Toxicity of the insecticide methoxychlor to the Dungeness crab Cancer magister

Abstract

The toxicity of methoxychlor, determined in acute and chronic studies using larval, juvenile, and adult stages of the Dungeness crab, Cancer magister Dana, was inversely related to the age of the crabs after hatching and increased with the length of exposure. The 96-h LC₅₀'s for zoeae, juveniles, and adults were 0.42, 5.10, and 130 μg/l, respectively. Levels causing decreased survival of these same stages during exposures of more than 60 days were 0.05, 0.40, and 4.0 μg/l, respectively. Hatching of eggs was not adversely affected by methoxychlor concentrations up to 10 μg/l, and molting from prezoeae to zoeae was reduced only 30% from controls at the latter exposure concentration. Methoxychlor concentrations of 0.05 and 4.0 μg/l delayed motting of larval and juvenile crabs, respectively, and this delay was as much as 10 days for the juveniles. Sensitivity of adult and juvenile crabs to methoxychlor increased during ecdysis. In uptake experiments, juvenile crabs concentrated methoxychlor more rapidly than did adults. Juveniles exposed to 2.0 μg/l of methoxychlor and adults exposed to 1.8 and 7.5 μg/l had whole body methoxychlor concentrations after 12 days of 0.88, 0.10, and 0.51 mg/kg, respectively. Loss of the pesticide from adult crabs was rapid, and was 95% complete after 15 days of depuration. Concentrations of methoxychlor in individual tissues were found to be highest in the exoskeleton, gill, and hepatopancreas, in declining order, with less than a two-fold difference among these tissues. About 81% of the methoxychlor measured in whole body samples was associated with the exoskeleton, but it is not known whether or not the pesticide was transported through the culticle to internal tissues.