Sediment-Bound Metals in a Protected Karstic Lagoon: Seasonal Dynamics and Ecological Risk to Biota and Public Health.

Coastal lagoons in karstic regions are highly vulnerable to anthropogenic inputs via permeable aquifers. This study evaluates heavy metal distribution and ecological/health risks in Ría Lagartos, Mexico. Surface sediments from eleven sites across three seasons were analyzed using geochemical indices (EF, Igeo, RI) and NOAA's SQuiRTs guidelines. Cadmium (Cd) and arsenic (As) were the primary contaminants, consistently exceeding SQuiRT thresholds with enrichment levels reaching "extremely severe". Spatial analysis linked hotspots to urban/waste sectors, with a Cd-Sn association indicating localized sources. While the overall potential ecological risk was low, localized exceedances for Cd, As, and Ni indicate specific ecotoxicological threats. Human health risk assessments identified significant concerns for arsenic exposure via ingestion, particularly for children. These findings emphasize the karst aquifer as a critical transport pathway and highlight the necessity for integrated geochemical and health monitoring in vulnerable coastal ecosystems.