Evaluation of an algal bioassay cage-culture turbidostat method for the toxicity assessment of effluents

The effectiveness of a computer-controlled cage-culture turbidostat (CCT) as an algal test was evaluated in comparison with three widely used aquatic toxicity test methods for the toxicity assessment of industrial effluents. Effluent samples were collected from two major industrial outfalls discharging to the Firth of Clyde, Scotland: Site A (Effluents 1 and 2) and Site B (Effluent 3). These samples were collected as part of the routine monitoring programme of the Clyde River Purification Board (since subsumed as part of the Scottish Environment Protection Agency). Each sample was tested for toxicity using a variety of ecotoxicological methods including the CCT, algal growth inhibition toxicity test (AGITT), oyster embryo–larval toxicity (OEL) test and Microtox™. The two algal bioassays, the CCT and AGITT, indicated the same ranking of effluent toxicity, in descending order 2, 1, 3. The OEL test was found to be the most sensitive method and Microtox™ the least sensitive of the tests used. The CCT was found to be easy to run and operate on a day-to-day basis. However, a limit to the number of assays that could be carried out in each experimental run, the time taken for each run and inability to perform rigorous analysis on the data make the CCT unsuitable for regulatory purposes in its present form.