Sodium Application Enhances DDT Transformation in a Long-Term Contaminated Soil

Bioremediation is an economically attractive option to remediate soil contaminated with DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] and other organochlorine pesticides. However, lack of DDT bioavailability in soil presents one major obstacle to this technology particularly in soils that have been contaminated for long periods. In this work, sodium ion (Na⁺) was applied to a long-term DDT contaminated soil as Na⁺ is known to disperse clays, which would potentially release and/or expose physically protected DDT thereby enhancing DDT bioavailability. Sodium ion addition significantly increased dissolved organic carbon (DOC) levels, anaerobic bacterial numbers and the amount of DDT residues measured in soil solution. DDT transformation ranged from 95% (30—80 mg Na⁺ kg^-1 soil) to 72% (no Na⁺ added) with the optimum level of DDT transformation occurring at 30 mg Na⁺ kg^-1 soil. Higher Na⁺ levels repressed DDT transformation and this appeared to be related to lower DOC levels and flocculation of soils. The anaerobic incubation conditions employed (high water content) prevented DDE [1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene] production and DDD [1,1-dichloro-2,2-bis(p-chlorophenyl)ethane] was the major breakdown product formed. Overall it appeared that Na⁺ has potential as a cheap and safe alternative to surfactants as a method for increasing DDT transformation in contaminated soil.