The purpose of the fifth section of this book is to identify and describe a number of new and significant issues and approaches in ecotoxicology, most of which have come into focus since the publication of the first edition of this book. These include endocrine-disrupting chemicals and endocrine active agents in the environment, the possible role of contaminants in the worldwide decline of amphibian populations, potential genetic effects of contaminants on animal populations, the role of ecotoxicology in industrial ecology and natural capitalism, the consequences of indirect effects of agricultural pesticides on wildlife, the role of nutrition on trace element toxicity in fish and wildlife, and the role of environmental contaminants on endangered species.
Over the last 5 years there has been a surge of reports in wildlife of suspect endocrine-disruptor-related effects based primarily on adverse reproductive and developmental effects.22-24 Collectively, there is some evidence of altered reproductive and developmental processes in wildlife exposed to endocrine disruptors, and in the United States, Congress has passed legislation requiring the Environmental Protection Agency to develop, validate, and implement an Endocrine Disruptor Screening Program (EDSP) for identifying potential endocrine-disrupting chemicals. A wide variety of chemicals have been reported as potential endocrine disruptors and are described by Gross and co-workers in Chapter 39 of this book. This chapter reviews and selectively summarizes methods for screening and monitoring of potential endocrine disruptors, the current evidence for endocrine-disrupting effects, and chemical classes in vertebrate wildlife and their potential modes of action. Classes of chemicals include polycyclic aromatic hydrocarbons; polychlorinated and polybromi-nated biphenyls, dibenzo-p-dioxins, dibenzo-p-furans; organochlorine pesticides and fungicides; some nonorganochlorine pesticides; complex environmental mixtures; and a few metals.
Over the past decade widespread population declines of amphibians have been documented in North America, Europe, Australia, and Central and South America.25-27 Population declines in eastern Europe, Asia, and Africa have been suggested as well but are not as well documented. Based on comparative toxicities of organic compounds and metals between amphibians and fish, the overall conclusions were that there was great variation among amphibian species in their sensitivity to metal and organic contaminants, that amphibians generally were more sensitive than fish, and that water-quality criteria established for fish may not be protective of amphibians.
Contaminants may be involved with amphibian population declines, including their possible interaction with other factors discussed by Sparling in Chapter 40.
Understanding changes to the genetic apparatus of an organism exposed to contaminants in the environment is essential to demonstrating an impact on parameters of ecological significance such as population effects. Genetic ecotoxicology attempts to identify changes in the genetic material of natural biota that may be induced by exposure to genotoxicants in their environment and the consequences at various levels of biological organization (molecular, cellular, individual, population, etc.) that may result from this exposure. Shugart, Theodorakis, and Bickham (Chapter 41) describe two major classes of effects studied in genetic ecotoxicology: (1) direct exposure to genotoxicants that have the potential to lead to somatic or heritable (genotoxicological) disease states and that could lower the reproductive output of an affected population, and (2) indirect effects from contaminant stress on populations that lead to alterations in the genetic makeup, a process termed evolutionary toxicology.28 These latter types of effects alter the inclusive fitness of populations such as by the reduction of genetic variability.
Industrial ecology is the study of the flows of materials and energy in the industrial environment and the effects of those flows on natural systems. Natural capitalism refers to the increasingly critical relationship between natural capital (i.e., natural resources), living systems and the ecosystem services they provide, and manmade capital. Natural capitalism and two of its subdisciplines, industrial and municipal ecology, are essential components in developing a sustainable relationship with natural systems and protecting both natural capital and the delivery of ecosystem services. Cairns (Chapter 42) discusses the role of ecotoxicologists in this sustainability.
Agricultural pesticides have been identified as contributing to the decline of farmland wildlife, although the impact is often exacerbated by other farm practices associated with intensive agriculture. Many species of farmland birds are in decline in the United Kingdom, and there is considerable evidence for the indirect effects of pesticides as the cause. Sotherton and Holland (Chapter 43) discuss how changes in chick survival drive the population size of the once common United Kingdom farmland grey partridge, and conclude that the timing and magnitude of changes in population size and chick survival are consistent with having been caused by the increased use of pesticides, which reduce the insect foods available for partridge chicks. Indirect effects are also likely to impact upon a wide variety of farmland wildlife that are dependent on the same food chain as the grey partridge, and evidence of this is starting to appear for some passerines.
Nutrition of test organisms is one of the most important variables in the conduct of any biological experiment. Deficiencies of vitamins, minerals, and other nutrients in the diet of captive and freeranging fish and wildlife can result in skeletal deformities, cataracts, histological lesions, abnormal behavior, and many other abnormalities. Excessive amounts of vitamins and minerals have also resulted in abnormalities. The quality of commercial or experimentally prepared diets of captive animals as well as diets consumed by wild animals can influence the acute and chronic toxicity of test compounds. Chapter 44 (Hamilton and Hoffman) examines interactions between nutrition and potentially toxic trace elements and interactions among trace elements. Limited information from dietary studies with trace elements, especially selenium, reveals that diet can have a profound effect on toxicity observed in contaminated ecosystems, yet water-quality standards are rarely derived taking this factor into account. Incorporation of dietary criteria into national criteria for trace elements will occur only after a sufficient database of information is generated from dietary toxicity studies. Recent findings with environmentally relevant forms of mercury (methylmercury) and selenium (selenomethionine) in birds have shown that mercury and selenium may be mutually protective to the toxicity of each other in adult birds but synergistic in combination to the reproductive process in embryos. Further studies are needed to examine the relationship between selenium, nutrition, and other trace elements that may be toxic by compromising cellular antioxidative defense mechanisms. There is also a need for comparative interaction studies in species of wild mammals.
The speed, severity, and taxonomic diversity of declining species is a major concern to ecologists because extinctions are taking place at a rate of approximately 100 species per day.29 Previously,
Wilson30 projected the loss of species at more than 20% of the planet's total biodiversity in 20 years. The last chapter (45) of this section by Pattee, Fellows, and Bounds examines the role of contaminants/pollution in the decline of species. Habitat destruction is the primary factor that threatens species and is listed as a significant factor affecting 73% of endangered species. The second major factor causing species decline is the introduction of nonnative species. This affects 68% of endangered species. Pollution and overharvesting were identified as impacting 38% and 15%, respectively, of endangered species. No other contaminant has impacted animal survival to the extent of DDT, which remains one of the few examples of pollution actually extirpating animal species over a significant portion of DDT's range. Once a species is reduced to a remnant of its former population size and distribution, its vulnerability to catastrophic pollution events increases, frequently exceeding or replacing the factors responsible for the initial decline. Therefore, large-scale environmental events, such as global warming, acid rain, and sea-level rise, attract considerable attention as speciation events, adversely affecting some species populations while causing other species to flourish.
The editors of this book conclude that with increasing loss of habitat the quality and fate of the remaining habitat becomes increasingly critical to the survival of species and ecosystems. Species that are endangered or at risk and that occupy a very limited geographical area could be easily decimated by a single event such as an oil or chemical spill or misapplication of pesticides. Furthermore, on a temporal basis where a large portion of a species population occupies a small geographical area, either in the course of its migration or on wintering grounds, any localized impact, whether pesticide-related (e.g., as reported by Hooper and co-authors, Chapter 25) or not, has the potential for serious consequences to populations. For these reasons the balance between shrinking habitat and anthropogenic stressors becomes increasingly crucial to sustain both ecosystems and species diversity.
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