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CHEMICAL CONTAMINANTS IN THE ARCTIC ENVIRONMENT –ARE THEY A CONCERN FOR WILDLIFE?

BIRGIT M. BRAUNE

Environment Canada, Science and Technology Branch, National Wildlife Research Centre,Carleton University, 1125 Colonel By Drive (Raven Road), Ottawa, Ontario K1A 0H3 Canada

E-mail: birgit.braune@ec.gc.ca

ABSTRACT.—Environmental contaminants are a global problem, and their presence in the Arcticreflects the way in which the Arctic interacts with the rest of the world. Most contaminants aretransported to the North on air and ocean currents from more southerly agricultural and industrialsources. Upon reaching the Arctic environment, many persistent contaminants bioaccumulate andbiomagnify in the food web, making those species feeding at high trophic positions more vulner-able to contaminant exposure via their diet. By examining contaminant levels in wildlife, we canlook for the arrival of new contaminants in the Arctic, as well as determine whether existing chem-ical contaminants of concern are increasing or decreasing. Historically, contaminants of concernincluded compounds such as the polychlorinated biphenyls (PCBs), and organochlorine pesticidessuch as dichlorodiphenyltrichloroethane (DDT). During the 1950s to 1970s, bioaccumulation oforganochlorine compounds such as DDT and its degradation product, dichlorodiphenyl -dichloroethane (DDE), were associated with eggshell thinning and reduced reproduction rates intop predatory species such as the Peregrine Falcon (Falco peregrinus). The majority of theselegacy persistent organic pollutants (POPs) have significantly declined in Arctic biota over thelast several decades. However, more recently, newer compounds such as brominated flame retar-dants (BFRs) and perfluorinated compounds (PFCs) have been detected in a wide variety of biotaincluding Arctic wildlife. Certain metals are also contaminating the Arctic environment. Elementalmercury (Hg0) is highly volatile, and gaseous Hg partitions readily into the atmosphere where itcan undergo long-range atmospheric transport to the polar regions which are global sinks for Hg.Although Hg occurs naturally in the environment, anthropogenic sources have been postulated tocontribute more significantly to the occurrence of Hg in the Arctic than natural emissions, result-ing in increasing Hg concentrations in a variety of Arctic biota, particularly in the Canadian Arcticand western Greenland. Recent warming ocean conditions and longer ice-free periods have alsoaltered prey availability in some areas of the Arctic, affecting nutrition and chemical contaminantprofiles. These changes in environmental conditions and contaminant exposure all contribute tothe complexity of interpreting the contaminant profiles found in Arctic biota. Received 1 March2011, accepted 19 April 2011.

BRAUNE, B.M. 2011. Chemical contaminants in the Arctic environment–Are they a concern forwildlife? Pages 133–146 in R. T. Watson, T. J. Cade, M. Fuller, G. Hunt, and E. Potapov (Eds.).Gyrfalcons and Ptarmigan in a Changing World, Volume I. The Peregrine Fund, Boise, Idaho,USA. http://dx.doi.org/ 10.4080/ gpcw.2011.0114

Key words: Contaminants, POPs, mercury, Arctic, wildlife, climate change.

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BIOTA AT NORTHERN LATITUDES are exposed toa variety of chemical residues that are, for themost part, transported there by the prevailingwinds, ocean currents and rivers (AMAP2009). Unlike metals, such as mercury, persist-ent organic pollutants are generated entirelyfrom anthropogenic sources (AMAP 2004). Inaddition to the legacy organochlorine contam-inants, such as the PCBs and DDT, otherclasses of chemical contaminants have beenfound more recently in the Arctic environment.These include the brominated flame retardantsand perfluorinated compounds.

Legacy Persistent Organic Pollutants.—Per-sistent organic pollutants (POPs), which havebeen banned or restricted in use, are generallyreferred to as legacy POPs. These include suchcompounds as the polychlorinated biphenyls(PCBs), and organochlorine pesticides such asdichlorodiphenyltrichloroethane (DDT), itsbreak-down product dichlorodiphenyldichloro -ethane (DDE), chlordane, hexabromobenzene(HCB), hexachlorocyclohexane (HCH), andmirex. In response to regulatory actions toreduce emissions (e.g. Stockholm Conventionon POPs, UN ECE Convention on Long-rangeTransboundary Air Pollution (LRTAP) POPsProtocol), most of the legacy POPs havedeclined in the Arctic environment as reflectedin time trends for air (Hung et al. 2010) andbiota (Rigét et al. 2010). However, because oftheir chemical characteristics, POPs willremain in the environment for many decadesto come.

Brominated Flame Retardants.—Brominatedflame retardants (BFRs) are chemicals used inmaterials to make them more fire-resistant.Examples include polyurethane foam, plasticsused in electronic equipment, circuit boards,expanded and extruded plastic (e.g. Styro-foam), and textile coatings (de Wit et al. 2010).Most BFRs are additives mixed into polymersand are not chemically bound to the materials,while others react chemically with the mate-rial. Those BFRs which are additives may sep-arate/leach from surface of product into

environment, while others enter the environ-ment through incomplete chemical reactionsand destruction of the material. BFRs havemany chemical characteristics which makethem behave in ways that are similar to POPs.Brominated organic compounds, such as poly-brominated diphenyl ethers (PBDEs),hexabromo cyclododecanes (HBCDs) andpolybrominated biphenyls (PBBs), have beendetected in a wide variety of biota includingArctic wildlife (de Wit et al. 2006). The UnitedStates is currently the only Arctic country pro-ducing BFRs (de Wit et al. 2010). Of the threetechnical PBDE products (Penta-BDE, Octa-BDE, Deca-BDE), Penta- and Octa-BDE werebanned in the European Union and in Norwayin 2004, and the sole manufacturer of thesetwo products in the United States voluntarilydiscontinued production in 2005 (de Wit et al.2010). Production of PBBs has also ceased. Asof 2008, however, there were no restrictions onthe production and use of technical HBCD.

Perfluorinated Compounds.—Poly- and per-fluorinated organic compounds (PFCs) areubiquitous in the Arctic environment.Although PFCs were commercialized over 40years ago, they received little attention untilthey were reported as contaminants in wildlifein the Arctic and elsewhere by Giesy and Kan-nan (2001). Since then, PFCs have been shownto be widespread in the environment and inwildlife (Houde et al. 2006, Lau et al. 2007,Butt et al. 2010). The chemical and thermalstability of PFCs has led to the manufacture ofa range of fluoropolymers used as lubricants,adhesives, stain and soil repellants, paper coat-ings, non-stick surfaces on cookware, and fire-fighting foams (Kissa 2001). The majorfluorinated compounds that have been meas-ured in the environment are the perfluorinatedsulfonates (PFSAs), of which perfluorooctanesulfonate (PFOS) is best known, and the per-fluorinated carboxylates (PFCAs) whichinclude perfluorooctanoate (PFOA) (Butt et al.2010). Regulation of PFCs is being discussedat both international and national levels, andPFOS has recently been nominated as a candi-

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date POP for the UN ECE LRTAP POPs Pro-tocol (AMAP 2009) and, in 2009, was listed asa POP to be regulated for restricted use underthe Stockholm Convention (Stockholm Con-vention on POPs 2010).

Mercury.—Although mercury (Hg) occurs nat-urally in the environment, emissions fromhuman activities, such as fossil fuel combus-tion, non-ferrous metal production, and wasteincineration, have been postulated to con-tribute more significantly to the occurrence ofHg in the Arctic than natural emissions(Pacyna 2005). The quantities of mercuryreleased from human activities have beenincreasing over the past 200 years, i.e. sincethe Industrial Revolution (Nriagu and Pacyna1988, Pacyna et al. 2006). This has resulted insignificant increases in biotic Hg levels overthat time period, even in regions that areremote from most anthropogenic sources, suchas the Arctic (Dietz et al. 2006, 2009).Although there is not yet a global policy toreduce emissions of mercury, many countriesare already taking steps to lower their emis-sions. In 2003, a Protocol on Heavy Metalswas adopted by the UN ECE LRTAP Conven-tion aimed at limiting emissions of mercuryand other metals from Europe and NorthAmerica.

HOW DO CHEMICAL CONTAMINANTS

REACH THE ARCTIC?

Winds, ocean currents and rivers are all poten-tial transport pathways for chemical contami-nants to reach the Arctic (AMAP 2009).Chemical characteristics, such as volatility andwater solubility, determine the potential of anorganic chemical to become an Arctic contam-inant (Wania 2003, 2006). Air is the mostimportant transport route to the Arctic forvolatile and semi-volatile contaminants includ-ing Hg (AMAP 2002). Many chlorinatedorganics are present as gases even at low tem-peratures and are absorbed from the gas phaseby water, snow, soil and plant surfaces (Brauneet al. 2005a). More recently, however, studies

have found that many non-volatile but highlystable compounds such as the highly bromi-nated compounds as well as the PFCAs andPFSAs are present in the Arctic (Muir and deWit 2010). Their presence may be due toatmospheric transport on particles, or to degra-dation of volatile precursors. For the morewater-soluble, less volatile contaminants,transport via ocean currents may be moreimportant than the atmospheric route (Li et al.2002, 2004). Unlike the atmospheric transportpathway, which can deliver contaminants frommid-latitudes to the Arctic within a few days orweeks, ocean transport is relatively slow and itmay take decades before contaminants reachthe Arctic (AMAP 2002). Waterborne contam-inants may also enter Arctic marine ecosys-tems via northward-flowing rivers draininginto the Arctic Ocean (Braune et al. 2005a).

Unlike other POPs, the two main classes ofPFCs found in the environment are not volatileand their transport pathways to the Arctic arecomplex. Two major potential pathways havebeen proposed. One pathway focuses onatmospheric transport of particles, or degrada-tion of volatile precursors to PFCAs in theatmosphere, and the second pathway involvesthe transport of directly-emitted PFCAs andPFSAs via ocean currents to the Arctic marineenvironment (Armitage et al. 2006, Wania2007).

Metals are naturally-occurring elements butare also generated through human activities.Elemental Hg (Hg0) is highly volatile, andgaseous Hg0 partitions readily into the atmos-phere where it can undergo long-range atmos-pheric transport. Due to a complex set offactors (Macdonald et al. 2005), polar regionshave become global sinks for Hg.

Relatively low levels of contaminants arefound in the terrestrial environment comparedwith the marine environment, especially in thehigh Arctic, due to snow cover in the winterand subsequent transfer of deposited contami-nants to freshwater systems during the rapid

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spring snow melt (Semkin 1996). The Cana-dian Arctic terrestrial environment, for exam-ple, has few significant contaminants issuesthat can be attributed to long-range transportand deposition of POPs and heavy metals, par-ticularly when compared with the freshwaterand marine environments (Gamberg et al.2005). The major contaminant concerns forterrestrial animals are from non-essential ele-ments such as cadmium (Cd) and Hg (Gam-berg et al. 2005).

CONTAMINANTS AND WILDLIFE

Persistent chlorinated and brominated organo-contaminants, as well as Hg, bioaccumulate inwildlife (Braune et al. 2005a). For example,concentrations of PCBs and Hg increase withage in Gyrfalcons (Falco rusticolus) (Ólafsdót-tir et al. 1995, Dietz et al. 2006). These com-pounds also biomagnify up the food chain(Braune et al. 2005a) making those speciesfeeding at high trophic positions more vulner-able to contaminant exposure via their diet(Hop et al. 2002, Borgå et al. 2004, Vorkampet al. 2004, Wolkers et al. 2004). Food webstudies in marine ecosystems suggest thatPFCs can also biomagnify but there have beenfew studies to date, and there have been nostudies carried out for terrestrial or freshwaterfood webs (Butt et al. 2010).

Seabirds feed at relatively high trophic posi-tions in Arctic marine food webs (Hobson et al.2002, Hop et al. 2002) and, therefore, seabirds,and in particular their eggs, have been used tomonitor contamination of the marine environ-ment in the Canadian Arctic since 1975(Braune 2007). At the time of egg formation,the lipophilic halogenated compounds aretransferred along with fat to the eggs thusreflecting the contaminant burden in thefemale at the time of laying (Verreault et al.2006). Unlike other halogenated organic con-taminants (e.g., PCBs, PBDEs), PFCs appearto bind to proteins rather than partition intolipid (Butt et al. 2010) but are found in eggs,as well (Houde et al. 2006, Verreault et al.

2007). Mercury is also readily transferred tothe eggs (Wiener et al. 2003). Contaminantburdens in the egg reflect residues assimilatedover a long time period by the female and, par-ticularly in migratory species, may integrateexposure from a number of different locations(Hebert 1998, Monteiro et al. 1999).

Contaminant concentrations can vary consid-erably among species depending on their feed-ing and migration strategies (Braune et al.2002, Buckman et al. 2004). For example, inGreenland, Peregrine Falcons (Falco peregri-nus) had higher levels of DDE, PCBs andother organochlorine contaminants in theirplasma compared with Gyrfalcons (Jarman etal. 1994). The authors attributed the differencein contaminant levels to the fact that Pere-grines, which themselves are migratory, con-sumed contaminated, migratory prey, both ontheir wintering and breeding grounds, whereasthe non-migratory Gyrfalcons consumed lowtrophic-level, non-migratory prey (e.g. ptarmi-gan, hare). Interpretation of contaminant con-centrations in biota may also be confounded ifpopulations vary their diet over trophic levelsthrough time (e.g. see Hebert et al. 1997,2000).

Spatial Patterns.—Compared with other cir-cumpolar countries, concentrations of manyorganochlorine contaminants in Canadian Arc-tic biota are generally lower than in the Euro-pean Arctic and eastern Greenland but arehigher than in Alaska, whereas Hg concentra-tions are substantially higher in Canada andwestern Greenland than elsewhere (Braune etal. 2005a). Spatial patterns of PBDEs inseabirds and marine mammals are similar tothose seen for PCBs, with the highest concen-trations found in organisms from East Green-land and Svalbard in the European Arctic,lower concentrations in the Canadian Arctic(except Hudson Bay), and the lowest concen-trations in Alaska (de Wit et al. 2010). Forexample, PBDE concentrations in eggs ofalcids and/or Northern Fulmars (Fulmarusglacialis) are generally lower in the Bering

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Sea, intermediate in Canada, western Green-land, Bjørnøya in the Barents Sea, northernNorway and the Faroe Islands, and highest onIceland, east Greenland and Svalbard in theEuropean high Arctic (de Wit et al. 2010). Asimilar pattern is seen for gulls (de Wit et al.2010).

Little is known about the BFR contaminationof the terrestrial ecosystem in the Arctic; how-ever, concentrations of terrestrial animals atlower trophic levels were found to be low (deWit et al. 2006, 2010), whereas they weremuch higher in terrestrial birds of prey, partic-ularly in Peregrine Falcons (de Wit et al.2006). For example, high BFR concentrationshave been found in eggs of predatory birdsfeeding on terrestrial mammals and birds, par-ticularly Peregrine Falcons in northern Sweden(Lindberg et al. 2004) and Norway (Herzke etal. 2001), and more recently at several sites inSouth Greenland (Vorkamp et al. 2005).

Although the marine ecosystem has been well-studied, there is a general lack of informationat the present time to define any circumpolartrends for PFCs (Butt et al. 2010). There arefew reports of PFCs in terrestrial wildlife butPFC levels have been measured in CommonLoons (Gavia immer), Mink (Mustela vison),Arctic Fox (Alopex lagopus) and Caribou(Rangifer tarandus) from the Canadian Arctic(Martin et al. 2004, Tittlemier et al. 2005). Ingeneral, PFOS and perfluorooctane sulfon-amide (PFOSA), as well as some of thePFCAs, were commonly detected (Butt et al.2010).

Large-scale spatial patterns of element concen-trations in tissues of terrestrial and freshwateranimals may reflect both geochemical environ-ments as well as anthropogenic inputs, as is thecase for Cd in Canadian Caribou, for example,which have higher Cd concentrations in someYukon herds where Cd is naturally higher inthe soils (Braune et al. 1999). A circumpolarsurvey of Cd in Willow Ptarmigan (Lagopuslagopus) also showed considerable variation in

Cd levels among regions but the median con-centration for Canada was much higher than inother countries, likely due to natural Cd expo-sure, possibly through a high intake of willow(Salix sp.) which is known to contain higheramounts of Cd than other food plants (Peder-sen et al. 2006). In the marine environment, thehighest Cd levels in seabirds were observed innortheastern Siberia and the lowest, in the Bar-ents Sea, with intermediate levels in ArcticCanada and Greenland (Savinov et al. 2003).For Hg, concentrations in seabirds from theBarents Sea were also lower than in Green-land, Canada, and northeast Siberia (Savinovet al. 2003). Although there are some spatialdifferences in Hg in the freshwater and terres-trial environments, most levels are low(AMAP 2002). It should be noted that spatialdifferences in contaminant levels may also beaffected by differences in available food items.

Temporal Trends.—The majority of legacyPOPs (e.g., PCBs, DDT) have significantlydeclined in Arctic biota over the last severaldecades (Rigét et al. 2010) whereas Hg hasincreased in a number of Arctic species (Rigétet al. 2011). The declines in the legacy POPsare a consequence of past national and regionalbans and restrictions on uses and emissions incircumpolar and neighbouring countries whichbegan in the 1970s for chlorinated pesticidesand PCBs (Muir and de Wit 2010). Seabirdeggs from the Canadian high Arctic reflect thedocumented decline in legacy POPs (Braune2007, Braune et al. 2007) as do eggs ofAlaskan Peregrine Falcons (Ambrose et al.2000). However, concentrations of Hg havebeen increasing in seabird eggs from the Cana-dian high Arctic (Braune 2007, Braune et al.2006). In fact, Braune et al. (2006) found thatHg levels in eggs of the Ivory Gull (Pagophilaeburnea) from the Canadian high Arctic, aspecies recently listed as “endangered” inCanada (COSEWIC 2010), were among thehighest ever reported for seabird eggs from theArctic marine environment. The pattern ofincreasing Hg concentrations in Canadian Arc-tic seabirds in recent decades supports the

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west-to-east circumpolar gradient in the occur-rence of recently increasing Hg trendsreflected in Arctic biota. A recent analysis ofHg time series for Arctic biota showed thatthere is a higher proportion of temporal trenddatasets, particularly for marine biota, in theCanadian and Greenland region of the Arcticshowing significant Hg increases than in theNorth Atlantic Arctic (Rigét et al. 2011). Thereasons for this are complex but likely involveanthropogenic and natural emissions coupledwith environmental and biological (e.g. food-web) processes which may also be affected byclimate change. In contrast, Hg in terrestrialbiota and freshwater biota, for the most part,showed either no change over time or adecreasing trend (Rigét et al. 2011). Likewise,Cd levels in biota and in the abiotic environ-ment are, for the most part, either stable ordeclining (Braune et al. 2005b).

Temporal trend studies for BFRs in Arcticwildlife have generated differing results withsome PBDEs showing increasing concentra-tions and others showing a tendency to leveloff or decline in response to reductions in useand emissions (de Wit et al. 2010). However,no uniform pattern in temporal trends emergesfor the Arctic. Concentrations of PBDEsincreased from 1986 to 2003 in Peregrine Fal-con eggs from South Greenland (Vorkamp etal. 2005). In the Canadian Arctic, PBDEs werefirst detected in seabird liver and eggs byBraune and Simon (2004). Subsequent retro-spective analyses and continued monitoringshowed that concentrations of total PBDE(ΣPBDE) concentrations in eggs of Thick-billed Murres (Uria lomvia) and Northern Ful-mars from the Canadian high Arctic steadilyincreased between 1975 and 2003 after whichtime, levels appear to have started to decline(Braune 2008). An increase in ΣPBDE concen-trations between 1976 and 2004 is alsoreflected in eggs of the Ivory Gull in the Cana-dian high Arctic (Braune et al. 2007). NorthAmerica accounted for most of the globaldemand for the commercial Penta-BDE prod-uct used in polyurethane foam (Hale et al.

2003), and the declining ΣPBDE concentra-tions observed in the seabird eggs after 2003may reflect the phasing out of Penta-BDEproduct usage in North America after 2005 (deWit et al. 2010).

As with the BFRs, there are inconsistencies inthe PFC temporal trends, most of which arefrom the North American Arctic and Green-land. Martin et al. (2004) screened livers ofNorthern Fulmars and Black Guillemots (Cep-phus grylle) collected from the Canadian highArctic in 1993 for the presence of PFCs andfound relatively low concentrations of bothPFOS and the PFCAs in both species. Subse-quent retrospective analyses showed that over-all PFC concentrations in livers of Thick-billedMurres and Northern Fulmars had increasedsignificantly from 1975 to 2003–2004 (Butt etal. 2007). A recent review by Butt et al. (2010)generally showed increasing trends from the1970s in Arctic wildlife, although some studiesfrom the Canadian Arctic showed recentdeclines in PFOS levels. Temporal trends ofPFCs in eggs of Swedish Peregrine Falconsalso showed increasing concentrations ofPFCAs whereas concentrations of PFOS lev-elled off after the mid-1980s (Holmström et al.2010). In contrast, Ringed Seals (Phoca hisp-ida) and Polar Bears (Ursus maritimus) fromGreenland continue to show increasing PFOSconcentrations. The inconsistency in the PFCtemporal trends between regions may representdifferences in emissions from source regions(Butt et al. 2010).

Effects.—Given the complex and dynamicenvironment in which animals live, it is diffi-cult to establish a cause-effect relationship forany one stressor. A recent assessment on theeffects of POPs on Arctic wildlife and fish con-cluded that there still remains minimal evi-dence that POPs are having widespread effectson the health of Arctic organisms, with thepossible exception of Polar Bears in EastGreenland and Svalbard, as well as SvalbardGlaucous Gulls (Larus hyperboreus) where

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studies have demonstrated sub-lethal physio-logical effects (Letcher et al. 2010).

Effect studies on wild terrestrial birds in theArctic have been limited to Peregrine Falcons,although laboratory studies have been carriedout using the American Kestrel (Falcosparverius). Population declines of PeregrineFalcons at a number of North American loca-tions during the mid-part of the last centurywere associated with DDE-induced eggshellthinning (Peakall et al. 1990). With the signif-icant decrease in most of the legacy POPsincluding p,p’-DDE, there has been an increasein eggshell thickness in Alaskan Peregrinesand no apparent exceedance of toxicity thresh-olds for the legacy POPs for eggs sampledbetween 1988 to 1995 (Ambrose et al. 2000).Peregrine Falcon eggs sampled from SouthGreenland between 1986 and 2003 alsoshowed a decreasing trend for the legacy POPs(Vorkamp et al. 2009), and Falk et al. (2006)demonstrated a significant long-term decreasein eggshell thinning in Greenlandic Peregrines.However, Johnstone et al. (1996) found noimprovement in eggshell thickness in eggssampled in the Canadian tundra during 1982–1986 and 1991–1994, although p,p’-DDEresidue levels did decline. A recent study onPeregrines from Sweden showed that the aver-age brood size decreased with increasingΣPBDE concentrations, suggesting thatPBDEs could influence reproduction in thisspecies (Johansson et al. 2009). However,Nordlöf et al. (2010) found no correlationbetween levels of BFRs and reproductive suc-cess in White-tailed Eagles (Haliaeetus albi-cilla) in four regions of Sweden. Letcher et al.(2010) concluded that there is currently a lowrisk from ΣPBDE and HBCD exposure in theeggs of Arctic birds with respect to the repro-ductive and developmental effects reported forcaptive Kestrels by Fernie et al. (2009). Theeffects of PFCs on wildlife are not well known,in particular for Arctic biota (Butt et al. 2010).However, a recent study showed a relationshipbetween blood plasma clinical-chemicalparameters and organohalogen compounds

including PFCs in chicks of three raptorspecies in northern Norway which suggestedpotential effects on liver, kidney, bone,endocrinology and metabolism (Sonne et al.2010).

Many high trophic level predators associatedwith marine and other aquatic ecosystems areexposed to Hg primarily as methylmercury(MeHg) in their diet, and in some areas of theArctic, Hg concentrations in marine food webshave significantly increased in recent decades(Rigét et al. 2011) suggesting that levels insome marine mammals, birds, and fish mayreach the point where adverse biologicaleffects might be expected (AMAP 2002).However, compared to the amount of contam-inant data available for the Arctic region,knowledge of the effects of these contaminantloads are very limited and, therefore, mostevaluations of potential toxic effects of con-taminants in wildlife are based on comparisonsof tissue residue levels with toxicity thresholdsderived from laboratory-based studies reportedin the literature. Exceedance of these toxicitythresholds, however, does not necessarilyresult in adverse biological effects or popula-tion-level impacts. For example, Hg levels in30% of the eggs of Peregrine Falcons sampledbetween 1991 and 1995 in Alaska exceededthe critical threshold for reproductive effects(Ambrose et al. 2000) although no causal asso-ciation with Hg was established. Likewise, Cdin some ptarmigan, Caribou and Moose (Alcesalces) in the Yukon Territory, which has highlevels of naturally-occurring Cd, are highenough to raise concern for kidney damage,but effects have not been documented (AMAP2002). Since Hg concentrations are stillincreasing in some Arctic animals (Rigét et al.2011), Arctic species (particularly top preda-tors) are likely to be exposed to increasing con-centrations of Hg for some time to come.

EFFECTS OF CLIMATE CHANGE

Many of the transfer, transformation and stor-age processes driving global contaminant

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cycles are likely to be significantly affected bythe impacts of climate change, especially aschanges in river runoff and precipitation pat-terns occur, ice and snow cover reduces, andpermafrost thaws in the Arctic (Macdonald etal. 2005). Not only could changes in seasonalice cover and temperature result in more re-emissions of contaminants to the air, but eco-logical changes, such as diet shifts andnutritional changes, disease, and species inva-sion may also be mediated by climate changewhich could alter patterns of contaminantexposure in biota (Muir and de Wit 2010). Forexample, there is evidence that earlier icebreak-up over the last 20 years in westernHudson Bay has caused a temporal shift in thediet of Polar Bears resulting in increased con-centrations of PBDEs and legacy POPs in thebears (McKinney et al. 2009). Gaston et al.(2003) have also associated the general warm-ing of Hudson Bay waters with a shift fromArctic Cod (Boreogadus saida) and benthicfish species to Capelin (Mallotus villosus) andSandlance (Ammodytes hexaptera) in the dietof Thick-billed Murres in northern HudsonBay which could also affect the exposure ofthose birds to contaminants. Similarly, Gadenet al. (2009) have postulated that the length ofthe ice-free season affects the prey composi-tion available to Ringed Seals in the westernCanadian Arctic, indirectly influencing Hguptake in the seals. Carrie et al. (2010) haveassociated increasing concentrations of PCBsand, in particular, Hg in Mackenzie River Bur-bot (Lota lota) with increasing algal primaryproductivity driven by warming temperaturesand reduced ice cover. They postulate that theincreased productivity increased the scaveng-ing rate of Hg from the water column, poten-tially enhancing MeHg production, andincreasing contaminant bioavailability to thefish. Clearly, there is already evidence that cli-mate change is affecting contaminant exposurein biota, but it will be some time before thecomplexities of these interactions are under-stood.

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