Anaerobic biodegradation of organochlorine pesticides in contaminated soil - significance of temperature and availability.

Anaerobic biodegradation of the pesticides: gamma-hexachlorocyclohexane, methoxychlor, o,p'- and p,p'-DDT in field polluted soil was tested at 12, 22 and 30 degrees C, using methanogenic granular sludge as inoculum. The contaminants were removed quite effectively at all temperatures and their removal rates increased 1.2-1.7 times with the increase in temperature. In most cases pesticide concentrations after an initial substantial decline remained almost constant until the end of experiment. These residual concentrations were also temperature dependent and they were 1.4-8.2 times higher at 12 degrees C than at 30 degrees C. DDT was degraded via DDD and accumulation of this metabolite was lower (19-64%) than the corresponding amount of removed DDT, especially at higher temperatures. Further transformation of DDD was confirmed by formation of p,p'-dichlorobenzophenone. Additional experiment demonstrated that removal was limited to readily desorbing fractions of pesticides, while their desorption-resistant fractions persisted in the soil. However, DDD metabolite was only partially removed despite its good desorbability.