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Issues in Risk Assessment
use and release rates rather than on monitoring or modeling studies. Risk characterization was only qualitative; it did not address such issues as the number and distribution of species that were vulnerable, or the degree of damage to the shellfish industry. Risk management actions were based on the demonstrable existence of hazard, on societal concern for the vulnerable species, and on the ready availability of alternative antifouling agents.
Some workshop participants were critical of the risk assessment approach adopted by Congress and state regulatory agencies. No attempt was made to plan and execute a formal risk assessment. Risk identification was based primarily on data on nonnative species. The Eastern oyster and blue crab, the species putatively at greatest risk, have been found to be less sensitive. Regulatory responses were based on findings of high environmental concentrations of TBT in yacht harbors and marinas, rather than in ecologically important regions such as breeding grounds. The central issue is whether a safe loading capacity (environmental concentration) of TBT for nontarget organisms can be defined, given substantially reduced rates of input. Recent information on fate and persistence, chronic toxicity, and dose-response relationships could support a more quantitative risk assessment with the possibility of more or less stringent restrictions.
CASE STUDY 2:Ecological Risk Assessment for Terrestrial Wildlife Exposed to Agricultural Chemicals
R. J. Kendall, Clemson University
The science of ecological risk assessment for exposure of terrestrial wildlife to agricultural chemicals has advanced rapidly during the 1980s. EPA requires detailed assessments of the toxicity and environmental fate of chemicals proposed for agricultural use (EPA, 1982; Fite et al., 1988). Performance of an ecological risk assessment requires data from several disciplines: analytical toxicology, environmental chemistry, biochemical toxicology, ecotoxicology, and wildlife ecology.
Addressing the ecological risks associated with the use of an agricultural chemical involves a complex array of laboratory and field studies—in essence, a research program. This paper provides examples of
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Issues in Risk Assessment
integrated field and laboratory research programs, such as The Institute for Wildlife and Environmental Toxicology (TIWET) at Clemson University. Preliminary toxicological and biochemical evaluations include measurements of acute toxicity (LC50 and LD50), toxicokinetics, and observations of wildlife in areas of field trials. Assessment of reproductive toxicity includes studies with various birds and other wildlife, particularly European starlings that nest at high densities in established nest boxes; these studies include measurements of embryo and nestling survival, postfledgling survival, behavior, diet, and residue chemistry (Kendall et al., 1989). Nonlethal assessment methods include measurement of plasma cholinesterase activity associated with organophosphate pesticide exposures (Hooper et al., 1989). A wide variety of birds, mammals, and invertebrates have been used in these studies.
End points evaluated in wildlife toxicological studies include mortality, reproductive success, physiological and biochemical changes, enzyme impacts, immunological impairment, hormonal changes, mutagenesis and carcinogenesis, behavioral changes, and residues of parent compounds and metabolites (Kendall, 1992).
The paper includes a case history of a comparative evaluation of Carbofuran and Terbufos as granular insecticides for control of corn rootworms. Carbofuran has been responsible for many incidents of wildlife poisoning and is recognized as being very hazardous to wildlife. In contrast, although Terbufos is highly toxic to wildlife in laboratory studies, exposure of wildlife under field conditions appears generally to be relatively low, and widespread mortality is not evident. Field studies of Terbufos conducted by TIWET might be the only ones conducted to date that satisfy EPA's requirements for a Level 2 field study, a more quantitative assessment of the magnitude of the effects of a pesticide than the qualitative Level 1 studies. (Level 2 studies are performed when toxicity tests and use patterns suggest a detailed study is warranted.) Data generated in those studies support an ecological risk assessment for Terbufos that is reported in the paper. However, the research program on Terbufos represents many years of effort with integration of laboratory and field research to achieve a full-scale level 2 study in just one geographic area on one crop. Ecological modeling techniques will be needed to generalize the results to other chemicals or to other situations.
