Effects of pH on the acute toxicity and uptake of [14C]pentachlorophenol in the midge, Chironomus riparius.

The acute toxicity of pentachlorophenol (PCP) was determined at pH levels 4, 6, 9 to the midge, Chironomus riparius, with the findings that PCP is of greatest toxicity at pH 4 and of least toxicity at pH 9. This differential toxicity is attributable to variations in uptake levels at the respective pH levels. At pH 4, PCP is fully protonated and therefore highly lipophilic. The amount of [14C]PCP present in the midges at 24 hr is thus highest at pH 4. Conversely, at pH 9, the compound is completely ionized. The reduction in lipophilicity at pH 9 decreases the ability of the compound to penetrate into the midge, thereby decreasing the observed toxicity of the compound.