Contaminação por metais pesados e agrotóxicos na bacia do Rio Marrecas (Paraná, Brasil): diagnóstico geoquímico multielementar, risco ecotoxicológico e insuficiência do monitoramento convencional

Abstract

The Marrecas River Basin, the primary public water supply for the municipality of Francisco Beltrão (PR), was assessed regarding the environmental quality of its surface water and sediments using energy-dispersive X-ray fluorescence spectrometry (EDXRF) for multielemental analysis and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for herbicide determination. The investigation spanned 28 sampling points in the water column and 25 in bottom sediments across the upper, middle, and lower reaches, during both dry spells and intense rainfall periods. Results revealed significant and ubiquitous copper (Cu) contamination in the water column. Even under a conservative estimate based on the upper limit of quantification, concentrations exhibit a striking anthropogenic geochemical enrichment in the water column (expressed as a mass percentage of the detected solid material), pointing to diffuse and persistent copper inputs into the river basin. Conversely, the sediments display a lithogenic signature consistent with the weathering of basalts from the Serra Geral Formation. Point anomalies of phosphorus (P), calcium (Ca), chromium (Cr), and nickel (Ni) suggest inputs from agro-industrial effluents, potentially from a slaughterhouse, characterizing an acute pollution event in the lower reach. The herbicides glyphosate, its metabolite AMPA, and glufosinate-ammonium were widely detected, with glyphosate appearing in 95.7% of the samples, evidencing diffuse and seasonal inputs driven by stormwater runoff (first flush). The Hazard Quotient (HQ) assessment indicated an extreme risk for copper in the aqueous phase and a high risk for zinc associated with sediments. Furthermore, the study demonstrated the structural insufficiency of the Water Quality Index (WQI) in detecting metal and pesticide contamination, as these parameters are absent from its formulation, rendering the actual anthropogenic pressure on the water source invisible. In conclusion, there is an urgent need for integrated monitoring programs that incorporate geochemical, ecotoxicological, and water quality indicators to ensure effective management of this river basin, overcoming the limitations of conventional approaches based solely on the WQI.