Linking current river pollution to historical pesticide use: Insights for territorial management?

International audiencePersistent organic pollutants like organochlorine pesticides continue to contaminate large areas worldwide raising questions concerning their management. We designed and tested a method to link soil and water pollution in the watershed of the Galion River in Martinique. We first estimated the risk of soil contamination by chlordecone by referring to past use of land for banana cultivation and took 27 soil samples. We then sampled surface waters at 39 points and groundwater at 16 points. We tested three hypotheses linked to the source of chlordecone pollution at the watershed scale: (i) soils close to the river, (ii) soils close to the sampling point, (iii) throughout the sub-watershed generated at the sampling point. Graphical and statistical analysis showed that contamination of the river increased when it passed through an area with contaminated plots and decreased when it passed through area not contaminated by chlordecone. Modeling showed that the entire surface area of the watershed contributed to river pollution, suggesting that the river was mainly being contaminated by the aquifers and groundwater flows. Our method proved to be a reliable way to identify areas polluted by chlordecone at the watershed scale and should help stakeholders focus their management actions on both hot spots and the whole watershed. (C) 2016 Elsevier B.V. All rights reserved

Résurrection du chlordécone par le glyphosate dans les Antilles françaises mise en évidence par une approche de rétro-observation de la Zone Critique

International audienceThe widespread use of pesticides in agriculture during the last several decades has contaminated soils and different Critical Zone (CZ) compartments. However, the long-term fate, storage, and transfer dynamics of persistent pesticides in CZ in a changing world remain poorly understood. In the French West Indies, chlordecone (CLD), a toxic organochlorine insecticide, was extensively applied to banana fields to control banana weevil from 1972 to 1993 after which it was banned. Here, to understand CZ trajectories we apply a retrospective observation based on marine sediment core analyses to monitor long-term CLD transfer, fate, and consequences in Guadeloupe and Martinique islands. Both island CLD sedimentary profiles show synchronous chronologies. We hypothesized that the use of glyphosate, a postemergence herbicide, from the late 1990s onward 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.L’utilisation généralisée de pesticides en agriculture au cours des dernières décennies a contaminé les sols et les différents compartiments de la zone critique (ZC). Cependant, le devenir à long terme, le stockage et la dynamique de transfert des pesticides persistants au sein de la ZC et dans un monde en mutation restent mal compris. Aux Antilles françaises, le chlordécone (CLD), un insecticide organochloré toxique, a été largement appliqué dans les champs de bananes pour lutter contre le charançon du bananier de 1972 à 1993, après quoi il a été interdit. Dans cette étude, pour comprendre la trajectoire d’évolution de la ZC, nous appliquons une approche basée sur la rétro-observation à partir de l’analyses de carottes de sédiments marins pour suivre le transfert à long terme du CLD, son devenir et ses conséquences dans les îles de Guadeloupe et de Martinique. Les profils sédimentaires de CLD des deux îles montrent des chronologies synchrones. Nous suggérons que l’utilisation du glyphosate, un herbicide de post-levée, à partir de la fin des années 1990, a induit une modification de la ZC avec une augmentation de l’érosion du sol conduisant à la libération du CLD stable stocké dans les sols des champs pollués. Les flux de CLD ont considérablement augmenté lorsque l’utilisation du glyphosate a commencé, entraînant une contamination généralisée des écosystèmes. Le glyphosate étant utilisé dans le monde entier, les stratégies de gestion des risques écotoxicologiques doivent tenir compte de la manière dont son application affecte le stockage des pesticides persistants dans les sols, la dynamique des transferts et la contamination généralisée

Evidence of Chlordecone Resurrection by Glyphosate in French West Indies

International audienceThe 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 in a changing world remain poorly understood. In the French West Indies, chlordecone (CLD), a toxic organochlorine insecticide, was extensively applied to banana fields to control banana weevil from 1972 to 1993 after which it was banned. Here, to understand CZ trajectories we apply a retrospective observation based on marine sediment core analyses 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 onward 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

Spatio-temporal variability of water pollution by chlordecone at the watershed scale: what insights for the management of polluted territories?

International audienceChlordecone, applied on soils until 1993 to control banana weevil, has polluted water 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 questions the interactions between practices and the environment that induce such variability. We analyzed hydrological and water pollution datasets from a 2-year monitoring program on the Galion watershed in Martinique (French West Indies). We conjointly analyzed (i) weekly chlordecone (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 a 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 conditions-notably drying periods-and 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