Investigation of Anthropogenic and Emerging Contaminants in Sinkholes (Cenotes) of the Great Mayan Aquifer, Yucatán Peninsula.

Abstract

Karst water bodies are vital groundwater resources particularly vulnerable to pollution. Protecting their water quality requires documenting contaminants traditionally associated with anthropogenic activities (metals, nutrients, and fecal indicator bacteria) as well as emerging contaminants, such as antibiotic-resistant organisms (AROs) and perfluoroalkyl substances (PFAS). This study detected contaminants in karst-associated water bodies on the Yucatán Peninsula, including 10 sinkholes (cenotes) and one submarine groundwater discharge (SGD) site. The concentrations of metals (strontium, cadmium, nickel, lead), nutrients (phosphate, silicate, ammonium, nitrate, and nitrite), and fecal indicator bacteria (fecal coliforms, Escherichia coli) were consistent with previous reports, sometimes exceeding recommended standards for groundwater or the protection of aquatic life. This included elevated lead (80.3 µg/L) and nitrate (413 μmol/L) concentrations at two cenotes, and elevated E. coli levels (167 - 1800 CFU/100 mL) in five cenotes. Additionally, 34 antibiotic-resistant E. coli strains were identified in nine cenotes and most strains were multidrug-resistant. Perfluorooctanesulfonic acid (PFOS) and perfluorohexanoic acid (PFHxA) were also detected in eight cenotes and the SGD, with total PFAS concentrations from 0.68 to 10.71 ng/L. The absence of associations between contaminants and urban cover suggests karst hydrology influences contaminant cycling-stable isotope signatures (δ¹⁸O, δ²H) confirming that most systems are interconnected to regional groundwater flows, that could allow contaminants to travel long distances. The Yucatán Peninsula's karst is an important freshwater reservoir used for consumption and recreation; the presence of contaminants and the karst's vulnerability to their spread raises concerns and highlights the need for continued monitoring and conservation.