Mathematical and physical interpretation of the transfer of labelled pesticides in water-unsaturated soils: examples of application

Studies were carried out for the purpose of predicting the behaviour of pesticides currently used in agriculture and their derivatives in the soil-water system. These studies are being continued with a view to gaining a more thorough knowledge of the quantities to be applied and the contribution they make as a function of climatic conditions. With the use of radioisotope-labelled products on top of a laboratory soil column under controlled conditions we can more easily monitor the variation in product concentrations in the percolation water as a function of time and the fate of those products in the soil. Experiments were performed in soil columns exposed to average climatic conditions with various pesticides (Neburon, Metoxuron, Chlortoluron and Nitrofene) applied at rates similar to those employed in agriculture. The results are compared with field data for the same products. The measurements (chemical concentrations and radioactivity of the percolating water) are interpreted. In the case of the pesticides used, it was found that the derivatives (little or none of the initial product) accumulated ultimately in the surface layers and that activity stemming from the derivatives migrated into the percolation water. (author)