Linking urban expansion to multi-contaminant pollution in karst aquifer cenotes

The Yucatán Peninsula (YP) hosts one of the largest karst aquifer systems in the world, directly connected to the surface through cenotes. These natural sinkholes are critical for the regional drinking-water supply but have increasingly been reported as reservoirs of environmental contamination. In this study, we evaluated water quality and contaminant profiles in nine cenotes located in Playa del Carmen, a rapidly urbanizing area on the Caribbean coast of the YP. The analyzed contaminants included potentially toxic elements (PTEs) in sediments, microplastics in water and sediments, and per- and polyfluoroalkyl substances (PFAS) in water, aiming to determine how urbanization influences water quality and contaminant accumulation. Urbanization levels, estimated from land-use changes since 2010, ranged from 0 to 100 %. Microplastics were detected in all cenotes, with the highest concentrations in sediments from the most urbanized sites. PFAS levels were also highest in cenotes with urbanization. PTE enrichment ranged from mild to severe, with cadmium, copper, and arsenic representing the most concerning elements. The Pollution Load Index confirmed that cenotes with greater urbanization also exhibited higher overall contamination. Collectively, these findings indicate that rapid and unplanned urban expansion, combined with inadequate or absent wastewater treatment, poses serious risks to the integrity and water quality of karst aquifer systems in the Yucatán Peninsula.