Risk of preeclampsia among women living in coastal areas impacted by sargassum strandings on the French Caribbean island of Martinique

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.

Central sleep apnea and exposure to ambient hydrogen sulfide emissions from massive strandings of decomposing sargassum in the Caribbean

BACKGROUND

Sargassum invasion of Caribbean and American shorelines is a recurring environmental hazard. Potential health effects of long-term chronic exposure to sargassum gaseous emissions, notably hydrogen sulfide (H2S), are overlooked. H2S plays an important role in neurotransmission and is involved in generating and transmitting respiratory rhythm. Central sleep apnea (CSA) has been attributed to the depression of respiratory centers.

OBJECTIVE

Evaluate the effects of exposure to sargassum-H2S on CSA.

METHODS

This study, set in the Caribbean, describes the clinical and polysomnographic characteristics of individuals living and/or working in areas impacted by sargassum strandings, in comparison with non-exposed subjects. Environmental exposure was estimated by the closest ground H2S sensor. Multivariate linear regression was applied to analyze CSA changes according to cumulative H2S exposure over time. Effects of air pollution and other sargassum toxic compounds (NH3) on CSA were also controlled.

RESULTS

Among the 685 study patients, 27 % were living and/or working in sargassum impacted areas. Compared with non-exposed patients, exposed ones had similar sleep apnea syndrome risk factors, but had increased levels of CSA events (expressed as absolute number or % of total sleep apnea). Multivariate regression retained only male gender and mean H2S concentration over a 6-month exposure period as independent predictors of an increase in CSA events. A minimal exposure length of 1 month generated a significant rise in CSA events, with the latter increasing proportionally with a cumulative increase in H2S concentration over time.

CONCLUSION

This pioneer work highlights a potential effect of sargassum-H2S on the central nervous system, notably on the modulation of the activity of the brain's respiratory control center. These observations, jointly with previous studies from our group, constitute a body of evidence strongly supporting a deleterious effect of sargassum-H2S on the health of individuals chronically exposed to low to moderate concentration levels over time.

Clinging fauna associated with nearshore pelagic sargassum rafts in the Eastern Caribbean: Implications for coastal in-water harvesting

Tropical Atlantic blooms of pelagic Sargassum species are associated with severe inundation events along the coasts of Caribbean and West African nations that cause extensive ecological and socioeconomic harm. The use of in-water harvesting as a management strategy avoids the plethora of challenges associated with shoreline inundations. Moreover, with a growing interest in the valorisation of this raw material, in-water harvesting provides the best opportunity to collect substantial amounts of 'fresh' sargassum that can be used in a variety of applications. However, in-water harvesting of sargassum will remove organisms associated with the floating habitat, resulting in loss of biodiversity, thus creating a potential management dilemma. To address this management concern, we assessed the clinging fauna associated with sargassum rafts at various distances from shore. From a total of 119 dipnet samples of sargassum, we recorded 18 taxa, across 6 phyla (Arthropoda, Mollusca, Chordata, Platyhelminthes, Nemathelminthes, Annelida) with the phylum Arthropoda being the most speciose (n = 10). Our multivariate and model selection analyses support that distance from shore and season are the most important drivers of variability in community composition and that season is the most important driver of individual abundance and number of taxa across samples. Overall, rafts within 0-3000 m of the shoreline of Barbados harbored low biodiversity and were dominated by small invertebrates (mean size: 5.5 mm) of no commercial value. Results suggest that biodiversity trade-offs associated with in-water sargassum harvesting in coastal areas are likely to be negligible.

A new Sargassum drift model derived from features tracking in MODIS images

Massive Sargassum stranding events affect erratically numerous countries from the Gulf of Guinea to the Gulf of Mexico. Forecasting transport and stranding of Sargassum aggregates require progress in detection and drift modelling. Here we evaluate the role of currents and wind, i.e. windage, on Sargassum drift. Sargassum drift is computed from automatic tracking using MODIS 1 km Sargassum detection dataset, and compared to reference surface current and wind estimates from collocated drifters and altimetric products. First, we confirm the strong total wind effect of ≈3 % (≈2 % of pure windage), but also show the existence of a deflection angle of ≈10° between Sargassum drift and wind directions. Second, our results suggest reducing the role of currents on drift to 80 % of its velocity, likely because of Sargassum resistance to flow. These results should significantly improve our understanding of the drivers of Sargassum dynamics and the forecast of stranding events.