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.

El objetivo es analizar el impacto de los residuos urbanos e industriales del municipio de Marau (Rio Grande do Sul -Brasil) en la calidad del agua del río Marau. Para ello, se evaluaron: pH, turbidez, conductividad eléctrica, tensión superficial, carbono orgánico, metales, nitrito, nitrato, cloruro, fosfato, sulfato y fósforo. Las colectas de agua del río ocurrieron en septiembre de 2014 y 2016 en los puntos: aguas arriba de la ciudad de Marau y de La curtiembre; aguas arriba de la curtimbre; en el punto de mezcla del efluente de La industria de curtiembre y el río; aguas abajo de la ciudad de Marau. El análisis físico-químico del agua mostró que los efluentes de la ciudad son la fuente principal de contaminación local, teniendo valores de Al, Pb y P mayores que los permitidos por La legislación. Se concluye que las actividades industriales y los efluentes no tratados de la ciudad de Marau tienen un impacto negativo en la calidad del agua del río.