Using single-species toxicity tests, community-level responses and toxicity identification evaluations to investigate effluent impacts

Whole effluent toxicity (WET) tests are increasingly used to monitor compli ance of consented discharges, but few studies have related toxicity measure d using WET tests to receiving water impacts. Here we adopt a four-stage pr ocedure to investigate the toxicity and biological impact of a point source discharge and to identify the major toxicants. In stage 1, standard WET te sts were employed to determine the toxicity of the effluent. This was then followed by an assessment of receiving water toxicity using in situ deploym ent of indigenous (Gammarus pulex) and standard (Daphnia magna) test specie s. The third stage involved the use of biological survey techniques to asse ss the impact of the discharge on the structure and functioning of the bent hic macroinvertebrate community. In stage 4, toxicity identification evalua tions (TIE) were used to identify toxic components in the effluent. Receivi ng-water toxicity and ecological impact detected downstream of the discharg e were consistent with the results of WET tests performed on the effluent. Downstream of the discharge, there was a reduction in D. magna survival, in G. pulex survival and feeding rate, in detritus processing, and in biotic indices based on macroinvertebrate community structure. The TIE studies sug gested that chlorine was the principal toxicant in the effluent.