The “Sarg As & Cld” project addresses the environmental impacts of Sargassum (Sar) piling up along shorelines or inland, in link with arsenic (As), a very toxic trace element naturally present in Sar, and chlordecone (CLD), known to accumulate in Sar washing ashore in places that connect with rivers flowing from banana plantation areas. The first task will be to develop analytical techniques for quantifying the various physico-chemical forms of As in Sar and in the leachates produced by dripping and rain falling on piles. The speciation of As in the soils below these piles will also be studied. The second task will be to determine the toxicity of these Sar leachates for test organisms, mainly representative of local wildlife (freshwater crustaceans and oysters from mangroves). Both As and CLD will be studied, whether separately or simultaneously present, to investigate possible synergic effects. The third task will be to develop a cost-effective, environmentally friendly process for removing As from Sar leachates. Laboratory development will be followed by a field trial in actual natural conditions. Activated carbon will be tested for CLD sorption. Treated leachates will be used in task 2. The fourth task will focus on the social acceptability of Sar stockpilings, investigating how the population feels about the management of the Sar washing ashore and especially about the real and assumed dangers of As and CLD, and assessing the inclinations of the population to come out in protest against Sar stockpiling. All results will be disseminated to the scientific community and stakeholders through task 5. The project is coordinated by the BRGM (Scientific and technical centre in Orléans, France, and its local Guadeloupe agency) with partners from the Universities of the Antilles, French Guiana, Orléans and TAMUG (USA), and the ADERA/UT2A association. The “Conservatoire National du Littoral, Guadeloupe” is the end-user associated with the project.