In Guadeloupe, the use between 1972 and 1993 of chlordecone, an organochlorine insecticide, has permanently contaminated the island's soil, thus contaminating the food chain at its very beginning. There is today a strong societal requirement for an improved mapping of the contaminated zones. Given the extent of the areas to be covered, carrying out soil tests on each plot of the territory would be a long and expensive process. In this article, we explore a method of demarcating polluted areas. The approach adopted consists in carrying out, using surface water analyses, a hydrological delimitation that makes it possible to distinguish contaminated watersheds from uncontaminated ones. The selection of sampling points was based on the spatial analysis of the actual and potential contamination data existing at the beginning of the study. The approach was validated by soil analyses, after having compared the contamination data of the watersheds with the soil contamination data of the plots within them. The study thus made it possible to highlight new contaminated areas and also those at risk of contamination and to identify the plots to be targeted as a priority during future analysis campaigns by State services.

Ce travail fait un état des lieux de la qualité temporelle et de la densité spatiale des séries pluviométriques du Cameroun, Gabon, Congo, RCA et RDC, en particulier sur la période récente (1973-2014) grâce à la base de données internationale GSOD. Face aux énormes lacunes observées, ces résultats vont permettre d'orienter les choix métrologiques et analytiques in situ du programme FORGREENE (Tropical forests greeness and cloudiness in Central Africa: present conditions and future evolution). Une comparaison avec des estimations satellitaires (de type RFE) indique aussi leur potentiel intéressant, à condition qu'elles s'appuient sur des validations in situ. (Résumé d'auteur)

While long-term organic fertilizer (OF) applications tend to decrease copper (Cu) and zinc (Zn) availability in agricultural soils, earthworm bioturbation has been reported to have the opposite effect. Thus, the consequences of OF amendments in earthworm-inhabited soils on Cu and Zn bioavailability to earthworms are still under debate. Here, we assessed the effect of a decade of agronomically realistic OF applications on Cu and Zn availability in earthworm-inhabited soils and the consequences on Cu and Zn bioavailability to earthworms. An epi-endogeic species (Dichogaster saliens) was exposed in microcosms to three field-collected soils that had received either no, mineral, or organic fertilization for a decade. Dissolved organic matter (DOM) properties (i.e., concentration, aromaticity, and binding properties toward Cu), pH, and Cu and Zn availability (i.e., total concentration and free ionic activity) were determined in the solution of the soil containing earthworms. Cu and Zn bioavailability was assessed by measuring the net accumulation (ng) and concentration of Cu and Zn in earthworms (mg kg−1). Despite soil Cu and Zn contamination induced by a decade of OF applications, organic fertilization induced an increase in soil pH and DOM properties that drove the reduction of Cu and Zn availability in earthworm-inhabited soils, while bioturbation had little effect on soil pH, DOM properties, and Cu and Zn availability. Consistently, Cu and Zn bioavailability to earthworms did not increase with OF applications. From an ecotoxicological perspective, our results suggest that agronomically realistic applications of OF for a decade should not pose a risk to earthworms in terms of Cu and Zn net accumulation, but further studies have to be undertaken to understand consequent long-term toxicity after exposure.

In the French West Indies, the chlordecone (organochloride pesticide) pollution is now diffuse becoming new contamination source for crops and environment (water, trophic chain). Decontamination by bioremediation and chemical degradation are still under development but the physical limitations of these approaches are generally not taken into account. These physical limitations are related to the poor physical accessibility to the pesticides in soils because of the peculiar structural properties of the contaminated clays (pore volume, transport properties, permeability, and diffusion). Some volcanic soils (andosols), which represent the half of the contaminated soils in Martinique, contain nanoclay (allophane) with a unique structure and porous properties. Andosols are characterized by pore size distribution in the mesoporous range, a high specific surface area, a large pore volume, and a fractal structure. Our hypothesis is that the clay microstructure characteristics are crucial physico-chemical factors strongly limiting the remediation of the pesticide. Our results show that allophane microstructure (small pore size, hierarchical microstructure, and tortuosity) favors accumulation of chlordecone, in andosols. Moreover, the clay microporosity limits the accessibility of microorganisms and chemical species able to decontaminate because of poor transport properties (permeability and diffusion). We model the transport properties by two approaches: (1) we use a numerical model to simulate the structure of allophane aggregates. The algorithm is based on a cluster–cluster aggregation model. From the simulated data, we derived the pore volume, specific surface area, tortuosity, permeability, and diffusion. We show that transport properties strongly decrease because of the presence of allophane. (2) The fractal approach. We characterize the fractal features (size of the fractal aggregate, fractal dimension, tortuosity inside allophane aggregates) and we calculate that transport properties decrease of several order ranges inside the clay aggregates. These poor transport properties are important parameters to explain the poor accessibility to pollutants in volcanic soils and should be taken into account by future decontamination process. We conclude that for andosols, this inaccessibility could render inefficient some of the methods proposed in the literature.

Chlordecone, 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.

Preservation of biodiversity and ecosystem services is critical for sustainable development and human well-being. However, an unprecedented erosion of biodiversity is observed and the use of plant protection products (PPP) has been identified as one of its main causes. In this context, at the request of the French Ministries responsible for the Environment, for Agriculture and for Research, a panel of 46 scientific experts ran a nearly 2-year-long (2020–2022) collective scientific assessment (CSA) of international scientific knowledge relating to the impacts of PPP on biodiversity and ecosystem services. The scope of this CSA covered the terrestrial, atmospheric, freshwater, and marine environments (with the exception of groundwater) in their continuity from the site of PPP application to the ocean, in France and French overseas territories, based on international knowledge produced on or transposable to this type of context (climate, PPP used, biodiversity present, etc.). Here, we provide a brief summary of the CSA's main conclusions, which were drawn from about 4500 international publications. Our analysis finds that PPP contaminate all environmental matrices, including biota, and cause direct and indirect ecotoxicological effects that unequivocally contribute to the decline of certain biological groups and alter certain ecosystem functions and services. Levers for action to limit PPP-driven pollution and effects on environmental compartments include local measures from plot to landscape scales and regulatory improvements. However, there are still significant gaps in knowledge regarding environmental contamination by PPPs and its effect on biodiversity and ecosystem functions and services. Perspectives and research needs are proposed to address these gaps.

Plants were sampled from four different types of chlordecone-contaminated land in Guadeloupe (West Indies). The objective was to investigate the importance of biological and agri-environmental parameters in the ability of plants to bioaccumulate chlordecone. Among the plant traits studied, only the growth habit significantly affected chlordecone transfer, since prostrate plants concentrated more chlordecone than erect plants. In addition, intensification of land use has led to a significant increase in the amount of chlordecone absorbed by plants. The use of Bayesian networks uncovers some hypothesis and identifies paths for reflection and possible studies to identify and quantify relationships that explain our data.

Chlordecone, an organochlorine insecticide, pollutes soils and contaminates crops and water resources and is biomagnified by food chains. As chlordecone is partly trapped in the soil, one possible alternative to decontamination may be to increase its containment in the soil, thereby reducing its diffusion into the environment. Containing the pesticide in the soil could be achieved by adding compost because the pollutant has an affinity for organic matter. We hypothesized that adding compost would also change soil porosity, as well as transport and containment of the pesticide. We measured the pore features and studied the nanoscale structure to assess the effect of adding compost on soil microstructure. We simulated changes in the transport properties (hydraulic conductivity and diffusion) associated with changes in porosity. During compost incubation, the clay microstructure collapsed due to capillary stresses. Simulated data showed that the hydraulic conductivity and diffusion coefficient were reduced by 95 and 70 % in the clay microstructure, respectively. Reduced transport properties affected pesticide mobility and thus helped reduce its transfer from the soil to water and to the crop. We propose that the containment effect is due not only to the high affinity of chlordecone for soil organic matter but also to a trapping mechanism in the soil porosity. (Résumé d'auteur)

The former use of chlordecone (CLD) in the French West Indies has resulted in long-term pollution of soils and of food chains. CLD may be transferred into eggs of hens reared outdoors, through polluted soil ingestion. Tropical volcanic soils display variable capacities of pollutant retention: CLD is less available and more persistent in andosol than in nitisol. The impact of soil type on CLD bioavailability to hens was tested through a relative bioavailability study. The deposition of CLD in egg yolk and in abdominal fat was measured in 42 individually housed laying hens fed with diets containing graded levels of CLD from polluted andosol, nitisol, or spiked oil during 23 days. Within each ingested matrix, the concentration of CLD in yolk and in abdominal fat linearly increased with the amount of ingested CLD (P<0.001). However, the response to andosol diets and to nitisol diets was not different from the response to oil diets (P>0.1), indicating that CLD was equally bioavailable to laying hens, irrespective of the matrix. This suggests that the hen's gastrointestinal tract efficiently extracts CLD from the two tropical volcanic soils, regardless of their retention capacity. Thus, hens reared on polluted soils with CLD may lay contaminated eggs. (Résumé d'auteur)

Chlordecone (CLD), an organochlorine insecticide, and other persistent organic pollutants continue to contaminate the environment worldwide and have adverse effects on human health through food exposure. Cucurbitaceae take up weathered hydrophobic pollutants from the soil and translocate them to their shoots. As Cucurbitaceae are an important part of the diet in the French West Indies, they are among the main contributors to total dietary intake of CLD. We analyzed the contamination by CLDs (CLD and 5b-hydroCLD) of four cucurbits grown in the field and/or in the greenhouse. Different physiological (crop species) and environmental (soil type, growth conditions) variables were shown to influence uptake of the pollutant from the soil by the crop. Cucurbita species (zucchini and pumpkin) were more contaminated than Cucumis sativus (cucumber), and Sechium edule (christophine or chayote) translocated CLDs to fruits very poorly compared with cucumber and pumpkin. Greenhouse conditions and non-allophanic (nitisols and ferralsols) soils favored plant contamination more than field conditions and allophanic soils (andosols). (Résumé d'auteur)