Surfactant-enhanced solubilization and anaerobic biodegradation of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane...

The hydrophobic pesticide 1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane (DDT) is a persistent contaminant in soils and sediments, although it has long been known to be biodegradable under anaerobic conditions. Addition of a nonionic surfactant was evaluated as a means of enhancing the solubilization, potential bioavailability, and anaerobic biodegradability of DDT and its metabolites--1,1-dichloro-2,2-bis(p-chlorophenyl)-ethane (DDD) and 1,1-dichloro-2,2-bis(p-chlorophenyl)-ethylene (DDE)--in an aged contaminated soil. Approximately 12 mg surfactant/g soil was required before concentrations greater than the critical micelle concentration were observed in the liquid phase in soil microcosms. At greater doses, solubilization of each DDT, DDD, and DDE isomer increased linearly with the surfactant dose. Solubilization data were consistent with equilibrium models that account for simultaneous partitioning of hydrophobic compounds between the aqueous, soil, and pseudomicellar phases. Significantly greater rates and extents of DDT degradation were observed in anaerobic microcosms that were regularly fed a cellulose substrate or amended with surfactant (with or without cellulose) relative to controls. The surfactant substantially increased the rate of DDT degradation during the first 9 weeks, although there were no significant differences between cellulose-fed microcosms and surfactant-amended microcosms after 31 weeks. In addition, DDD accumulated at less than stoichiometric amounts in surfactant-amended microcosms, whereas DDD accumulated nearly stoichiometrically with DDT loss in all other microcosms. Concentrations of DDE were unchanged throughout the course of the microcosm experiment.