Assessment of potentially toxic elements in surface sediments along the lower Coatzacoalcos River basin, Mexico

Surface sediments from the lower Coatzacoalcos River basin were analyzed to assess the distribution of potentially toxic elements (PTE: Cr, Cu, Pb, Zn), identify sites of ecotoxicological concern, and elucidate the sedimentary processes controlling their accumulation. The Coatzacoalcos River estuary (southern Gulf of Mexico) lies within one of Mexico's major industrial corridors, while small urban settlements and extensive agricultural areas impact the lower basin. Several sampling sites displayed concentrations of Cr (47.5-85.9 μg g^-1), Cu (15.0-37.4 μg g^-1), Pb (6.6-14.6 μg g^-1), and Zn (80.5-178.3 μg g^-1) above background values, although only minor enrichments were observed. Ecological risk indices did not discriminate between sites, indicating an overall low to moderate risk for benthic biota. In contrast, benchmark-based classifications suggested a rare risk for Cu, Pb, and Zn, and an occasional risk for Cr. Principal component analysis revealed that PTEs accumulation is likely influenced by lithogenic sources, fine-grained sediments, and geochemical phases, including organic matter and carbonates. This region has been projected as a strategic hub for national logistics and economic development, and these findings provide valuable information to help mitigate potential environmental impacts from the anticipated industrial expansion.