urbaniak et al., 2012a; Skłodowski et al., 2014; Kiedrzyńska et al., 2014b, 2015).
In addition, constructed dam reservoirs also play an increasingly important role in the improvement of river water quality. Because they are usually constructed in the middle or downstream section of the river, they intersect with its continuum, thus acting as traps for suspended matter (Krasa et al., 2005; Kentzer et al., 2010; Li et al., 2011; Ran et al., 2013) and for their associated chemical toxicants (Devault et al., 2009; Chi et al., 2011), resulting in improved downstream water quality (Kentzer et al., 2010). Our earlier study (Urbaniak et al., 2014b) demonstrated 37, 56, and 29% decreases in the respective concentrations of penta-, hexa-, and hepta-CDDs and -CDFs in sediments along the Sulejów Reservoir. In addition, the total PCDD + PCDF concentrations were reduced below the dam by 21% during flooding and by 24% during stable flow, while the comparative TEQ concentrations were reduced by 69% at flooding and 36% during serene flow (Urbaniak et al., 2014b), thus resulting in improved water quality. These findings clearly demonstrate the potential role played by a lowland reservoir in the reduction of PCDD and PCDF concentrations transported along the river continuum.
To summarize, one of the priority tasks of recent research on PCDDs and PCDFs is to determine their emission, transport, and deposition in ecosystems, as this would represent an essential step toward regulating their allocation and diminishing
their concentrations. This study attempted to do this by describing not only the occurrence of PCDDs and PCDFs in water ecosystems but also determining the factors influencing their transport along the river continuum under different hydrological conditions. It also proposes synergistic solutions based on environmentally friendly ecological biotechnologies, which enable the allocation of these toxic compounds to be regulated within the catchment–river–reservoir scale, thus decreasing the risk they pose to humans and wildlife.
Conclusions
1. Increased concentrations of PCDDs, PCDFs, and TEQs occur at higher Pilica River flow rates. The main factors identified were the hydrological conditions occurring in the river itself and its catchment in combination with the diffuse sources of pollution, related mostly to runoff of atmospheric and agricultural origins, including pesticide and fertilizer inputs.
2. Changes were observed in the PCDD and PCDF ratio, with a strong predominance of PCDFs during flooding and stable water stages but lower levels at low flow as a result of PCP and Na-PCP usage and the physicochemical properties of PCDFs, which have higher water solubility than PCDDs. Moreover, increased OCDD and OCDF contents were observed with decreasing water flow. The most probable reason for these relationships is the impact of insufficiently treated wastewater during the low water flow period.
3. With regard to the PCDD and PCDF loads, the results show that spring floods play a dominant role in their transport. During such events, the total PCDD + PCDF loads were from 3 to 27 times higher than those observed during stable and low flow, respectively; in the case of the TEQs, the burdens increased by 55 times.
4. The findings, together with those of our previous surveys, demonstrate that diffuse sources of pollution play a key role during the period of high water flow (flooding season), whereas point sources of pollution, including municipal and industrial wastewater treatment plant discharges, mainly determine the PCDD and PCDF concentrations seen during low water periods.
AcknowledgmentsThis research was supported by the Polish Ministry of Science and Higher Education, Project N305 365738 “Analysis of point sources pollution of nutrients, dioxins and dioxin-like compounds in the Pilica River catchment and draw up of reclamation methods.” We would also like to thank Maciej Skłodowski, MSc, and Aleksandra Rucińska, MSc, for their help during sample collection.
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