Competitive adsorption and desorption of glyphosate and phosphate on clay silicates and oxides

Abstract

Competitive adsorption of glyphosate and phosphate on goethite and gibbsite and on illite, montmorillonite and two kaolinites differing in surface area was evaluated. The results show that glyphosate and phosphate are competing for the adsorption sites, but the degree of competition depends on the adsorbent. On goethite the competition is very much in favour of phosphate, on gibbsite the competition is closer, but still phosphate is favoured, while on illite, montmorillonite and kaolinite the competition is almost equal. The amounts of glyphosate and phosphate, which can be adsorbed also depends on the adsorbent: the oxides adsorb more than the clay silicates. The amount adsorbed on kaolinite was dependent on the specific surface area. Changes in the surface area did not affect the competition between glyphosate and phosphate for adsorption sites. The results indicate that differences among soils of different mineralogical composition regarding the adsorption of glyphosate and phosphate can be expected.

Influence of humic substances on phosphate adsorption by aluminium and iron oxides

“…The continued increasing phosphate adsorption by the aluminium oxide may be due to aluminium oxide dissolution and subsequent precipitation of aluminium phosphate (Lookman et al, 1997) or to migration of phosphate into the solid mass as shown for phosphate adsorption by ferrihydrite (Willett et al, 1988). The comparatively fast adsorption by the well-crystallised goethite is in agreement with previous studies on rate of adsorption by amorphous to poorly ordered compared to well-crystallised oxides (Gimsing and Borggaard, 2002;Strauss et al, 1997;Willett et al, 1988). The binding or affinity constant (K) increases with equilibration time for the poorly ordered oxides but is constant (or tends to decrease) for the goethite (Tables 2A, 2B and 2C).…”

“…Accordingly, high amounts of glyphosate and phosphate were adsorbed by synthetic oxides, while pure clay silicates adsorbed much less of both adsorbates Borggaard, 2001, 2002). However, while phosphate was strongly preferred by goethite and adsorbed phosphate almost prevented glyphosate adsorption (Gimsing and Borggaard, 2001), affinities by gibbsite and clay silicates for the two adsorbates were more equal (Gimsing and Borggaard, 2002). Furthermore, for these adsorbents, adsorption of glyphosate and phosphate was partly additive as total adsorption of glyphosate plus phosphate from a mixture of the two adsorbates was significantly higher than the amount adsorbed from solutions containing only glyphosate or phosphate (Gimsing and Borggaard, 2002).…”

Glyphosate and phosphorus leaching and residues in boreal sandy soil

“…Competition between glyphosate and phosphorus was first reported by Sprankle et al (1975a and b) and Hance (1976). In fact, an increase in phosphorus (P) status renders the glyphosate sorption more reversible (de Jonge et al 2001;Gimsing and Borggaard 2002;Laitinen et al 2008). Therefore, it is most probable that the same factors affect the leaching and transport of both glyphosate and phosphorus.…”

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;…”