Delineating distinct sediment pollution signatures from diverse sources in a heavily contaminated estuary near an area of high cancer and cardiovascular mortality.

Our study aimed to identify specific pollution signatures in marsh sediments using geochemical tracers in the highly polluted Odiel-Tinto Estuary prior to a planned restoration of the affected marshes. Tidal marshes in this estuary are heavily polluted from different sources such as acid mine drainage, industrial activities (including phosphogypsum stacks) and agricultural runoffs. We analysed the total concentrations of 48 chemical elements, pH, electrical conductivity, redox potential and texture of surface sediments from six marsh areas in the Odiel-Tinto Estuary and one in the adjacent Piedras Estuary. Spatial distribution maps were created using inverse distance weighting to visualise the distribution of elements associated with different pollution sources. We identified a specific pollution signature for PG stacks that distinguishes metal exposure from the other pollution sources in the Odiel-Tinto Estuary, such as acid mine drainage near mining waste deposits, an abandoned foundry and areas under intensive agricultural cultivation. Our results provide a valuable tool for discriminating between pollution sources, quantifying the most impacted areas of the salt marsh, assigning responsibility to the various polluting entities within the estuary, and setting a starting point to evaluate the impact of the RESTORE 2030 restoration plan in the Odiel-Tinto Estuary. The specific sediment pollution signatures identified may also be used as a reference to determine the impact of future interventions on existing pollution sources in estuaries or marshes polluted with phosphogypsum.