DEGRADATION OF ACETANILIDE HERBICIDES IN HISTORY AND NONHISTORY SOILSFROM EASTERN VIRGINIA

The degradation of C-14-labeled metolachlor, acetochlor, and pretilach lor in control and soils with 10-yr metolachlor-history or 3-yr butyla te history was studied by monitoring the evolution of (CO2)-C-14 in so il biometer flasks. The degradation rate of C-14-phenyl-labeled metola chlor was similar in soils with 0- and 10-yr metolachlor history over 52 d. C-14 was released from carbonyl-labeled metolachlor about 40% fa ster than from phenyl-labeled metolachlor in both soils, Soil steriliz ation by autoclaving reduced significantly the metolachlor degradation rate in both soils. Degradation of C-14-labeled EPTC in soils with 3- yr butylate history was much faster than in soils with no history. Soi l sterilization reduced the EPTC degradation rate, confirming microbia l degradation. The degradation rates of acetochlor, metolachlor, and p retilachlor were similar in soils with and without butylate history. M ost of the C-14 that remained in history and nonhistory soils was extr actable with ethyl acetate or sodium hydroxide. Three major metabolite s of metolachlor and EPTC were detected by thin-layer chromatography ( TLC) of extracts from both soils, In contrast to the situation with ca rbamothioate herbicides, soils exposed repeatedly to metolachlor or ot her acetanilides are not prone to become adapted to these herbicides. Soils with carbamothioate history did not exhibit any apparent cross-a daptation toward acetanilide herbicides.