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Adsorption and degradation of phenoxyalkanoic acid herbicides in soils: A review

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The primary aim of this review on the phenoxyalkanoic acid herbicides (2,4‐D, MCPA, dichlorprop‐P, mecoprop‐P, 2,4‐DB and MCPB) was to compare the extent of their adsorption in soils and degradation rates to assess their potential for groundwater contamination. We found that adsorption decreased in the sequence 2,4‐DB > 2,4‐D > MCPA > dichlorprop‐P > mecoprop‐P. Herbicides are predominantly adsorbed as anions – on organic matter and through a water‐bridging mechanism with adsorbed Fe cations, and their neutral forms are adsorbed mainly on organic matter. Adsorption of anions of 2,4‐D, MCPA, dichlorprop‐P and mecoprop‐P is inversely correlated with their Log D values, and modeling of adsorption of the compounds based on this relationship is possible. The predominant dissipation mechanism of herbicides in soils is bacterial degradation. The contribution of other mechanisms, such as degradation by fungi, photodegradation or volatilization from soils is much smaller. The rate of bacterial degradation decreased in the following order: 2,4‐D > MCPA > mecoprop‐P > dichlorprop‐P. It was found that 2,4‐D and MCPA have the lowest potential for leaching into groundwater, and mecoprop‐P and dichlorprop‐P have slightly higher potential. Because of limited data on adsorption and degradation of 2,4‐DB and MCPB, estimation of their leaching potential was not possible. This article is protected by copyright. All rights reserved

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