Bioavailability and biodegradation rate of DDT by Bacillus sp. B75 in the Presence of dissolved humic substances

Abstract

Abstract The effects of dissolved humic substances, prepared from a humic volcanic ash soil, on the bioavailability and Modegradation rate of DDT (1,1,1-triehloro-2,2-bis(4-chlorophenyl)ethane) by Bacillus sp. B75 in tenfold diluted nutrient broth were examined. Dissolved humic acid (DHA) decreased the biodegradation rate of DDT significantly while the effect of dissolved fulvic acid (DFA) was negligible. The initial DDT degradation rates followed first order kinetics. The higher the DHA concentration, the greater the decrease in the degradation rate. The increase in the apparent solubility of DDT by DHA and DFA suggested that DDT was bound to DHA and DFA, The addition of DHA significantly decreased the amount of DDT sorbed by the bacterial cells whereas in the case of DFA addition the decrease was negligible. These data suggest that the rate constants for DDT degradation are correlated with the amount of DDT sorbed to the Bacillus cells which represents the bioavailable DDT.