Chlordecone, a toxic organochlorine insecticide, is a major long term source of pollution of soils and water resources in West Indies. Allophanic soils have been strongly polluted and we show that the clay microstructure should be an important physicochemical characteristic limiting the transfer of the pesticide in water. We demonstrate the fractal structure of the allophane clay, at the nanoscale and show that it exist a correlation between the allophane fractal structure and the poor pesticides transfer from allophanic clay to water. We propose that the fractal features and associated poor low transport properties could explain why allophane clay is able to retain pesticides. Comparatively, these allophanic clays could be highly polluted but less contaminant for water resources and diffusion in environment.