Colloid transfer by subsurface drainage.

During the drainage season, significant quantities of suspended matter can be exported from a drain collector. Their nature has been determined with a methodology linking chemical analysis, X-ray diffraction, and electronic microscopy associated with image analysis. The majority of these particles are smaller than 200 nm. They are composed of 2:1 phyllosilicates and iron particles usually in amorphous form. Cs-137, phosphorus and organic matter clearly demonstrate the superficial origin of these particles. Drainage modifies natural leaching of soil by exporting definitively particles from the soil profile. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.