Geochemical fractionation of mercury and trace metals in river sediments of the Almadén mining district (Spain): implications for ecological risk

Sediments in the Valdeazogues River basin, part of Spain's Almadén mercury mining district, act as both sinks and potential sources for trace metals, posing persistent ecological risks despite mine closure. The study found that mercury (Hg) exhibits significant enrichment with concentrations up to 277.4 μg g⁻¹, far exceeding background levels, while manganese (Mn), zinc (Zn), and lead (Pb) also show elevated levels. Geochemical fractionation revealed that Hg, Mn, and Zn are more mobile compared to copper (Cu), nickel (Ni), and Pb, which are predominantly bound in the residual fraction. A screening-level ecological risk assessment indicated potential concern primarily for Hg, Mn, and Zn due to their higher proportions in non-residual fractions, suggesting greater bioavailability and mobility. This research underscores the need for continued monitoring and management of these sediments to mitigate long-term environmental threats.

Garcia-Ordiales, E., Barral, N., Higueras, P., Cienfuegos, P., & Barquero, J. I. (2026). Geochemical fractionation of mercury and trace metals in river sediments of the Almadén mining district (Spain): implications for ecological risk. Environmental Research, 305, 125064. https://doi.org/10.1016/j.envres.2026.125064