The effect of dissolved glyphosate upon the sorption of copper by three selected soils E. Morillo * , T. Undabeytia, C. Maqueda, A. Ramos Instituto de Recursos Naturales y Agrobiolog  ıa (CSIC), Avenida de Reina Mercedex, Apdo. 1052, 41080 Sevilla, Spain Received 22 January 2001; received in revised form 8 November 2001; accepted 9 December 2001 Abstract The effect of the pesticide glyphosate (GPS) on adsorption processes of copper onto three soils of different char- acteristics has been studied. Cu adsorption decreases in general with increasing GPS concentration in solution, due principally to the lower equilibrium pHs, although this is not the only variable affecting copper adsorption. For the same pH values, Cu adsorption is higher in two of the three soils in the presence of GPS, but for the third soil, Cu adsorption is higher in the absence of GPS. This behavior is explained by the possibility of GPS adsorption on these soilsandbytheformationofCu-GPScomplexesinsolution.ThesoilsshowingahigherCuadsorptioninthepresence of GPS than in its absence for the same pH are able to adsorb this pesticide. In these soils, copper can be adsorbed directlyonthesoilsurfaces,andalsothroughtheformationofbondswithGPSpreviouslyadsorbed.Thethirdsoilwas not able to adsorb GPS. Consequently, all the pesticide remained in solution, forming strong Cu complexes with low tendencytobeadsorbedonthissoil.Forthisreason,theconcentrationoffreeCuinsolutionisdrasticallyreduced,and the adsorption of copper on this soil is lower. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Adsorption; Heavy metals; Copper; Pesticide; Glyphosate; Soils 1. Introduction The application of Cu fertilizers on soils which are low in available micronutrients, and the continuous use of Cu-containing fungicides, have increased soil Cu content. This Cu content may adversely affect soil ecol- ogy, agricultural production or product quality, and water quality. These effects are closely related to both thebiologicalavailabilityandthemobilityofCu,which in turn are controlled by the chemical speciation. It is generally assumed that the concentration of Cu in soil solution is controlled by adsorption/precipitation processes(DuquetteandHendershot,1990).Theuptake ofmetalions,andofCuinparticular,bysoilsandtheir colloidalcomponentsisstronglyaffectedbysoilsolution parameters such as pH and competing or complexing ions. Cu ions in natural systems are in part present as dissolved metal–ligand complexes because of the vast abundance of such ligands. The influence of ligands on Cu uptake, as on that of other metals, is manifested in different ways. In the simplest case, dissolved ligands compete with the solid phase for the metal cation, causing a decreased adsorption of the metal. This de- creased adsorption can be compensated by other forms of ligand–metal–solid interactions, as occur in oxide minerals in which the formation of ternary complexes promotesmetaladsorption(Schindler,1990;Stadlerand Schindler, 1993). ThedegreetowhichCureactsindependentlyorasa complex for sorption sites can affect the retention of both Cu and ligand in the surface of the soil colloids and/orthemigrationanddistributionofcopperthrough thesoilprofileorleachingtogroundwater.Therefore,it Chemosphere 47 (2002) 747–752 www.elsevier.com/locate/chemosphere * Corresponding author. Tel.: +34-5-462-4711; fax: +34-5- 462-4002. E-mail address: morillo@irnase.csic.es (E. Morillo). 0045-6535/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0045-6535(01)00338-1