Ecological Risk Assessment of Metal Contamination in Groundwater and Sediments Along the Ruta de los Cenotes, Mexican Caribbean

Metal contamination in karst aquifers is a growing concern in rapidly urbanizing coastal regions. The Ruta de los Cenotes in Quintana Roo comprises groundwater-fed cenotes of high hydrogeological and ecological relevance. This study characterized the hydrogeochemical setting of five cenotes along a coastal–inland gradient, quantified metals in groundwater and sediments, and assessed ecological risk. Groundwater was sampled at 1, 15, and 25 m during dry and rainy seasons, and sediments at 30 m depth. Metals (Al, Ba, B, Cd, Cr, Cu, Fe, Li, Ni, Pb, and Zn) were determined by ICP-OES. Coastal and transitional cenotes showed calcium-sulfate waters and EC > 1200 µS/cm, whereas inland cenotes showed calcium-bicarbonate waters and EC < 1000 µS/cm. Multivariate analysis identified mineralization gradients during the dry season and site-specific variability during the rainy season. In groundwater, Al reached 0.487 mg/L in A-Ha, exceeding the NOM-127-SSA1-2021 limit of 0.20 mg/L. Al, Fe, Li, Cu and Zn were the main contributors to high ecological risk, with Al (RA = 3043.75) and Fe (RA = 74.15) showing the highest values during the rainy season. Overall, risk rankings differed seasonally, with Li > Cu > Zn > Fe > B > Ba in the dry season and Al > Fe > Zn > Cu > Cr in the rainy season. Sediment-associated ecological risk was highest at one coastal cenote (RI = 1868.66), driven mainly by Cd (2.17 mg/kg). These results provide quantitative information that can support future assessments and monitoring of metal-related vulnerability in karst ecosystems.