Assessing Contaminant Sensitivity of Endangered and Threatened Species: Toxicant Classes

Under the Federal Insecticide, Fungicide and Rodenticide Act, the Toxic Substances Control Act and the Clean Water Act, the U.S. Environmental Protection Agency (EPA) is charged with determining if the manufacture, use, or disposal of a chemical will present an unreasonable risk of harm to the environment. Typically, management decisions are based on protecting populations of organisms. However, the Endangered Species Act requires that, in some cases, managers must estimate the take of individuals to determine if the loss of individuals might adversely affect a population of an endangered or threatened (listed) species. The most direct assessment would be to determine the sensitivity of a listed species to a particular contaminant or perturbation. However, this direct approach would be time consuming and expensive because it might require development of organism culturing and handling procedures, some species may not be amenable to culture, there might be multiple species to be considered, and would be contaminant specific. It is not possible to test all listed species that may need protection from environmental contaminants. Therefore, decisions need to be made for listed species using toxicity data obtained from standard test procedures and using surrogate organisms typically tested in laboratory toxicity assessment (e.g., rainbow trout Oncorhynchus mykiss, fathead minnow Pimephales promelas, and the cladoceran Ceriodaphnia dubia). These surrogate species are easily tested using standardized methods; however, there is concern that these species or procedures may not adequately represent populations of listed species. By evaluating the sensitivity for a number of listed species, it is possible to make generalizations regarding the protection afforded listed species through standard regulatory programs. This research project had two objectives: (1) determine the relative sensitivity to contaminants of listed species using standard acute toxicity tests; and (2) determine the degree of protection afforded listed fish species through the use of standard species used in whole effluent toxicity tests. Previous cooperative research conducted between the EPA and U.S. Geological Survey primarily evaluated the similarity in response to five chemicals with different modes of actions (carbaryl, copper, 4-nonylphenol, pentachlorophenol and permethrin) between surrogate (rainbow trout and fathead minnows) and listed species within the same taxonomic family (Salmonidae, Cyprinidae) using standard toxicity tests. The present study expands this data base by testing five additional species with these five chemicals. Species were listed either by the U.S. Fish and Wildlife Service (FWS) or state agencies or were species identified as surrogates in FWS Recovery Plans. Organisms included: (1) the Family Percidae fountain darter (Etheostoma rubrum, Federally listed), greenthroat darter (Etheostoma lepidum, state listed - Texas); (2) the Family Acipenseridae, shovelnose sturgeon (Scaphirhynchus platorynchus, identified as surrogate for the Federally listed pallid sturgeon - Scaphirhynchus albus); (3) the Family Poeciliidae, Gila topminnow(Poeciliopsis occidentalis, Federally listed); and (4) the Family Bufonidae, boreal toad tadpoles (Bufo boreas, state listed - Colorado). The data we have generated indicated that in 96-h acute toxicity tests, if rainbow trout is used as a test species, a species typically used in pesticide registration or water quality criteria derivation, those procedures which protect the rainbow trout would likely be protective of most listed aquatic fish species. If a safety factor is needed to estimate 96-h LC50s for listed fish species, our data indicates that 0.5 would be a conservative estimator. Also, if EPA water quality criteria are recalculated by eliminating certain species from the data set, such as rainbow trout, then listed fish species might not be adequately protected.