Copper speciation and mobility in glyphosate co-contaminated soils: a microcosm and X-ray absorption spectroscopy study

Abstract

Context The effect of glyphosate–copper complex on copper mobility had been studied in aqueous conditions. The effect on copper distribution through the soil profile is little understood and controversial. Aims This study aims to investigate the effect of glyphosate on copper mobility and distribution through the soil profile and to identify the specific copper binding change at the molecular level. Methods The experiments were performed in microcosm soil spiked with copper and glyphosate. Sequential extraction and X-ray absorption spectroscopy techniques were applied for copper speciation. Key results The organic bound fraction was the highest fraction (50%) in the top soil layer, while Cu(CH3COO)2 (43%) and Cu(NO3)2 (49%) were the highest fraction in linear combination fit (LCF) analysis. In the presence of glyphosate, the readily mobile fraction of copper (water soluble and exchangeable fractions) increased, while the mobilised fractions decreased within 1 day of glyphosate application. The LCF analysis revealed that CuSO4 and Cu3(PO4)2 increased in the presence of glyphosate. The effects of glyphosate were no longer detected by 14 days after application. During the 40 days of the experiment, the released copper did not leach beyond 4 cm deep in soil. Conclusions The existence of glyphosate in soil induced the release of copper into the readily mobilised fraction within 1 day of glyphosate contamination. The effect was found within 4 cm depth and declined in correspondence with the degradation half-life of glyphosate. Implications The finding is important in evaluating the risk of metal diffusion and nutrient leaching from co-contaminated soil through the soil profile over time and at a molecular scale.