Toxicity of the organophosphate pesticides chlorpyrifos and dimethoate to Neomysis integer (Crustacea: Mysidacea)

The United States Environmental Protection Agency routinely use the sub-tropical mysid Americamysis (=Mysidopsis) bahia (Peracarida: Mysidacea) in laboratory testing to measure the toxicity of contaminants and to assess the potential hazards of toxic chemicals to the natural aquatic environment. The use of A. bahia in laboratory toxicity testing has extended to Europe, however, there is increasing interest in using indigenous species for predicting toxicity hazards to European waters. Neomysis integer (Leach) is the most common member of the hyperbenthic fauna of Western European estuaries and has been proposed as an alternative to the standard American species (A. bahia) for toxicity testing. Adult N. integer were exposed to chlorpyrifos and dimethoate (both widely used organophosphate pesticides) in flow-through and semi-static acute toxicity tests. Neomysis integer was more sensitive to chlorpyrifos (96 h LC50 of 0.13 μg chlorpyrifos l−1) than dimethoate (96 h LC50 of 540 μg dimethoate l−1). Juvenile N. integer, collected within 24 h of release from ovigerous females, were equally tolerant to chlorpyrifos as adult mysids (96 h LC50 of 0.19 μg chlorpyrifos l−1). Gas chromatographic analysis of chlorpyrifos in the water samples revealed that considerable degradation or loss (>50%) occurred within 24 h in the semi-static exposure vessels, highlighting the advantages of flow-through testing facilities. Although the 96 h LC50 for chlorpyrifos was higher for N. integer than for A. bahia (e.g. 0.035 μg chlorpyrifos l−1), it was comparable with those of other frequently-used test species (0.1–6.0 μg chlorpyrifos l−1). The results support the use of N. integer as an alternative to A. bahia for the testing of toxicants and the evaluation of toxic contamination events in European estuaries.