Temporal and spatial variation in hydrogen sulfide (H₂S) emissions during holopelagic Sargassum spp. decomposition on beaches

Background: Since 2011, over 30 tropical Atlantic nations have experienced substantial landings of holopelagic Sargassum spp. Its decomposition results in the production of hydrogen sulfide (H₂S), which, in elevated concentrations, can pose a threat to human health. This study aims to enhance our understanding of the temporal and spatial variability in H₂S emissions during the decomposition of Sargassum on beaches. The primary objective is to assess potential exposure risks for local populations, tourists, and cleanup workers.

Methods: H₂S levels were monitored using a SENKO sensor (SGTP-H₂S; limit of detection 0.1-100 ppm; resolution 0.1 ppm) at four distances from Sargassum accumulation points of (0, 10, 30, and 40 m) in Puerto Morelos, Mexico, during 2022 and 2023.

Results: Elevated concentrations of H₂S were detected beneath the Sargassum piles, with 23.5% of readings exceeding 5 ppm and occasional spikes above 100 ppm. Above the piles, 87.3% of the measurements remained below 2 ppm, and the remainder fell between 2.1 and 5.2 ppm. At 10 m from the shoreline, 90% of measurements registered below 0.1 ppm, and the remaining 10% were below 2 ppm. Readings at 30 and 40 m consistently recorded levels below 0.1 ppm. H₂S concentrations positively correlated with Sargassum pile height, the temperature beneath the piles, and wind speed.

Conclusions: Our findings suggest no immediate and significant exposure risk for residents or tourists. However, Sargassum cleanup workers face a higher exposure risk, potentially encountering concentrations above 5 ppm for nearly one-fourth of the working time.