Epilithic biofilms as bioindicators of water contamination by pesticides in Protected Areas from Atlantic Forest

Protected Areas (PAs) provide crucial refuges for biodiversity and are essential for preserving natural habitats, supporting species survival, and providing ecosystem services such as water purification and soil conservation. However, their effectiveness may be compromised by external anthropogenic pressures, including pesticide contamination, a major threat, particularly to aquatic ecosystems. In this study, we examined the occurrence and spatial distribution of pesticides using epilithic biofilms as bioindicators within PAs of the Atlantic Forest and their surrounding landscapes. Our objective was to evaluate the effectiveness of these PAs in mitigating pesticide contamination in watercourses and to investigate how land use patterns influence the presence of pesticide residues. The findings revealed residues of 14 pesticide compounds and one metabolite across 19 sampling sites. Glyphosate and its metabolite AMPA were the most concentrated herbicides, primarily outside PAs (up to 405 μg kg^-1 and 395 μg kg^-1, respectively). Although we observed higher average concentrations of insecticides (2.38 μg kg^-1) and fungicides (4.63 μg kg^-1) within PAs, there were no statistically significant differences in the concentrations of the three pesticide classes between PAs and external areas. This indicates that PAs did not provide an effective buffer against pesticide contamination in freshwater. Positive correlations between fungicides and exotic cultivated forests suggest that these land uses are key contamination sources. The majority of the detected compounds lack legal thresholds set by Brazilian federal legislation for freshwater conservation, emphasizing the need for regulatory updates. Epilithic biofilms proved effective in revealing pesticide presence and offered complementary insights to surface water analyses. Nevertheless, our study also showed that PAs alone are insufficient to prevent contamination without integrated land-use management, highlighting the need for more rigorous pesticide regulation, monitoring, and management to safeguard freshwater biodiversity. Conservation strategies should incorporate aquatic ecosystems and address surrounding land use to enhance the protective role of PAs in landscapes undergoing agricultural pressures.