Biofilmes epilíticos como matriz inovadora e complementar para o monitoramento de agrotóxicos no meio aquático: ênfase ao glifosato

Abstract

The increasing use of pesticides has induced great environmental concern due to the high ecological risk of aquatic contamination. Thus, microorganisms that inhabit rivers are among the first aquatic organisms to come into contact with residues of these contaminants. Recently, epilithic biofilms have come to be used as a matrix for environmental contamination studies, as they act as bioaccumulators of organic and inorganic compounds. The objective of this research was to investigate the impacts of agricultural activities on surface water contamination with pesticides, with emphasis on glyphosate and its metabolite AMPA, using three monitoring matrices (water, suspended sediments, and epilithic biofilms) and with emphasis on the resilience of glyphosate and AMPA in biofilms. Three watersheds were monitored: one representative of "Modern Agriculture" in a subtropical environment (Quinze de Novembro/RS); one representative of the recent expansion of agriculture over the Pampa biome with Agrarian Reform Settlement (Júlio de Castilhos/RS); and the last one, representative of Argentine agriculture (Quequén Grande - Buenos Aires province). The thesis was presented in three studies. In the first, it was evident that glyphosate and AMPA are bioaccumulated in epilithic biofilms and, were detected in all monitoring sites, in concentrations ranging from 195 to 7673 μg kg-1 for glyphosate and from 225 to 4180 μg kg-1 for AMPA, being that these compounds are also permanently impregnated in the sediments. Also noteworthy was the fungicide tebuconazole, detected in all biofilm’s samples. The second study showed that natural biofilms previously impregnated with glyphosate and AMPA, once transferred to an aquatic environment less contaminated with such compounds, are not able to self-deepen, keeping the initial contamination with them. The phylum Proteobacteria was benefited by the high concentrations of these two xenobiotics. The microbial community is highly and constantly stressed, with difficulties in self-deepening. The third, carried out in the Quequén Grande river basin in Argentina, showed that atrazine was the only compound with 100% detection in the water matrix, and was not detected in sediments and biofilms. Herbicides were detected in 100% of biofilms, in concentrations ranging from 1.61 μg kg-1 (imazethapyr) to 655.00 μg kg-1 (glyphosate), with emphasis on glyphosate and its metabolite AMPA. Biofilms allowed integrative analysis of compounds, especially in comparison with point water sampling, and can bioaccumulate pesticide molecules, providing much more advanced insight into the degree of contamination of the aquatic environment, than the use of active water and even suspended sediment sampling. In addition, studies in subtropical regions with soybean and other transgenic crops must include glyphosate and its metabolite AMPA.