Chlordecone, applied on soils until 1993 to control banana weevil, has polluted waters resources in the French West Indies for more than 40 years. At the watershed scale, chlordecone applications were not homogenous, generating a spatial heterogeneity of the pollution. The roles of climate, hydrology, soil, agronomy and geology on watershed functioning generate a temporal heterogeneity of the pollution. This study question the interactions between practices and the environment that induce such variability. We analyzed hydrological and water pollution datasets from a two years monitoring program on the Galion watershed in Martinique (French West Indies). We conjointly analyzed: i) weekly CLD concentration monitored on 3 river sampling sites, ii) aquifer piezometric dynamics and pollutions, and iii) agricultural practices on polluted soils. Our results showed that chlordecone pollution in surface waters are characterized by annual trends and infra-annual variations. Aquifers showed CLD concentration 10 times higher than surface water, with CLD concentration peaks during recharge events. We showed strong interactions between rainfall events and practices on CLD pollution requiring a systemic management approach, in particular during post cyclonic periods. Small sub-watershed with high CLD pollution, appeared to be substantial contributor to CLD mass transfers to the marine environment via rivers, and should therefore receive priority management. We suggest increasing stable organic matter return to soil as well as external input of organic matter to reduce CLD transfers to water. We identified hydrological conditionsnotably drying periodsand tillage as the most influential factors on CLD leaching. In particular, tillage acts on 3 processes that increases CLD leaching: organic matter degradation, modification of water paths in soil and allophane clay degradation.
The widespread use of pesticides in agriculture during the last several decades has contaminated soils and different Critical Zone (CZ) compartments, defined as the area extended from the top of the vegetation canopy to the groundwater table, and it integrates interactions of the atmosphere, lithosphere, biosphere, and hydrosphere. However, the long-term fate, storage, and transfer dynamics of persistent pesticides in CZ under a changing world remain poorly understood.In the French West Indies (FWI), chlordecone (CLD), a toxic organochlorine insecticide, was extensively applied to banana fields to control the banana weevil from 1972 to 1993, when it was banned. Here, to understand CZ trajectories we apply a retrospective observation based on marine sediment core analysis to monitor long-term CLD transfer, fate and consequences in Guadeloupe and Martinique islands. Both CLD profiles show synchronous chronologies. We hypothesized that the use of glyphosate, a postemergence herbicide, from the late 1990s onwards induced CZ modification with an increase in soil erosion and led to the release of the stable CLD stored in the soils of polluted fields. CLD fluxes drastically increased when glyphosate use began, leading to widespread ecosystem contamination. As glyphosate is used globally, ecotoxicological risk management strategies should consider how its application affects persistent pesticide storage in soils, transfer dynamics and widespread contamination.
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