The social and environmental legacy of marine mine tailings disposal: Lessons from Portmán Bay for sustainable mine closure and coastal restoration

Marine disposal of mine tailings represents one of the most persistent environmental legacies associated with metal mining worldwide. Portmán Bay (SE Spain) is one of the Mediterranean's most severely mining-impacted coastal environments, following the discharge of ∼56 Mt of flotation tailings. This review assesses the mineralogical, geochemical, ecological, geotechnical, socioeconomic and climate-related consequences of mine-tailings disposal in Portmán Bay. The tailings remain a major reservoir of potentially toxic elements, mobilised through sediment resuspension, submarine groundwater discharge, pore-water exchange and sediment geochemical processes. Approximately 48 Mt of mine tailings remain within the bay, posing risks of sediment instability, contaminant remobilisation and ecosystem degradation that may be exacerbated under future climate-change scenarios. Five management scenarios were qualitatively evaluated, from natural attenuation and in situ containment to complete tailings removal. The assessment compares the occurrence, persistence and uncertainty of impact pathways rather than providing a quantitative risk analysis. Alternatives retaining mine waste within the bay preserve most long-term environmental pressures despite differences in engineering intervention and implementation costs. Complete removal followed by secure onshore containment, although technically challenging, appears feasible using established dredging, containment and monitoring technologies and offers the greatest potential for environmental risk reduction, ecosystem restoration, climate resilience and future resource recovery. The analysis highlights the importance of governance, stakeholder engagement and climate-informed planning, while demonstrating how scientific and governance-related uncertainties influence long-term restoration outcomes. Portmán Bay provides an internationally relevant case study for the management and restoration of legacy marine tailings in coastal environments.