Abiotic degradation of the herbicide rimsulfuron on minerals and soil

The photochemical behaviour of the sulfonylurea herbicide rimsulfuron, N-[[(4,6-dimethoxy-2- pyrimidinyl)amino]carbonyl]-3-(ethylsulfonyl)-2-pyridinesulfon amide, on silica and clay minerals, used as soil surrogates, was investigated and compared to a natural soil sample. The antagonistic behaviour of adsorption process and chemical degradation with respect to photodegradation was assessed and the formation of photoproducts was also determined. Results showed that all chemical and photochemical processes responsible for the disappearance of the herbicide follow a second order kinetic. The photochemical degradation of rimsulfuron was strongly affected by retention phenomena: with increasing of the adsorption capability of supports the photoreactivity of the herbicide decreased. The extraction rate of the herbicide covered the following values: soil 59.5%, illite 48.5%, aerosil 22.2%, montmorillonite 21.0%, showing that silica and clay minerals can retain and protect rimsulfuron from photodegradation much more than soil. Though, adsorption of the herbicide was always accomplished to a chemical reactivity of solid substrates. N-[(3-ethylsulfonyl)- 2-pyridinyl]-4,6-dimethoxy-2-pyridineamine and N-(4,6-dimethoxy-2-pyrimidinyl)-N-[(3-(ethylsulfonyl)- 2-pyridinyl)]urea were found both as photochemical and chemical metabolites.