Clyde E. Goulden

The Clean Water Act of 1977 states, ''It is the national policy that the discharge of toxic pollutants in toxic amounts be prohibited" (Peltier and Weber, 1985, p. 1). Thorough assurance that this goal is met would require complete chemical profiles of every effluent; knowledge of the sensitivity of all potentially affected organisms to all chemicals in effluents, including both direct toxic effects and indirect effects, such as the effects of toxins on forage species; and an understanding of all synergistic interactions between compounds in effluents. It is not feasible to obtain such comprehensive information.

The U.S. Environmental Protection Agency (EPA) concluded that a cost-effective alternative approach would be to measure effluent toxicity by exposing aquatic organisms to effluents in "bioassays." Bioassays measure "the potency of any stimulus, physical, chemical, or biological, physiological or psychological, by means of the reactions that it produces in living matter" (Finney, 1952a, p. 1). The rationale is that through bioassays, test organisms reveal whether an effluent is toxic. This paper describes the development of the bioassay approach and evaluates whether through its use ecosystems can be sufficiently protected from toxic materials.

The basic design of bioassays was developed in the nineteenth century, but test species were used as an assay of exposure to some stimulus well before that time. Finney (1952b) suggests that the basic principles of bioassays are found in early texts and quotes an example: