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Pollution of soils and ecosystems by a permanent toxic organochlorine pesticide: chlordecone—numerical simulation of allophane nanoclay microstructure and calculation of its transport properties

1 Institut Méditerranéen de Biodiversité et d’Ecologie marine et continentale (IMBE), UMR CNRS 7263, Aix Marseille Université, Avignon Université,13331, Marseille Cedex 03, France;
2 IRD UMR 237-Campus Agro Environnemental Caraïbes-B.P. 214 Petit Morne, 97232, Le Lamentin, Martinique;
3 Cirad/CAEC, UPR fonctionnement agroécologique et performances des systèmes de culture horticoles, B.P. 214 Petit Morne, Martinique, F-97285, Le Lamentin, France;
4 UPR Fonctionnement écologique et gestion durable des agrosystèmes bananiers et ananas, CIRAD, Capesterre-Belle-Eau, Guadeloupe, F-97130, France;
5 Cirad UR HortSys, TA B-103/PS4, Boulevard de la Lironde, F-34398 Montpellier Cedex5, France

Special Issues: Pollution and Chemicals in the Environment

Pest control technology was introduced into the tropics without considering the specificity of their ecosystems and the risk of pollution was underestimated. Some volcanic soils (andosols) contain nanoclay (allophane) with a unique structure and porous properties compared to crystalline clays. Andosols are characterized by large pore volume and pore size distribution, a high specific surface area, and a fractal structure. These soils are more polluted than the other kinds of tropical soils but release less pollutants (chlordecone) to water and plants. The literature shows that the allophane microstructure favors accumulation and sequestration of chlordecone, an organochlorine pesticide, in andosols.
We used 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 structural features, pore volume and tortuosity, and its transport properties, hydraulic conductivity and diffusion. We show that transport properties decrease because of the presence of allophane. We propose that low hydraulic conductivity and diffusion are important parameters to explain the high concentrations and trapping of pollutants in andosols.
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