MICROBIAL-DEGRADATION OF DDT AT EXTREMELY LOW CONCENTRATIONS

Two soil bacteria, Bacillus sp. B75 and an unidentified Gram-variable rod B116, degraded 1,1,1-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-d ichloro-2,2-bis(4-chlorophenyl)ethylene, 1,1-dichloro-2,2-bis(4-chloro phenyl)ethane and other acetone/hexane-extractable compounds, and thei r proportion were identical between 160 pg/ml and 100 ng/ml of DDT con centration levels except for the different proportion of metabolites i n the B116 culture. A large part of DDT was sorbed to both bacterial c ells in 48 hr even at extremely low concentration levels, suggesting t hat the uptake rate of DDT by the bacteria does not limit the degradat ion rate. These findings indicate that there is no threshold concentra tion for bacterial degradation of DDT under the presence of other carb on and energy sources.