Critical internal and aqueous lethal concentrations of chlorobenzenes with the crab Portunus pelagicus (L).

The toxicity of a series of chlorobenzenes to juvenile crabs Portunus pelagicus (L) was investigated. These compounds are lipophilic with a strong capacity to bioconcentrate. An increase in toxicity during molting was observed. There was also an increase in toxicity with increasing log Kow and molecular weight, which was best described using nonlinear regression equations relating LC50 and log Kow. Chlorobenzene residues in animals that died from the exposures were measured and the critical internal lethal concentration and volume fraction were estimated for each compound. A mean concentration value of 3.24 mumol g-1 on a wet weight basis and a mean volume fraction of 0.140 cm3 toxicant cm-3 tissue lipid were determined at time zero. However, these values decreased with increasing periods of exposure according to first-order kinetics with a constant rate of 0.0287 hr-1. This indicates that toxicity is a function of both concentration in the tissues and the period during which it has been present. The critical internal lethal concentrations measured in this study were not consistent with the constant critical internal concentration/critical volume fraction hypotheses.