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Cite this document
One of the key assumptions implicit in developing national water quality criteria is that the data base used to derive the criteria includes data from a reasonable cross section of the aquatic communities to be protected. This requires testing not only a large number of species but those species that represent a variety of taxonomic and functional groups. Implicit also is the assumption that the species tested represent the full range of sensitivities expected in the population as a whole and that neither overly sensitive nor resistant species are unduly represented in the data base. Examination of the national toxicity data base indicated that the toxicity data which it contains does not meet these assumptions because (for 21 priority pollutants) 40% of the data are on a few regularly tested species such as bluegill and fathead minnow and one quarter of the data are on only two families. Daphnidae and Salmonidae. Furthermore, for many chemicals, many of the species that have been tested are restricted to the northeastern and/or upper midwest portions of the United States. The problem of nonrepresentative testing is further complicated by the fact that toxicity data for some of the commonly tested species (e.g., rainbow trout) are often replicated and verified by several investigators, whereas data on other species are not. This is particularly true of the toxicologically sensitive species. Finally, the evidence suggests that sensitive species may be overrepresented in the national toxicity data base.
The net result is that we now have a great deal of data about a few species, but little or no data about the vast majority of species. Nor do the data available necessarily represent a reasonable cross section, based on sensitivities or ecological importance. The above assertions will be supported using examples from the national data base and from data bases on individual chemicals. This indicates a need for information on a wider variety of organisms in order for the national data base to be representative of the full range of sensitivities expected in the population as a whole. While it is recognized that it will not be possible to conduct tests on all species, the underlying distribution of the data base should be understood before appropriate statistical methods can be developed to derive national water quality criteria for the protection of aquatic life. This may require some testing of representative species from sensitive and insensitive groups. Additional implications of the actual distribution of the national toxicity data base will be discussed.
aquatic toxicology, water quality criteria, methodology, data base, priority pollutants, national guidelines
Director, Midwest Regional Office, EA Engineering, Science and Technology, Northbrook, Ill
Director, Environmental Toxicology, EA Engineering, Science and Technology, Sparks, Md
ChairmanBiologist, Water Quality Subcommittee, Utility Water Act GroupDuke Power Company, Charlotte, NC