Mapping total mercury in rivers of Mato Grosso: baselines and contamination hotspots by biome

Mercury (Hg) contamination is a critical environmental and public health concern due to its toxicity, persistence, and ability to biomagnify through aquatic food webs. This study mapped total mercury (HgT) concentrations in sediments from rivers across Mato Grosso, integrating geochemical parameters (HgT, organic matter, C/N ratio) and granulometric fractions. Statistical analyses included correlation, regression (OLS and GLM with Gamma distribution), and non-parametric comparisons (Kruskal-Wallis with post hoc tests). HgT concentrations ranged from 1.4 to 948.1 µg.kg⁻¹, with an overall mean of 109.1 ± 165.8 µg.kg⁻¹. Significant positive associations were observed between HgT and both organic matter (r = 0.50) and the C/N ratio (r = 0.70), with the latter emerging as the strongest predictor of Hg variability. Basin-level comparisons revealed that the Amazon had the highest mean concentrations (242.0 µg.kg⁻¹), followed by the Upper Paraguay (47.9 µg.kg⁻¹) and the Araguaia (29.3 µg.kg⁻¹). At the river scale, the Guaporé (731.5 µg.kg⁻¹) and Xingu (233.7 µg.kg⁻¹) were identified as contamination hotspots. Most rivers remained below the Threshold Effect Level (TEL = 170 µg.kg⁻¹) set by CONAMA Resolution 454/2012, but the Xingu exceeded the TEL and the Guaporé surpassed the Probable Effect Level (PEL = 486 µg.kg⁻¹), indicating high ecological risk. This study offers essential insights for environmental monitoring, water management, and biodiversity conservation, supporting Brazil’s commitments under the Minamata Convention. Keywords: conservation, ecotoxicology, Hg, sediments.