Diagnosis and Management of Field Pollution in the Case of an Organochlorine Pesticide, the Chlordecone

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A conceptual model of organochlorine fate from a combined analysis of spatial and mid- to long-term trends of surface and ground water contamination in tropical areas (FWI)

In this study, we investigated the management of long-term environmental pollution by organic pollutants such as organochlorine pesticides. We set out to identify conditions that are conducive to reducing pollution levels for these persistent molecules and then propose a conceptual model of organochlorine fate in water. Our approach looked at spatio-temporal changes in pollutant contents in surface water (SW) and groundwater (GW) on a large scale, in order to decipher the respective roles of soil, geology, hydrology and past treatment practices. The case of chlordecone (CLD) on the island of Martinique (1100&thinsp;km2) was selected given the sampling campaigns carried out since 2007 over more than 150 sites. CLD, its metabolite chlordecone-5b-hydro (5bCLD) and the metabolite-to-parent-compound ratio were compared. As regards the spatial variability of water contamination, our results showed that banana cropping areas explained the location of contaminated SW and GW, whereas the combination of soil and geology factors explained the main spatial variability in the 5bCLD∕CLD ratio. For temporal variability, these conditions defined a high diversity of situations in terms of the duration of pollution, highlighting two groups: water draining old geological formations and ferralsols or vertisols vs. recent geology and andosols. A conceptual leaching model provided some key information to help interpret downward trends in CLD and 5bCLD observed in water. Lastly, a conceptual model of organochlorine fate is proposed to explain the diversity of the 5bCLD∕CLD ratio in water. Our conclusions highlight the combined role of soil and groundwater residence time for differentiating between conditions that are more conducive, or not, to the disappearance of CLD from the environment. This paper presents a model that provides an overall perception of organochlorine pesticide fate in the environment.</p

Removal of mango inflorescence increases fruit set and does not affect yield (Mangifera indica cv. Cogshall)

International audienceMango is the fifth fruit in the world in regards to production volume. Although this has increased strongly in the past 15 years, yields are still low and irregular. The most frequent hypothesis found in the literature to explain this is that the availability of carbohydrate can limit the formation of reproductive organs and growth and that high carbon mobilization during flowering can limit sugar availability for fruit growth. Furthermore, a long fruit growth period could reduce the formation of flowering twigs. A one-year experiment was carried out at CIRAD research station in Reunion Island with the objective to reduce energy loss during flowering to optimize, at tree level, source/sink relationships during fruit growth. As compared to control trees (with no removal of inflorescence) and trees where the distal half of each inflorescence was removed, removing 50% of the inflorescences increased fruit set and maintained yield and fruit siz

Young flush thinning in mango (cv. cogshall) controls canopy density and production

International audienceAlthough mango has been grown for a very long time and cultivation is increasing, productivity is still low and irregular. In this work, we took up the common hypotheses in which fruiting under hot subtropical conditions competes strongly for limited carbon resources, and the strategy of the mango tree is to adjust carbon investment between the fruit and vegetative compartments. If flowering is too abundant for mango tree, the assimilates produced by photosynthesis will not fit the demand during fruit set and growth. However, rather than favouring vegetative development by heading cuts, we decreased the number of vegetative flushes (physiological sinks) by thinning cuts of young flushes as soon as they appear in order to improve their development and to increase flower induction in their terminal bud. In Reunion Island, we developed a young flush thinning cut protocol which aimed at optimising, at mango tree level, the source/sink relationships for carbohydrates with the objective to increase total yield and mango quality. The pruning method involved the removal of young yellow coloured twigs as soon as they appeared at each flush period. This one-year trial showed that the yield of treated trees was similar to that of control trees but individual fruit weight was greater. Moreover, some fruiting sites were stimulated and overall tree functioning was more homogeneous, in terms of phenology and successions of flushes. The pruned trees set delayed vegetative flush that led to delayed flowering and by consequence to delayed fruit maturation and harvest. This thinning cut of young flushes decreased canopy density, with limited branching. These results could bring about the development of new orchard management practices leading to orientated production of good standard quality mangoes. Ongoing studies aim at adapting this thinning cut procedure to other cultivars in various site

Des parcelles aux cours d'eau : transferts de chlordécone dans les eaux

International audienceThe book deals with a long term pollution problem, generated by the former use of organochlorine pesticides. Through a case study of the chlordecone pollution in the French West Indies, the authors illustrate a global and systemic mobilization of research institutions and public services. This "management model", together with its major results, the approach and lessons to be learned, could be useful to other situations. This book gathers all the works that have been carried out over the last ten years or more and links them to decision makers’ actions and stakeholders’ expectations. This reference fills a gap in the literature on chronic pollution

Natural nano materials trapp pollutants in soils

Persistent pesticides led to long term pollution of soils and consequently contaminate rivers, groundwater, ecosystems and finally human beings. Volcanic soils (andosols) are generally more polluted than the other kinds of tropical soils but data show that andosols release less pesticides to percolating water and crops. Andosols contain amorphous clays (allophane) which present unique structures and physical properties compared to crystalline clays. Allophane aggregates have physical features very close to that of nano porous materials like synthetic gels: large pore volume and water content, a broad pore size distribution, a high specific surface area and a fractal structure. The aim of the study was to show the influence of the features (nano materials structure, shrinkage during drying) of these natural gels on the pesticide retention. Our study confirms that the soil to crop pesticide transfer is lower in andosols compared to other volcanic soils. Associated to high organic matter content, the allophane microstructure favor pollutants (chlordecone) accumulation in soils. We put forth the importance of the nano porous features of allophane (the associated tortuous microstructure) but also the pore collapse during drying, for pollutant trapping in soils

Chlordecone retention in the fractal structure of volcanic clay

Chlordecone (CHLD), a soil and foodstuff pollutant, as well as an environmentally persistent organochlorine insecticide, was used intensively in banana fields. The chlordecone uptake of three crops was measured for two types of polluted soils: allophanic and non-allophanic. The uptake is lower for allophanic soils even if their chlordecone content is higher than with non-allophanic soils. The fractal structure of the allophane aggregates was characterized at the nanoscale by small angle X-rays scattering, pore size distribution and transmission electron microscopy. We showed that clay microstructures should be an important physico-chemical factor governing the fate of chlordecone in the environment. Allophanic clays result in two counterintuitive findings: higher contaminant trappings yet lower contaminant availability. We propose that this specific, tortuous structure, along with its associated low accessibility, partly explains the low availability of chlordecone confined in allophanic soils. Capsule The fractal and tortuous microstructure of allophane clay favours the chlordecone retention in soils and disfavours the crop uptake

Soil interfaces in a changing world

The context of this study is the pollution of soils and water by a persistent organo-chlorinated insecticide, chlordecone, in a tropical environment. The application of chlordecone to control the banana black weevil has led to continuing diffuse pollution of soils, and to its being a source of contamination for cultivated plants, as well as for terrestrial and marine ecosystems. Chlordecone is toxic and stable and is considered to be a persistent organic pesticide. Consequently, the amounts of chlordecone that could migrate through the environment and contaminate agricultural products need to be controlled. We measured the impact of two composts (5% weight) on chlordecone sequestration in andosols. To this end, we first characterized the transfer of chlordecone from soil to water, and then its transfer from soil to plants. After 3 months of maturation, soil-water and soil-plant transfers were reduced by a factor of from 3 to 10. We also showed that adding compost to contaminated soils increases chlordecone sequestration because it leads to changes in soil microstructure in the form of pore collapse and closure of the fractal structure of the allophane content

Crisis Management of Chronic Pollution: Contaminated Soil and Human Health

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