Health risks and cross-border environmental exposure: A binational study of the San Diego-Tijuana-Rosarito Pacific Ocean coastline

The Pacific coastline along the US-Mexico border is increasingly contaminated by the binational Tijuana River. The topic has garnered significant political interest in both countries, but little is known about the binational health implications of this pollution. This mixed methods study explored self-reported health risks associated with interactions with specific beach sites across the San Diego-Tijuana-Playas de Rosarito region, among residents, workers, and coastal visitors in 2024–2025. A non-probability online survey was distributed at beaches and among coastal communities, and completed by n = 390 participants. Associations between coastal interactions and self-reported health conditions were assessed using adjusted and unadjusted odds ratios. Additional in-depth qualitative interviews were conducted with three local health professionals. Ethnographic field notes were collected by study staff during survey recruitment and coastal site field work. Triangulating these information sources, we find that coastal visitors encounter substantial environmental hazards, including high enterococci levels at specific coastal water sites. The most prevalent self-reported health issues were respiratory conditions (47 % of participants), eye allergies (16 %), gastrointestinal conditions (15 %), and ear infections (11 %). Multivariate analysis showed higher odds of these outcomes among residents and visitors of certain coastal sites, as well as those who practiced aquatic sports, and those who reported encountering unpleasant conditions at local beaches (e.g. trash or human feces). Findings suggest that recreational activities, contact with polluted water, and passive environmental exposure—via air and sand contact—may contribute to the region’s health burden. These results support the implementation of planetary health approach and increased binational collaboration to improve infrastructure and environmental monitoring.