TOXIC EFFECTS OF POLLUTANTS ON THE MINERALIZATION OF 4-CHLOROPHENOL AND BENZOATE IN METHANOGENIC RIVER SEDIMENT

The toxic effects of pollutants on the mineralization of 2 mug/L [U-C- 14]-4-chlorophenol and benzoate were studied in microcosms with methan ogenic sediment from a little harbor in the Rhine River. In contrast w ith studies using a high substrate concentration, no lag time was obse rved and the half-lives for 4-chlorophenol and benzoate were 1.6 and 0 .55 h, respectively. The effect of increasing additions of benzene, ch loroform, 1,2-dichloroethane, pentachlorophenol, and zinc on each mine ralization reaction was measured. Toxicity data were fitted with a log istic dose-effect curve. The IC10 is defined as the concentration of a toxicant inhibiting the mineralization rate for 10%. The IC10 concent rations of benzene, chloroform, 1,2-dichloroethane, pentachlorophenol, and zinc on the benzoate mineralization were 150, 0.04, 71, 6, and 84 2 mg/kg sediment dry weight, respectively. This latter value includes the background concentration of 800 mg Zn/kg sediment. The mineralizat ion of 4-chlorophenol and benzoate showed similarities in the sensitiv ity to these toxicants. 4-Chlorophenol can be degraded via benzoate, w hich might explain the similarities in sensitivity of both mineralizat ion reactions. Chloroform proved to be extremely toxic to anaerobic mi neralization reactions, which might be attributed to the formation of very toxic and reactive intermediates formed during the slow anaerobic degradation of the chloroform in anaerobic sediments. Sediment qualit y criteria derived solely from standard toxicity tests using aerobic o rganisms may lead to complete inhibition of several important microbia l processes in anaerobic sediments.