Wildlife TOXICOLOGY Revisited
Reflecting on wildlife toxicology’s short past, one can foresee its important future.
RONALD J. KENDALL PHILIP N. SMITH TEXAS TECH UNIVERSITY
wenty years ago, a feature article entitled “Wildlife Toxicology” appeared in ES&T that posed the hypothesis, “Human health is believed to be threatened by exposure to such chemical contaminants as agricultural pesticides and industrial waste. Does it not stand to reason, therefore, that the health of wildlife could be affected similarly by toxic chemical pollutants?” (1). Now, with more sophisticated tools and techniques at our disposal (2), the issues of the response of wildlife to chemical contaminants and the interrelationship of that response to human health are still growing as an interdisciplinary study.
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Quantifying the impacts of contaminants on wildlife populations remains as difficult a task as it was 20 years ago (3). For example, how does one determine the number or percentage of a wildlife species that is killed outright, made more susceptible to diseases or predation, or suffers reproductive impairment after exposure to toxic chemicals? In this article, we will discuss how rapid expansion of environmental toxicology has produced a growing number of wildlife toxicologists to find answers to these questions. These toxicologists are developing and using ecological and related acute and chronic toxicological information to study organisms potentially affected by environmental contaminants.
What is wildlife toxicology?
THOMAS R. RAINWATER
Wildlife toxicology is the study of how environmental contaminants affect the well-being, general health, and reproduction of wild species (1). Well-being implies, for example, that neither significant increase in the probability of being preyed upon nor an aberration in migratory behavior exists. Good general health implies that the organism or population exists in a sustainable, homeostatic condition with its environment, and therefore, can survive in various environ-
mental situations. Because the reproductive process is often very sensitive to chemical influences, these studies are a high priority in wildlife toxicology. Although there are no clear taxonomic guidelines, the term “wildlife” generally pertains to vertebrate animals living in a natural, undomesticated state. In the early years, wildlife toxicology research focused on wildlife with economic benefits, in terms of hunting and fishing, sources of food, nature photography, or aesthetic appreciation. This emphasis derived from the rationale that the most studied species should be either beneficial or detrimental to human society (4). Although “value-added” species such as birds and mammals are still quite important, the present discussion includes issues related to amphibians and reptiles as these taxa have been receiving more attention in terms of their susceptibility to contaminant exposure. Wildlife toxicology is truly interdisciplinary in nature. It draws on several subdisciplines, among which are analytical toxicology, biochemical toxicology, and ecotoxicology, which concerns the effect of contaminants on the ecology of wildlife species, including the effects on a species’ behavior and foraging strategies (5). The field of wildlife toxicology has benefited from scientists whose diverse research interests help as-
© 2003 American Chemical Society
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PHILIP N. SMITH
The discovery that organochlorine pesticides could reduce eggshell thickness in raptorial species is perhaps the most well-known and extensively documented event in wildlife toxicology. During the 1940s and 1950s, Derrick Ratcliffe of the British Nature Conservancy noted a decline in peregrine falcons (Falco peregrinus) across Europe. Soon thereafter, correlations between eggshell thickness and reproductive failure in these falcons, other raptors, and piscivorous (fish-eating) avian species were discovered (6). These findings, and evidence of exposure among humans, ultimately led to the ban on DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) in the United States in 1973. In addition, a number of events raised society’s awareness and prompted the public’s interest in environmental issues, and thus wildlife toxicology. Rachel Carson’s book Silent Spring (7) fueled the debate on environmental contaminants’ effects on humans and wildlife and brought these important issues to the attention of the American public. Many credit Silent Spring for spurring the ensuing environmental movement. Carson’s cautionary words on the potential impacts of anthropogenic substances in the environment have inspired many environmental scientists and bring public awareness to these issues even to this day. Common throughout the world today, Earth Day observations began in 1970, launched in a speech by then U.S. Senator Gaylord Nelson. Indeed, Earth Day was styled after the Vietnam War-era protests but was designed to increase awareness of our impact on the environment. As a freshman at the University of South Carolina in 1970, the senior author wore a replica Earth Day flag patch sewn on a nylon jacket. Asked by a passerby, “Are you a communist?”, the response was, “No, ma’am, but I am concerned about the environment.” In 1979, the Society of Environmental Toxicology and Chemistry (SETAC) was founded to fill the need for a professional organization dedicated to research on issues of environmental contamination. Among its early membership, SETAC included many of the first wildlife toxicologists, and today, it remains an important organization for the dissemination
KEVIN D. REYNOLDS
Early discoveries and influences
of wildlife toxicology research. SETAC remains the largest and most influential organization for environmental and wildlife toxicology professionals and has become global in stature and reach. The early days of wildlife toxicology and SETAC saw extensive use of relatively simple experimental methods, including generation of LD50 (lethal dose for 50% of test group) and LC50 (lethal air or water concentration for 50% of test subjects) values. Generally speaking, overt lethality was the most common endpoint assessed by wildlife toxicologists. These methods were adapted from traditional toxicology. A new era of intensive synthetic chemical usage in the mid-1900s unfortunately resulted in many instances in which acute toxicity levels of contaminants created “die-offs” among wildlife. Environmental regulations evolved, slowly at times, to address the booming industrial and agricultural chemical industry’s capacity to produce and disseminate toxic substances into the environment. Discoveries of wildlife mortality in the field led wildlife toxicologists to initiate laboratory dosing experiments using wild, inbred, or domestic animal models to establish benchmark data on acute and chronic toxicity of environmental contaminants, including pesticides, petroleum, and industrial waste products. For example, Aulerich and Ringer used PCB-laden fish to evaluate lethality and reproductive impairment of mink that had begun to decline around the Great Lakes in the late 1960s and early 1970s (8). However, to generate statistically meaningful data sets in light of inherent variability of wildlife species, many of the early wildlife toxicity studies ironically resulted in the overkill of both laboratory animals and wildlife. Efforts to develop and validate sublethal indicators of exposure and effect for sometimes-critical wildlife populations were intensified. Many of the well-known environmental contaminants, such as DDT, PCBs, and various metals, have been studied extensively for toxicity among wildlife. Although there is still much to be learned about the effects of these chemicals alone, and particularly in mixtures, much progress has been made over the past 20 years. Today, sublethal chronic testing of single and multiple contaminants focusing on alterations in wildlife physiological processes, reproductive success, and/or fitness have become more common than the lethality tests, which provided the earlier benchmark toxicity values. SCOTT T. MCMURRAY
sess risk to wildlife from environmental contaminants. Initially, biologists, chemists, veterinarians, and pharmacologists sharing an interest in the effects of chemicals on wildlife and humans were involved in the study of wildlife toxicology, but lacked a unified perspective. Academic programs specifically devoted to the interdisciplinary training of wildlife toxicology professionals were not available until the 1980s.
Addressing the problem Although human health continues to be the main concern of regulators, understanding the effects of chemicals on wildlife became important in the development of regulations governing their manufacture and use. In 1942, the U.S.
SCOTT T. MCMURRAY SIMON BACKLEY
line for examining environmental issues facing wildlife populations and incorporating exposure and effects assessments into a quantitative process that accounts for associated uncertainties in regulatory decision making. In 1998, this document was replaced with EPA’s Guidelines for Ecological Risk Assessment, which was designed to improve the quality and consistency of the risk assessment process (10). This framework allows for the assessment of toxic chemical impacts and other stressors on ecological systems. In the formulation phase, a conceptual model is usually developed that describes routes of exposure, biota of concern, and anticipated effect endpoints. The actual risk of chemicals to wildlife or biota is then determined using exposure and effects data for the chemicals of interest. Toxicity data for species of concern at either the individual or population level may be incorporated in the risk characterization phase (11). Exposure and effects data accumulated in the analysis phase are combined, and the risk potential is characterized. On the basis of the result, management steps can be taken, generally involving decreasing the exposure portion of the assessment, in order to decrease the overall risk. EPA has published a good example of an ecological risk assessment involving the exposure of wildlife to the insecticide carbofuran (2,3-dihydro-2,2dimethyl-7-benzofuranol methylcarbamate) (12). This study documented widespread and repeated mortality events, particularly where birds ingested carbofuran granules in agricultural systems. According to legislation promulgated by FIFRA, chemicals in the environment could not pose unreasonable adverse effects to birds or other wildlife populations. In addition, the Migratory Bird Treaty Act protects species internationally by prohibiting the killing of migratory songbirds or waterfowl with a pesticide. The 1990s presented several issues with direct consequence to wildlife toxicology, but endocrinedisrupting properties topped the list. With the hypothesis that these compounds impact reproduction in wildlife, Theo Colborn’s book, Our Stolen Future, stimulated an intense debate (13). Guillette et al. reported alterations in alligator sex hormones and gonadal development related to environmental contaminants in Florida (14). The combination of these and other findings generated intense scientific debate, workshops, and ultimately books addressing the potential influence of contaminants on endocrine function (15). In response, EPA established the Endocrine-Disrupting Substance Testing Advisory Committee to examine this issue and make recommendations on testing and regulation of endocrinedisrupting chemicals in 1996. PHILIP N. SMITH
Congress passed the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) to deal with pesticide registration, efficacy, and use under jurisdiction of the U.S. Department of Agriculture. FIFRA became the Federal Environmental Pesticide Control Act in 1972, charging the U.S. EPA with determining if pesticides represented “unreasonable risks” to people, the environment, and wildlife. Other congressional acts, including the Toxic Substances Control Act of 1976 and the Comprehensive Environmental Response, Compensation and Liability Act (Superfund) of 1980, have added strength to governmental control of chemicals and their releases into the environment that may impact wildlife populations. These acts indirectly led to increased funding for research in wildlife toxicology in the late 1980s and early 1990s, fueled by the need to evaluate the risk of agrochemicals on wildlife (5). Often, large complex field studies were combined with intensive laboratory testing on fish, birds, and mammals to provide data for registering and labeling a chemical or pesticide. These studies often included carcass searches in treated and untreated fields as well as chemical analysis of soil, vegetation, excrement, foot washes, and biological tissues. Bioassays ranging from cholinesterase measurements to induction of metabolizing enzymes evaluations aided in assessing physiological responses to chemical exposure, thus allowing spatial analysis of exposure and effects. Moreover, population level indices of contaminant effects, such as reproductive success and survival, helped assess contaminant effects beyond the individual level. However, in the late 1980s and early 1990s, changes in EPA policy reduced requirements for extensive field studies. The U.S. federal government demonstrated early concern for wildlife interactions with environmental contaminants. The U.S. Fish and Wildlife Service’s (USFWS’s) Environmental Contaminants Program began in the 1950s. It became intimately involved with environmental quality issues similar to EPA, but its mission focused on the health and well-being of fish and wildlife. Today, USFWS has approximately 75 locations throughout the United States, and contaminant specialists within the USFWS focus on pollution prevention, contaminant identification and risk assessment, cleanup, and technical support for other USFWS biologists. In 1992, EPA released an ecological risk assessment framework in which the evaluation of wildlife health, reproduction, and survival were established as criteria for registering chemicals for commercial use and contaminants found on hazardous waste sites (9). This document provided the necessary out-
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Because of declining populations and the discovery of malformations in amphibians and reptiles, they have received much attention from the general public and biologists in the past decade (19). Numerous studies have indicated dramatic reductions in amphibian populations worldwide, with explanations such as climatic change; parasitic, bacterial, or viral infections; and increased predation (20). Undoubtedly, environmental pollutants have contributed to this decline, generating great interest among wildlife toxicologists. In 1998, the U.S. federal government established the interagency Task Force on Amphibian Declines and Deformities to examine the changes seen in amphibian populations. Although amphibians have become a major focus, reptiles remain relatively underrepresented in the wildlife toxicology literature (21). As new analytical tools and methods 182 A ■ ENVIRONMENTAL SCIENCE & TECHNOLOGY / MAY 1, 2003
improve our abilities to evaluate subtle changes in environmental quality and wildlife health, additional challenges are sure to emerge.
In the future Wildlife toxicologists have much more sophisticated tools now than 20 years ago. New analytical equipment and more economical technologies, such as enzyme-linked immunosorbent assays, passive sampling devices, and accelerated solvent extractors, have improved detection capabilities and removed many of the restrictions on measuring contaminants in various environmental matrices. For example, until the 1990s, no reliable method was available to detect perchlorate in water at the parts-per-billion concentrations now commonly detected in environmental samples. Scientists at the California EPA developed a new method in the 1990s sensitive enough to reveal widespread contamination of ground and surface waters in that state and elsewhere. The analytical method was evaluated and refined for detection of perchlorate in soil, sediment, and plants (22), but a method for tissue came only recently (23). Tools for assessing physiological changes in wildlife related to environmental contaminants have also become increasingly more sophisticated. Polymerase chain reaction, DNA fingerprinting, cDNA microarrays, and other molecular techniques now provide more detailed information on the impacts of chemicals beyond individual and cellular levels. Thus, studies of contaminant effects on wildlife today may include measurement endpoints on all levels, from molecular, cellular, organ system, individual, and population to entire ecosystems. Clearly, the health of the environment influences the viability of people and wildlife. Current risk assessments for chemicals in the environment that establish protective limits for humans often rely on wildlife exposure data. Therefore, wildlife toxicologists have an opportunity to participate in regulatory processes aimed at protecting environmental and human health. The field of wildlife toxicology continues to evolve, while maintaining its original interdisciplinary nature by enlisting diverse specialists to help understand complexities of contaminant movement, fate, bioavailability, and physiological, population, and ecosystem TODD ANDERSON
Endocrine disrupters remain an issue of concern as new chemicals with these types of properties are identified. Recently, perchlorate, a thyroid hormone inhibitor, gained national attention due to its widespread distribution in groundwater and surface water supplies. Figures 1 and 2 (also, see photo below) show how perchlorate detected in numerous plant, fish, and wildlife species (16) can effectively inhibit metamorphosis and shift sex ratios in amphibians (17, 18). As endocrinealtering chemicals continue to emerge, the demand for studies to examine their effects on wildlife will increase.
The bullfrog (Rana catesbeiana) larvae, collected from a perchlorate-contaminated pond undergoing metamorphosis, is shown here. Perchlorate inhibits thyroid-dependent metamorphic processes, including forelimb emergence, hind-limb growth, and tail resorption in bullfrogs. This specimen shows adequate front- and hind-limb emergence, but it has not begun to resorb its tail.
effects. In the future, wildlife toxicologists could contribute significantly to assessing the global threats of chemical contamination, and they also have the expertise in environmental assessments to understand, and perhaps counter, potential terrorist attacks with chemical and biological agents. Attacks with biological or chemical weapons intended for humans or livestock could have simultaneously devastating effects on wildlife resources and biodiversity (24).
cluding the first author on this manuscript. We wish to recognize his contributions to the field. Ronald J. Kendall is the director and Philip N. Smith is an assistant professor at the Institute of Environmental and Human Health, a joint venture between Texas Tech University and Texas Tech University Health Sciences Center. Kendall also chairs the Department of Environmental Toxicology at Texas Tech University. He is actively engaged in environmental toxicology and chemistry research. As an ecotoxicologist, Smith’s research interests center on ecological and physiological characteristics of organisms, populations, and environments that contribute to contaminant exposure and physiological and population-level responses to contaminant exposure. Address correspondence to Kendall at TIEHH, Box 41163, Lubbock, TX 79409-1163 or
[email protected].
References
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The field of wildlife toxicology continues to grow because the need for data to address the response of wildlife to contaminants has become increasingly important to the general public, regulatory agencies, and even the scientific community. As our analytical, biochemical, and molecular techniques continue to improve, we become more proficient in assessing the health and status of wildlife populations in their natural environment. We predict that the field of wildlife toxicology will continue to make dramatic advances during the next 20 years because our health is integrally connected to the health of the environment.
Acknowledgment The authors would like to dedicate this manuscript to the memory of Patrick F. Scanlon, Professor of Wildlife Sciences, Department of Fisheries and Wildlife Sciences, at Virginia Polytechnic Institute and State University, Blacksburg, Virginia, who passed away March 4, 2003. Prof. Scanlon mentored many graduate students in wildlife physiology and toxicology, in-
(1) Kendall, R. J. Environ. Sci. Technol. 1982, 16, 448A–453A. (2) Kendall, R. J.; et al. Casarett & Doull’s Toxicology: The Basic Science of Poisons, 6th ed.; Klassen, C. C., Ed.; McGrawHill: New York, 2001; Chapter 29. (3) Kendall, R. J., Lacher, T. E., Jr., Eds. Wildlife Toxicology and Population Modeling; SETAC Special Publication Series. Lewis Publishers: Chelsea, MI, 1994. (4) Giles, R. H., Jr. Wildlife Management; W. H. Freeman: New York, 1978. (5) Kendall, R. J. Environ. Sci. Technol. 1992, 26, 239–245. (6) Ratcliffe, D. A. Nature 1967, 215, 208–210. (7) Carson, R. Silent Spring; Houghton-Mifflin: Boston, 1962. (8) Aulerich, R. J.; Ringer, R. K. Arch. Environ. Contam. Toxicol. 1977, 6, 279–292. (9) Framework for Ecological Risk Assessment; US EPA/630/ R-92/001; U.S. Environmental Protection Agency; U.S. Government Printing Office: Washington, DC, 1992. (10) Guidelines for Ecological Risk Assessment. Fed. Regist. 63, 26,846–26,924. (11) Kendall, R. J.; Akerman, J. Environ. Toxicol. Chem. 1992, 11, 1727–1749. (12) Houseknecht, C. R. A Review of Ecological Assessment Case Studies From a Risk Perspective; EPA/630/R-92-0051993; U.S. Environmental Protection Agency; U.S. Government Printing Office: Washington, DC, 1993; Vol. 3. (13) Colborn, T.; Dumanoski, D.; Myers, J. P. Our Stolen Future Plume: New York, 1996. (14) Guillette, L. J., Jr.; Gross, T. S.; Masson, G. R.; Matter, J. M.; Percival, H. F.; Woodward, A. R. Environ. Health Perspect. 1994, 102, 680–688. (15) Kendall, R. J.; Dickerson, R. L.; Giesy, J. P. Suk, W. A. Principles and Processes for Evaluating Endocrine Disruption in Wildlife; Society of Environmental Toxicology and Chemistry (SETAC) Press: Pensacola, FL, 1998. (16) Smith, P. N.; Theodorakis, C. W.; Anderson, T. A.; Kendall, R. J. Ecotoxicology. 2001, 10, 305–313. (17) Goleman,W. L.; Urquidi, L. J.; Anderson, T. A.; Kendall, R. J.; Smith, E. E.; Carr, J. A. Environ. Toxicol. Chem. 2002, 21, 424–430. (18) Goleman, W. L.; Carr, J. A.; Anderson, T. A. Environ. Toxicol. Chem. 2002, 21, 590–597. (19) Campbell, K. R.; Campbell, T. S. Environ. Toxicol. Chem. 2002, 21, 894–898. (20) U.S. Fish and Wildlife, Department of Environmental Quality, Amphibian Declines and Deformities; http:// contaminants.fws.gov/Issues/Amphibians.cfm. (21) Sparling, D., Linder, G., Bishop, C., Eds.; Ecotoxicology of Amphibians and Reptiles; Society of Environmental Toxicology and Chemistry: Pensacola, FL, 2000. (22) Ellington, J. J.; Evans, J. J. J. Chromotogr. A. 2000, 898, 193–199. (23) Anderson, T. A.; Wu, T. H. Bull. Environ. Contam. Toxicol. 2002, 68, 684–691. (24) Dudley, J. P.; Woodford, M. H. Bioscience 2002, 52, 583–592. MAY 1, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY ■ 183 A
