AQUATIC TOXICITY TESTS FOR THE CONTROL OF EFFLUENT DISCHARGES IN THE UK - THE INFLUENCE OF TEST PRECISION

The initiative by the River Purification Boards (RPBs), National River s Authority (NRA) and Her Majesty's Inspectorate of Pollution (HMIP) t o control certain complex and toxic effluent discharges by direct toxi city assessment places great emphasis on the use of aquatic toxicity t ests, Like all biological and analytical measurements, determinations of toxicity exhibit variability, When setting 'Toxicity-based Consents ' (TBCs) and monitoring for compliance with such consents, it is impor tant to understand and if possible control this variability. The impli cations of toxicity test variability for the way TBCs may be set and m onitored are discussed; including a consideration of monitoring consen ts based on a single exposure concentration (limit) test and procedure s involving a range of exposure concentrations (concentration-response test). We also review the precision of data arising from acute aquati c toxicity test methods which may be used for the control and monitori ng of complex effluents in the UK. This includes the variability that occurs when repeated tests are carried out on different occasions with in the same laboratory (repeatability) and also within different labor atories (reproducibility). Particular attention is given to acute test s using Daphnia magna, the only method for which there is a large amou nt of published information on the precision of toxicity data.