Effect of soil organic matter destruction on sorption and photolysis rate of rimsulfuron

In order to elucidate the behaviour of sulphonylurea herbicides in soil and the influence of soil organic matter (OM), the sorption and photolysis reactions of rimsulphuron have been studied in a soil suspension and on the sorbed phase. An Italian soil sampled from Sellata Mountain was utilized for sorption and light irradiation experiments. Natural soil samples and samples oxidized with H2O2 (to destroy OM) were treated with the herbicide and exposed to light irradiation or kept in the dark, as control sorption samples. The irradiation was carried out using a solar simulator (Suntest). Kinetic parameters of reactions were calculated. Herbicide sorption was ascertained to be the more important reaction in the soil, but the retention of rimsulphuron was significantly diminished after H2O2 treatment of soil and the consequent reduction of the natural organic matter content. Photoreaction kinetics of the herbicide were influenced by the sorbent capability of soil samples used in the experiments and the natural organic content.