Interaction between glyphosate and montmorillonite in the presence of artificial seawater

Rodrigo C Pereira; Antonio C S da Costa; Flávio F Ivashita; Andrea Paesano Jr; Dimas A M Zaia

doi:10.1016/j.heliyon.2020.e03532

Interaction between glyphosate and montmorillonite in the presence of artificial seawater

Heliyon. 2020 Mar 6;6(3):e03532. doi: 10.1016/j.heliyon.2020.e03532. eCollection 2020 Mar.

Authors

Rodrigo C Pereira¹, Antonio C S da Costa², Flávio F Ivashita³, Andrea Paesano Jr³, Dimas A M Zaia¹

Affiliations

¹ Laboratório de Química Prebiótica, Departamento de Química-CCE, Universidade Estadual de Londrina, 86051-990, Londrina, PR, Brazil.
² Departamento de Agronomia-CCA, Universidade Estadual de Maringá, 87020-900, Maringá, PR, Brazil.
³ Departamento de Física-CCE, Universidade Estadual de Maringá, 87020-900, Maringá, PR, Brazil.

Abstract

Glyphosate (N- (phosphonomethyl) glycine) is one of the most widely used herbicides in the world. In the literature, there are several studies describing the interaction between glyphosate and clay minerals. However, there is a lack of data of this interaction in marine environments. In this research, we examined the adsorption of glyphosate onto montmorillonite in the presence of artificial seawater. Mössbauer data showed that the interaction of the phosphonate group of glyphosate with Fe²⁺ of montmorillonite prevents its oxidation to Fe³⁺. X-ray diffractograms showed that glyphosate adsorption takes place only onto the montmorillonite surface and not in its interlayers. Infrared spectroscopy data demonstrate that the interaction between glyphosate and montmorillonite could be through the amino group. FT-IR spectra of aqueous solutions of salts of seawater showed that Ca²⁺ interacts with glyphosate of the phosphonate group, thus causing an increase in its adsorption onto montmorillonite. However, glyphosate dissolved in 0.50 mol L^-1 NaCl and 0.034 mol L-1MgCl2 solutions showed the lowest adsorption onto montmorillonite. In addition, the adsorption of glyphosate onto montmorillonite decreased when the NaCl concentration increased. The results fitted the Sips isotherm model, probably because the Ca²⁺ interacts with glyphosate, making the adsorption process more homogeneous. Thus, n values for Freundlich and Sips isotherm models decreased with an increase in ionic strength. Glyphosate and ions of artificial seawater increased the pH_pzc of montmorillonite.

Keywords: Adsorption; Clay; Environmental science; Glyphosate; Montmorillonite; Physical chemistry; Seawater.