Epilithic biofilms are communities of microorganisms composed mainly of microbial cells, extracellular polymeric substances from the metabolism of microorganisms, and inorganic materials. Biofilms are a useful tool to assess the impact of anthropic action on aquatic environments including the presence of pesticide residues such as glyphosate. The present work seeks to monitor the occurrence of glyphosate and AMPA residues in epilithic biofilms occurring in a watershed. For this, epilithic biofilm samples were collected in the Guaporé River watershed in the fall and spring seasons of 2016 at eight points. Physicochemical properties of the water and biofilms were determined. The determination of glyphosate and AMPA was performed using an ultra-high performance liquid chromatograph coupled to a tandem mass spectrometer. The concentrations of glyphosate and AMPA detected in epilithic biofilms vary with the season (from 90 to 305 μg kg-1 for glyphosate and from 50 to 240 μg kg-1 for AMPA, in fall and spring, respectively) and are strongly influenced by the amount of herbicide applications. Protected locations and those with poor access not demonstrate the presence of these contaminants. In the other seven points of the Guaporé River watershed, glyphosate was detected in concentrations ranging from 10 to 305 μg kg-1, and concentrations of AMPA ranged from 50 to 670 μg kg-1. An overview of the contamination in the Guaporé watershed shows that the most affected areas are located in the Marau sub-watershed, which are strongly influenced by the presence of the city of Marau. This confirms the indiscriminate use of glyphosate in the urban area (weed control, domestic gardens and horticulture) and constitutes a problem for human and animal health. The results showed that biofilms can accumulate glyphosate resulting from the contamination of water courses and are sensitive to the sources of pollution and pesticides present in rivers.

Glyphosate is the most widely used herbicide in Argentina. The strong sorption of glyphosate to the mineral fraction of the soil can be affected by environmental conditions and agricultural management, such as the application of fertilisers. This work aimed to study the effect of pH and the presence of inorganic phosphate on the affinity of glyphosate for nine different surface soils of Argentina. The effect of pH on glyphosate sorption was investigated by batch experiments with pH adjusted between 3 and 12. The greatest glyphosate adsorption occurred at a certain pH value and then adsorption decreased with increasing or decreasing pH. The effects of pH on adsorption could be described by a model that includes changes in electrical potential. The effect of inorganic phosphate on glyphosate adsorption was studied by batch experiments in the presence of 0.5 or 1 mM phosphate. The results showed a significant competition between phosphate and glyphosate in all soils. The Freundlich glyphosate coefficients decreased by 40%–65% with phosphate in solution, and the amount of glyphosate adsorbed decreased between 1% and 5%, depending on the particular characteristics of the soil. For the glyphosate‐phosphate competition, the competition terms were not reciprocal with each other because the competition between ions for adsorption sites also involves electrical effects. Highlights: There is a pH at which glyphosate shows a higher affinity for the soil. The presence of phosphate significantly reduces the adsorption of glyphosate to the soil. The effects of pH can be explained by rather small changes in the estimated surface potential.

A rapid analytical methodology has been developed for multi-residue determination of pesticides in soils using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) with a triple quadrupole analyzer. Soil samples were collected from 12 representative agricultural areas in Argentina, and 18 pesticides were selected on the basis of their use. Special attention was paid to minimize sample preparation, making easier the method application to routine analysis. Several extraction procedures were tested, performing a careful study on matrix effects. The method finally proposed (extraction with acetonitrile and a subsequent 2-fold dilution with water without any clean-up step) was fully validated at 0.05 and 0.5 mg kg⁻¹ on the basis of European SANCO 12571/2013 and 825/00 guidelines. The method applicability and robustness were demonstrated by analysis of quality control (QC) samples, consisting of eleven soils spiked at 0.5 mg kg⁻¹. These soil samples were collected from different experimental plots, and were very diverse in their physico-chemical characteristics. The methodology developed is of easy application, there is low consumption of solvents and reagents, and no clean-up is required despite the complexity of the soil matrix. In the near future, the method developed will be used to monitor the presence of pesticides in large agricultural areas of Argentina.