| Abstract
| - Alachlor and metolachlor are dechlorinated and transformedinto their corresponding ethane sulfonic acid (ESA)metabolites in soil. In a field-disappearance study, it wasshown that alachlor ESA was formed at a faster rateand at concentrations 2−4 times higher than metolachlorESA, conforming with the observed longer disappearancehalf-life of metolachlor (15.5 d) in the field as compared toalachlor (8 d). Runoff data also showed higher concentrationsof alachlor ESA as compared to metolachlor ESA, eventhough they were applied at the same levels. Data from soilcores showed transport of the ESA compounds in soil toas far down as 75−90 cm below the surface, at concentrationsranging from less than 0.5 μg/L to about 50 μg/L. Incontrast, no parent herbicide was detected at these depths.This observation correlates with the higher log Kocvalues for alachlor (3.33) and metolachlor (3.01) relative totheir corresponding ESA metabolites, alachlor ESA(2.26), and metolachlor ESA (2.29).
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