Effect of soil moisture on the fate of radiolabelled DDT and DDE in vitro

The effect of soil water content on the fate of applied 14C labelled 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (p,p′-DDT) and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (pp′-DDE) was examined over a 42 day period in laboratory microcosm experiments. Residues released as CO2and volatiles during the experiments were measured, as were acetone/hexane extractable and unextractable (bound) residues at the conclusion of the experiments. Release of 14CO2 was low (>0.7% of added label) under unflooded conditions and virtually zero from flooded soil. Autoclaving soil prior to the experiment essentially eliminated 14 C02 release. In unflooded, unautoclaved treatments mean binding of pp′-DDT and pp′-DDE ranged between 6.7 and 9.7%. Increased binding of pp′-DDT (24.5%) and pp′-DDE (11.5%) was observed under flooded unautoclaved conditions. Reducedp,p′-DDT binding was observed where flooded soil was autoclaved prior to the experiment. Flooding soil containing 14C-pp′-DDT resulted in considerable accumulation of labelled pp′-DDD, demonstrating the capacity within the soil for this transformation, and suggesting that the absence of relatively rapid DDT degradation via pp′-DDD is due to prevailing conditions, rather than the lack of degradative capacity within the microbiota.