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Kansas Water Science Center

Preferential Dealkylation Reactions of s-Triazine Herbicides in the Unsaturated Zone

By M.S. Mills and E.M. Thurman

Abstract

The preferential dealkylation pathways of the s-triazine herbicides, atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), propazine (2-chloro-4,6-bis(isopropylamino-s-triazine), simazine (2-chloro-4,6-bis(ethylamino-s-triazine), and two monodealkylated triazine metabolites, deisopropylatrazine (DIA: (2-amino-4-chloro-6-ethylamino-s-triazine) and deethylatrazine (DEA: (2-amino-4-chloro-6-isopropylamino-s-triazine) were investigated on two adjacent Eudora silt-loam plots growing corm (Zea mays L.). Results from the shallow unsaturated zone and surface-water runoff showed preferential removal of an ethyl side chain from atrazine, simazine, and DIA relative to an isopropyl side chain from atrazine, propazine, and DEA. It it hypothesized that deethylation reactions may proceed at 2-3 times the rate of deisopropylatrazine reactions. It is concluded that small concentrations of DIA reportedly associated with the degradatin of atrazine may be due to a rapid turnover rate of the metabolite in the unsaturated zone, not to small production levels. Because of continued dealkylation of both monodealkylated metabolites, a strong argument is advanced for the presence of a didealkylated metabolite in the unsaturated zone.

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Mills, M.S. and Thurman, E.M., 1994, Preferential dealkylation reactions of s-triazine herbicides in the unsaturated zone [abst.]: Environmental Science & Technology, v. 28, no. 4, p. 600-605.

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