Halogenated hydrocarbons, including 1,1,1-trichloro-2,2-di(4-chlorophenyl) ethane (DDT) and its metabolites 1,1-dichloro-2,2-bis(4-chlorophenyl) ethane (DDD) and 1,1-dichloro-2,2-bis(4-chlorophenyl) ethylene (DDE), are often detected in soils and sediments, where high concentrations of black carbon and sulfides co-exist. In this study, we found that the transformation of DDX (DDT, DDD, and DDE) requires both sulfides and black carbon. All DDX decay followed first-order kinetics, with half-lives (t1/2) calculated to be 6.7±0.3 days, 19.8±1.1 days and 28.9±1.2 days at pH 7 for DDT, DDD, and DDE, respectively. The formation of chloride suggests that dechlorination of DDX took place in the presence of black carbon and sulfides. DDD and DDMU were identified as degradation products in addition to chloride, suggesting an overall detoxification process during the degradation of DDX by sulfide in the presence of black carbon. To better understand the reaction pathways, electrochemical cells and batch reactor experiments with sulfide-pretreated carbon were used to differentiate reaction pathways. Our results suggest that DDT and DDD are transformed via elimination and/or nucleophilic substitution pathways, while DDE degradation involves reductive dechlorination. This research lays the groundwork for developing an alternative in-situ remediation technique for rapidly decontaminating soils and sediments to lower toxic products under environmentally relevant conditions.

Pyrogenic carbon materials in facilitating the abiotic degradation of DDT and its metabolites

253rd National Meeting (2017)

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