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
Issues in Ecology Number 12 Summer 2004 Among the new organic contaminants of greatest concern the greatest concern PBDes areused in thousands of consume are synthetic musk fragrances,PBDE flame retardants,and products from fire-resistant textiles and upholstered fumiture to fluorinated surfactants. computers and televisions.Global demand for theseadditives Synthetic Fragrances.Syntheticmusk fragrances aresemi increased from 40,000 tons in 1992 to 67,125 tons in 1999. Theteta-andpertaBDEsTeEandne DE)are of greates wildlife TeBDE and PeBDE a icals writh erties similar to those of some PCBs.A highe synthetic fragrances areon the U.S.HPVC list but haveonly recently been studied as contaminants in any natural systemin solid phase hemical,but it may degrade in sunlight and in the ragrances used are edia form eks knov HHCB em adian A 0f1981to200.2 Flugrinated surfactants scientists have recently documented four synthetic compo nds wereproduced in19 for useas widespread contamination of wildlifeand the general human ds ted isa term early 21 ns of synth be organic mole me sin th n bonds.Th compounds.Recent measurements of the econ pounds in s region, chr disruption in fish.(Hormonally actives chemical that mimicor interfere with hormone function and can distort properties of perfluorinat ce I era rey ted anon sphys mu d PF the polveyclic musk fragrance AHINalld n dis ent.Worldwide diss nination of perfluorinated acids must therefore oour by way xylene were effectively banned from use as fragrances in 2002 of an airbomeneutral derivative that yields the free acid wheni U.S.HPV Wi espread detection of precursors of PFOSand their ngev h heUnited Sta m n nds ha aha y whic donot havetorenort how much thevuse ormanufacture.They also donot have to report any estimates on how much synthetic fragrance may ultimately be discharged into theenvironmen PFOS has been detected in the blood of ringed seals from the eco mpacts of s cond of n rthern f a,d cts of the nds in Eu in polar bear livers range fron wtweight.makniheanhaogn ram o for these fragrances. contaminant in these mammals.? duct n ve me chemicals as pote Mercury fateand in methodology,especially in the caseof fluorinated organics. globalpollutant and can bemobilized into the atmosphere from many human activities,including municipal trash incineratior ppagtpo burning of high sulfu coal (whic
5 Issues in Ecology Number 12 Summer 2004 Among the new organic contaminants of greatest concern are synthetic musk fragrances, PBDE flame retardants, and fluorinated surfactants. Synthetic Fragrances. Synthetic musk fragrances are semivolatile and lipophilic (literally “fat-loving” because they are attracted to fatty tissues) compounds that are added to a wide range of personal care products, including perfumes, cosmetics, soaps, and shampoos as well as laundry detergents.15 These synthetic fragrances are on the U. S. HPVC list but have only recently been studied as contaminants in any natural system in this country. The most common synthetic fragrances used are two nitro musks called musk xylene and musk ketone and two polycyclic musks known as HHCB (hexahydrohexamethylcyclopentabenzopyran) and AHTN (hexamethyltetraline). In Europe, approximately 6,500 metric tons of these four synthetic compounds were produced in 1999 for use as consumer product additives.16 In the early 1980s, concentrations of synthetic musk fragrances were discovered in animal tissues for the first time. Since then, there has been an increasing awareness of the ubiquitous distribution and possible toxicological effects of these compounds. Recent measurements of these compounds in wastewater effluent and in air and water in the Great Lakes region, for instance, have illustrated that ecological exposures are chronic and likely to be increasing.17 This is cause for concern because both HHCB and AHTN have been shown to exhibit hormonal disruption in fish.18 (Hormonally active substances are chemicals that mimic or interfere with hormone function and can distort normal reproductive development, alter behavior, and impair disease resistance in wildlife and humans.) Several studies with cell cultures indicate that musk xylene, musk ketone, p-aminomusk xylene (a major breakdown product of musk xylene), and the polycyclic musk fragrance AHTN all demonstrate estrogenic activity in laboratory tests.In Europe, musk ketone and musk xylene were effectively banned from use as fragrances in 2002 because of their reported toxicities.19 Although HHCB and AHTN are both on the U. S. HPVC list, their use in personal care and household products is privileged information in the United States, and companies that use them do not have to report how much they use or manufacture. They also do not have to report any estimates on how much synthetic fragrance may ultimately be discharged into the environment. Because of this, ecological impacts of these compounds can only be identified through field and toxicological studies conducted long after exposures have begun. Fortunately, thanks to the intense interest in the fate and impacts of these compounds in Europe, analytical methods have been developed and standards are available for these fragrances. For the vast majority of high production volume chemicals identified as potentially bioaccumulative and persistent, however, there are no trace analytical methods available for tracking their fate and impacts.20 Many of the recently initiated measurements of organic chemicals have been made using advances in analytical methodology, especially in the case of fluorinated organics. Flame retardants. Among the newly emerging chemical contaminants of aquatic environments, the PBDE flame retardants and the perfluorinated surfactants discussed below have generated the greatest concern. PBDEs are used in thousands of consumer products from fire-resistant textiles and upholstered furniture to computers and televisions. Global demand for these additives increased from 40,000 tons in 1992 to 67,125 tons in 1999.21 The tetra- and pentaBDEs (TeBDE and PeBDE) are of greatest concern, and their concentrations are increasing in humans and wildlife.22 TeBDE and PeBDE are multimedia chemicals with physical properties similar to those of some PCBs. A higher brominated product, decabromodiphenyl ether (DecaBDE), is a solid phase chemical, but it may degrade in sunlight and in the tissues of fish to these lower brominated multimedia forms.23 Researchers measured a nine-fold increase in PBDEs in the tissues of ringed seals from the western Canadian Arctic over the period of 1981 to 2000.24 Fluorinated surfactants.Scientists have recently documented widespread contamination of wildlife and the general human population with perfluorinated acids.25 “Perfluorinated” is a term used to describe organic molecules that are fully fluorinated, meaning fluorine atoms have replaced all hydrogen atoms in the carbon-hydrogen bonds. The most widely known perfluorinated acids are perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA); however, similar compounds having longer or shorter perfluorinated chains are also produced or exist as impurities within manufactured formulations. These important industrial chemicals fall into the category of surfactants because they are surfaceactive agents that repel water and oil or resist heat or other chemicals. The major use of PFOS is in treating fabric surfaces for stain resistance. The existing database describing physical properties of perfluorinated acids, including PFOS and PFOA, is severely limited because of their anomalous physical and chemical behavior. The properties of PFOS and PFOA suggest that they are poor candidates for long-range airborne transport, yet they have been discovered throughout the global environment. Worldwide dissemination of perfluorinated acids must therefore occur by way of an airborne neutral derivative that yields the free acid when it degrades.26 Widespread detection of precursors of PFOS and PFOA in the air in North America is providing increasing evidence that this is indeed the means by which these nonvolatile compounds have become such widespread contaminants.27 Over the past decade, researchers have found PFOS in birds, fish, and marine and land mammals around the world. For example, PFOS has been detected in the blood of ringed seals from the northern Baltic Sea, the eastern Canadian arctic, and Svalbard; the blood and liver of northern fur seals from Alaska; and the livers of polar bears from northern Alaska.28 PFOS concentrations in polar bear livers range from 1 to 5 micrograms per gram of tissue (wet weight), making it the most prominent organohalogen contaminant in these mammals.29 Mercury Mercury is a metallic element (Hg) that has been extracted for centuries from sulfide ore or cinnabar (HgS). It has become a global pollutant and can be mobilized into the atmosphere from many human activities, including municipal trash incineration, burning of high sulfur coal (which contains cinnabar) in coalfired power plants, metal smelting, chlorine-alkali plants, cement
Issues in Ecology Number 12 Summer 2004 making,and gold extraction,as well as from use of mercury- mercury (Hg)s Theremaining balanceofthe mercury exists a based fungicides in latex paints and the paper and pulpindustry. RGM,as particulate complexes of divalent mercury,and in the Mercury in itselemental state has low reactivity and a long organic form asmonomethylmercury. atmospheric resi a s have be deposited on land and waterby snow and rainfall.Particulate threefold sincethe beginningof the industrial ageThisestimate forms of mercury fall as dry deposition. has been supported by data from several field-based studies of and wetland Themass balar at5 00to6,0 cury input by sited on the have been declining since then It has been estimated that oceans via runoff.Refinement of mass balance calculations human activities contribute 70to8percent of the total annual has led some researchers to conclude that dry deposition of mercury emissions to the atmosphere and that more than95 percent of mercury vapor in the atmosphere exists aselementa he total mercury input to the ocear ospheric nitrogen compounds(the major chemical forms of atmosphericnitrogen ReducedNitrogen Agricultural Ammonia/Ammorium(NH/NH) Livestockwaste(volatilizedNH) ion&landdearing Urban Rural(non-agricultural) atertreatment(volatilizedNH) Nahdamnimamecaicomutes Wastew Biomassbuming(forestandgrassfires) Dust and aerosols Oxidized Nitrogen Urban Rural (non-agricultural) NitrogenOxides(NO/NO./NO.) Biomassbuming PhotolysisofN,O(air,land,water) 8ay Agricultural Natural ??=possible,but little knownabout,sources 6
6 Issues in Ecology Number 12 Summer 2004 making, and gold extraction, as well as from use of mercurybased fungicides in latex paints and the paper and pulp industry. Mercury in its elemental state has low reactivity and a long atmospheric residence time, thus allowing it to be mixed in the atmosphere on a global scale, while the oxidized forms are removed by wet and dry deposition.30 Oxidized reactive gaseous mercury (RGM), for example, is very soluble in water and is effectively deposited on land and water by snow and rainfall. Particulate forms of mercury fall as dry deposition.31 The total mass of mercury in the atmosphere has been estimated at 5,000 to 6,000 metric tons, and approximately half of that was generated by human activities.32 Atmospheric concentrations of mercury peaked in the 1960s and 1970s and have been declining since then.33 It has been estimated that human activities contribute 70 to 80 percent of the total annual mercury emissions to the atmosphere and that more than 95 percent of mercury vapor in the atmosphere exists as elemental mercury (Hg).34 The remaining balance of the mercury exists as RGM, as particulate complexes of divalent mercury, and in the organic form as monomethyl mercury.35 Although atmospheric concentrations have been declining for several decades, mass balance calculations that relate net mercury accumulation in the atmosphere with net loss indicate that human inputs of mercury to the atmosphere have increased threefold since the beginning of the industrial age.36 This estimate has been supported by data from several field-based studies of dated sediment cores from lakes and wetlands.37 The mass balance calculations also suggest that a legacy of mercury inputs is stored in terrestrial landscapes since only 5 percent of the atmospheric mercury deposited on the land is carried to the oceans via runoff. Refinement of mass balance calculations has led some researchers to conclude that dry deposition of RGM from the atmosphere can represent up to 35 percent of the total mercury input to the ocean.38 Table 1 - Natural and anthropogenic sources of atmospheric nitrogen compounds (the major chemical forms of atmospheric nitrogen compounds are the reduced, oxidized and organic forms). Sources (in approximate order of importance) Agricultural Livestock waste (volatilized NH3 ) Chemical fertilizers (volatilized NH3 ) Biomass burning Dust from deforestation & land clearing Urban & Rural (non-agricultural) Wastewater treatment (volatilized NH3 ) Fossil fuel combustion (from automobile catalytic converters) Natural Biomass burning (forest and grass fires) Decomposition of organic matter Dust and aerosols Volcanism Urban & Rural (non-agricultural) Fossil fuel combustion mobile & stationary engines powerplants & industrial Natural Biomass burning Lightning Photolysis of N2 O (air, land, water) Dust and aerosols generated by storms Microbially-mediated volatilization Agricultural Dust and volatilization of wastes?? Urban & Rural (non-agricultural) Dust/aerosols?? Natural Atmospheric photochemical and lightning Biological production in oceans?? ?? = possible, but little known about, sources Chemical Form Reduced Nitrogen Ammonia/Ammonium (NH3 /NH4 + ) Oxidized Nitrogen Nitrogen Oxides (NO/NO2 - /NO3 - ) Organic Nitrogen (Dissolved and Particulate)
Issues in Ecology Number 12 Summer 2004 while the mass balancehas identified themagnitudeof the flux to the north atlantic Ocean basin is approximately 11.2 various fluxes and pools of mercury and possible pathways for teragrams(trillion grams)per year and accounts for 46 to57 contamination ofland and water,it doesnotprovideinformation percent ofits"new"nitrogen input.This is comparableto the on the true partitioning of various forms of mercury in the new"nitrogen inputs delivered totheoceanby rivers. Indeed ngo orth American continenta atmosphere excee nitrogen se arriving by rivers potential for atmospheric deposition of mercury.for example depends upon the distribution of various forms of mercur in Table2-Estimated contributionsofatmosphericdeposition of nitrogen to"new"nitrogen inputs in diver se estuarine,coasta d,th sources,whil and opene sources (we and/or ) pherically dep instrumentation allows for real-time measur mercury as RGM,particulate mercury,and gaseous mercury at the picogram or sub-picogram level.The simultaneous mea surement of the RECEIVINGWATERS DEPOSIED ns,an t mercury near point sources,at din remote are BalticSea(Proper) Nutrients W+D,I 1060%W,1 Waquoit Bay,MA.USA 29%W,1+0 and mar sphericdeposition,either as rain Ne York Bicht USA plant growth (primary production)beca setheir concentratior Bamnegat Bay,USA 40%W,I+O control thegrowth of algae,which form thebaseof aquatic food Chesapeake Bay,USA deRiver,MD,US trace s such a ngan copper, d, d um By 409%W+D,】 mo Sarasota/Tampa Bay,FL,USA 30%W+D,1 ine estuarine anda few fresh Mississippi River Plume,USA 2-5%W+D,I+0 Nitrog deposition.In the marineenvironment iron hasbeen thesubject Excessivenitrogen loading toestuarineand coastalwaters is sing interest because recent studies have shown that this sprimary pro he open nd y,hyp PepOshaeecivedatentiominfreshwatere and associated habitat loss which are most oftenphosphoruslimited. As asignificant source of"new"nitrogen,atmospheric Early studiesonhuman-generated contaminantsdelivered to deposition is both a local and regional issue becauseemission ystems via ere id aftecte am-an my. id. nosty generat ing adiv in the Unitedstates with reducdnit array of human activities and,toa lesser extent natural pro making up the rest.Rapidly expanding livestock(swine,cattle (Table 1).These compounds include inorganic reduced forms andpoultry)operations in the Midwest and Mid-Atlanticregions have accelerat ds).Du fold d H)d .which c deposition at the National deposition ranges from 400 to more than 1,200 kilograms per Acid Deposition Programnetwork site in Duplin County,North hectareeach year and represents 40percent Carolina,alocation that hasexperienced a rapid rise in animal waters(a opean operationsd e2)."Onalargerscale,nitrogen
7 Issues in Ecology Number 12 Summer 2004 While the mass balance has identified the magnitude of the various fluxes and pools of mercury and possible pathways for contamination of land and water, it does not provide information on the true partitioning of various forms of mercury in the atmosphere. This information is vital for predictive modeling of global mercury cycling and the effectiveness of mercury reduction strategies, and it continues to be an active topic of research. The potential for atmospheric deposition of mercury, for example, depends upon the distribution of various forms of mercury in emissions and plumes. Both particulate mercury and RGM are likely be deposited closer to their local or regional sources, while gaseous mercury is expected to be transported long range and have a one to two year residence time in the atmosphere. Current instrumentation allows for real-time measurement of atmospheric mercury as RGM, particulate mercury, and gaseous mercury at the picogram or sub-picogram level. The simultaneous measurement of these various atmospheric forms has allowed for analysis of phase distribution of mercury near point sources, at offshore oceanic stations, and in remote areas. Nutrients A significant and increasing source of nutrients to freshwater and marine ecosystems is atmospheric deposition, either as rain or snow or as dry deposition of particles and gases. The nutrients that have received most attention are those that are essential for plant growth (primary production) because their concentrations control the growth of algae, which form the base of aquatic food webs. These nutrients include nitrogen, phosphorus, iron, and trace elements such as zinc, manganese, copper, cobalt, molybdenum, boron, and selenium. By far, the greatest attention has been focused on nitrogen because it is the most common limiting nutrient in marine, estuarine, and a few freshwater systems. Nitrogen is also a highly significant component of atmospheric deposition.39 In the marine environment, iron has been the subject of increasing interest because recent studies have shown that this metal limits primary production in some open ocean waters.40 Iron can also act synergistically with nitrogen to enhance algal production in coastal and ocean waters.41 Both nitrogen and phosphorus have received attention in freshwater ecosystems, which are most often phosphorus limited. Early studies on human-generated contaminants delivered to ecosystems via the atmosphere identified nitrogen as a major nutrient constituent of both rain- and dry-fall.42 Atmospherically deposited nitrogen provides aquatic systems with a variety of biologically available nitrogen compounds, reflecting a diverse array of human activities and, to a lesser extent, natural processes (Table 1). These compounds include inorganic reduced forms (ammonia, ammonium), inorganic oxidized forms (nitrogen oxides, nitrate, nitrite), and organic forms (urea, amino acids, and unknown compounds). During the past century, atmospherically deposited nitrogen has increased tenfold, driven by trends in urbanization, industrial expansion, and agricultural intensification.43 Nitrogen deposition ranges from 400 to more than 1,200 kilograms per hectare each year and represents from 10 to more than 40 percent of the “new” nitrogen coming into North American and European inland and coastal waters (Table 2).44 On a larger scale, nitrogen flux to the North Atlantic Ocean basin is approximately 11.2 teragrams (trillion grams) per year and accounts for 46 to 57 percent of its “new” nitrogen input.45 This is comparable to the “new” nitrogen inputs delivered to the ocean by rivers.46 Indeed, in the waters of the North American continental shelf, nitrogen inputs via the atmosphere exceed those arriving by rivers.47 Excessive nitrogen loading to estuarine and coastal waters is the key cause of accelerating eutrophication and the associated environmental consequences, including algal blooms, decreases in water clarity, toxicity, hypoxia or anoxia (oxygen-depleted or “dead zones”), fish kills, declines in submerged aquatic vegetation, and associated habitat loss.64 As a significant source of “new” nitrogen, atmospheric deposition is both a local and regional issue because emission sources may be situated either within or far outside affected watersheds.65Nitrogen oxides, mostly generated by fossil fuel combustion, account for 50 to 75 percent of nitrogen pollution in the United States, with reduced nitrogen and organic nitrogen making up the rest. Rapidly expanding livestock (swine, cattle and poultry) operations in the Midwest and Mid-Atlantic regions have accelerated the generation of nitrogen-enriched wastes and manures, and 30 to 70 percent or more of this may be emitted as ammonia (NH3 ) gas. This has led to local and regional increases in ammonium (NH4 + ) deposition, which can be seen in a twodecade analysis of atmospheric nitrogen deposition at the National Acid Deposition Program network site in Duplin County, North Carolina, a location that has experienced a rapid rise in animal operations during this period (Figure 3).66 In Western Europe, where animal operations have dominated agricultural production for the Table 2 - Estimated contributions of atmospheric deposition of nitrogen to “new” nitrogen inputs in diverse estuarine, coastal and open ocean waters. When identified, the sources (wet: W and/or dry deposition: D) and chemical forms (inorganic: I and/ or organic: O) of atmospherically deposited nitrogen are indicated48. RECEIVING WATERS Baltic Sea (Proper)49 ~ 30 W+D, I Kiel Bight (Baltic)50 40% W, I North Sea (Coastal)51 20-40% W+D, I Western Mediterranean Sea52 10 60% W, I Waquoit Bay, MA, USA53 29% W, I+O Narragansett Bay, USA54 12% W, I+O Long Island Sound, USA5 20% W, I+O New York Bight, USA56 38% W, I+O Barnegat Bay, USA57 40% W, I+O Chesapeake Bay, USA58 27% W, I+O Rhode River, MD, USA59 40% W, I+O Neuse River Estuary, NC, USA60 35% W, I+O Pamlico Sound, NC, USA61 ~ 40% W+D, I Sarasota/Tampa Bay, FL, USA62 30% W+D, I Mississippi River Plume, USA63 2-5% W+D, I+O PERCENT OF “NEW” NITROGEN THAT IS ATMOSPHERICALLY DEPOSITED
Issues in Ecology Number 12 Summer 2004 betterpartof thepast century,ammonium is themost abundant months whenplant nutrient demands are highest,phosphorus formof atmospherically deposited nitrogen inputs fromsurface runoff are minimal.At the same time,dry Phosphorus is acomponent of atmospheric deposition,buti and windy conditions ter dtofavor und to dust parti tha such as dust and periods.Further windblown soils. Accordingly,in 450 ● agricultu reg 400 45 ded r20.63 .73 and 4 350 arid regionswhere 35 osition rates in soils are readily 30 various geo transported by graphic regions 25 ve to to bemost highly 量200 ●。 enriched with case of nitrogen phosphorus. 150 ● emissions from Even in these 100 1 菌营鹿蓉套富喜落空索雷 菌雪商营喜店草落露 rally highes gen inputs Year Year Fromaneco In the case logical perspec Figure3-A20yearNationalAcdDeposit ofiron and other epo tive, NH metals,atmos phosphorus thannitrogen is required for supplies of these nutrients to balanced plant growth.Therefore,inphosphorus-limited lakes, coastaland open ocean waters.Iron can be transported over rivers,reservoirs,and evensomemarinesystems suchas theeastem great distances,as demonstrated by the iron-enriched Saharar Mediterranea Sea,atmosphericphosphorus inputs can bea gtutiemt contributes from 5to 15 ne of the externally su rated b volcanicemissions and by various continental pollution sources concentrations of total dissolvedphosphorus in rainfall ranged including power plant,automotive,and industrialemissions.? perliter at nine sites,and total wet While thereisuncertainty about the hemicalforms and behavio deposition rangec ms per square mete ally deposited iron thatenters theocean,there i rninaboutperntofhewholelke'sphosphorus budget.Inalpine Lake Tahoeon theCalifornia-Nevada border, EMISSIONDEPOSIIONANDEATEPROCESSESANDSCALES 25percentofannualpho-phorusinputs whi hep The th ajor atmosph icpathways by whichper nt of the enter v es su as sea are as (1)wet den osition via rain,snow,and fog,(2)dry of total phosphorus loadings to water bodies from all sources.It deposition of particles,and (3)gaseous exchange between the remains unknown whether phosphorus transported into aquatic air and water(Figure4).Many urbanindustrialcentersarelocated systems by river or air differs in its availability for stimulating on or near coastal estuaries and the Great Lakes.Emissionso plant growth ants into theu tmosphere are refle varies withthe ericdep osition of both nit P s Fo ample,dur onthiandaoeratr reover and ab
8 Issues in Ecology Number 12 Summer 2004 better part of the past century, ammonium is the most abundant form of atmospherically deposited nitrogen.67 Phosphorus is a component of atmospheric deposition, but it typically occurs at concentrations less than a few percent those of nitrogen.68 This is especially true in regions where wet exceeds dry deposition, since phosphorus is usually bound to particles such as dust and windblown soils. Accordingly, in agricultural regions where phosphorus is applied as a fertilizer, or in arid regions where soils are readily transported by wind, atmospheric deposition tends to be most highly enriched with phosphorus.69 Even in these situations, phosphorus inputs rarely exceed nitrogen inputs. From an ecological perspective, however, phosphorus may be of considerable importance since far less phosphorus than nitrogen is required for balanced plant growth.70 Therefore, in phosphorus-limited lakes, rivers, reservoirs, and even some marine systems such as the eastern Mediterranean Sea, atmospheric phosphorus inputs can be a significant nutrient source. For example, in Mid-western lakes, including the Great Lakes, atmospheric deposition of phosphorus contributes from 5 to 15 percent of the externally supplied phosphorus.71 In a recent study of the Mid-Atlantic coastal region, concentrations of total dissolved phosphorus in rainfall ranged from 4 to 15 micrograms per liter at nine sites, and total wet deposition ranged from 3.9 to 14 milligrams per square meter per year across the region.72 Annual total phosphorus loading to Lake Michigan in 1976 was 1.7 million kilograms per year, representing about 16 percent of the whole lake’s phosphorus budget.73 In alpine Lake Tahoe on the California-Nevada border, atmospherically deposited phosphorus accounts for approximately 25 percent of annual phosphorus inputs, while in the phosphoruslimited eastern Mediterranean Sea, atmospheric deliveries represent about 10 percent of the “new” phosphorus. Overall, it appears that airborne phosphorus typically accounts for 10 to 20 percent of total phosphorus loadings to water bodies from all sources. It remains unknown whether phosphorus transported into aquatic systems by river or air differs in its availability for stimulating plant growth. Atmospheric deposition of both nitrogen and phosphorus varies with the seasons. For example, during the dry summer months when plant nutrient demands are highest, phosphorus inputs from surface runoff are minimal. At the same time, dry and windy conditions tend to favor transport of dust. Since phosphorus is often bound to dust particles, it is possible that atmospherically deposited phosphorus assumes a more important role as a source of “new” phosphorus during these crucial growth periods. Further investigation and quantification are needed of absolute and seasonal atmospheric phosphorus deposition rates in various geographic regions relative to other phosphorus input sources. In the case of nitrogen, emissions from agricultural, urban, and industrial sources are generally highest in summer. In the case of iron and other metals, atmospheric deposition, mainly in the form of dust, is a major source of “new” supplies of these nutrients to coastal and open ocean waters.74 Iron can be transported over great distances, as demonstrated by the iron-enriched Saharan dust storms that travel thousands of kilometers over the subtropical North Atlantic to “fertilize” iron-deficient and nutrient-poor waters as far away as the Caribbean Sea and the Eastern Seaboard of the United States.75 Iron and trace metals are also generated by volcanic emissions and by various continental pollution sources, including power plant, automotive, and industrial emissions.76 While there is uncertainty about the chemical forms and behavior of atmospherically deposited iron that enters the ocean, there is little doubt that it represents an important source of “new” iron in an environment that is otherwise free of external iron inputs.77 EMISSION, DEPOSITION, AND FATE PROCESSES AND SCALES The three major atmospheric pathways by which persistent organic pollutants enter water bodies such as the Great Lakes, Chesapeake Bay, other coastal estuaries, and the coastal and open sea are as (1) wet deposition via rain, snow, and fog, (2) dry deposition of particles, and (3) gaseous exchange between the air and water (Figure 4). Many urban industrial centers are located on or near coastal estuaries and the Great Lakes. Emissions of pollutants into the urban atmosphere are reflected in elevated local and regional pollutant concentrations and also in areas of intense localized atmospheric deposition that are over and above Figure 3– A 20 year National Acid Deposition Program Network (NADP) nitrogen depositional record for monitoring station NC35 in Duplin Co., NC, showing increases in NH4 + deposition over time. This area has experienced an increase in livestock operations during this period
Issues in Ecology Number 12 Summer 2004 the regional signal.for example.the southern basin of Lake organicpollutants Thatisbecausethelakeiscold nutrientpoor ha Michigan and northern Chesapeake Bay are subject to a large surface area that oovers most ofits watershed and the urban contaminationby airpollutants(PCBs,polyaromatichydrocarbons and industrialdensity in the area islow.Cold water and alarge (PAHs),mercury,and tracemetals)becauseoftheir proximity to surfacearea enhancethe lake'ssensttivity to atmospheric inputsan rializ ed and olatilization.Duringth nd coastal Iake Michig and in the air tially at about 20 Chesapeake Bay near Baltimorecompared to the regionalsigna Higheratmospheric concentrationsof pollutants are ultimately particles and sink to thelakebottom this sedimentation proces reflected in increased precipitation and dry particle inputs o contan inants to the lakeor toestuarinewate hance walerairewdhangeisthedopimamto ay are in appr the pathways tooverallwae must beevaluated in terms of The twoto five fold highe of toxaphene(an insecticide banned in the United Statesince 1990)than PCBs in facilities,pollution fromupstream river flow,and mobilization of Lake Superior has been attributed to a lower sedimentation rate sediments er w del relativeto theotherGreat Lakes me le.The half-fe PCB ofth decline in LakeSt ed to12ye twoexamples Intum,polluted waterbodies may becomesources odegonalatm be faster were it not for the higher atmosphericconcentrations d for PCBsi e air. has Lake Mi e and deliver is believed tobe minimal Although atrazine for PCBsand PAHsin the Chesapeake Bay. ershed-to-wate tend e tem are most sensitive to outary inputs the lakee mpa Aquatic and Terrestrlal Ecosystem controlled by the long watershed serve as Link residence times in wate minatontc anmdhrloratrs nt of the in the Mid-Atlantic fields is lost by runof States,forexample. to riversand lakes and nce of atmosph another 1 percent to sources of contamin quantities of this ation is hest demon pesticide that are stratedby chemicalmas applied combine with Superior, Figure4-Schematicshowingthepathways,distributionand foodwebinterac of the d prime example of an aquaticsystemin which wet and dry de significant accum They can alsobe deposited on terrestrialsystemsand thenenter aquaticsystem ulation of atrazine in ia snow melt and run-off.Pollutantscan also re-enter the atmosphere,where they can be transported and begin the cycle again. atmosph sot persister or no role in the re
9 Issues in Ecology Number 12 Summer 2004 the regional signal. For example, the southern basin of Lake Michigan and northern Chesapeake Bay are subject to contamination by air pollutants (PCBs, polyaromatic hydrocarbons (PAHs), mercury, and trace metals) because of their proximity to industrialized and urbanized Chicago and Baltimore, respectively. Concentrations of PCBs and PAHs are significantly elevated in Chicago and coastal Lake Michigan78 and in the air over Chesapeake Bay near Baltimore79 compared to the regional signal. Higher atmospheric concentrations of pollutants are ultimately reflected in increased precipitation and dry particle inputs of contaminants to the lake or to estuarine waters, as well as enhanced air-water exchange of organic compounds such as PCBs and PAHs.80 Of course, the relative importance of these atmospheric pathways to overall water pollution must be evaluated in terms of other inputs, including discharges from wastewater treatment facilities, pollution from upstream river flow, and mobilization of pollutants from sediments. All three atmospheric pathways deliver pollutants directly to the water surface. This is especially significant for water bodies that have large surface areas compared to the area of the watershed that supplies their runoff. The Great Lakes and coastal seas are two examples. In turn, polluted water bodies may become sources of contaminants to the local and regional atmosphere as gases are lost from the water column to the air. This has been demonstrated for PCBs in the Great Lakes regions of southern Lake Michigan and Green Bay;81 for PCBs, PAHs, polychlorinated dibenzo-p-dioxins and –dibenzofurans (PCDD/Fs), and nonylphenols in the New York-New Jersey Harbor Estuary;82 and for PCBs and PAHs in the Chesapeake Bay.83 In contrast, many aquatic systems have large watershed-to-water area ratios. In these systems, deposits of atmospheric pollutants onto forests, grasslands, crops, paved areas, and other land surfaces in the watershed serve as important sources of runoff contamination to down-stream lakes and estuaries. This is true of most lakes and estuaries in the Mid-Atlantic States, for example. The relative importance of atmospheric deposition versus other sources of contamination is best demonstrated by chemical mass balances (Figures 5 and 6). Lake Superior, the largest and most pristine of the Great Lakes, is a prime example of an aquatic system in which the atmosphere must play a dominant role in inputs and losses of persistent organic pollutants. That is because the lake is cold, nutrient poor, has a large surface area that covers most of its watershed, and the urban and industrial density in the area is low. Cold water and a large surface area enhance the lake’s sensitivity to atmospheric inputs and air-water exchange through outgassing or volatilization. During the 1980s, for instance, the PCB burden in Lake Superior decreased exponentially at about 20 percent a year, primarily because of outgassing losses to the air.84 Although some PCBs bind to organic particles and sink to the lake bottom, this sedimentation process does not provide permanent removal of these contaminants from the water column. Thus, water-air exchange is the dominant loss mechanism. PCBs in the water column today are in approximate equilibrium with atmospheric concentrations. The two-to-five fold higher concentration of toxaphene (an insecticide banned in the United State since 1990) than PCBs in Lake Superior has been attributed to a lower sedimentation rate and colder water temperatures relative to the other Great Lakes.85 Outgassing is an important loss mechanism for toxaphene, just as it is for PCBs, but on a longer time scale. The half-life for PCB decline in Lake Superior waters is 3.5 years compared to 12 years for toxaphene.86 Clearance of toxaphene by volatilization would be faster were it not for the higher atmospheric concentrations generated by continued outgassing of toxaphene from agricultural soils in the southern states upwind from Lake Superior. The pesticide atrazine provides a counter example to PCBs and toxaphene since it is delivered to water bodies mainly by riverine transport of agricultural runoff, and the role of atmospheric delivery is believed to be minimal. Although atrazine has a 30- to 90-day half-life in soils, transport into rivers and lakes significantly extends its half-life. Lake Michigan and other large aquatic systems are most sensitive to tributary inputs of atrazine, but the longterm impacts on the lake environment are controlled by the long residence times in water and the slow rates at which the compound is transformed.87 Only about 1 percent of the atrazine applied to crop fields is lost by runoff to rivers and lakes and another 1 percent to aerial transport. Nevertheless, the large quantities of this pesticide that are applied combine with efficient transport, slow transformation rates, and long residence times in water to cause significant accumulation of atrazine in aquatic systems. The atmosphere plays little or no role in the reFigure 4 – Schematic showing the pathways, distribution and food web interactions of persistent organic pollutants entering and leaving aquatic systems (modified from D. Muir). Pollutants can be bound to particles or in gaseous phase and can be deposited directly on aquatic ecosystems via both wet and dry deposition. They can also be deposited on terrestrial systems and then enter aquatic systems via snow melt and run-off. Pollutants can also re-enter the atmosphere, where they can be transported and begin the cycle again