Tourism, temporal fluctuation, and hurricane-driven sunscreen contamination in the groundwater of the Yucatán Peninsula

Cancún’s popularity as a tourist destination places significant pressure on its freshwater aquifer, particularly through cenotes (sinkholes) that directly connect surface activities to groundwater. Emerging contaminants such as sunscreen UV filters can enter this system and based on prior toxicological studies, have the potential to reach the ocean and harm aquatic ecosystems which include contributing to coral bleaching. This study combines two complementary field surveys conducted by our research group in the Riviera Maya, Quintana Roo, México, to examine how tourism intensity and extreme weather are associated with sunscreen contamination of the region’s karst aquifer. In July 2022, water samples were collected hourly throughout the day at a heavily touristed cenote (VL), a remote cenote without tourist activity (AA), and a public supply well (P52) near Puerto Morelos to evaluate temporal fluctuations in eight organic UV filters using a modified version of EPA Method 1,694 with Liquid chromatography–mass spectrometry (LC–MS/MS). In July 2024, the same tourist cenote (VL) and public well (P52) were resampled, along with two additional limited-tourism cenotes (YK, LL), before and after Hurricane Beryl (July 5, 2024), and analyzed by LC–MS/MS for seven organic UV filters and by inductively coupled plasma atomic emission spectroscopy (ICP-OES) for the mineral filters ZnO and TiO₂. Five of the eight organic UV filters tested in 2022, including 4-methylbenzylidene camphor and butylmethoxydibenzoylmethane, were detected even in the remote cenote without tourist presence, indicating background contamination, while total hourly concentrations at the tourist cenote peaked above 700 ppb and were significantly higher than at the low-tourism site ( p < 0.004). In 2024, chemical sunscreen concentrations at the drinking water supply well increased (147.8%) after Hurricane Beryl, and concentrations at the most heavily used tourist cenote increase by 360.9%, while cenotes with limited tourism remained comparatively stable. Although these pre- and post-hurricane differences were not statistically significant given the limited number of samples, they are presented here as descriptive evidence of a possible storm-associated pulse in contamination. Phenyl benzimidazole sulfonic acid (PBSA) was the most ubiquitous compound detected across both surveys, found in nearly every sample (up to 172.9 ppb), consistent with its high water solubility. Together, these findings show that the Yucatán Peninsula’s karst aquifer experiences both chronic, tourism-driven sunscreen contamination that fluctuates hour-to-hour and acute increases in contamination following extreme rainfall events. These complementary contamination pathways underscore the need for continuous monitoring and management strategies, including regulation of UV-filter ingredients, to protect this vulnerable, groundwater-dependent coastal region. Although the present study examines the response to a single hurricane event and does not itself assess long-term trends in storm frequency or intensity, these findings are relevant as hurricanes are projected to intensify under climate change.