Toxic effects of pentachlorophenol and other pollutants on the mineralization of acetate in several soils.

The mineralization of [14C]acetate was studied in bottles with fresh soil and groundwater. Addition of toxicants inhibited the formation of 14CO2 and dose-effect curves were obtained. The acetate mineralization was not inhibited by zinc, cadmium, K2Cr2O7, chloropyrifos, and paraquat in an acid sandy soil at 1000 mg/kg dry soil. The IC10 is the toxicant concentration which inhibits 10% of the initial mineralization rate. The IC10 concentrations for 3,4-dichloroaniline, triphenyltin, and orthoxylene were 48, 96, and 730 mg/kg, respectively, in the acid sandy soil. The IC10 of pentachlorophenol was measured in samples from the acid sandy soil and in several other soil and subsoil samples. The geometrical mean of the 13 IC10 values was 16 mg pentachlorophenol/kg. A statistical method was used to calculate the PCP concentration above which 5% of the most sensitive acetate-mineralizing communities in all soils are influenced. The best estimate of this concentration is 0.3 mg PCP/kg but to be on the safe side the 95% confidence level of this concentration is 25 micrograms/kg.