Assessment of hydrogen sulfide exposure in shoreline cleanup workers during the 2025 Atlantic Sargassum bloom

• Hydrogen sulfide (H 2 S) exposure was evaluated among Sargassum cleanup workers. • Atmospheric H 2 S concentrations exceeded 1 ppm in 46.3% measurements, exceeded 10 ppm in 1.7%, and reached peaks of 50.8 ppm • Self-reported common symptoms include itching, burning sensations, headaches, dermatitis, and fatigue. • An 8-hour permissible exposure limit of no more than 1 ppm of H 2 S is recommended to protect workers. Since 2011, massive blooms of pelagic Sargassum spp. have emerged as a recurrent environmental crisis across the tropical Atlantic. Along affected coastlines, thousands of tons can accumulate annually, releasing toxic gases during anaerobic decomposition and posing potential health risks. Hydrogen sulfide (H₂S) is of concern due to its adverse effects on the respiratory, neurological, gastrointestinal, and ocular systems. This study quantified H₂S exposure among Sargassum cleanup workers in the Mexican Caribbean during the unprecedented 2025 bloom, the largest recorded to date. 35 workers were equipped with a portable personal sensor (1 ppm resolution; 1-100 ppm detection range) that recorded H 2 S concentration at 1-s intervals throughout Sargassum removal activities. H 2 S concentrations ranged from