Toxic effects of pollutants on the mineralization of chloroform in river sediments

The influence of pollutants on the formation of 14CO2 from 3 micrograms/liter labeled chloroform was studied in anaerobic Dutch river sediments. All incubations were performed under anaerobic conditions. Addition of toxicants to sediment microcosms showed logistic dose-effect curves. The concentration giving 10% inhibition of the chloroform mineralization rate (IC10) was derived from these dose-effect curves. The IC10 values of added cadmium, chloropyrifos, benzene, mercury, or 1,2-dichloroethane were 1300, 1300, 140, 90, and 0.07 mg/kg dry sediment, respectively. Mud samples taken at different dates from the same site indicated a significantly different sensitivity to added pentachlorophenol and zinc. The IC10 of added pentachlorophenol was 150 mg/kg in one and 15 mg/kg in another sample. Chloroform-mineralizing bacteria are very sensitive to addition of zinc. The IC10 of added zinc was 700 mg/kg for one sample and 11 mg/kg for another sample of the sediment which contained a background concentration of 800 mg Zn/kg. Therefore, a partial inhibition of the mineralization of chloroform by the high concentrations of zinc present in Dutch river sediments cannot be excluded. The high concentration of zinc might cause persistence of otherwise biodegradable pollutants in Dutch sediments.