Metals in the Del Plata Basin: occurrence, spatial patterns, and ecological risk

Metal pollution represents a pervasive environmental issue across aquatic ecosystems worldwide. This study provides the first integrated compilation and assessment of metal and metalloid concentrations in water and sediments across the Del Plata Basin (DPB), the second largest basin on South America, over the last decade, alongside an Ecological Risk Assessment using the Risk Quotient (RQ) approach. Results reveal an uneven spatial distribution of metal monitoring, with data concentrated in densely populated regions such as the de la Plata River metropolitan coastline and extensive knowledge gaps elsewhere. Copper and mercury emerged as the main contaminants of concern at the basin scale, with mean concentrations of 24.48 ± 35.14 µg/g and 7.28 ± 8.06 µg/L for Cu in sediment and water, respectively, and 47.61 ± 105.54 µg/g and 7.74 ± 2.65 µg/L for Hg. Chromium and cadmium showed localized but substantial contamination, with mean concentrations of 29.71 ± 43.73 µg/g and 6.59 ± 20.77 µg/L for Cr, and 42.20 ± 155.36 µg/g and 0.62 ± 0.64 µg/L for Cd, in sediment and water, respectively. Concentrations of many metals, mainly Cd, Cu, and Pb, frequently exceeded international water quality guidelines, underscoring the absence of coordinated regional legislation and harmonized monitoring strategies. RQ was generally higher in sediments, where Hg and Cd accounted for 56% and 32.81% of high-risk records, respectively, whereas Cu accounted for 35.35% of high-risk water records. Overall, by identifying priority contaminants and critical knowledge gaps, this study provides a robust scientific framework to support transboundary coordinated monitoring, ecological risk assessment and evidence-based management across one of the world's largest river basins.