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Massive Sargassum beachings occurred since 2011 on Caribbean shores. Sargassum inundation events currently involve two species, namely S. fluitans and S. natans circulating and blooming along the North Atlantic subtropical gyre and in the entire Caribbean region up to the Gulf of Mexico. Like other brown seaweeds, Sargassum have been shown to bioaccumulate a large number of heavy metals, alongside with some organic compounds including the contamination by historical chlordecone pollution in French West Indies (FWI), an insecticide used against the banana's weevil Cosmopolites sordidus. The present study reports, during two successive years, the concentration levels of heavy metals including arsenic in Martinique and Guadeloupe (FWI). We found that Sargassum can also accumulate a high concentration of chlordecone. Sargassum contamination by chlordecone is observed in areas close to contaminated river mouth but can be partly due to chlordecone desorption when secondary drifted on chlordecone-free shore. Our results further demonstrate that algae bleaching raises a number of questions about inorganic and organic pollutant (i) bioaccumulation, at sea for arsenic and close to river plumes for chlordecone, (ii) transport, and (iii) dissemination, depending the shoreline and the speciation for arsenic and/or metabolization for both., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Sargassum strandings in the coastal environment can introduce arsenic into food webs. In this context, we assessed the risk of exposure to arsenic for consumers of Caribbean bivalves. In 2019, specimens of Asaphis deflorata and Phacoides pectinatus were collected in an Atlantic coastal zone of Martinique (island) to monitor the presence of arsenic species by LC-ICP-MS. The total arsenic (tAs) concentrations were, on average, 34.4 ± 3.8 and 76.9 ± 22.3 µg . g -1 dry weight for P. pectinatus and A. deflorata, respectively. Seven compounds of arsenic were detected in bivalve soft bodies. In P. pectinatus, monomethylarsonic acid was present at a relatively significant concentration (≈ 29.6%). These results were coupled with survey data collected in 2013 and again in 2019, from the main consumers of bivalves. The tAs intake was up to 6 mg . day -1 for a 240 g (wet weight) meal of bivalves. In addition, we proposed toxicological reference doses also based on detected toxic forms of arsenic and tested their relevance. We concluded that monitoring of total arsenic would be sufficient to ensure the protection of bivalve consumers. Consumption patterns expose consumers to a potential health risk. However, due to a decrease in consumption frequency associated with the depletion of bivalve resources by decomposing Sargassum mats, arsenic exposure has decreased. In the French Caribbean, this is the first study on the risk of human arsenic contamination from the ingestion of bivalves. This study is a contribution to the monitoring of arsenic in the Caribbean coastal environment., (© 2022. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Massive Sargassum sp. beachings have been occurring on Caribbean shores since 2011. The sargassum involved in such events are S. fluitans and S. natans, two drifting species whose proliferation has been observed in the southern North Atlantic Ocean. Both for reasons of environmental and sanitary assessment and repurposing, Sargassum sp. that is ashore piled up on beaches and decaying must be studied. Studies are required because of the concerning content of pelagic arsenic reported in the literature. They are also needed owing to Sargassum sp. contamination subsequent to historical pollution in the French West Indies by chlordecone, an insecticide used against the banana weevil Cosmopolites sordidus. The present study aims to describe the contamination and decontamination toxicokinetics of arsenic and chlordecone for Sargassum sp. stranding on shores and shallows in the Caribbean, in order to support the decision-making of the authorities involved. In situ and in mesocosm experiments performed in the present study show that Sargassum sp. contamination by chlordecone is mainly done after 2 h of exposition and reaches equilibrium after a day of exposure in polluted water, but BCF study suggests that the phenomenon is not actively supported (passive soption only). Arsenic transudation is intense in the case of immerged algae both. Half of the arsenic content is transudated after 13 h at sea and will transudate until vestigial arsenic concentration. Sargassum sp. contamination by arsenic, due to phytoaccumulation offshore, is broadly homogeneous before decay, and then leaks lead rapidly to a decrease in concentration in Sargassum sp. necromass, questioning the subsequent contamination of the coastal environment., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.)