PERSISTENCE AND MOVEMENT OF SETHOXYDIM RESIDUES IN 3 MINNESOTA SOILS

The persistence and movement of sethoxydim residues were determined in the top 45 cm of an Estherville sandy loam (sl), Port Byron silt loam (sil), and Webster clay loam (cl) in the field. Analysis of sethoxydi m residues simultaneously quantified parent and eight metabolites by c onversion to a common volatile end product, 3-[2(ethylsulfonyl)propyl] -pentanedioic acid dimethyl ester, followed by analysis using gas chro matography (GC) and a flame photometric detector. Recovery of residues from soil spiked with 100 mu g kg(-1) was 86 +/- 21%. Residues remain ing in soil 21 days after treatment (DAT) in 1989 were 37, 51, and 29% of the applied sethoxydim in the sl, sil, and cl, respectively, while in 1990, 86, 52, and 24% remained in the sl, sil, and cl, respectivel y. Alachlor remaining 21 DAT in 1989 was 66, 52, and 65% of that appli ed in the sl, sil, and cl, respectively, while in 1990, it was 16, 13, and 100% in the sl, sil, and cl, respectively. Atrazine had the great est % of applied chemical remaining 21 DAT in 1989: 100, 71, and 73% i n the sl, sil, and cl, respectively. Of the atrazine applied in 1990, atrazine remaining 21 DAT was 87% in the sl, 42% in the sil, and 100% in the cl. Over all soils and years, the amount of total sethoxydim re sidues remaining 137 DAT was the least of the three herbicides. In ter ms of leaching, sethoxydim residues showed least movement, with minima l detections below O to 15 cm. Although sethoxydim appears to be advan tageous over alachlor and atrazine in terms of potential impact on gro und water quality, additional information regarding composition of the detected residues is needed to better assess its environmental impact .