Chronic toxicity of ethyl parathion and isobutoxyethanol ester of 2,4-dichlorophenoxyacetic acid to estuarine juvenile and adult crabs.

The chronic toxicity of ethyl parathion and isobutoxyethanol ester of 2,4-dichlorophenoxyacetic acid was determined for the crabs Uca uruguayensis and Chasmagnathus granulata collected in Argentina in 1989. Parathion toxicity was more time-dependent than 2,4-D. Four-week LC50 values for parathion were size and species independent, as expected under chronic exposure conditions. As shown in previous studies, the opposite was noted when crabs were exposed to acute exposure. Parathion was much more toxic than 2,4-D, in all cases. Also, parathion exerted a very much lower chronic lethal effect than other pesticides at a fraction of the respective acute LC50. A different susceptibility between sexes was found in C. granulata exposed to 2,4-D.