Sediment toxicity testing using large water-sediment ratios: an alternative to water renewal

Deterioration of overlying water quality during toxicity tests with benthic invertebrates is a serious problem with some sediments. One solution is pe riodic renewal of overlying water. However, this is either labour intensive or requires construction and maintenance of special equipment. Furthermore , water renewal has the potential for flushing toxic chemicals out of the t est chamber and establishes nonequilibrium conditions between the water and sediment. An alternative is testing under static conditions using atypical test Vessels (e.g. Imhoff settling canes) with a large water volume (11) o verlaying a much smaller sediment volume (e.g. 15 mi). This results in dram atic improvement of overlying water quality compared to standard static tox icity tests. Compared to water renewal, the test method is much simpler, al l toxic substances leached from the sediment are retained in the test vesse l, and contaminant concentrations in water and sediment have more time to e quilibrate. Chronic sediment toxicity tests (10-28 days) have been conducte d successfully under these conditions with Chironomus riparius, Hexagenia s p., Hyalella azteca and Tubifex tubifex. (C) 1999 Elsevier Science Ltd. All rights reserved.