Ambient Toxicity Monitoring Program

Ambient toxicity testing, as a water quality assessment tool, complements chemical monitoring by allowing observation of toxic effects on laboratory test species selected as surrogates for indigenous species. Potential sources of toxicity include a variety of nonpoint and point sources, agricultural and urban runoff, hazardous waste sites, and municipal and industrial discharges. Biosurveys also characterize effects of toxicity, although aquatic community impairment resulting from conventional pollutants or habitat degradation may overshadow effects of toxicants. Laboratory toxicity testing also offers the ability to observe reproductive or teratogenic effects that may not be apparent from a community-level biosurvey.

The Region 6 ambient toxicity monitoring program was established in 1990 to encourage States to integrate ambient toxicity testing into water quality assessments, to encourage States to acquire testing capabilities, to assess potential toxicity in Region 6 waterbodies, and to evaluate the effectiveness of implemented toxicity control measures. States, Tribes, and local agencies participate in the program by periodically collecting samples at monitoring sites. Samples are tested in the Region 6 Houston Laboratory using standard methods. Lab personnel forward results to the Region 6 Water Quality Protection Division and the collecting agency. To date, more than 2,000 tests have been conducted on samples collected from 250 stations.

Regional staff recommend quarterly collection of water samples and biannual collection of sediment for a minimum of one year per station. Continued monitoring is recommended for waterbodies that exhibit toxic effects. The database also includes the results of one-time sample collections made during special studies. This report summarizes data collected to date and informs potential data users of the existence and capabilities of the program and database. The validation of toxicity test results using in situ toxicity testing and biosurveys for selected waterbodies are also discussed.

About one-fourth of the stations sampled on multiple dates have exhibited recurrent lethal or sublethal toxic effects. This percentage is high, because investigators often target waterbodies with known or suspected water quality problems.

The primary objective of the program is to identify waterbodies that may be affected by toxicity; therefore, "toxic effects" include any test endpoint that differs significantly from the endpoint observed in a laboratory control. Ambient water samples are analyzed without dilution, based on the assumption that this approach best represents instream conditions. Waterbodies that have exhibited recurrent toxicity are candidates for more intensive assessments, aimed at confirming the occurrence of toxic conditions or aquatic life use impairment, and for determining sources or causes of toxicity.

The ambient toxicity monitoring program has provided a useful assessment tool for the identification of waterbodies with the potential for aquatic life impairment. Responses from participating agencies suggest that interest in the program remains high. Requests for increased resources for testing and additional testing capabilities (bulk sediment & marine tests) have been received. Opportunities for aquiring these capabilities should be explored.