title: Soil sorption of acidic pesticides: modeling pH effects.
abstract: A model of acidic pesticide sorption in soils was developed from theoretical modeling and experimental data, which initially considered a combination of a strongly acidic pesticide and a variable-charge soil with high clay content. Contribution of 2,4-D [(2,4-dichlorophenoxy) acetic acid] anionic-form sorption was small when compared with molecular sorption. Dissociation of 2,4-D was not sufficient to explain the variation in Kd as a function of pH. Accessibility of soil organic functional groups able to interact with the pesticide (conformational changes) as a function of organic matter dissociation was proposed to explain the observed differences in sorption. Experimental 2,4-D sorption data and K(oc) values from literature for flumetsulam [N-(2,6-difluorophenyl)-5-methyl [1,2,4] triazolo [1,5-a] pyrimidine-2-sulfonamide] and sulfentrazone [N-[2,4-dichloro-5-[4-(difluromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl] phenyl] methanesulfonamide] in several soils fit the model.
authors.affiliation: Embrapa Environment. C.P. 69, 13820-000 Jaguariúna, SP, Brazil. spadotto@cnpma.embrapa.br
authors.forename: Claudio A
authors.initials: CA
authors.lastname: Spadotto
authors.forename: Arthur G
authors.initials: AG
authors.lastname: Hornsby
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates; D000077215:Clay; D006863:Hydrogen-Ion Concentration; D008962:Models, Theoretical; D010575:Pesticides / Q000737:chemistry*; D012989:Soil Pollutants
chemical_list: D000538:Aluminum Silicates; D010575:Pesticides; D012989:Soil Pollutants; D000077215:Clay