This study focuses on the transformation of organic pollutants on soil surface under the influence of the light excitation. Two main organic compounds were used as model molecules, phenylbenzoquinone (PhQ) and a carbamate pesticide, carbaryl. We used several supports : three model supports (silica, sand of Fontainebleau and kaolinite) and a real soil of the region of Orange (France). The phototransformation was carried out using a device that simulates the solar radiation (l > 300 nm). The study of the spectroscopic features of PhQ on solid support shows a broad band of absorption that presents bathochromic and hyperchromic effects. During irradiation, the concentration and the thickness of film were found to be important parameters to be considered in order to avoid the screen as well as diffusion effect. The optimal value of the thickness was determined roughly to 100 μm in order to minimise the diffusion effect. The mechanism of transformation of PhQ is similar to that observed in aqueous solution with the formation of the unique photoproduct 2-hydroxybenzofuran. The process involves the triplet excited state of PhQ. After this work, the first studies are on the phototransformation of carbaryl and other pesticides on model supports. Furthermore, the molar absorption coefficient and quantum yield have been determined in order to confirm the bathochromic and hyperchromic effect and also the increase of the quantum yield (10 times for carbaryl). The degradation process was most effective when the particle size increases. Moreover, from the analytical studies the photodegradation mechanism was suggested involving several reactions such as photofries, photohydrolyse, dimerisation and hydroxylation. The second part of the present work was dedicated to the study on real soil. An original protocol had to be set up. It consisted on a prefractionation of soil followed by a chemical treatment to minimise the impact of organic matter. Concerning the phototransformation of carbaryl, it was shown that the degradation at the surface of soil and its fractions is effective and that the organic matter has a beneficial effect at low concentrations and inhibition effect at high concentrations. Furthermore, fractionation revealed that photodegradation is more important when the fractions are composed of large particles. Finally, the formation of reactive species (HO• and 1O2) was observed consistently and efficiently for fractions without organic matter suggesting transformation processes induced by the mineral part of the supports.
