Biodegradation of 2,4- and 2,6-dinitrotoluene by freshwater microorganisms. (Reannouncement with new availability information)

The microbial degradation of 2,4- and 2,6-dinitrotoluene was complete or nearly complete in surface water from two locations downstream from the Radford Army Ammunition Plant. No degradation was detected in surface water from four local (Frederick, MD area) sites. Either isomer could serve as a sole carbon and energy source, with about 60 percent of substrate carbon appearing as CO2, and with an increase in the population of degrading organisms. In both the rate of mineralization in percent degraded per day increased with increasing substrate concentration. At 2,4-Dinitrotoluene, 2,6-Dinitrotoluene, Microbial degradation, Mineralization 10 mg/L, degradation rates of 32 and 14.5 percent/day were observed for the 2,4 and 2,6 isomers, respectively. At very low concentrations of the 2,6 isomer a degrading population did not develop, and significant degradation did not occur. The rate of substrate utilization was far greater, and the lag time shorter, for the 2,4 isomer, consistent with a far greater density of 2,4-DNT degraders. Mixed enrichment cultures were developed for each DNT isomer separately, by sequential transfer to increasing substrate concentrations. maximum substrate concentrations utilized were about 130 mg/L, and cell yields of 6.8 to 7.3 X 105 CFU/ug input DNT were calculated. Disappearance of 2,4-DNT in themore » presence of high concentrations of 2,4-DNT Mixed enrichment culture approximated first-order kinetics; pseudo-first order rate constants varied from 0.043 to 0.190 min-1. The mean second-order constant was 3.9 X 10-10 ml/cell min. If one assumes a concentration of 106 cells/ml, at 250C, a half-life of 29.7 hours can be estimated for this isomer.« less