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2F - Site Specific Testing (MOP/99) Predicting receiving water impacts: laboratory single-species tests and in-situ bioassays. Wilding, Joanna1, Maltby, Lorraine1, 1 The University of Sheffield, Sheffield, South Yorkshire, UK ABSTRACT- One use of laboratory single-species toxicity tests is the assessment of effluent toxicity. Through using biological responses to measure effluent toxicity, contaminant interactions or unidentified sources of toxicity can be addressed. Single-species toxicity tests directly monitor the biological damage an effluent can cause to an organism, and have been utilised in predicting the impact an effluent may have on aquatic populations, community structure and ecosystem function. However, the extrapolation between results of single-species laboratory tests and receiving water impacts has previously focused on benthic macroinvertebrate community structure in effluent dominated river systems. Here we focus on standardised laboratory toxicity tests and incorporate the use of in-situ bioassays alongside macroinvertebrate community structure to address receiving water impact. The predictive abilities of Daphnia magna effluent and ambient toxicity tests were investigated at ten watercourses where receiving water effluent concentrations ranged from 17 to 100%. Three in-situ bioassays (Alnus glutinosa decomposition, Gammarus pulex and D. magna feeding inhibition) were used as multiple lines of evidence to compare water quality and ecosystem function, upstream and downstream of an effluent discharge. The benthic macroinvertebrate community was also sampled. Results of these instream studies were compared to predictions of ecosystem impairment, made from effluent and ambient toxicity tests using D. magna lethal (immobilisation) and sublethal (feeding rate) responses. Predictions made from D. magna lethality tests failed to predict statistically significant changes in receiving water quality and ecosystem function, or alterations in macroinvertebrate community structure. However, D. magna sublethal responses were consistent predictors of ecosystem impairment. The importance of toxicity test endpoint sensitivity and the use of in-situ bioassays when addressing receiving water impact is discussed. Key words: Gammarus pulex, whole effluent toxicity, macroinvertebrates, Daphnia magna |
