Catálogo de publicaciones - libros

This chapter presents background information on the Great Lakes and summarizes the content of each chapter of this book.

This chapter reviews the scientific understanding of the concentrations, trends, and cycling of polychlorinated biphenyls (PCBs) in the Great Lakes. PCBs were widely used in the Great Lakes region primarily as additives to oils and industrial fluids, such as dielectric fluids in transformers. PCBs are persistent, bioaccumulative, and toxic to animals and humans. The compounds were first reported in the Great Lakes natural environment in the late 1960s. At that time, PCB production and use was near the maximum level in North America. Since then, inputs of PCBs to the Great Lakes have peaked and declined: sediment profiles and analyses of archived fish indicate that PCB concentrations have decreased markedly in the decades following the phase-out in the 1970s. Unfortunately, concentrations in some fish species remain too high for unrestricted safe consumption. PCB concentrations remain high in fish because of their persistence, tendency to bioaccumulate, and the continuing input of the compounds from uncontrolled sources. PCBs are highly bioaccumulative and many studies have shown that the complex food webs of the Great Lakes contribute to the focusing of PCBs in fish and fish-eating animals. PCB concentrations in the open waters are in the range of 100–300 pg L, and are near equilibrium with the regional atmosphere. PCBs are hydrophobic yet are found in the dissolved phase of the water column and in the gas phase in the atmosphere, and they continue to enter the Great Lakes environment. The atmosphere, especially near urban-industrial areas, is the major source to the open waters of the lakes. Other sources include contaminated tributaries and in-lake recycling of contaminated sediments. Until these remaining sources are controlled or contained, unsafe levels of PCBs will be found in the Great Lakes environment for decades to come.

The history of “dioxin”, PCDD/F, contamination in the Great Lakes is reviewed. Occurrence, geographical distribution, and temporal trends in air, water, sediments, fish, seabirds, snapping turtles, and humans are presented, and eco/human toxicological implications reviewed. Patterns and concentrations in sediment indicate that atmospheric input dominated in Lake Superior, lower Lake Michigan, and Lake Erie. Inputs from the Saginaw River to Lake Huron and Fox River to upper Lake Michigan added some PCDD/F loading to these lakes above atmospheric deposition. Lake Ontario was heavily impacted by input of PCDD/Fs, particularly 2378-TeCDD, from the Niagara River. Sediment core and biomonitoring data revealed that PCDD/F contamination peaked in most lakes in the late 1960s to early 1970s, followed by rapid, order of magnitude declines in the mid- to late 1970s. The downward trend stalled in some lakes in the 1980s, but seems to have continued after the late 1990s, probably in response to various remediation efforts and reductions in PCDD/F emissions to the atmosphere. During the height of contamination, effects attributed in whole or in part to PCDD/F contamination included reproductive failure in lake trout and herring gulls in Lake Ontario. AHR-mediated sublethal effects may still be occurring in seabirds and fish, but much of this is thought to be due to dioxin-like PCBs rather than PCDD/Fs.

Pesticides have been widely and heavily used in agriculture in the Great Lakes Basin (approximately 93000 tons were used in 1995 alone). Herbicides account for two-thirds of the total pesticides used. Herbicide usage in seven of the Great Lakes states (Illinois, Indiana, Michigan, Minnesota, Ohio, Pennsylvania, and Wisconsin) constituted approximately 50% of the total usage in the USA. The pesticide use is concentrated in the corn- and soybean-growing areas of the southern Lake Michigan Basin and western Lake Erie Basin of the Great Lakes. Organochlorines (OC) such as DDT and dieldrin were the major pesticides used in the Great Lakes Basin prior to 1970s. The past usage of OC insecticides was large enough to cause effects on the Great Lakes ecosystem. Whereas environmental concentrations of OC pesticides in the Great Lakes Basin have generally declined during the past 20 years, concerns nevertheless remain, because these substances persist in the environment and accumulate in the food chain. There continue to be fish consumption advisories based on unacceptable levels of OC pesticides in sport and commercial fish from the Great Lakes. Atmospheric transport from agricultural regions in the USA and Canada, where these pesticides were used extensively in the past, continues to be a source of contamination in the Great Lakes. Hazardous waste sites with elevated levels of OC pesticides represent another source. In the 1980s and the 1990s, OC pesticides were replaced with new-generation pesticides, which are more target-specific and less persistent. Among herbicides, atrazine, metolachlor, cyanazine, acetolachlor, and alachlor account for about 53% of the total usage, and among insecticides, organophosphates (OP) such as malathion, chlorpyrifos, terbufos, diazinon, and methyl-parathion account for 72% of the total usage in the late 1990s. Various monitoring programs have shown that the levels of OC pesticides have declined steadily until the 1980s, and thereafter the rate of this decline has slowed. The relative slow decline or steady state in OC levels in the 1990s was thought to be due to release/re-suspension and/or recycling of these compounds through the Great Lakes ecosystem. Atmospheric deposition has become an increasingly significant route of entry of OC pesticides into the Great Lakes ecosystem, although such depositions have decreased recently, and the lakes are now acting as a source via the degassing of these compounds. Most of the current-use pesticides are not bioaccumulative; however, because of the high volume of their usage, these compounds are present in Great Lakes waters. The most frequently detected herbicides in waters include several triazines (atrazine, cyanazine, and simazine), acetanilides (metolachlor and alachlor), and 2,4-D. In addition to streams and rivers, atmospheric transport is a pathway for current-use pesticides in the Great Lakes. The occurrence of in-use pesticides in surface waters follows broad and complex patterns in land use and associated pesticide use. In general, concentrations showed an increasing gradient from north to south, with Superior < Huron < Ontario < Erie. Although most of the current-use pesticides are not bioaccumulative, exposure of aquatic organisms to these compounds can be deleterious. Current-use pesticides can undergo environmental and biological transformations, although the degradates of the most heavily used herbicides found in surface water have not been studied widely. In many cases, methods to assess the fate of current-use pesticides and their degradates in the environment are not available. Future investigations should focus on the fate and effects of current-use pesticides.

Toxaphene is a major persistent organic contaminant in air, water and fish in the Great Lakes. The story of toxaphene in the Great Lakes, like that of most other persistent organochlorine compounds, has only become clear after the ban on the use of this pesticide in the mid-1980s. Although much of the peer-reviewed literature on environmental fate of toxaphene has involved measurements in the Great Lakes, delineating the extent of contamination has proved very challenging because of the difficulties involved with quantifying this multicomponent mixture. The spatial and temporal trends of toxaphene in the Great Lakes are now reasonably well documented. The highest concentrations in fish and lake water are found in Lake Superior. Concentrations of toxaphene declined in lake trout from Lakes Michigan, Huron and Ontario during the 1990s (with half-lives of 5–8 years) but not in Lake Superior. Recent measurements suggest no declines from the mid-1990s to 2000 in all four lakes. Modeling has demonstrated that colder temperatures and low sedimentation rates in Lake Superior, and to some extent in Lake Michigan, conspire to maintain high toxaphene concentrations in the water column. Sediment core profiles from Lake Michigan, Ontario and Superior all show declining inputs in the past 10–20 years, mirroring reduced emissions following toxaphene deregistration in the USA in 1986. Atmospheric transport of toxaphene from agricultural soils in the southern USA continues and modeling results suggest that 70% of the atmospheric inputs to the Great Lakes are due to long-range atmospheric transport and deposition from outside the basin itself. Some degradation is apparent in the Lake Superior food web based on nonracemic enantiomer fractions for selected chlorobornanes, but for most congeners this process is slow and does not result in negative food web biomagnification in Lake Superior. High proportions of hexa- and heptachlorobornanes have been found in some lake sediments and tributary waters, indicating that slow degradation, mainly via dechlorination, is proceeding within the Great Lakes basin.

Toxaphene concentrations probably did not reach levels that would, by themselves, cause effects on salmonid reproduction, survival or growth in the Great Lakes. The levels and effects of toxaphene in fish-eating birds and mammals (such as mink) in the Great Lakes have never been thoroughly investigated; however, it seems likely that exposure levels for birds and mammals would have been lower than for PCBs. In some Great Lakes jurisdictions, concerns remain about human exposure to toxaphene via consumption of Lake Superior lake trout. Given the long half-lives in fish and water, elevated toxaphene is likely to remain a contaminant issue in the Great Lakes until the middle of the twenty-first century.

This review examines the sources and occurrence of polychlorinated naphthalenes (PCNs) in the Great Lakes environment and summarizes current knowledge of the toxicity, analysis, and environmental chemistry and fate of these compounds. PCNs have entered the Great Lakes through the production and use of Halowax technical mixtures, as trace contaminants in Aroclor PCB mixtures, and through industrial processes such as chlor-alkali production and waste incineration. Air concentrations of PCNs were highest in urban areas, and congener profiles indicate that evaporative emissions relating to past uses are the dominant sources, but combustion processes also contribute. Sediment measurements indicate that the highest concentrations are in the Detroit River, and congener profiles indicate Halowax contamination from past inputs. Fish from this area had the highest reported concentrations in the Great Lakes region, followed by lake trout from Lake Ontario. Estimates of dioxin toxic equivalents (TEQ) of PCNs indicate their contributions are as important as the dioxin-like PCBs in some aquatic species, and more important in air and sediments. No time trend information for PCNs in the Great Lakes exists, and further spatial assessment, and TEQ comparisons of PCNs, PCDD/Fs, and PCBs in additional fish species, should be undertaken.

Polycyclic aromatic hydrocarbons (PAHs) are produced during the incomplete combustion of organic material. They can also be produced through natural, non-combustion processes, and may be present in uncombusted petroleum. Uncombusted petroleum can be a direct source to the waters of the Great Lakes, but combustion sources discharge PAHs into the coastal atmosphere. Atmospheric deposition of combustion related PAHs seems to be the dominate source to the Great Lakes, except in nearshore areas where point sources can be significant. Once airborne, PAHs partition in the atmosphere between the gas and particle phases and can undergo long-range transport. During transport, PAHs can be degraded or modified by photochemical reactions. Both the original PAH species and their degradation products can be washed out of the atmosphere by wet and dry deposition, air–water exchange and air–terrestrial exchange. Once in an aquatic system, PAHs partition between the dissolved and particle phases. In general, PAHs are particle reactive and settle out in sediments. PAH contamination of Great Lakes sediments are higher in the nearshore regions where ports, harbors, and urban/industrial areas are the densest. In the open lake area, sediment concentrations are rather uniform, with Lake Superior having slightly less PAHs in its surficial sediments. That portion of the PAHs that does not partition to particles can bioaccumulate in the lipid reserves of organisms. PAHs accumulated in an organism may be metabolized to more toxic by-products or exert toxicity in its original form. When combined with ultraviolet radiation this toxicity is greatly enhanced. In coastal areas where concentrations can be quite high, PAHs can be toxic to all forms of aquatic life during at least part of their life cycle. PAHs are expected to remain an ecological threat to the Great Lakes well into the future. The threat may even increase with the increasing combustion needed for the increasing population centers and greater transportation needs. Of particular concern is the short-term increase in PAH concentrations that can result from the dredging of ports and harbors where highly contaminated sediments have been buried.

Brominated flame retardants in the Great Lakes have not been as well studied as many of the polychlorinated pollutants, especially s, but in the last 5–10 years there has been some significant progress. The ubiquity of these compounds in the sediment and fishes of the lakes has now been well established, and perhaps more alarmingly, it is now known that the concentrations of some of these compounds are actually increasing. This observation is particularly important given that the concentrations of most of the other persistent organic pollutants in the lakes are decreasing. Despite their production cessation in the mid-1970s, polybrominated biphenyls are still present in fishes and sediment from most of the lakes. In general, these PBB concentrations are decreasing slowly, if at all. Polybrominated diphenyl ethers are present in air, fishes, birds, and sediment from the lakes. In lake trout and in herring gull eggs, the PBDE concentrations have been doubling every 3–5 years; in sediment cores, the doubling time is ∼15 years. Hexabromocyclododecanes (HBCD) are also present in fishes and sediment from the lakes, but at much lower levels compared to the PBDEs. Two novel flame retardants (1,2-(2,4,6-tribromophenoxy)ethane (TBE) and 1,2,3,4,5-pentabromoethylbenzene) have been found in the air and sediment of the lakes. Clearly, it would be good to monitor the concentrations of all of these compounds in (at least) the sediment and fishes of the lakes to determine long-term trends. One might want to focus especially on those BFRs that will continue to be in production; these include deca-BDE (congener 209), HBCD, and TBE.

Perfluoroalkyl acids (PFAs) are released to the environment via their manufacturing processes, their use in commercial products, or indirectly via oxidation of precursor molecules containing perfluoroalkyl chains. PFA precursors are diverse and include poly- and perfluorinated alcohols and perfluoroalkyl sulfonamide derivatives. Products in which PFAs and their precursors have been used include wetting agents, lubricants, stain resistant treatments, and fire-fighting foams. The PFAs in the environment comprise two general classes: perfluoroalkyl carboxylates such as ()CO and perfluoroalkyl sulfonates, such as CF(CF)SO. The predominant PFA in biota samples from the Great Lakes is perfluorooctane sulfonate (PFOS), but a homologous series of perfluoroalkyl carboxylates, where  = 6 − 13, is also detected in most samples at lesser concentrations. The environmental behavior of most PFAs is not well studied, and our knowledge of the physicochemical properties of PFOS and PFOA is limited. Both compounds are persistent in the environment and are not expected to volatilize into the atmosphere to a significant extent, but have much greater water solubilities than similar chlorinated compounds. Concentrations of PFOS in surface waters are usually less than those of perfluorooctanoic acid (PFOA), but PFOS accumulates in aquatic organisms to a greater extent and appears to biomagnify in the food web of the Great Lakes region. PFAs and/or their precursors have been measured in air, surface waters, sediments, aquatic invertebrates, and in the tissues of fish, fish-eating water birds, mink, otter, and other wildlife from in and around the Great Lakes. Although the sources of PFAs to the Great Lakes are not well understood, fluorotelomer alcohols (FTOHs) and perfluorooctylsulfonamides degrade to perfluoroalkyl carboxylates and PFOS, respectively, in laboratory studies. Based on preliminary and incomplete information, current concentrations of PFOS in the Great Lakes environment do not seem to be sufficient to pose a significant risk to most aquatic organisms including fish. However, the margins of safety are less for mammals such as mink and birds and when the concentrations of all PFAs are considered together, current concentrations may pose risk to some sensitive species.