This article was downloaded by: [National Sun Yat-Sen University] On: 21 August 2014, At: 04:46 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Toxicological & Environmental Chemistry Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gtec20 An opinion on the distribution and behavior of chemicals in response to climate change, with particular reference to the Asia-Pacific region Ross Sadler a , Albert Gabric b , Glen Shaw c , Emily Shaw b & Des Connell b a School of Public Health, Griffith University, Logan Campus, University Drive , Meadowbrook, QLD 4131, Australia b School of Environment, Griffith University, Nathan Campus , 170 Kessels Road Nathan, QLD 4111, Australia c School of Public Health, Griffith University, Gold Coast Campus , QLD 4222, Australia Published online: 16 Aug 2010. To cite this article: Ross Sadler , Albert Gabric , Glen Shaw , Emily Shaw & Des Connell (2011) An opinion on the distribution and behavior of chemicals in response to climate change, with particular reference to the Asia-Pacific region, Toxicological & Environmental Chemistry, 93:1, 3-31, DOI: 10.1080/02772248.2010.505195 To link to this article: http://dx.doi.org/10.1080/02772248.2010.505195 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.
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This article was downloaded by: [National Sun Yat-Sen University]On: 21 August 2014, At: 04:46Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Toxicological & EnvironmentalChemistryPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/gtec20
An opinion on the distribution andbehavior of chemicals in responseto climate change, with particularreference to the Asia-Pacific regionRoss Sadler a , Albert Gabric b , Glen Shaw c , Emily Shaw b & DesConnell ba School of Public Health, Griffith University, Logan Campus,University Drive , Meadowbrook, QLD 4131, Australiab School of Environment, Griffith University, Nathan Campus , 170Kessels Road Nathan, QLD 4111, Australiac School of Public Health, Griffith University, Gold Coast Campus ,QLD 4222, AustraliaPublished online: 16 Aug 2010.
To cite this article: Ross Sadler , Albert Gabric , Glen Shaw , Emily Shaw & Des Connell (2011)An opinion on the distribution and behavior of chemicals in response to climate change, withparticular reference to the Asia-Pacific region, Toxicological & Environmental Chemistry, 93:1,3-31, DOI: 10.1080/02772248.2010.505195
To link to this article: http://dx.doi.org/10.1080/02772248.2010.505195
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the“Content”) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.
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Toxicological & Environmental ChemistryVol. 93, No. 1, January 2011, 3–31
An opinion on the distribution and behavior of chemicals in response
to climate change, with particular reference to the Asia-Pacific region
Ross Sadlera*, Albert Gabricb, Glen Shawc, Emily Shawb and Des Connellb
aSchool of Public Health, Griffith University, Logan Campus, University Drive, Meadowbrook,QLD 4131, Australia; bSchool of Environment, Griffith University, Nathan Campus, 170 KesselsRoad Nathan, QLD 4111, Australia; cSchool of Public Health, Griffith University, Gold CoastCampus, QLD 4222, Australia
(Received 9 July 2009; final version received 25 June 2010)
There is a general lack of knowledge as regards the effects of climate change onpollutant behavior. This is particularly true of the Asia-Pacific Region (APR).This region has major significance in terms of global pollutant emission and alsodisplays a wide variety of environments. This review presents the authors’opinions on possible implications of climate change for pollutant behavior in theAPR. Although differing responses can be expected across the region, there areclear implications as regards the short- and long-term behavior of pollutants.Effects can be predicted through modeling, but further data are required formodel calibration. Nevertheless, it can be predicted that climate change will affectprocesses including global distillation of persistent organic pollutants, airbornetransport of heavy metals, half-life of readily degradable pollutants, andeutrophication in water bodies. Particulates are expected to play a central rolein mediating the effects of climate change, and successful predictive models willneed to be based on particulate-mediated transport and behavior. Climate changealso has the potential to cause an increase in the intensity and frequency ofharmful algal blooms in aquatic environments throughout the region, withsignificant implications for supply of both food and drinking water.
The term Asia-Pacific region (APR) generally applies to littoral East Asia, Southeast Asia,and Oceania. Although an imprecise geographical descriptor, the term Asia-Pacificbecame popular since the late 1980s as the economies within this heterogeneous regionflourished. Figure 1 gives an illustration of the APR, along with ocean currents in theregion. For the purposes of this review, the APR will be taken to include Australia, Brunei,Cambodia, People’s Republic of China, Taiwan, Fiji, India, Indonesia, Japan, Kiribati,North and South Korea, Laos, Malaysia, Marshall Islands, Federated Statesof Micronesia, Nauru, Nepal, New Zealand, Palau, Papua New Guinea, Philippines,Samoa, Singapore, Solomon Islands, Thailand, Timor-Leste, Tonga, Tuvalu,Vanuatu, Vietnam, and the United States territories of American Samoa, Guam, and
Northern Mariana Islands. Some of the conclusions may also be applied to othercomparable areas of the world, such as parts of South America, South Africa.
The science of climate change has evolved considerably over the past decade, and thepossibility of dangerous climate change in future is generally (although not universally)accepted by scientists (AAAS 2007). However, our ability to detect changing climatictrends is limited by short meteorological records. This is particularly true in some parts ofthe APR, where reliable, detailed meteorological time series do not exist for longer than100 years.
In the APR, the demonstration of deviations from the climatic norm is complex. Inaddition to the lack of climatological monitoring data, the APR is characterized byextremes of climate, even in so-called ‘‘normal seasons.’’ Events such as tropical cyclones,droughts, and heavy snowfall or snow melt are common in individual parts of the APR. Itfollows that any pattern of climate change will be superimposed on this noisy background.For the purpose of regional climate projections, the Intergovernmental Panel on ClimateChange (IPCC) divides Asia into several subregions namely, North Asia, Central Asia,Tibetan Plateau, West Asia (Middle East), East Asia, South Asia and South East Asia,and treats Australia and New Zealand, and the Pacific Islands separately (IPCC 2007a).
An examination of the trends in these areas demonstrates considerable spatialvariability. For example, there is a demonstrable increase in temperature in many areas,whereas others such as Central Siberia have recorded decreasing summer temperatures.Since 1905, temperatures in Northeast China have increased in winter but decreased insummer. It has often been hypothesized (and observed) that minimum temperatures seemto increase more than maximum temperatures. The observed trends in mean annualprecipitation are similarly variable, with significant decreases in the annual range inSouthEast Asia, increases in Northwest Australia and Java, but decreases in NortheastAustralia (IPCC 2007b).
Many manifestations of climate change (e.g., increased incidence of droughts) areextreme in nature. Some changes may be more subtle than mere reductions/increases inannual rainfall. For example, an examination of the annual rainfall in Central India
Figure 1. Global map of major ocean currents.
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between 1951 and 2000 shows a relatively constant value, but an increase in the rainfalldelivered by heavy monsoonal downpours (Goswami et al. 2006).
The objectives of this review are to present the authors’ opinions regarding the effectsof climate change on dynamic chemical processes in the APR environment. Studies thathave already been undertaken in terms of the effect of climate change on pollutantbehavior pertain to other geographical regions (Macdonald et al. 2003a, 2003b; DallaValle, Codato, and Marcomini 2007). Because climate warming has proceeded faster inArctic regions, than elsewhere, the most definite empirical evidence of this link tocontaminants comes from this region. Hence, the study of Macdonald et al. (2003a, 2003b)is of particular overall significance to the prediction of climate change effects worldwide.This present review will consider chemical rather than ecological consequences of climatechange. A recent review of the ecological consequences of climate change has appeared(Schiedek et al. 2007). The only ecological process to be considered in depth by this reviewwill be the occurrence of harmful algal blooms (HAB) because of the obvious chemicalimplications. We present this review with the objective of initiating discussion in thescientific community on climate change as it specifically affects pollutant behavior in theAPR. This review also represents a further contribution to the literature on subject ina global context.
Significance of the APR as a global source of chemical pollutants
Growth in global greenhouse gas emissions since 2000 has exhibited a sharp rise. Therehave been significant increases in the energy intensity of gross domestic product (GDP)(energy/GDP) and the carbon intensity of energy (emissions/energy), coupled withcontinuing increases in population and per capita GDP. Nearly constant or slightlyincreasing trends in the carbon intensity of energy have been recently observed in bothdeveloped and developing regions. The growth rate in emissions is strongest in rapidlydeveloping economies, particularly China. Together, the developing and least developedeconomies (forming 80% of the world’s population) accounted for 73% of the growthin global emissions growth in 2004 (Raupach et al. 2007).
New consumers in developing economies possess over one-fifth of the world’s cars,a proportion that is rising rapidly. Global CO2 emissions from motor vehicles, of whichcars make up 74%, increased during 1990–1997 by 26% a rate four times greater than thegrowth of CO2 emissions overall (Myers and Kent 2003). The situation is exacerbated bythe relatively high proportion of two-stroke engines in the APR (Kojima, Brandon, andShah 2000). The largest source of particulate of polycyclic aromatic hydrocarbons (PAHs)in the APR is gasoline and diesel vehicle emissions (cf Lee and Kim 2007).
The APR is of global significance as a source of persistent organic pollutants (POPs).The available information on the occurrence of POPs in the APR has been reviewed byTanabe (2007). He concluded that there were hot spots of POPs pollution in areas of heavyuse. Elevated levels of hexachlorocyclohexane (HCH) were found in India and SouthChina, while dichlorodiphenyltrichloroethanes (DDTs) were high in China and Vietnam.Pentabromodiphenylethers (PBDEs) were found to be increasing substantially in thecoastal waters of Hong Kong. Tanabe (2007) concluded that the region of East Asia regionis probably a global source of these contaminants. The APR constitutes the only currentsource of production of DDT. In 2005, total global production was estimated at 6269 t(a.i.), of which approximately 4250 t (a.i.) were produced in India alone. China is also amajor producer, about 55% being used as an intermediate in the production of dicofol and
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the remainder sold for direct use. North Korea is thought to produce about 300 t (a.i.) per
year (UNEP 2007).The increasing heavy industry (Fang et al. 2004), domestic fossil fuel consumption
throughout the region (Park, Kim, and Kang 2002) as well as high-volume motor traffic
(Hien et al. 2006) are all the significant sources of PAHs. A rather complex situation
prevails in the Asian environment and some initiatives have been undertaken to determine
the relative contributions of the sources. The subject of PAH behavior is subsequently
discussed in the section on particulates.A similar situation exists with inorganic chemicals. For example, China is one of the
major global sites of production and use of mercury compounds, with coal combustion
being the major source (cf Pacyna et al. 2003). A number of countries in the APR (namely,
Philippines, Indonesia, Vietnam, China, Papua New Guinea, Russia, and Mongolia) are
reported to use mercury for the extraction of gold. Generally, these operations are small
and dispersed. It has been estimated that as much as 95% of the mercury used in these
operations is lost to the environment and that these emissions comprise about 10% of the
global total (UNEP 2003). The United Nations Environment Program (UNEP) is
currently reviewing the global situation as regards cadmium and lead. Japan and China are
the largest producers of cadmium worldwide (Nordic Council of Ministers 2003). In view
of the fact that Australia, China, Russia, and North Korea are amongst the most
significant producers of lead on a global scale, a similar situation can be expected
to pertain to lead (US Bureau of Mines 1993).
Impacts of climate change on chemical behavior
Distribution of POPs and other organics
In terms of chemical behavior, the underlying physical processes are governed by
physicochemical properties of the pollutants, such as the octanol–water partition
coefficient (KOW), octanol-air partition coefficient (KOA), and Henry’s law constant.
In terms of global warming, the effect on these parameters will vary. KOW shows only a
weak dependency on temperature (Connell 2005) and KOA has a somewhat more
pronounced one, increasing log linearly with the reciprocal of temperature (Harner
and Mackay 1995). Temperature dependence of the Henry’s law constant varies
among different classes of chemicals, being maximum with compounds that are polar or
have significant hydrogen bond interaction capacity (Staudinger and Roberts 2001;
Kuhne, Ebert, and Schuurmann 2005). A number of other environmental factors
are known to affect Henry’s law constants and the significance of these on climate
change is shown in Figure 2. It is clear that in addition to temperature, suspended solids,
salinity, and dissolved organic matter can all be expected to affect the observed Henry’s
law constant, under conditions of climate change. The observed effect will therefore
depend upon which of these factors comes into play in the environment under
consideration.Of particular significance to climate change effects on chemicals is the influence that
climate perturbations will have on global transport of chemicals (i.e., movement from one
part of the APR to another or movement from the APR to other parts of the world).
In terms of polar migration potential, Wania (2006) divided environmental organics into
four categories, which could be distinguished by any two out of three of the parameters
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namely, octanol–water partition coefficient; octanol–air partition coefficient, and air-
water partition coefficient:
(1) ‘‘Fliers,’’ which have a logKOA56.5 or logKAW40 and are so volatile that they
are unlikely to deposit on the earth’s surface, even at the poles.(2) ‘‘Single hoppers,’’ which have KOA410 and hence will readily sorb to particles,
their overall transport being in this form, between the point of sorption and the
poles.(3) ‘‘Multiple hoppers,’’ which have KAW between �4 and 0 and will be subject to
transport by global distillation (Wania and Mackay 1995).(4) ‘‘Swimmers,’’ which have KAW5�2, which undergo significant meridional
transport in the oceans.
The demarcations among these groups are not absolute and some chemicals
(particularly those whose physicochemical properties are at the border between one
group and another) can exhibit both types of behavior (Wania 2006).Climate change will have at least some influence on the behavior of all groups.
Substances in the group (4) are dealt with in a subsequent section. Increased temperatures
resulting from climate change (especially significant rises caused by extreme weather
events) would be likely to favor ‘‘flier’’-type behavior among chemicals at the border of
groups (1) and (3). Because group (1) chemicals are not sorbed onto particulates, the
expected prevalence of cloud-free days could lead to higher photodegradation.In the case of climate change effects, groups (2) and (3) will be the most susceptible to
changes in behavior. The expected rise in particulates and prevalence of dust storms as a
Figure 2. Effect of various environmental parameters on Henry’s law constant, of significance toclimate change.
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result of climate change (see below), will tend to favor transport of ‘‘single hoppers’’ andwill also reduce their potential for atmospheric degradation.
The potential climate change effects on ‘‘multiple hoppers’’ is more complex, especiallyas applied to the APR. Although there has been ample evidence of global distillationeffects in the northern hemisphere, the situation in the southern hemisphere is far lessdefined. The so-called ‘‘grasshoppering’’ process which underpins global distillation ismediated by successive cycles of suspension and deposition (Wania and Mackay 1995).It is noteworthy that the atmospheric condensation step may involve deposition ontoparticulates (Wania and Mackay 1997) and on reaching the earth’s surface, thesesubstances could again find their way into the atmosphere through evaporation(the particulates could include precipitation).
The theory and also practical observations regarding global distillation suggest thatcompounds such as HCHs and hexachlorobenzenes (HCBs) will migrate preferentially tothe polar regions, while others such as DDT will be deposited preferentially at the mid-latitudes (Wania and Mackay 1996). If global warming occurred uniformly across theregion, then there should be relatively little effect on the pattern of pollutant deposition.But as the pattern of global warming tends to be accentuated in the Polar Regions, therewill be a shift in the area of deposition of chemicals. Temperature differentials, however,are not the only factors to be considered in the movement of organics. Precipitation playsan important part in removing particulates from the atmosphere. As is apparent from theforegoing comments, the general trend throughout the APR is toward decreased rainfall,albeit with an increase in heavy rains delivered through monsoon and other extremeevents. A modified delivery pattern such as the one observed in Central India (Goswamiet al. 2006) could actually enhance the distribution of POPs, by increasing the timeavailable for pollutant volatilization between rainfall events.
Long-term regional monitoring data that could support these trends are fairly rare andmay be complicated by local emissions. For example, Macleod, Riley, and McKone (2005)employed a global mass balance model (BETR Global) to determine the effects of theNorth Atlantic Oscillation (NAO) on atmospheric PCB concentrations. Using historicaldata from 11 sites in the Northern Hemisphere, they were able to obtain satisfactorycorrelations in a number of cases. The authors predicted that the maximum variability inatmospheric PCB concentrations likely to be ascribable to NAO would be a factor of two.At other sites, such as Hazelrigg (UK), the monitoring data did not support the modelpredictions, probably as a result of local emissions. Generally, the most significantcorrelations were found during winter and spring. This underlines the difficultiesencountered with monitoring data of this kind, difficulties that are likely to be evenmore accentuated in the APR. To date, no comparable study has been performed with theSouthern Oscillation Index. Wurl et al. (2006) reported a study of PCB congeners in theIndian Ocean area. Unlike the trend observed with many organochlorine pesticides, wherelevels have decreased since the 1990s (as a result of banning), PCBs are still present atsignificant concentrations in the air column. The authors believed that military dumpingand unregulated waste combustion are responsible for some of the observed elevatedconcentrations. Some POPs (e.g., Lindane) were still in use in certain countries (namely,Malaysia) during the study period. The climate change predictions that are in place for theAPR offer some clear possibilities for disruption of the global distillation pattern. Forexample, it has been postulated that the existing Hadley cell could undergo equatorial driftand the normal tropical winds would be replaced by a westerly superrotation(Pierrehumbert 2000). Figure 3 shows the aspects of global distillation as they will beaffected by climate change.
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It has been suggested that alpine ecosystems may provide a model for global transportof POPs (Daly and Wania 2005). Glaciers are known to be a dominant source of POPs in
other parts of the world (cf Blais et al. 2001) and it is unlikely that this would not be truefor the APR as well. The APR possesses some major mountain systems, such as the
Himalayas. There has been very little research defining the situation with POPs in thesesystems. It is known that the Himalayas are showing marked effects of climate change as
indexed by snowmelt and of the retreat of glaciers (Cyranoski 2005). They will, therefore,be an important site of activity as regards the climate change, particularly the release of
contaminants across the air–ice interface.Although somewhat less studied than the Arctic, the Antarctic has the potential to be a
major site at which the efforts of climate change effects will be manifested. Clear evidence
of ice melt has already been produced and Lenton et al. (2008) consider that rapid sea levelrise (41m per century) is more likely to come from the West Antarctic ice sheet than from
the Greenland Ice Sheet. Such a loss of the sorption interface would cause a majorredistribution of POPs in the Antarctic environment, with a renewed potential for
bioaccumulation and exchange with the atmosphere.Apart from global distillation, there are other transport pathways for POPs.
Macdonald et al. (2003b) noted that climate change scenarios in the arctic regions could
result in changes from air to sea transport for particle-bound POPs. The consequences ofthis would be expected to differ in the Asia-Pacific Region than in the Atlantic, because of
the strong coupling between the Antarctic Intermediate Water and the tropical Pacificprocesses (Pierrehumbert 2000).
Krummel et al. (2005) described the deposition of PCBs in North American lakes. Thisdistribution appeared to be correlated with the return of salmon to those lakes for
spawning, which subsequently die and release their pollutant load to the lakes. It is
possible that other fish which exhibit similar behavior could also perform a similarfunction. Climate change may influence their choice of different river systems for spawning
and hence, a modified pollutant distribution may be a consequence. The entire subject ofbiovector transport has been examined by Blais et al. (2007) and could extend well beyond
the realm of fish to include migratory birds and even marine mammals. It is clear thatclimate change has the ability to affect this form of transport significantly, although the
relative contribution of biovector transport, particularly to the APR is yet to bedetermined.
Figure 3. Migration processes for POPs as modified by climate change.
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These effects will be generally long term in nature and will reflect the prolongedinfluence of climate change. But climate change will also be reflected in the behavior oforganic pollutants at a more local level with consequences of a more short-term nature.Perturbations of climate such as two or three particularly hot and dry summers, severemonsoons, etc., will exert a major influence over effects of this kind. The organicpollutants that will be most clearly affected by such changes will be those whose behaviorand persistence are most directly affected by environmental parameters. Thus, climatechange effects at this level have the potential to affect pesticides currently in use, as well asPOPs. Figure 4 shows a modeling scenario in which diazinon in soil is exposed to anaverage night temperature increase of 5�C and an average day temperature increase of 3�C(Wu and Nofziger 1999). Although such increases are above long-term projections forclimate change, there is abundant evidence of local increases of this magnitude over theperiod of the model prediction (less than 2 years). The result is clearly a shorter half-life fordiazinon in soil, which may result in scenarios of increased application.
Temperature is only one of the climate change factors that could change the behaviorof organic pollutants in environmental matrices. Phenomena such as extreme weatherevents, rises in sea level, etc., also have the potential to change the behavior of organicpollutants, particularly at a local level. For example, increased sediment loads areassociated with the runoff from tropical rainfall events. It is well known that in Australiaat least, the highest erosion and runoff of pesticide-containing material occurs duringintense, short duration rainfall events (Connolly, Silburn, and Freebairn 2002). This isalmost certainly the case with most countries of the APR. Given the fact that such eventswill almost certainly increase in some areas as a result of climate change, increased exportof particle-bound organics can be expected to occur. Connolly, Silburn, and Freebairn(2002) have noted that agricultural soils are particularly vulnerable to erosion by heavyrainfall events following prolonged dry periods. This effect is most pronounced with shrink
Figure 4. Modeling of Diazinon concentration in soil under climate change conditions showing howsmall changes in the range of daily temperatures can affect the of organism persistence.
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swell soils that have not been cropped for some time – precisely the situation that wouldarise in the case of predicted climate change scenarios. Degradation of filter strips andriparian zones, in general, would be another consequence of climate change in areas wherethere is a significant decrease in rainfall and this would exacerbate the situation described.The organic pollutants carried by particulates include not only pesticides (Ghadiri andRose 1991) but also endocrine disrupting substances (Zhou et al. 2007).
Changes in environmental conditions, such as the one that may result from climatechange can also influence environmental behavior of pesticides through effects onbiotransformation (Table 1). For example, aldrin, applied to the soil surface will, giventime, epoxidize and the pesticide transported to lower layers of the soil will consist of amixture of aldrin and its epoxidation product dieldrin. Under relatively dry conditions, theepoxidation will be able to proceed to a greater extent before transport out of the aerobiclayer of the soil occurs. In contrast, under comparatively wet conditions, the aldrin anddieldrin will be transported out of the surface layer before conversion has proceeded tosuch a significant extent. The effect is most noticeable with clay soils, (Figure 5) wherepesticide transport is relatively slow, compared to sandy soils (Sadler, White, andConnell 1997).
Climate change also has the potential to affect behavior of organic pollutants througheffects on biomagnification. Macdonald, Mackay, and Hickie (2002) suggested thatenvironmental processes could be classed as either solvent switching or solvent depletion,depending upon whether or not they involve a change in fugacity. It was furtherhypothesized that solvent depletion processes, which involve a fugacity change, are morelikely to be affected by climate change through alterations to trophic structure or bychanging efficiencies of fat transfers i.e., extent of solvent depletion; (Macdonald et al.2003a). Because biomagnification is a solvent depletion process in contrast tobioconcentration, it will be more susceptible to climate change. Some evidence in supportof this has been produced particularly in Arctic regions. The trophic magnification factorsfor p, p0-DDE are consistently positive and vary by a factor of two from tropical to polarlatitudes in freshwater food webs (Kidd et al. 2005)
Distribution of heavy metals
Many of the observations regarding the effects of climate change on the behavior oforganic pollutants will have parallels as regards heavy metal distribution. Although intheir inorganic form, most heavy metals (with the important exception of mercury) areprobably not subjected to global distillation, long-range atmospheric transport is animportant phenomenon. Lee et al. (2007) studied the content of the air masses in HongKong and Guangzhou and produced evidence of long-range transport of heavy metalcontaminants from the northern inland areas of China to the coast of South China.Using back trajectory analysis, Lee et al. were able to identify three separate air massesthat would transport different heavy metal pollutant loads to the study areas.Winter months were characterized by higher 206Pb/207Pb and 208Pb/207Pb ratios, indicatingthe influence of northern inland areas of China and the Pearl River delta, while thelower ratios observed during the summer months indicated the South Asian region andmarine sources.
Clearly, climate change has the potential to alter these transport patterns througheffects upon prevailing winds and currents. For example, wind shifts on one of these daysproduced enhanced levels of Cd, Cu, Mn, Pb, V, and Zn at one of the monitoring stations
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Table 1. Consequences of climate change and their implications for environmental chemistry.
Climate changephenomenon Immediate consequences
Environmental chemistryimplications
Changes in landtemperatures
Altered pattern of agriculturaluse
Altered spectrum and rate ofpesticide entry into theenvironment
Increases in air particulates Greater sorption of pollutantsGlobal distillation effects
Increases in smog and ground-level ozone
Highly reactive oxidizingatmosphere
Possible dissolution of CO2 inseawater leading toacidification of oceans
Probable interferences withprocesses such as calcifica-tion and hence destructionof coral reefs
Figure 5. Effect of prevailing conditions on transformation and soil transport of aldrin. Wet–dryregimes have maximum effect in regions with clay soils and are of less significance in sandy soils.
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in Hong Kong. This resulted from a modified trajectory in which the air mass picked upsignificant vehicle and industrial emissions from China and Taiwan.
Climate change stressors also have the potential to alter the behavior of heavy metals inwater, soils, and sediments, and these effects will predominantly be manifest in the ‘‘local’’as opposed to the regional environment. One of the most important climate change effectsinfluencing the behavior of heavy metals will be a change in the frequency of extremeweather events. This has particular relevance to the APR in terms of heavy metal exportfrom agricultural land (Ongley 1996), urban areas (Al-Mamun et al. 2006), and mine sites(Jones, Hennessy, and Abbs 1999). It is generally agreed that the transport of heavy metalsfrom these non point sources will occur almost exclusively as particulates and the details ofthis process are further considered in the following section. The result is an increase inlevels of heavy metals in the sediments. As with the air emission study in Hong Kong,(described above) lead isotope ratios have been used to trace the origin of heavy metalsdeposited in sediments (Vicente-Beckett et al. 2006). Even in areas where climate changeprojections are for decreased rainfall, overall stormwater runoff resulting from moreintense extreme weather events is seen as the major process by which climate change willaffect the transport of heavy metals in the environment (Bridgewater 1999). In addition toexport from agricultural and other lands, extreme weather events will also cause increasedpollutant loads through their effects on improperly stored chemicals. This would be ofparticular significance to some countries of the APR, where chemical storage standards arerather lax.
Moreover, it should be noted that some contaminants such as mercury scale with riverflow. Even if the average annual river flow remains constant, a river may shift to moreepisodic peak and low flows as a result of climate change. In such a situation, the rivercould be expected to transport more mercury. The phenomenon, which has beendemonstrated with respect to snowmelt in Vermont (cf Stanley et al. 2002), would also beapplicable to climate change induced perturbations of this kind.
Rises in sea level, which have been predicted to accompany climate change and arealready being observed in some South Pacific Islands, provide a significant pathway bywhich the environmental behavior of heavy metals may be altered. Considerable effort hasbeen devoted to understanding the situation that may exist in the case of mangrovecommunities (cf Gilman et al. 2006). Mangrove forest sediments can provide a sink fortrace metals because the mangroves create a baffle that promotes the accumulation of fine-grained sediment rich in, which is usually sulfidic due to the presence of sulfate-reducingbacteria. Direct adsorption, complexing with organic matter, and the formation ofinsoluble sulfides, all contribute to the trapping of metals. The concentration and chemicalspeciation of the metals are influenced by the distribution of geochemically distincthorizons within the sediment. In horizons with a pH47 and an Eh5�150mV (reductionhorizons), metals are largely present as sulfide-bound species, whereas in horizons with apH57 and an Eh4þ100mV (oxidation horizons), most metals are present as exchange-able or oxide-bound species (Clark et al. 1998). Mangrove soils in the intertidal zoneprovide a convenient sink for anthropogenic inputs of heavy metals (Tam and Wong1996).
Of the various climate change factors that could potentially affect the growth ofmangroves; namely, increased temperatures, increased levels of CO2, and rise in sea level,the latter is considered to be probably the most significant (Field 1995). Studies withmangroves in pot culture have revealed a decrease in mangrove growth with increasedwater levels (Ellison and Farnsworth 1997). If translated into the mangrove ecosystem,the resulting changes in the community could be accompanied by expression of the
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acid-producing potential of mangrove soils (Mackey and Mackay 1996), with aconcomitant redistribution of heavy metals sorbed to this matrix.
Rising water levels associated with global climate change may also have implicationsfor the methylation of mercury and its accumulation in fish. There are indications ofincreased formation of methyl mercury in small, warm lakes, and in many newly floodedareas (UNEP 2003). Although no data are available for the Asian or southern Pacificregion, a recent study by Sunderland et al. (2009) has suggested a rise in the observedmercury concentrations of the northern pacific, probably results from lateral transport ofAsian anthropogenic deposits. Moreover, the authors demonstrated a positive relationshipbetween increasing rates of organic carbon remineralization and methylated Hgconcentrations, pointing to a link between organic carbon utilization and mercurymethylation in the open ocean. It was, therefore, concluded that settling particulateorganic carbon could provide a source of inorganic mercury to microbially activesubsurface waters and by furnishing a substrate for microbial activity, facilitate watercolumn methylation. Thus, the increased primary productivity that can be expected tooccur from increased temperatures and nutrient inputs as a result of climate change in theAPR could be expected to result in increased mercury methylation and to haveconsequences for other parts of the world as well.
It may also be inferred from studies of arctic lakes that climate change has the ability toaffect mercury fate (Outridge et al. 2007; Stern et al. 2009). High Arctic lakes such as thosestudied by Outridge et al. (2007) are ideal for investigating the effects of climate change oncontaminant cycling, because their carbon sources and biological communities aresimplified compared to those in other areas. From studies of sediment cores in two Arcticlakes, these authors concluded that around 78% of the observed mercury increases in thesestudy sites were due to increases in autochthonous primary productivity, via scavenging byalgae and/or suspended detrital algal matter. Only the remaining 22% could be attributedto long-range atmospheric transport.
It is clear that both algal scavenging and transport processes would be positivelyinfluenced by climate change. Algal scavenging would be a particularly important processfor food webs and the increase in primary productivity within the Arctic has beenimplicated as a causal factor for increases in mercury levels of ringed seals (Gaden et al.2009).
The significance of these processes to the wider APR is less clear. But of the factorsidentified by Outridge et al. (2008), the following could be expected to be positivelyaffected by climate change in the more general areas of the APR: coastal erosion; marineprimary productivity and mercury scavenging; and mercury methylation. As pointed outby Outridge et al. (2008), far less is understood in terms of the process of mercurydemethylation and particularly the extent of the process at lower latitudes. A furtherinvestigation of this factor is required before definite predictions can be made for tropicaland subtropical waters.
Ocean acidification has the potential to release metals from sediments. As regards mostelements in normal aquatic environments, significant shifts in speciation generally do notoccur close to the pH that is usually encountered. Hence, the magnitude of the changesprojected in ocean pH as a result of climate change (Section 3.4) is unlikely to causesignificant changes in any but the most sensitive elemental equilibria. Around a pH of 8however, cadmium exhibits a transition from the insoluble carbonate to soluble ions(USEPA 2007). Thus, decreases of ocean pH could cause a significant liberation ofcadmium existing in the carbonate form. Cadmium exists as a carbonate both in mineralsand also coral skeletons (Matthews, McDonough, and Grottoli 2006). It is of significance
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that cadmium has also been identified as the prosthetic group in diatom carbonicanhydrase (Lane et al. 2005) and hence, cadmium liberated from its carbonate form byocean acidification would be available to diatoms, including HAB organisms such asPseudo-nitschia. The possibility also exists that the pH shifts in ocean waters as a resultof climate change may exert physiological effects on organisms by altering the mixof carbonate species and silicate species.
Another possible pathway for entry of a specific heavy metal into the environment as aresult of climate change is the use of copper as an algicide. The potential for increase inHABs as a result of climate change is discussed in a subsequent section and similarcomments also apply to aquatic macrophytes. Copper sulfate dosing is frequently used as ameans of controlling growth of nuisance plant species in water bodies and this practise willalmost certainly become more prevalent in areas where climate change results in aproliferation of this kind. Because of the relatively rapid sorption of copper ions ontosediments, the effects of such dosing will generally be limited to an area close to the pointof application, although copper ions sorbed to suspended particulates may be transportedfurther. Both sedimentary and suspended particulate copper will be subject to re-releasephenomena.
Finally, it is possible that other effects of climate change may exert an influence on theenvironmental behavior of heavy metals. For example, an increased delivery of plantnutrients is a likely consequence of climate change (see below). This process has beenshown to reduce metal uptake by certain aquatic plants which are an important part of theAsian ecosystem (Gothberg et al. 2004).
Role of particulates
It is clear from the previous discussion that changes in the transport and distributionof particulates in all sectors of the environment will be one of the key consequences ofclimate change. Particulates can interact with the so-called ‘‘global distillation’’ phenom-enon. But the sorption of organics, heavy metals, and other environmental agents ontoparticulates (cf Kookana et al. 2002) will afford a means of transport through a number ofalternative pathways.
The same process will have consequences for nutrient transport, through the movementof bound nitrogen and phosphorus forms (Hunter et al. 2001). In terms of the sorption ofchemicals by soils and sediments, key factors identified include organic matter and claycontents, soil pH, water content, and temperature (Ahmad and Kookana 2002). Amongstthese parameters, those most likely to be affected by climate change are organic mattercontent, water content, and soil temperature. It is well known that organic matter plays amajor part in the process (Karickhoff 1981). Hence, any process with the potential to alterthe soil organic matter component will have the ability to change the extent to whichchemicals are sorbed to organic phases in soils and sediments. Soil organic matter is morerapidly mineralized under tropical rather than temperate conditions (Grisi et al. 1998).Hence, increased temperatures associated with climate change (particularly those arisingfrom short-term perturbations, particularly in daily minima) would lead to more rapidmetabolism of soil organic matter. It is interesting to note that there is some evidencefor control of soil organic matter properties by the temperature–precipitation ratio(Zech, Haumaier, and Kogel-Knabner 1989).
Soil organic matter may be roughly broken down into the categories of humic andnon humic components, the humic matter generally being a stronger sorbent for
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non ionic compounds. Aromaticity of soil organic matter is a key factor in the sorption of
non ionic pesticides as are the lignin and charcoal contents (Ahmad and Kookana 2002).Soil temperature is known to influence the sorption behavior of chemicals, although
the effects are compound specific or at least specific to particular groups of chemicals.
In some cases, elevation of temperature leads to greater sorption of certain types of
pesticides and in other cases, it results in decreased sorption (Ahmad and Kookana 2002).
Thus, increases in mean temperature associated with climate change can be expected
to change pesticide sorption characteristics, but it is not possible to make generalpredictions.
In the case of inorganic contaminants, many of the processes described above will
again be operative. The association of metals with particulates is a product of the effect of
complexing ligands, ionic strength, pH, and the competition of solutes for the surface sites
(Strawn and Sparks 1999). Clearly, all of these parameters may be altered in a climate
change scenario. In addition, the equilibrium constants for the reactions vary as a function
of temperature. Hence, increased water temperatures associated with climate change
will also affect these complexation reactions.Evidence has also emerged that the particle concentration (or at least apparent particle
concentration) can affect the particle association constant. This may reflect aggregation of
particles or bridging of particles by species such as phosphate. Either way, it is clear that
the climate change induced increase of particle concentration also has the potential to
affect sorption behavior of metals. The magnitude of the observed effect varies dependingon conditions and the specific heavy metal involved.
While most attention as regards the particulate-mediated transport of sorbed
contaminants has concentrated on movement of suspended sediments by water, this is
by no means the only pathway available (Figure 6). Sorbed contaminants can be moved by
transport of fine particulates through air. Australia and China are just two countries in the
APR to record an increased frequency of dust storms in recent years. This pathway has
particular significance in the case of desertification associated with climate change.
Erel et al. (2006) have noted the importance of this pathway for the transport of pollutants
Figure 6. Schematic diagram showing possible effects of climate change on particulate-mediatedtransport of pollutants.
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by desert dust storms in the Middle East. Evidence has also been obtained suggesting thetransport of various compounds with African dust to the Caribbean (Prospero and Nees1986). Although the origin of the particulates is soil, they are commonly found to beenriched in heavy metal pollutants such as mercury. Unfortunately, much less informationis available regarding the mechanisms for sorption of inorganic or organic pollutantsto airborne particulates than for the corresponding situation with sediments.
Contaminants in soil may be mobilized as a result of colloid-facilitated processes(cf Grolimund and Borkovec 2005). It is likely that climate change will increase colloid-mediated transport in soils through the operation of several processes. Longer periods ofdry weather will tend to increase cracking of soil and allow channeling of particulate-containing aqueous phases. In addition, extreme weather events will have the effect ofcausing sudden decreases in divalent cation concentration on the surface layer, hencepromoting colloid release.
It is more difficult to speculate on the effects that climate change may have with respectto organic pollutants sorbed to atmospheric particulates. A limited amount of research hasbeen undertaken with regard to the effect of seasons on the sorption of PAHs toparticulates in the APR and the results are conflicting. Panther, Hooper, and Tapper(1999) identified the factors that would be expected to influence the atmospheric levels ofPAHs as: (1) increased photolytic degradation during the summer; (2) transport ofpollutants from other sources, (3) removal of PAH via wet deposition and in-cloudscavenging mechanisms; and (4) volatilization of lower molecular weight species duringperiods of high temperature. Similar results were obtained by investigators whostudied benzo(a)pyrene levels in the atmosphere of three New Zealand cities(Khanal and Shooter 2004). Park, Kim, and Kang (2002) identified temperature andhumidity as the most important environmental factors controlling the levels of the morevolatile PAHs in Seoul’s atmosphere. Hien et al. (2006) believed that changes in winddirection and speed were the major causative factors of the observed seasonal differencesin Vietnam.
Thus, higher temperatures associated with climate change might lead to increased lossof volatile PAHs from particulates, and altered large-scale wind patterns (cf Pierrehumbert2000) could lead to a global redistribution of PAHs, increasing levels in some areas.Photolytic degradation could be increased during the relatively cloud-free periodsassociated with lengthy dry weather, while the relative importance of wet depositionand cloud scavenging mechanisms would decrease.
Particulates and ecological/public health effects
Particulates can exert an effect upon public and/or ecological health in a number of ways.First, through direct effects of the particles themselves and their sorbed contaminants. Thesituation is far more complex than is reflected by gross metrics such as PM2.5 (Samet et al.2005). Correlations between levels of air particulates and public health effects have alreadybeen implied by studies of the effects of forest fires in SouthEast Asia. Moreover, it hasbeen shown that the majority of PAHs sorbed to roadside dust in Asian cities arecorrelated with the respirable (50.5 mm) fraction (Hien et al. 2006).
The concept of sorbed contaminants and public health effects has received someattention, but far less consideration has been given to the possibility that particulatesthemselves may have a direct effect. Clearly, this is the case with aerosols, such as thosecontaining acidic components (Gwynn, Burnett, and Thurston 2000). General increases insuch aerosols are predicted as a result of climate change, although given the affinity of acid
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aerosols for particles, it is quite likely that they will exert their effect as sorbates ratherthan as acidic aerosols per se (IPCC 2007a).
An increase in HABs is another possible consequence often linked with climate changein at least some areas of the APR (Garnett et al. 2003). The so-called ‘‘red tide’’ events(resulting from dinoflagellate blooms in ocean waters) are associated with the productionof a variety of toxic compounds, which often exert their public health effects throughaccumulation in the muscle tissue of edible seafood. But it has also been shown thataerosols arising from red tides also carry toxins. Cheng et al. (2005) observed brevitoxin-containing aerosols from a red tide of Karenia brevis in the Gulf of Mexico. The toxin wasassociated with particles of diameter 6–12 mm and the authors speculated that the aerosolmay have been produced by a breakup from whitecap waves.
Second, it has been shown that dust particles are effective vectors for the transport ofmarine diseases (Harvell et al. 1999) and there can be a little doubt that the same is trueof human diseases as well (Griffin, Kellogg, and Shinn 2001).
It can safely be assumed that this pathway of transport for both pollutants and diseaseswill increase as a result of climate change events.
Acidification of oceans
The topic of ocean acidification and climate change has been the subject of a recent review(Doney et al. 2009). Since the beginning of the industrial era, the oceans have absorbed127� 18 billion metric tons of carbon as carbon dioxide from the atmosphere. Althoughthis absorption has some positive benefits on the reduction of global warming, it canpotentially have a deleterious effect on marine systems. It has been estimated that abouthalf of the carbon dioxide arising from fossil fuel combustion and cement manufacture hasfound its way to the oceans and resides in the upper 400m (Thacker 2005).
A prediction of the expected shifts in chemical species can be made from Eh–pHdiagrams (Snoeyink and Jenkins 1980). The concentration of calcium carbonate present inthe water column has been shown to have a direct relationship to the growth rate of coralsand hence, any process that reduced the concentration of the carbonate species (e.g., a fallin pH) would potentially decrease calcification (Hoegh-Guldberg et al. 2007). This hasbeen observed in at least some laboratory studies. The possibility also exists thatacidification of the oceans could lead to calcium carbonate dissolution, as would bepredicted by equilibrium diagrams (Buddemeier, Kleypas, and Aronson 2004; Kleypaset al. 2005).
Compounding the effects of acidification and temperature changes on coral bleachingand reef degradation are the effects of agricultural and urban runoff. These couldreasonably be expected to contain herbicides and other pesticides, plus elevated levels ofsediments (WHO 2000; AAS 2003). The presence of photosystem II herbicides in runoffhas the potential to inhibit photosynthesis by organisms that live in symbiosis with coralreefs (Shaw, Lam, and Mueller 2008). This, in turn, is predicted to act synergistically withelevated temperature in causing coral bleaching and reefal degradation.
Two different forms of calcium carbonate are produced by marine organisms.Corals and mollusks secrete aragonite, whereas foraminifera and calcifying macroalgaesecrete calcite. The few studies that exist suggest that increased carbon dioxide levels inoceans will also reduce calcification rates among these organisms (Kleypas et al. 2005;Doney et al. 2009). There can be expected to be particular sensitivity in areas with shallowaragonite horizons, such as the North Pacific. The uptake of anthropogenic carbon
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dioxide has caused these horizons to shoal by 50–100m since preindustrial times so that
they are particularly subjected to upwelling processes (Feely et al. 2008). Such regions
will be hotspots for ocean acidification effects on coral reefs.The translation of atmospheric CO2 levels into ocean pH is a more difficult operation
than it might seem. It has been estimated that atmospheric emissions of 5000 and
20,000 PgC would produce global ocean surface pH reductions of 0.8 and 1.4 units,
respectively, by the year 2300. At the lower level, the surface ocean would be
undersaturated with aragonite and at the higher level, it would become undersaturated
with respect to calcite as well (Caldeira and Wickett 2005).When predicting the effect of climate change on corals or any other calcifying
organisms, it is important to realize that these organisms will also be subjected to other
stresses, in addition to those resulting from increased carbon dioxide. Although accurate
predictions can be made of the effects of acidification by the use of modeling, the role
played by temperature increases and other effects of climate change need to be taken
into account. Claims have been made for both antagonistic and synergistic effects
of acidification and temperature with respect to coral growth (Thacker 2005).
Nutrients in aquatic systems
It is clear that nutrients will be affected significantly by the climate change scenarios
described. A long-held cornerstone of describing the behavior of nutrients in the
oceans has been the so-called Redfield ratio, i.e., that C:N:P will lie in the ratio of
106 : 16 : 1. This ratio has been established as a fairly universal parameter. However, the
situations induced by climate change may not satisfy these criteria and hence, Redfield
ratios may not apply under such conditions. This has been observed in at least some
instances (Thacker 2005).Michaels, Karl, and Capone (2001) discussed possible models for nutrient behavior in
ocean ecosystems with particular reference to climate change. They considered input of
nutrients from dust storms to be of particular significance to this process and noted that, in
contrast to the classical Redfield model, at least some components of the C, N, and P
system would not be at steady state conditions, under the influence of climate change.
Associated with such conditions would be increased uptake and fixation of CO2 and
probably nitrogen, in addition to deposition of organic nitrogen containing particulates. In
terms of transport of nutrients, dust has been shown to be a significant factor as regards
both Asian and African systems (Garrison et al. 2003).Because of the involvement of ferredoxin in nitrogen fixation, this process has a high
requirement for iron. The possibility exists that some of the iron requirement will be
satisfied via dust deposition (Boyd et al. 2004). Through this pathway, climate change may
result in enhanced nitrogen fixation. In a study conducted in the North Pacific, Young
et al. (1991) suggested that the arrival of an atmospheric dust plume gradually converted
the ocean phytoplankton ecosystem from a situation of iron limitation to one of limitation
by other nutrients.In assessing the overall effects of climate change on nutrient behavior in aquatic
environments, it is important to consider not just the static pool sizes of the substances
involved, but also the dynamic situation. The data required for successful operation of
these models will, therefore, represent an increase in sophistication over the relatively
simplistic ‘‘total’’ parameters currently used to represent nitrogen and phosphorus.
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Figure 7 shows some of the processes that would lead to changes in the Redfield ratio,outlined above (cf Michaels, Karl, and Capone 2001).
Not a great deal is known regarding the bioavailability of the nitrogen and phosphorusfractions associated with particulate matter and the situation is likely to be complex(cf Sigleo and Shultz 1993). The value of the available information is limited by thechaotropic conditions generally used in predigestion during laboratory analysis to liberatethe molecules from their combined state. The agents employed would release not onlybioaccessible fractions but also more firmly bound forms.
Impact of climate change on bio-synthesis of toxic chemicals
Climate change can be expected to have an effect on HABs. While HABs are a naturalphenomenon, the frequency, intensity, and distribution of HABs has increased globally inrecent decades (Van Dolah 2000; GEOHAB 2001; Hayes et al. 2001). In the future, therewill be increasing interaction between human and coastal areas. Thus, HABs will likely bean important human health and environmental concern in the future (GEOHAB 2001).Scarcity of water in inland areas as a result of desertification will also mean that suppliesmay have to be drawn from sources that were traditionally avoided because ofproblems with HABs. The main factors affecting the distribution of HABs are nutrientsand physical conditions, such as temperature and mixing (Smayda 1997). Due to thediversity of HABs, these factors will have different impacts on individual species and willbe further discussed.
The increase in HABs in recent decades is believed to be largely due to anthropogenicincreases in nutrients (Zingone and Enevoldsen 2000; Fristachi and Sinclair 2008).For example, cultural eutrophication is believed to be the main cause of blooms of thetoxic dinoflagellate K. brevis (Brand and Compton 2007), the toxic diatom Pseudo-nitschia
Figure 7. Nutrient processes as a result of climate change (modified from Michaels, Karl, andCapone (2001)). Increased inputs of nutrients and iron will be experienced as a result of atmosphericdeposition and extreme weather events.
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calliantha (Spatharis et al. 2007) and the toxic cyanobacterium Nodularia spumigena(Sellner 1997). In a study dealing with a specific part of the APR (namely, QueenslandAustralia), Garnett et al. (2003) observed that increased night temperatures producedincreased growth of the toxic cyanobacterium, Cylindrospermopsis raciborskii. At low lightintensities, there was a slight negative correlation with toxin production and a slightpositive one at high light intensities. Microcystis aeruginosa on the other hand, onlyexhibited increases in growth rate with increasing temperature at higher light intensities.Mesocosm studies demonstrated the ability of cyanobacteria (particularly C. raciborskii torespond quickly to inputs of phosphorus and to a lesser extent, nitrogen). They concludedthat C. raciborskii could increase its geographical range and/or dominance to moretemperate areas of Queensland.
While enhanced nutrient conditions often do lead to increases of HABs, it hasalso been demonstrated that they may favor the competitors of HAB organisms(Zingone and Enevoldsen 2000). The ratio of nutrients may also be an important factorin determining whether harmful algal species will dominate in a community. For example,Hodgkiss and Ho (1997) attributed HABs in Tolo Harbour, Hong Kong, to a reductionin the N:P ratio. Furthermore, different nutrient ratios would be expected to havevarying effects on each taxonomic group of HABs due to differences in their physiologicalattributes (Zingone and Enevoldsen 2000). For example, toxic cyanobacteria arefavored in high iron and phosphorus conditions, but not in high nitrogenconditions (Hood et al. 2001). These variations in response to nutrients between differenttaxa of HABs make predicting the response of HABs to changes in nutrients a complexprocess.
While the diverse range of harmful algal species will have adaptations to differentphysical conditions, there are some common conditions that are associated with a majorityof HABs. First, most HABs have been observed to occur when the water body is stratifiedand thus has limited vertical mixing (e.g. Tang et al. 2003; Trainer et al. 2007). This islikely to be because stratification favors dinoflagellates and cyanobacteria, which are thedominant HAB organisms in marine and freshwater environments, respectively (Smayda1997; Sherman et al. 1998).
The second physical condition common to a number of observed HABs is increasedtemperatures at the time of the bloom (e.g. Tang et al. 2003; Yang and Hodgkiss 2004;Tang et al. 2006). Furthermore, the toxicity of a HAB may be higher at high temperatures,as is the case with blooms of the dinoflagellate Pfiesteria piscida (Burkholder and Glasgow1997). However, due to the diversity of harmful algae, this trend is not always seen. Forexample, the toxic dinoflagellate, Alexandrium catenella, has its distribution limited totemperate waters and has been found to be more toxic at low temperatures(GEOHAB 2001; Sekiguchi et al. 2001).
Climate change involves shifting precipitation patterns with respect to both space andtime. Thus, future climate change scenarios will involve both increased precipitation as aresult of extreme weather events and also desertification, through perturbation of naturalseasons (IPCC 2007a, 2007b). Increased precipitation intensity as a result of global climatechange is expected to increase the amount of continental runoff (Labat et al. 2004).Increased runoff leads to an increase in the fluvial supply of nutrients into coastalenvironments (Ringuet et al. 2003). Therefore, it would be expected that HABs wouldincrease in the future due to further increases in nutrients. In the case of harmful algalspecies that are favored in low nutrient conditions, these species may bloom less frequentlyor become limited in their distribution. However, overall it would be expected that thefrequency and intensity of HABs will increase with increased nutrients and that HABs may
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occur in areas in which they were previously limited by low nutrient levels, thereforeexpanding their distribution.
An increase in drought frequency from global climate change would be expected tolead to an increase in major dust storm events in a number of countries (e.g. Prospero andNees 1977; Goudie and Middleton 1992). The implications of dry deposition interms of nutrient and iron availability have been described in the previous section.Aeolian deposition of dust is a major source of iron in the global ocean and therefore isbelieved to a major environmental factor controlling cyanobacterial blooms(Michaels et al. 1996; Karl et al. 2002; Boyd et al. 2004). Thus, increased dust depositionas a result of global climate change may be expected to result in increasedcyanobacterial blooms. New nitrogen introduced during cyanobacterial blooms throughdinitrogen fixation may then allow succession of other phytoplankton species.For example, this was seen to be the case in Florida where blooms of the toxicdinoflagellate Gymnodinium breve followed a large bloom of the cyanobacteriumTrichodesmium (Lenes et al. 2001).
Warming of the oceans and freshwater systems as a result of global climate changewould be expected to alter the distribution, frequency, and intensity of HABs. Species thatare currently limited to warm waters, such as the highly toxic dinflagellate, Pyrodiniumbahamense, may be expected to increase their range into higher latitudes as a result ofglobal warming. Indeed fossilized cysts of P. bahamense reveal that in the past they werealso distributed in temperate regions, presumably when temperatures were warmer thanthey are at present (Zingone and Enevoldsen 2000). Conversely, some species such asA. catenella, that are limited to temperate waters may be expected to have theirdistribution reduced as a result of increasing sea surface temperatures. Overall, however,there appears to be the general trend that HABs occur during periods of increasedtemperature (e.g. Tang et al. 2003, 2006; Yang and Hodgkiss 2004) and therefore, it wouldbe expected that HABs would increase in the future as a result of global climate change.Historical records support this prediction as it has been found in geological records thatHABs were more prevalent in periods of warm sea surface temperatures (Mudie, Rochon,and Levac 2002).
Freshwater runoff induces stratification in denser, higher salinity environments(Smayda 1997). Therefore, an increase in runoff as a result of global climate changewould be expected to increase stratification in water bodies that did not previously stratify.In the future, stratification may be expected to occur more frequently and to occur inwater bodies that did not previously stratify, resulting in an increase in the frequencyand distribution of HABs.
Ciguatera fish poisoning is an example that has been well studied and is predicted tobecome more abundant due to the effects of climate change. Ciguatera fish poisoning isproduced by the presence of ciguatoxins at the microgram per kilogram level in the flesh ofa variety of tropical reef fish (Bagnis 1993, Chinain et al. 1999; Lewis 2001; Pierce andKirkpatrick 2001). Ciguatoxin precursors are produced by marine dinoflagellates, notablyGambierdiscus toxicus, and these precursors are accumulated by herbivorous fish,biomagnified through carnivorous fish species and oxidized to ciguatoxins (Lewis andHolmes 1993; Backer and McGillicuddy 2006; Villareal et al. 2006). Usually considered ofimportance to the Pacific nations, ciguatera is now of considerable significance to Asiancountries such as Hong Kong through the import of live reef fish species for humanconsumption (Wong et al. 2005).
The potential of climate change to result in coral deaths has been described in theprevious section. Colonization of dead corals by filamentous and calcareous macroalgae is
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common after coral bleaching events and this produces a favorable environment for
benthic dinoflagellates such as G. toxicus (Lehane and Lewis 2000; Backer and
McGillicuddy 2006; Villareal et al. 2006). It is, therefore, predicted that an increased
incidence and severity of coral bleaching events as a result of global warming and its
secondary effects, will result in an increased frequency of ciguatera fish poisoning episodes
(Hall, D’Souza, and Kirk 2007).In addition, it has been reasonably suggested that the range of toxic marine
dinoflagellates will extend to higher latitudes, thus producing ciguatoxic fish in locations
previously considered to be outside the range of G. toxicus colonization (Patz, Olson, and
Gray 2006). Recently, ciguatera fish poisoning has been shown to occur from consumption
of pelagic carnivorous fish from the northern rivers area of New South Wales, Australia
(Safefood NSW 2002). This region has not previously been associated with ciguatera
poisoning. Recent research in French Polynesia has identified significant correlations
between ciguatera incidence rates and local sea surface temperature increases
(Chateau-Degat et al. 2005).The role of climate change in the expansion of HABs is difficult to test because of the
complexity of overlying issues (e.g., inputs from the increased activity of aquaculture) and
a general lack of reliable long-term historical data (Van Dolah 2000). Edwards et al. (2006)
examined long-term spatial variability in a number of HABs (in the northeast Atlantic and
North Sea) using data from the continuous plankton recorder. Over the last four decades,
some dinoflagellate taxa showed pronounced variation in the south and east of the North
Sea, with the most significant increases being restricted to the adjacent waters off Norway.
This was one of the areas, identified through consideration of NAO data as being highly
vulnerable to effects of HAB formation. There currently being no parallel studies in the
southern hemisphere, a need exists for study in this area, particularly in relation to the
Southern Oscillation Index.
Conclusions
It is clear that climate change has the potential to create a variety of effects within the
APR and this review has presented the authors’ opinions on possible changes that may
occur. In our view, these effects are not simple or uniform and different effects will be
observed across the region. Climate change has implications for both the short-and
long-term behavior of pollutants at a region-specific level across all environmental media.
For example, effects can be predicted in terms of processes including global distillation of
POPs, airborne transport of heavy metals, half life of readily degradable pollutants, and
eutrophication in water bodies. In terms of HABs, there is the potential for increases in the
intensity and frequency of both marine and freshwater species. In particular, it is
now becoming apparent that ciguatera fish poisoning will become an increasing health
issue in a warming world, as will the presence of certain cyanobacterial toxins in
drinking water reservoirs. The central role of particulates in mediating the effects
of climate change has been clearly demonstrated and the most successful models in terms
of predicting environmental effects of climate change will be those that are centered
around particulate-mediated transport and behavior. Modeling is a useful tool in
prediction of effects, but is presently limited by the absence of data required for the model
calibration. Thus, there exists an urgent need for the development of region-specific
models to predict the behavior of chemicals of concern in the Asian environment.
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A corollary of this requirement is the collection of data relevant to the developmentof models and their ultimate calibration.
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