Potential Ecological Risk Index and Metal Fate in a Karstic Tropical Lagoon: Chelem, Yucatan, Mexico

Chelem is a karstic lagoon with urban settlements, economic activities, and environmental services, making it highly vulnerable to metal contamination. This study evaluated metal sediment contamination using enrichment factor, geoaccumulation index and ecological risk index across dry, rainy and Nortes seasons. Cadmium and arsenic concentrations exceed the SQuiRTs thresholds for early biota damage. Metal distribution was driven by submerged groundwater discharges, co-transport with fine particular matter in rainy and Nortes seasons, and direct inputs from urban wastewater and port operations. Cadmium, arsenic and tin exhibited minor to moderate enriched levels. Geoaccumulation index classified the lagoon from minor to highly contaminated. Despite this, the overall ecological risk index remained low. However, sediment-bound metals may already affect local biota and pose future risks to fisheries and human health. These findings highlight the need for continued monitoring and improved management to prevent long-terms ecological and public health impacts in this vulnerable karstic system.