Seasonal changes in acute toxicity of cadmium to amphipod Corophium volutator

In vivo bioassays are frequently used to assess the ecotoxicological risks of contaminated sediments. For quality assurance purposes, these bioassays are accompanied by reference toxicity tests. For the bioassay with Corophiu m volutator, this reference toxicity test is an acute water-phase test with cadmium. Approximately 80 water-phase tests were conducted in the period 1 991-1998. Corophium volutator shows a significant seasonal variation in res ponse to cadmium, with a high LC50 in the winter period and a low LC50 in t he summer period. Same variation can be found if Corophium is held in the l aboratory instead of freshly collected in the field and if synthetic water is used instead of natural filtered seawater. The observed seasonal variati on is not caused by the fact that the organisms are collected in the field or by the variation in seawater used for the water-phase tests.