Sorption of Glyphosate on Soil Components: The Roles of Metal Oxides and Organic Materials

Abstract

Predicting the behavior, fate, and transport potential of a herbicide in any soil involves understanding the sorption characteristics. The sorption characteristics of glyphosate (GPS) on soil and their main components were investigated, indicating that the mineral phase is more important than the organic carbon in adsorption of GPS. Sorption isotherms were determined from each component using the batch equilibrium method at various concentrations (5, 10, 15, 20, 25, and 30 mg L −1 ) and sorption affinity of GPS was approximated by the Freundlich equation. The sorption strength K f [mg kg −1 (L mg −1 ) −n ] across the various components ranged from 2.1-134.9 while the organic carbon-normalized Freundlich sorption capacity values, K foc , ranged from 1.28-3.53 mg kg −1 -OC/(mg L −1 ) n . Infrared Fourier transform spectroscopy (FTIR) of the components showed significant structural differences. The results suggest that the presence of the oxides and hydroxides iron, in particular in soil solutions, enhanced GPS adsorption. They also suggest that reduction in OC% due to various treatments may enhance the remobilization of GPS into the aqueous phase (i.e., groundwater), though at different rates. Comparatively, contribution of surface area to the adsorption of GPS on the various components proved more significant than contents of organic carbon.

Glyphosate sorption to soils and sediments predicted by pedotransfer functions

“…Finally, glyphosate and phosphate have been reported to exhibit similar sorption mechanisms, thereby leading to potential competition for sorption sites (Gimsing and Borggaard 2002). These sorption mechanisms are evidenced by the influence of clay content (Beltran et al 1998;Borggaard and Gimsing 2008;da Cruz et al 2007;Dion et al 2001;Ololade et al 2014;Pessagno et al 2008;Singh et al 2014;Xu et al 2009), iron-and aluminum-oxide content (de Jonge et al 2001;Gimsing et al 2004Gimsing et al , 2007Mamy and Barriuso 2005;Morillo et al 2000;Pessagno et al 2008;Wang et al 2005), pH (Accinelli et al 2005;Al-Rajab et al 2008;Borggaard and Gimsing 2008;da Cruz et al 2007;de Jonge and Wollesen de Jonge 1999;Dousset et al 2007;Gimsing et al 2004;Mamy and Barriuso 2005;Xu et al 2009;Zhou et al 2004), phosphorus content (de Jonge et al 2001;Gimsing and Borggaard 2002), organic carbon (Albers et al 2009;da Cruz et al 2007;Morillo et al 2000;Ololade et al 2014;Pessagno et al 2008;Wang et al 2005) and the cation exchange capacity (CEC) (da Cruz et al 2007;de Jonge and Wollesen de Jonge 1999;Mamy and Barriuso 2005;…”

“…The formation of strong Fe-O-P(glyphosate) and Al-O-P(glyphosate) bonds by ligand exchange between the glyphosate phosphonate group and singly coordinated Al-OH and Fe-OH groups on the surfaces of variably charged soil minerals has been proposed as a possible sorption mechanism (Borggaard and Gimsing 2008;de Jonge et al 2001;Dideriksen and Stipp 2003;Mamy and Barriuso 2005;Morillo et al 1997;Nicholls and Evans 1991;Piccolo et al 1994;Wang et al 2006). This mechanism is deemed to occur preferentially on the broken edges of layer silicates, poorly ordered silicates or iron-and aluminum oxides (Borggaard and Gimsing 2008;Dideriksen and Stipp 2003;Laitinen et al 2008;Morillo et al 1997;Ololade et al 2014;Piccolo et al 1994). The formation of complexes between glyphosate phosphonate groups and the soil-exchanged polyvalent cations has also been suggested to be responsible for the strong sorption of glyphosate to soil (Borggaard and Gimsing 2008;de Jonge et al 2001;de Jonge and Wollesen de Jonge 1999;Mamy and Barriuso 2005;Mcconnell and Hossner 1985;Vereecken 2005).…”

“…Moreover, the soil pH may also be involved in sorption mechanisms. A rise in pH, leading to increased negatives charges of both soil and glyphosate may consequently result in greater electrostatic repulsion (Candela et al 2007;de Jonge and Wollesen de Jonge 1999;Mcconnell and Hossner 1985;Morillo et al 2000;Ololade et al 2014;Wauchope et al 2002). Finally, glyphosate and phosphate have been reported to exhibit similar sorption mechanisms, thereby leading to potential competition for sorption sites (Gimsing and Borggaard 2002).…”

“…Since the 1990s, glyphosate has been the most heavily used pesticide worldwide for weed control in agriculture, forestry and urban landscapes, with postemergent applications (Candela et al 2007;Kogan et al 2003;Ololade et al 2014;Rampoldi et al 2011;Székacs and Darvas 2012). Despite glyphosate's strong tendency to sorb to soils, its intensive use may be associated with a risk of freshwater and groundwater contamination.…”

“…Sorption to soil is controlled by the chemical and physical properties of the pesticide and of the soil (Aparicio et al 2013;Gevao et al 2000). Accurate predictions of sorption coefficients for a given combination of pesticides, and soils require an understanding of the underlying mechanisms and associated soil properties involved in sorption (Ololade et al 2014).…”