The Myth of the Most Sensitive SpeciesMultispecies testing can provide valuable evidence for protecting the environment

F or the past 30 years, aquatic toxicologists have been engrossed in the search for "the most sensitive species." If one could find this most sensitive species and then use it to set standards for toxic materials and other stressors in natural systems, presumably all other species and all other activities at higher levels of biological organization could be protected. Weis (1985 and see box, opposite) recently restated this notion, commenting on an article by Kimball and Levin (1985) espousing the need for tests at higher levels of biological organization than single species. Although single species toxicity tests form the backbone of our environmental safety testing, I contend that multispecies testing can provide valuable additional evidence for protecting the environment. A number of assumptions are inherent in the most sensitive species approach, although these are not always explicitly stated: