Persistence and Movement of Sethoxydim Residues in Three Minnesota Soils

Abstract

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 sethoxydim residues simultaneously quantified parent and eight metabolites by conversion to a common volatile end product, 3-[2(ethylsulfonyl)propyl]-pentanedioic acid dimethyl ester, followed by analysis using gas chromatography (GC) and a flame photometric detector. Recovery of residues from soil spiked with 100 μg kg-1was 86 ± 21%. Residues remaining 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, respectively. Alachlor remaining 21 DAT in 1989 was 66, 52, and 65% of that applied 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 greatest % of applied chemical remaining 21 DAT in 1989: 100, 71, and 73% in 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 residues remaining 137 DAT was the least of the three herbicides. In terms of leaching, sethoxydim residues showed least movement, with minimal detections below 0 to 15 cm. Although sethoxydim appears to be advantageous over alachlor and atrazine in terms of potential impact on ground water quality, additional information regarding composition of the detected residues is needed to better assess its environmental impact.