Mobility of organotin pesticides: azocyclotin and cyhexatin in clayey and sandy soils from the Northern Parana state - Brazil

Azocyclotin and cyhexatin are pesticides commonly used to control mites. However, these organotin compounds are highly harmful to the aquatic ecosystem and supposedly mobile in the soil. There are no clear and objective rules of use and few studies dedicated to its environmental behavior. Hence, a new method was developed using high-performance liquid chromatography with photodiode-array detection for quality assurance and quality control purposes (QA/QC) in addition to environmental assessment. Hysteresis index (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 HI of −0.15 and 7.8×10−4 for clayey and sandy soil samples, respectively. Although cyhexatin was practically immobile for both soil samples, it can mobilize as an azocyclotin metabolite, increasing the environmental impact and risk for agricultural uses.