Legacy pollution from historical mining in the Suances Estuary (N Spain): Challenges for ecological recovery

Estuaries and similar coastal areas are among the most vulnerable ecosystems worldwide, facing environmental degradation due to anthropogenic pressures that demand a comprehensive evaluation of their historical trajectories. The study integrates benthic foraminifera, trace metals (Zn, Pb, Cd, and Hg), and short-lived radionuclides (²¹⁰Pb and ¹³⁷Cs) to reconstruct the environmental evolution of the heavily polluted Suances Estuary (N Spain). The investigation focuses on the estuary’s response to the cessation in 2003 of historical mining activities of one of Europe’s largest carbonate-hosted Pb-Zn ore bodies, the Reocín metalliferous deposit. A total of twenty-two surface sediment samples and a short sediment core (47 cm in length) were analyzed. Core samples revealed elevated concentrations of Zn (>10,000 mg kg⁻¹), Pb (max. 2700 mg kg⁻¹), Cd (35.3 mg kg⁻¹), and Hg (41 mg kg⁻¹), exceeding both local baselines and sediment quality guidelines. While a downward trend in surface metal concentrations was observed between 2003 and 2022, the documented spatial heterogeneity suggests ongoing sediment redistribution. Foraminiferal standing crops remain extremely low (1–510 living individuals per 80 cm³), indicating continued ecological stress. Although the Reocín mine was closed more than two decades ago and industrial discharges have been reduced, pollution likely remains as a significant obstacle to environmental recovery. Additionally, the sedimentary record reveals the evidence of an accidental failure in waste storage facilities occurred in 1960, which released substantial volumes of mine tailings into the basin, including the estuary. These events, further comprising the reliability of sediment dating methods based on ²¹⁰Pb, reinforce the importance of a multidisciplinary approach in studying historically contaminated estuaries.