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TECHNICAL REPORTS

Ground Water Quality

The Acetochlor Registration Partnership

Prospective Ground Water Monitoring Program

^a LFR Levine·Fricke, 1413 Woodlawn Avenue, Wilmington, DE 19806
^b Monsanto Company, 800 North Lindbergh Boulevard, St. Louis, MO 63167
^c Dow AgroSciences LLC, 9330 Zionsville Road, Indianapolis, IN 46268
^d Klein & Associates, 12917 Topping Estates Drive, Town & Country, MO 63131
^e Syngenta Ltd., Jealott's Hill Research Station, Bracknell, Berkshire, England RG42 6ET

^* Corresponding author (andy.newcombe{at}lfr.com)

Received for publication November 11, 2004. The Acetochlor Registration Partnership conducted a prospective ground water (PGW) monitoring program to investigate acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)-acetamide] transport to ground water at eight sites. The distribution of soil textures among these sites was weighted toward coarser soil types, while also including finer-textured soils that dominate most corn (Zea mays L.)-growing areas of the United States. Each site consisted of a 1.2-ha test plot adjacent to a 0.2-ha control plot. Suction lysimeters and monitoring wells were installed at multiple depths within each test and control plot to sample soil-pore water and near-surface ground water. Irrigation was applied to each site during the growing season to ensure water input of 110 to 200% of average historical rainfall. Acetochlor dissipated rapidly from surface soils at all sites with a DT₅₀ (time for 50% of the initial residues to dissipate) of only 3 to 9 d, but leaching was not an important loss mechanism, with only 0.25% of the 15312 soil-pore water and ground water samples analyzed containing parent acetochlor at or above 0.05 µg L^–1. However, quantifiable residues of a soil degradation product, acetochlor ethanesulfonic acid, were more common, with approximately 16% of water samples containing concentrations at or above 1.0 µg L^–1. A second soil degradation product, acetochlor oxanilic acid, was present at concentrations at or above 1.0 µg L^–1 in only 0.15% of water samples analyzed. The acetochlor PGW program demonstrated that acetochlor lacks the potential to leach to ground water at detectable concentrations, and when applied in accordance with label restrictions, is unlikely to move to ground water at concentrations hazardous to human health.

Abbreviations: ARP, Acetochlor Registration Partnership • DT₅₀ and DT₉₀, times for 50 and 90% of the initial residues to dissipate, respectively • ESA, ethanesulfonic acid • LOD, limit of detection • LOQ, limit of quantitation • OXA, oxanilic acid • PGW, prospective ground water