title: Influence of copper on the adsorption and desorption of paraquat, diquat, and difenzoquat in vineyard acid soils.
abstract: Retention of the cationic herbicides paraquat (PQ), diquat (DQ), and difenzoquat (DFQ) in two vineyard soils with a different management history and retention capacity was examined. The influence of copper on the ability of the soils to retain the herbicides was determined by comparing the results of adsorption and desorption tests on untreated and Cu-enriched soil samples, and also on soils that were previously treated with EDTA to extract native copper. The three herbicides were strongly adsorbed by both soils. Soil 1 exhibited linear adsorption isotherms for PQ and DFQ with partition coefficients, KD, of 1.28 x 103 and 1.37 x 103 L kg-1, respectively, and a Freundlich-type isotherm for DQ with a linearized partition coefficient, KD*, of 1.01 x 103 L kg-1. On the other hand, soil 2 exhibited curved isotherms and smaller KD* values (viz. 106, 418, and 28 L kg-1 for PQ, DQ, and DFQ, respectively). Using EDTA to extract copper from the soils released new sites for the herbicides to bind. The three herbicides exhibited strong hysteresis in the adsorption-desorption process. Extracting copper decreased the percent desorption of PQ and DQ; on the other hand, it decreased the affinity of DFQ for the resulting vacant adsorption sites. Similarly, competitive adsorption tests with copper and the herbicides revealed that the metal was only capable of displacing DFQ from adsorption sites. The behavior of this herbicide in the soils was consistent with a specific adsorption model. The disparate behavior of the two soils toward the herbicides was a result of the adsorption sites in soil 1 being less extensively occupied than those of soil 2 in the adsorption tests. The effect of copper on the adsorption of DFQ in the two soils was acceptably reproduced by an adsorption model involving Coulombic and specific sorption with competition from the metal.
authors.affiliation: Soil and Agricultural Science Group, Plant Biology and Soil Science Department, and Nutrition and Bromatology Group, Analytical and Food Chemistry Department, Faculty of Food Science and Technology, University of Vigo, Ourense Campus, 32400 Ourense, Spain.
authors.forename: Miriam
authors.initials: M
authors.lastname: Pateiro-Moure
authors.forename: Cristina
authors.initials: C
authors.lastname: Pérez-Novo
authors.forename: Manuel
authors.initials: M
authors.lastname: Arias-Estévez
authors.forename: Eugenio
authors.initials: E
authors.lastname: López-Periago
authors.forename: Elena
authors.initials: E
authors.lastname: Martínez-Carballo
authors.forename: Jesús
authors.initials: J
authors.lastname: Simal-Gandara
mesh_terms: D000327:Adsorption; D003300:Copper / Q000494:pharmacology*; D004178:Diquat / Q000737:chemistry*; D006540:Herbicides / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D010269:Paraquat / Q000737:chemistry*; D011720:Pyrazoles / Q000737:chemistry*; D012987:Soil / Q000032:analysis*; D027843:Vitis / Q000254:growth & development
chemical_list: D006540:Herbicides; D011720:Pyrazoles; D012987:Soil; C031394:difenzoquat; D003300:Copper; D004178:Diquat; D010269:Paraquat