Impacts of Atmospheric Pollution on Aquatic Ecosystems
Impacts of Atmospheric Pollution on Aquatic Ecosystems Issues in Ecology Published by the Ecological Society of America Number 12, Summer 2004
Issues in Ecology Number 12 Summer 2004 Impacts ofAtmospheric Pollutants on Aquatic Ecosystems SUMMARY Considerable progress hasbeen made in reducing the dischargeofatmosphericpollutants from point sources such as effluent pipes.Amoredifficult challenge involvesidentifyingand controllingenvironmentalcontaminants generatedby dispersedor nonpoint sourcessuch as automobileexhaust,pesticideapplications andmyriad commercalandindustrialprocesses.Nonpoint nitionhas so farbeengiventothe far-rangingenvironmentaloonsequences oftoxicsubstancesand nutrients that aretransported via theair. ds Theseindudelong-regnizedpersistentorganicp Mercury:Oxidized formsofmercury readily rain fromtheairontoterrestrialandaquaticeoosystems Insediments,they canbetransformedintomonomethylmercury,the formmosttoxicto fish and thewildlifeandhumansthat consume fish Nutrients:Atmospherictransport is asignificant and increasingsource ofplant nutrients to freshwater and marine ecosystems and can accelerateeutrophicationof thesewaters. Areviewoftheavailablescientificinformationindicates that Thepollutants thataremostlikely topresentecological risksare those that are(1)highly bioaccumulative,buildingup tohigh levelsin animal tissueseven when concentrationsin the water remain relatively low,and (2)highly toxic,sothat they causeharmatcomparativelylow doses Atmosphere-water interactions that control the input and outgassing of persistent organic pollutants in aquaticsystems of food webs. Although the effectsof va any region e,ca For many organicpo es,non-atmospheri concentrations oforganochlorinesin air masses and snow fromnorthem andalpineregionsaregenerally low,thefood web dynamics,physiologies,and life cycles ofcold region animalsallow these contaminants tobebiomagnified to extraordinary degreesinfood chains. Atmospherically deposited contaminantsaregenerated largely by human activities,and reducing the extent andimpactsofthis increasingly significantsourceofenvironmentalpollution will requiregreater recognition,monitoring andultimately,regulation. over Lonesome Pointon LakeSuperior,GrandMarais,MI(courtesy theUS EnvironmentalProtection Agency Service)
1 Issues in Ecology Number 12 Summer 2004 Impacts of Atmospheric Pollutants on Aquatic Ecosystems SUMMARY Cover Photo: Fog over Lonesome Point on Lake Superior, Grand Marais, MI (courtesy the U.S. Environmental Protection Agency and U.S. Fish and Wildlife Service). Considerable progress has been made in reducing the discharge of atmospheric pollutants from point sources such as effluent pipes. A more difficult challenge involves identifying and controlling environmental contaminants generated by dispersed or nonpoint sources such as automobile exhaust, pesticide applications, and myriad commercial and industrial processes. Nonpoint pollutants can travel far from their sources when they are discharged into rivers or enter the atmosphere. While waterborne contaminants have received growing attention, little recognition has so far been given to the far-ranging environmental consequences of toxic substances and nutrients that are transported via the air. This report reviews three categories of airborne pollutants that we consider of greatest concern, both for their ecological effects and their impacts on the health of fish, wildlife, and humans: · Organic compounds: These include long-recognized persistent organic pollutants and a vastly larger group of chemicals such as brominated flame retardants, water-repellent coatings, and synthetic fragrances that remain largely unmonitored and unregulated. · Mercury: Oxidized forms of mercury readily rain from the air onto terrestrial and aquatic ecosystems. In sediments, they can be transformed into monomethyl mercury, the form most toxic to fish and the wildlife and humans that consume fish. · Nutrients: Atmospheric transport is a significant and increasing source of plant nutrients to freshwater and marine ecosystems and can accelerate eutrophication of these waters. A review of the available scientific information indicates that: · The pollutants that are most likely to present ecological risks are those that are (1) highly bioaccumulative, building up to high levels in animal tissues even when concentrations in the water remain relatively low, and (2) highly toxic, so that they cause harm at comparatively low doses. · Atmosphere-water interactions that control the input and outgassing of persistent organic pollutants in aquatic systems are critically important in determining the cycling and residence times of these compounds and the extent of contamination of food webs. · Although the effects of various types of pollutants are usually evaluated independently, many regions are subject to multiple pollutants, and their fate and impacts are intertwined. The effects of nutrient deposition on coastal waters, for instance, can alter how various organic contaminants and mercury are processed and bioaccumulated, and ultimately, how they affect aquatic organisms. · For many organic pollutants, even long-banned chemicals such as PCBs and other organochlorines, non-atmospheric sources have been well controlled while atmospheric sources have either been neglected or ignored. · Ecological effects of airborne organochlorines are a particular concern at high latitudes and altitudes. Even though concentrations of organochlorines in air masses and snow from northern and alpine regions are generally low, the food web dynamics, physiologies, and life cycles of cold region animals allow these contaminants to be biomagnified to extraordinary degrees in food chains. Atmospherically deposited contaminants are generated largely by human activities, and reducing the extent and impacts of this increasingly significant source of environmental pollution will require greater recognition, monitoring, and ultimately, regulation
Issues in Ecology Number12 Summer 2004 Impacts of Atmospheric Pollutants on Aquatic Ecosystems b DeborahL.Swackhamer,Hans W.Paerl,StevenJ.Eisenreich,James Hurley,KeriC.Hombuckle, MichaelMcLachlan,David Mount,Derek Muir,andDavidSchindler INIRODUCTION Sinceairmovesrapidly,atmosphericpollutantscan travellong distancesquickly and be deposited on distant watersheds.The onsOver the past several decd made d forapantdoerh es.Ana efuent pipes A more been toidentify and posited in a particulr watershed (Fgure 1)Airshedsdiffer fo control environmental contaminants generated by dispersed or each form of every pollutant and are determined by modeling ombileehaustlivesokwas atmospheric deposition of each chemical.They are useful commer er travel far souroes when the倒 stem of concern or flow into riversor enter theair This report reviews three In particular,volatile chemicals- those that evaporatereadily-car or thei health of a widera can either be deposited directly including lower levels of the food nverteb dep ans The ("indirect"deposition)Deposition First semi-volatile organic of thesepollutants can occur via contaminantsoften have propertie that allow them to persist in the ouds and minute particulate matter to aquatic organisms at lower Rates of wet deposition aremost Sound and AltamahaSound (listed fromnorthtosouth)2These levels of the food web,as well as influenced by how readily th to fish and to the wildlife and olve in water,while irshedsshow the geographic area that contains the emission ans that eat fish The ratesofdr re ver rganic rom esticides and poly chlorinated biphenyls(PCBs)to which they arebeing deposited.Chemicals deposited toaquatic brominated flame-retardants,water-and stain-repellent coatings ercur can ordry d n In may also be transformed into once they are deposited on and travel through watersheds.Until recently is bioaccumulative and can harm fish,wildlife,and humans. Finally,the significance of inorganic forms of nutrients a atmospheric pollu s ha Deen gaining increa d att and dry deposition onto la sed and aquati culprit in th
2 Issues in Ecology Number 12 Summer 2004 Impacts of Atmospheric Pollutants on Aquatic Ecosystems by Deborah L. Swackhamer, Hans W. Paerl, Steven J. Eisenreich, James Hurley, Keri C. Hornbuckle, Michael McLachlan, David Mount, Derek Muir, and David Schindler INTRODUCTION Over the past several decades, the United States has made considerable progress in reducing the amount of pollutants discharged from identifiable point sources such as municipal effluent pipes. A more difficult challenge has been to identify and control environmental contaminants generated by dispersed or nonpoint sources such as automobile exhaust, livestock wastes, fertilizer and pesticide applications, and myriad commercial and industrial processes. These nonpoint pollutants can travel far from their sources when they seep or flow into rivers or enter the air. In particular, volatile chemicals – those that evaporate readily – can be carried through the atmosphere and fall on parts of the world far removed from their origins. They can either be deposited directly onto terrestrial and aquatic ecosystems (“direct” deposition) or deposited onto land surfaces and subsequently run off and be transferred into downstream waters (“indirect” deposition). Deposition of these pollutants can occur via wet or dry forms. Wet deposition includes rain, snow, sleet, hail, clouds, or fog, while dry deposition includes gases, dust, and minute particulate matter. Rates of wet deposition are most influenced by how readily the chemicals dissolve in water, while rates of dry deposition are very sensitive to the form (gas or particle) of the chemicals and the “stickiness” of the surface upon which they are being deposited. Chemicals deposited to aquatic ecosystems can re-volatilize and thus be redistributed via the atmosphere. During atmospheric transport, pollutants also can be transformed into other chemicals, some of which are of greater concern than those originally released to the atmosphere. Pollutants may also be transformed into other chemicals once they are deposited on and travel through watersheds. Until recently, however, little recognition has been given to the environmental consequences of toxic substances and nutrients that fall from the air as wet and dry deposition onto land-based and aquatic ecosystems. Since air moves rapidly, atmospheric pollutants can travel long distances quickly and be deposited on distant watersheds. The “airshed” for a particular body of water can encompass hundreds of miles. An airshed defines the geographic area that contains the emissions sources that contribute 75 percent of the pollutants deposited in a particular watershed1 (Figure 1). Airsheds differ for each form of every pollutant and are determined by modeling atmospheric deposition of each chemical. They are useful theoretical tools for explaining atmospheric transport and for illustrating the need to control emission sources far removed from the ecosystem of concern. This report reviews three categories of atmospheric pollutants that we consider of greatest concern, both for their ecological effects and their impacts on the health of a wide range of biota, including lower levels of the food web (algae, macrophytes, and invertebrates), fish, wildlife, and humans. These categories include organic compounds, mercury, and inorganic nutrients. First, semi-volatile organic contaminants often have properties that allow them to persist in the environment for very long periods, to bioaccumulate (that is, build up in animal tissues), and to be toxic to aquatic organisms at lower levels of the food web, as well as to fish and to the wildlife and humans that eat fish. These persistent organic pollutants include a wide range of chemicals from pesticides and polychlorinated biphenyls (PCBs) to brominated flame-retardants, water- and stain-repellent coatings, and synthetic fragrances. Second, the metal mercury can be transported in the atmosphere and fall onto terrestrial and aquatic ecosystems as precipitation or dry deposition. In aquatic systems, mercury may eventually be transformed into monomethyl mercury, a form that is bioaccumulative and can harm fish, wildlife, and humans. Finally, the significance of inorganic forms of nutrients as atmospheric pollutants has been gaining increased attention. Nutrient-laden runoff from the land has long been acknowledged as a culprit in the over-enrichment and eutrophication of coastal Figure 1 – Principal nitrogen oxide airsheds and corresponding watersheds for Hudson/Raritan Bay, Chesapeake Bay, Pamlico Sound, and Altamaha Sound (listed from north to south).2 These airsheds show the geographic area that contains the emissions sources that contribute 75 percent of the nitrogen oxide deposited in each watershed. Via atmospheric transport, pollutants such as nitrogen oxide can impact watersheds hundreds of miles away
Issues in Ecology Number 12 Summer 2004 waters.Now.atmospheric nitrogen deposited in coastal and organisms and biomagnify (increase inconcentration as they move estuarine waters has been shown to be a major nutrient source in p)in food chains some coastal regions.The result can be excessive algal Most atmospherically-transported chemicals that also (phytoplankton)growth,oxygen depletion,degradation ofmarine bioaccumulate,such as PCBs and chlorobenzenes,are known as ssof both biodiversity and commercially valuable ultimedia chemicals"because they can bedistri uted throug tha determine whether or not a chemical is e Stockholn Conventionaldrin.chlordane.dieldrin.dichlorodi intrinsic toxicity,how long it can persist in air without phenyltrichloroethane(DDT),endrin,heptachlor,hexa decomposing(or without transforming to achemical of greater chlorobenzene,mirex,toxaphene,PCBs polychlonnated dibenz )wh p-diokinsan ans (P ultimedi on sited in e and icale that Usually,theemission,airbometr ort fate and ocological sediments.(Cong ersare members of family of chemicals tha impacts of these three classes of pollutants are considered have the same basic structure but have different amounts of independently.However,while these contaminants may be chlorine.) their impactson the environmen Persistent organic poll ants, ockholm su duc rs in ert with de tion ofpo sthe risk th and one or more organic contaminants.Thus,the effects of rsist because of their extraordinary resistance to derra dation nutrients on coastal ecosystems and their food webs can alter and because contaminated sources such as agricultural soils or PCB-containing building materia kD dd pollutants,their characteristics.and soures The secnd section retardantsand chlorinated alkane explores atmosphere-water interactions that determine the fate Chemicals that accumulate largely in one environmental and pe mpacted primar tobe very per nutrient dep sition and the fateand im acts are ely of concern locally.fo examplein agricultural streams and wetlands near fields wher monitoringof atmosphericpollutants. atrazineisappliedSimirly alkylphenolsandacid phamaceutica present an exposure risk to a Organic Compounds but thosphe als adhe nospheric aerosols and are soon removed h Theorganiccompounds that merit concernas atmospheric rainfall.Thus they travelonly short distances in the atmosphere pollutants have diverse chemical structures,sources,and use and are generally not a concern for remote aquaticenvironment eithe as deliberately produce where tmospheric depostion is the predominantsou ads pes ollutio of the m micals that have mui Although diversestructurally,the organic chemicals that are characteristics but are rapidly degraded either in theatm transported atmospherically,deposited into remoteenvironments, or in the biosphere.Examples of this group are the 2.3and 4 and h nan healt y na propert pe s,and mono, m to th resistance to degradation by ultraviolet light and oxidation by might lead toexposureof some quatic or terrestrial organisms hydroxyl radicals)to be transported long distances,and (3)impart but the ecompounds would likely bebroken down durin tively high s and resista ody and thus allow them toaccumulate in expected to b
3 Issues in Ecology Number 12 Summer 2004 waters. Now, atmospheric nitrogen deposited in coastal and estuarine waters has been shown to be a major nutrient source in some coastal regions. The result can be excessive algal (phytoplankton) growth, oxygen depletion, degradation of marine habitats, and loss of both biodiversity and commercially valuable fish and shellfish species. The properties that determine whether or not a chemical is likely to become a “problem” in aquatic ecosystems include its intrinsic toxicity, how long it can persist in air without decomposing (or without transforming to a chemical of greater concern), whether it bioaccumulates, how it interacts with other chemicals, whether it re-volatilizes, and how it is transformed once deposited in water. Usually, the emission, airborne transport, fate, and ecological impacts of these three classes of pollutants are considered independently. However, while these contaminants may be generated by different sources, their impacts on the environment cannot be evaluated separately. Many coastal regions are subject to pollution from multiple sources, and the atmospheric deposition of nutrients often occurs in concert with deposition of mercury and one or more organic contaminants. Thus, the effects of nutrients on coastal ecosystems and their food webs can alter how various organic contaminants and mercury are processed, how they build up in the food web, and ultimately, how these toxic chemicals affect fish, wildlife, and humans. The first section of this report examines these three classes of pollutants, their characteristics, and sources. The second section explores atmosphere-water interactions that determine the fate and persistence of airborne pollutants in freshwater and marine ecosystems. The third discusses the factors that determine whether atmospherically delivered pollutants present a risk to fish, wildlife, and humans. The fourth section looks at the relationship between nutrient deposition and the fate and impact of organic pollutants. The fifth and final section outlines priorities for regulation and monitoring of atmospheric pollutants. POLLUTANTS OF CONCERN Organic Compounds The organic compounds that merit concern as atmospheric pollutants have diverse chemical structures, sources, and uses. They can generally be categorized either as deliberately produced substances such as pesticides, industrial compounds, and their persistent degradation products, or as byproducts of fossil fuel combustion or impurities in the synthesis of other chemicals. Although diverse structurally, the organic chemicals that are transported atmospherically, deposited into remote environments, and build up to levels that can affect wildlife and human health, have a relatively narrow range of physical and chemical properties (see Box 1). These are properties that (1) allow them to move in measurable quantities from land and water surfaces to the atmosphere, (2) give them sufficient stability (in the form of resistance to degradation by ultraviolet light and oxidation by hydroxyl radicals) to be transported long distances, and (3) impart a relatively high affinity for fatty tissues and resistance to breakdown in the body and thus allow them to accumulate in organisms and biomagnify (increase in concentration as they move up) in food chains. Most atmospherically-transported chemicals that also bioaccumulate, such as PCBs and chlorobenzenes, are known as “multimedia chemicals” because they can be distributed through air, water, and soil rather than a single medium. Virtually all of the persistent organic pollutants listed under the Stockholm Convention — aldrin, chlordane, dieldrin, dichlorodiphenyltrichloroethane (DDT), endrin, heptachlor, hexachlorobenzene, mirex, toxaphene, PCBs, polychlorinated dibenzop-dioxins and –dibenzofurans (PCDD/Fs) — are multimedia chemicals.6 A few highly chlorinated PCDD/F and PCB congeners are solid phase chemicals that concentrate solely in soils and sediments. (Congeners are members of a family of chemicals that have the same basic structure but have different amounts of chlorine.) Persistent organic pollutants, as defined by the Stockholm Convention, are now scheduled for either global bans (chlorinated pesticides) or emission reductions (by-products such as PCDD/ Fs). Nevertheless, the risk they present to the environment will persist because of their extraordinary resistance to degradation and because contaminated sources such as agricultural soils or PCB-containing building materials continue to re-supply the atmosphere. In addition, the Priority Substances List in the European Water Framework Directive includes many of these same chemicals, as well as polybrominated diphenyl ethers (PBDEs) used as fire retardants and chlorinated alkanes. Chemicals that accumulate largely in one environmental medium (air, water, or soil) are generally not a concern for ecosystems impacted primarily by atmospheric pollution. For example, the herbicide atrazine is known to be very persistent in nutrient-poor waters, but little of it volatilizes to the atmosphere. Because of this, its impacts are largely of concern locally, for example in agricultural streams and wetlands near fields where atrazine is applied.7 Similarly, alkyl phenols and acid pharmaceuticals present an exposure risk to aquatic life in receiving waters near municipal waste treatment plants.8 Substantial concentrations of alkyl phenols are also observed in the atmosphere above estuaries receiving wastewater effluents, but these chemicals adhere efficiently to atmospheric aerosols and are soon removed by rainfall.9 Thus they travel only short distances in the atmosphere and are generally not a concern for remote aquatic environments where atmospheric deposition is the predominant source of pollution. It is more difficult to classify the atmospheric pollution potential of the many semi-volatile chemicals that have multimedia characteristics but are rapidly degraded either in the atmosphere or in the biosphere. Examples of this group are the 2, 3 and 4- ring polyaromatic hydrocarbons (PAHs), organophosphorus pesticides, and mono-, di- and trichlorobenzenes. Under some circumstances, concentrations of these chemicals could build up even in remote environments if rates of atmospheric and water degradation are low – for example, in cold climate regions. This might lead to exposure of some aquatic or terrestrial organisms, but these compounds would likely be broken down during metabolism by vertebrates and thus would generally not be expected to build up in food webs. This generality needs to be
Issues in Ecology Number 12 Summer 2004 Box1 Log Kaw The combination of physicalproperties that give [A]gas phas rise to environmentally mobile and ioaccumulative substances is best viewed by a Log Koa the key partition 0 one medium (e.g.air)compared to anothe dium(e.gwater)atequilibrium Forexample B]AqU has if a chemical hasan air-water partition coeffic Br10 PBDE Atrazine B(a)P an indexoftoxicity becausesolubility inoctanol 2 3 4 5 6 micssolubility in biological lipid tissuesand ndicates thepotential for bioaccumulation.Van Log Kow Figure2-Plot of ents,air-wa air.aque entry into the environment (B)aqueous phase contaminantsaccumulateor aretransported asa functionof their physicalchemica micals that partition into the aqueous properties Many toxicchemicalsaremultimedia andpartition intomorethanone environment regardlessofmodeofentry,(C)solid Jt. m Tovis assessed on a case-by-case basis,however,since our ability to list includes 2,863 organic chemicalsproduced or imported at predict such biotransformations in the food web is weak. ng( Since the late 1990s.there has been a major increase in chemicals in comm roe as of 1981 of whichabout2 704an measurement and detection of organicchemicals that are not considered HPVCsbased on production levels greater than 1,000 presently dassifiedaspersistentorganicpollutants inwaters affected tons per year and 7,842 arelow production volumechemicals h rates of 10 to 1000 tons per year. h (PBDEs) operation XeoPmue5 mkehundreds of everyday EU and other ntor 2000.that lis products from non-stick cookware and water-and stain- contained 5,235 substances produced at levels greater than repellent coatings for carpetsand raincoats tocosmetics, 1,000 tons globally. s( s)use nics mental persistence, manu aty,the c found in paints and adhesives as wellas fluids used in Councilof Chemical Associationshas established ntly inusesuch asendosulfan and lindane HPVCs for which f datas etsontoxicity and envi mental fat owever,th full data sets
4 Issues in Ecology Number 12 Summer 2004 assessed on a case-by-case basis, however, since our ability to predict such biotransformations in the food web is weak.10 New emerging organic contaminants of interest Since the late 1990s, there has been a major increase in measurement and detection of organic chemicals that are not presently classified as persistent organic pollutants in waters affected by atmospheric contaminants. These chemicals include: • polybrominated diphenyl ether flame retardants (PBDEs) widely used in polymers and textiles; • fluorinated surfactants used to make hundreds of everyday products from non-stick cookware and water- and stainrepellent coatings for carpets and raincoats to cosmetics, paper products, and polymers for electronics; • chlorinated naphthalenes (PCNs) used in cable insulation, wood preservation, electronics manufacturing, and dye production; • chlorinated alkanes (also known as chlorinated paraffins) found in paints and adhesives as well as fluids used in cutting and machining metals; and • pesticides currently in use such as endosulfan and lindane. Even this expanded list, however, represents only a tiny fraction of the chemicals in commerce or even of the subset known as “high production volume chemicals” (HPVCs). The U.S. HPVC list includes 2,863 organic chemicals produced or imported at levels greater than 450 tons per year.11 In the European Union, the European Inventory of Existing Commercial Chemical Substances lists 100,195 “existing chemicals” – meaning chemicals in commerce as of 1981 — of which about 2,704 are considered HPVCs based on production levels greater than 1,000 tons per year and 7,842 are low production volume chemicals produced at rates of 10 to 1,000 tons per year.12 The Organization for Economic Cooperation and Development maintains an HPVC list based on a compilation of the U.S., E.U., and other national inventories. In 2000, that list contained 5,235 substances produced at levels greater than 1,000 tons globally. While the majority of these HPVCs are probably not a concern with regard to their environmental persistence, bioaccumulation, and toxicity, the chemical industry has recognized that data are lacking for many of these chemicals. In the absence of data, production volume is assumed to be a surrogate for occupational, consumer, and environmental exposure.13 The International Council of Chemical Associations has established a list of 1,000 HPVCs for which full data sets on toxicity and environmental fate are to be developed by 2004.14 However, this will leave more than 50 percent of high production volume chemicals without full data sets. Box 1 — Physical and Chemical Properties of Atmospherically Transported Organic Chemicals The combination of physical properties that give rise to environmentally mobile and bioaccumulative substances is best viewed by a two-dimensional plot of the key partition coefficients (Figure 2). Partition coefficients describe how much of a contaminant will be in one medium (e.g. air) compared to another medium (e.g. water) at equilibrium. For example, if a chemical has an air-water partition coefficient of 2, then there will be twice as much of the chemical in air than in water when expressed in equivalent concentrations. The octanol-water partition coefficient (Kow) is commonly used as an index of toxicity because solubility in octanol mimics solubility in biological lipid tissues and indicates the potential for bioaccumulation. Van de Meent et al.3 proposed classifying chemicals as either (A) gas phase chemicals that partition into the gas phase regardless of their mode of entry into the environment, (B) aqueous phase chemicals that partition into the aqueous environment regardless of mode of entry, (C) solid phase chemicals that partition into soils and sediments, and (D) multimedia chemicals that partition into more than one environmental medium. To visualize these categories, a global scale multimedia model (similar to GloboPOP4 ) was applied that assumed no degradation except in air (class A), water (class B), and soil (class C). The shaded areas in Figure 2 reflect substances with a wide range of air-water and octanol-water partition coefficients, which indicate their relative affinity for air vs. water or for the lipid tissues of organisms vs. water, respectively. Figure 2 – Plot of the two key partition coefficients, air-water partition coefficients (log Kaw) and octanol-water partition coefficients (log Kow), illustrating predicted environmental media (gas—air, aqueous—water, and solid—soil) where organic contaminants accumulate or are transported as a function of their physical chemical properties5 . Many toxic chemicals are multimedia and partition into more than one medium