Ambient Toxicity Monitoring Program

Environmental Protection Agency (EPA) Region 6 initiated an effluent toxicity testing program in 1981. The Regional laboratory conducted standard tests by evaluating the response of organisms exposed to municipal and industrial effluents. Besides detection of effluent toxicity, results have been used to evaluate the sensitivity of test methods, and the relative toxicity of standard industrial categories (Crocker et al. 1989). Although useful from a regulatory standpoint, effluent testing is of limited value for water quality assessment, because of the inability to identify potential synergistic or antagonistic effects of multiple pollutant sources. Also, both point and nonpoint sources, such as agricultural and urban runoff, hazardous waste sites, and municipal and industrial discharges, may be sources of toxic pollutants.

Ambient toxicity testing, as a water quality assessment tool, complements chemical-based monitoring with the direct assessment of the effects of ambient water or sediment on test species selected as surrogates for indigenous species. Investigators have documented the ability to predict instream aquatic community response based on results of effluent and/or ambient toxicity testing (Bastian et al. 1990; Birge et al. 1989; Eagleson 1990; Kolbe 1995; Mount et al. 1985a-b and 1986a-d).

Biosurveys provide a direct assessment of aquatic community health; however, aquatic community impairment resulting from conventional pollutants or habitat limitations may overshadow potential effects of toxicants or confound interpretation of assessment results. Laboratory toxicity testing allows observation of water quality effects alone, under controlled laboratory conditions. U.S. EPA (1991) and Mount (1994) provide more extensive information on the strengths and limitations of chemical testing, toxicity testing, and biosurveys.

In 1990, the Region 6 Ambient Toxicity Testing Program was initiated to encourage State, Tribal, and local agencies to integrate ambient toxicity testing into water quality assessments and acquire testing capabilities, to assess potential toxicity in Region 6 waterbodies, and to evaluate the effectiveness of implemented toxicity control measures. Samples are tested by the Region 6 Houston Laboratory. Lab personnel forward results to the Region 6 Water Quality Protection Division and the collecting agency.

Over 2,000 tests have been conducted on samples from over 250 sites. This report will summarize data collected to date and inform potential data users of the existence and capabilities of the database.