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Kansas Water Science Center

Formation and Transport of the Sulfonic Acid Metabolite of Alachlor and Metolachlor in Soil

By D.S. Aga and E.M. Thurman

ABSTRACT

Alachlor and metolachlor are dechlorinated and transformed into their corresponding ethane sulfonic acie (ESA) metabolites in soil. In a field-disappearance study, it was shown that alachlor ESA was formed at a faster rate and at concentrations 2-4 times higher than metolachlor ESA, conforming with the observed longer disappearance half-life of metolachlor (15.5 d) in the field as compared to alachlor (8 d). Runoff data also showed higher concentrations of alachlor ESA as compared to metolachlor ESA, even though they were applied at the same levels. Data from soil cores showed transport of the ESA compounds in soil to as far down as 75-90 cm below the surface, at concentrations ranging from less than 0.5 /L to about 50 /L. In contrast, no parent herbicide was detected at these depths. This observation correlates with the higher log Koc values for alachlor (3.33) and metolachlor (3.01) relative to their corresponding ESA metabolites, alachlor ESA (2.26) and metolachlor ESA (2.29).

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Aga, D.S., and Thurman, E.M., 2001, Formation and transport of the sulfonic acid metabolites of alachlor and metolachlor in soil: Environmental Science and Technology, v.35, p. 2455-2460.

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