Mobility of Organotin Pesticides: Azocyclotin And Cyhexatin In Clayey And Sandy Soils From The Northern Paraná State - Brazil
Abstract Azocyclotin and cyhexatin are pesticides commonly used in mite control. However, these organotin compounds are highly harmful to the aquatic ecosystem and supposedly mobile in the soil. In addition to not existing defined rules of use, few studies have been carried out on organotins' behavior and environmental control. Liquid chromatography has been pointed out for the OTC quantitation because of gas chromatography's thermal stability and derivatization limitations. Hence, a new high-performance liquid chromatography method with photodiode array detection (HPLC-PDA) was developed for quality assurance and quality control (QA/QC) and environmental performance assessment purposes. Hysteresis index (\emph{HI}) and mobilization factor were determined from sorption/desorption in sandy and clayey soils to assess mobility and environmental risk. Mobilization was observed for the two compounds by applying the dual-mode Freundlich-Langmuir model to the isotherms. Azocyclotin showed greater mobility, 23\% and 19\%, and \emph{HI} of $-$0.15 and 7.8$\times$10$^{-4}$ for clayey and sandy soil samples, respectively. Although cyhexatin was practically immobile for both soil samples, it can be mobilized as an azocyclotin metabolite, increasing the environmental impact and risk for agricultural uses.
