RELATION BETWEEN TOXICITY AND ACCUMULATION OF CHLOROPHENOLS AT VARIOUS PH, AND THEIR ABSORPTION MECHANISM IN FISH

The relation between the acute toxicity and accumulation of 12 chlorop henols in goldfish exposed to media containing the chemicals at Variou s pH, and also the transport mechanism of chlorophenols from the surro unding water in the fish were investigated. Both the acute toxicity an d accumulation of chlorophenols increased with increasing number of su bstituted chlorine atoms, although the magnitude of their increase dec reased with increasing pH. For each chlorophenol, both the toxicity an d the amount accumulated in the surviving fish was almost unchanged in the range of pH < pK(a), but abruptly decreased with increasing media pH in the range of pH > pK(a). On the other hand, the amount found in the dead fish was little dependent on the pH of media. The distributi on ratio (K) between the medium (compartment I) and fish body (compart ment II) was calculated on the basis of the assumption that only the u ndissociated form migrates between the two compartments by diffusion a nd that the ratio of the concentration of the undissociated form in co mpartment I to that in compartment II is proportional to the partition coefficients in 1-octanol-water and n-heptane-water systems. A good c orrelation was observed between log bioconcentration ratio (BCR) and l og K value calculated by using the partition coefficient in the 1-octa nol-water system. From these results, it is concluded that the transfe r of chlorophenols from media to fish body, in which the formation of intermolecular hydrogen bond between the hydroxyl group in the chemica ls and the components in gill membranes plays an important role, is ma inly caused by the passive diffusion of the undissociated form through the membranes, and the concentration of the chemicals in the fish bod y does not readily reach a lethal level with increasing pH of the medi um owing to the increased conversion of the undissociated form to the dissociated form, resulting in the reduction of the toxicity of chloro phenols in the fish. However, the BCR was a little higher than that es timated from the concentration of the undissociated form in the media. The reason was presumed that the pH near the outer surface of the gil l membranes is lower than that of the media.