Surfactant-enhanced anaerobic degradation of 1,1,1-trichloro-2,2-bis-(p-chlorophenyl)-ethane (DDT)

The pesticide DDT is a persistent contaminant in soils and sediments. Although it has long been known to be biodegradable under anaerobic conditions, little is known about the specific factors that cause it to be recalcitrant in anaerobic environmental systems or about the microorganisms responsible for its degradation.; The addition of the nonionic surfactant Brij 30 was evaluated as a means of enhancing solubilization, potential bioavailability and biodegradability of DDT and its metabolite DDD. Experiments were performed with both a DDT-contaminated soil and in soil-free liquid suspension. Detailed analyses of electron donors and potential electron acceptors were performed to provide insights into modes of microbial metabolism under these conditions.; In sealed anaerobic microcosms containing aged contaminated soil and liquid medium with surfactant, DDT was degraded at significantly greater rates and extents than in microcosms without surfactant. Concentrations of the dechlorination product DDD increased but did not accumulate stoichiometrically with DDT disappearance. The presence of added carbon source did not significantly increase the ultimate extent of DDT degradation. Decreases in surfactant concentration over time suggested use of surfactant as either a carbon source or as an electron donor in the dechlorination process. Subsequent experiments were conducted with surfactant in the absence of soil to characterize the mode of DDT degradation and the role of the surfactant.; In soil-free microcosms using butyrate or hydrogen as potential electron donors, surfactant was observed to significantly increase the extent of DDT degradation but with little accumulation of DDD. Significant release of chloride was observed (approximately 3 mumol chloride per mumol DDT degraded) in microcosms amended with butyrate. Microcosms with both hydrogen and butyrate added as electron donors exhibited the greatest extent of DDT degradation with virtually no accumulation of DDD, while microcosms with hydrogen alone exhibited substantially less degradative activity. Protein yields correlated with both sulfate reduction and DDT degradation in surfactant-amended microcosms, suggesting that DDT degradation may be mediated by anaerobic sulfate-reducing organisms. Headspace hydrogen threshold concentrations in several of these microcosms were consistent with those typically observed in cultures dominated by sulfate-reducing organisms.; In addition, Brij 30 surfactant has been implicated as an electron donor in these systems. The hydrophobic moiety of this surfactant appears to be degraded under sulfate-reducing conditions and the electrons donated appear to be used predominately for growth and dechlorination in cultures amended with butyrate only. These findings strongly suggest that surfactant can play a role in enhanced bioremediation, not only as a means to enhance bioavailability, but as an agent to promote microbial dechlorination.