Acute toxicity of the insecticides endosulfan, chlorpyrifos, and malathion to the epibenthic estuarine amphipod Gammarus palustris (Bousfield)

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Abstract
The acute effects of three commonly used pesticides were evaluated using the epibenthic, estuarine amphipod Gammarus palustris. This species is most abundant in intertidal salt marshes and has a cosmopolitan distribution. Laboratory bioassays were conducted under static and static‐renewal conditions. Median lethal concentrations of endosulfan and chlorpyrifos were much lower at all exposure time points than malathion in the static exposures (e.g., 96‐h LC50 = 0.43 μg/L for endosulfan, 0.30 μg/L for chlorpyrifos, and 4.65 μg/L for malathion). A similar pattern of toxicity was noted in the static‐renewal exposures, with statistically significant differences in toxicity observed between the static versus static‐renewal exposures for endosulfan at the 48‐h time point, at none of the time points for chlorpyrifos, and at all three time points (48, 72, and 96 h) for malathion. The sensitivity of G. palustris was generally comparable to LC50 values found in the literature for other crustaceans, particularly for the 96‐h exposures. Evaluation of field contaminant data, compared with the laboratory toxicity data, indicated that this species could serve as a useful bioindicator of contaminant stress in salt marsh habitats.