BIOLOGICAL INTERFERENCE IN THE WHOLE EFFLUENT TOXICITY PROTOCOL: MEASUREMENT, ELIMINATION AND IMPACT ON PERMIT IMPLEMENTATION

Whole Effluent Toxicity test failures, even if not caused by toxicity, have a potential regulatory impact on wastewater and industrial communities; biological interference has been identified as one factor that may cause such a false-positive indication of toxicity. As a result, a method has been developed to identify this effect and unmask a toxic response if present. The method exposes a split sample of effluent water to UV radiation; both samples are subsequently examined for toxicity using EPA's short term method for chronic toxicity. If a significant toxicity end-point is established by the Chronic WET test, biological interference can be identified by examining the concentration response from both samples. If a significant concentration response is eliminated by the UV treatment, a reasonable conclusion is that the toxicity end-point was a false positive indication of toxicity produced by biological interference.After considerable review of the research findings, a facility permit was modified, and approved by the Colorado State regulatory agency, to include a review of (1) WET concentration response data and (2) the results of UV treatment on a split sample prior to making a conclusion that a WET test end-point failure is confirmed.