AMBIENT BIOASSAYS FOR ASSESSING WATER-QUALITY CONDITIONS IN RECEIVINGSTREAMS

The purpose of this paper is to show how short-term laboratory tests, conducted according to US Environmental Protection Agency (EPA) proced ures, can be used effectively to assess water-quality conditions in st reams or rivers that receive pollutants from industry or municipal or agricultural areas. Standardized, short-term tests with fish, aquatic invertebrates or algae are commonly used to estimate the acute or chro nic toxicity of wastewaters; this is referred to as effluent testing. The methods used for testing effluents also can be used to assess wate r quality in receiving streams: in this application, the procedures ar e referred to as ambient testing. Despite similarity in methods, the m ajor objective of effluent testing differs importantly from that of am bient testing. In effluent testing, the key objective is to determine how toxic an effluent is; in ambient testing, the main objective usual ly is that of determining if the water at a site is toxic. This differ ence is subtle but very important: it shapes the strategy for cost-eff ective ambient testing, and determines the framework for effective sta tistical analysis and interpretation of ambient toxicity test results. Specific case-study examples are provided demonstrating the kinds of information that can be extracted from ambient toxicity testing by use of different statistical methods, including analysis of variance, con tingency-table analysis, and two types of multivariate procedures (pri ncipal components analysis and logistic regression). Examples also are given supporting the idea that an effective ambient testing programme should be long-term, and contain a diagnostic-testing component analo gous to the toxicity identification procedures used to supplement effl uent-testing programmes. Recommendations derived as 'lessons learned' from large-scale ambient toxicity testing programmes for receiving str eams at Department of Energy facilities include: (1) testing more freq uently with one species (preferably Ceriodaphnia) generally is more ef fective, in terms of information gained per dollar spent, than testing less frequently with two or more species; (2) use five or more sites per test period, plus two or more reference sites, whenever possible; (3) use four to six test periods per year; and (4) use diagnostic test ing to supplement the ambient-testing programme. Various laboratory an d in situ methods for environmental assessment are now under developme nt, but these methods probably will not gain acceptance for use in reg ulatory situations for many years. Rapid growth in need for ecological risk assessments outstrips the rate at which new test procedures are approved for regulatory purposes. Thus, laboratory tests for estimatin g possible environmental impacts of toxic or disruptive pollutants are likely to be used more frequently during the next decade.