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 b3 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, dichlorodi￾phenyltrichloroethane (DDT), endrin, heptachlor, hexa￾chlorobenzene, mirex, toxaphene, PCBs, polychlorinated dibenzo￾p-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