Microbial Degradation of DDT at Extremely Low Concentrations

Abstract

Two soil bacteria, Bacillus sp. B75 and an unidentified Gram-variable rod B116, degraded l,l,l-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT) at extremely low concentration levels in the range of 10 pg/ml to 100 ng/ml in one-tenth diluted nutrient broth. Higher than 88% of DDT was degraded after 2 weeks of incubation. The metabolites produced, 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene, 1, l-dichloro-2,2-bis(4-chlorophenyl)ethane and other acetone/ hexane-extractable compounds, and their proportion were identical between 160 pg/ml and 100 ng/ml of DDT concentration levels except for the different proportion of metabolites in the B116 culture. A large part of DDT was sorbed to both bacterial cells in 48 hr even at extremely low concentration levels, suggesting that the uptake rate of DDT by the bacteria does not limit the degradation rate. These findings indicate that there is no threshold concentration for bacterial degradation of DDT under the presence of other carbon and energy sources. © 1993, Pesticide Science Society of Japan. All rights reserved.