Adsorption of Glyphosate on the Clay Mineral Montmorillonite:  Effect of Cu(II) in Solution and Adsorbed on the Mineral

Abstract

Adsorption-desorption of the herbicide glyphosate (GPS) onto the clay mineral montmorillonite has been studied in presence of copper, in order to clarify the effects that this strongly complexing metal could have on the availability and mobility of GPS in soil environment. In contrast with previous findings, GPS adsorption on montmorillonite decreases in the presence of Cu, in solution or adsorbed on the mineral, due to the formation of Cu-GPS complexes that have a lower tendency to be adsorbed on montmorillonite than the free GPS. GPS adsorption is higher at pH 4.2 than at pH 6.8, both in the presence and in the absence of Cu, but the decrease in GPS adsorption in the presence of Cu is lower at pH 4.2 than at pH 6.8, since at this latter pH the concentration of Cu-GPS complexes in relation to free GPS in solution is high. It is commonly believed that GPS remains almost permanently adsorbed onto soils and has very limited mobility, but GPS desorption experiments show that the amount of GPS desorbed from montmorillonite is not negligible and increases in the presence of Cu. These experiments lead to the conclusion that, in relation to GPS release from soil, it is necessary to take into account not only the type of soil to which it is applied (e.g., whether it has high clay minerals content) but also whether there is any element in the soil solution or adsorbed on the soil capable of forming strong complexes with GPS.

Effect of copper on the adsorption of p-nitrophenol onto soils

“…However, little attention has been given to determine the effect of heavy metals on the adsorption of organic contaminants on soils. Similarly not much is known about the adsorption of heavy metals on soil as affected by organic contaminants (Maqueda et al, 1998;Gimsing et al, 2004a;Morillo et al, 1994Morillo et al, , 1997Morillo et al, , 2000Morillo et al, , 2002. Adsorption and desorption of copper on montmorillonite were affected by the presence of a cationic pesticide chlordimeform (Maqueda et al, 1998).…”

“…Copper adsorption decreased when both adsorbates were adsorbed simultaneously, indicating a competition between copper and chlordimeform for interlamellar positions. Morillo et al (1994Morillo et al ( , 1997Morillo et al ( , 2000Morillo et al ( , 2002 studied the mutual influence of glyphosate and copper adsorption on montmorrillonite and soil. Glyphosate adsorption on montmorillonite decreased in the presence of Cu in solution or adsorbed on the mineral.…”

Effect of lead on the sorption of phenol onto montmorillonites and organo-montmorillonites

“…Compared with the extensive separate studies on the sorption of heavy metals and organic chemicals onto clays and organoclays, there is little information on the effect of heavy metals on the sorption of organic chemicals and vice versa [21][22][23][24]. Generally, clays are known to effectively sorb mostly heavy metals, while organoclays are adsorbents of organic contaminants.…”

“…Cu adsorption decreased when both adsorbates were adsorbed simultaneously, indicating a competition between Cu and chlordimeform for interlamellar positions. Morillo et al [22,23,27,28] studied the mutual influence of glyphosate and Cu adsorption on montmorillonite and soil. Glyphosate adsorption on montmorillonite decreased in the presence of Cu in solution.…”

How Early Diagenesis Reveals in Situ Biodegradation of Herbicides in Sediment

“…-pH and redox modification that could modify the sorption of molecules: even if chemicals are not degraded, their sorption could be modified directly (Morillo et al, 1997, for glyphosate andHermosin &Cornejo, 1993, for 2-4D) or indirectly -due to desorption of desorbing promoters like Fe(II) (Klupinski & Chin, 2003) or Cu(II) for glyphosate (Morillo et al, 1997). Desorption could facilitate biodegradation too (Walker et al, 2001) and, therefore has a major effect on herbicide fate (Daniels et al, 2000).…”