Fate of the organotin pesticide azocyclotin in aquatic microcosms

The fate of the organotin acaricide azocyclotin was studied in fresh water microcosms. The 14C-labelled test substance was applied particle bound by simulating a runoff event in concentrations of 5, 15, 35, 135 und 405 μg/l, respectively. The fate of the parent compound and its metabolites in water and sediment were analyzed over a period of 7 months. Effects on plankton and benthon as well as physico-chemical water parameters are reported by Fliedner et al. [1] (this issue). The results elucidate that sedimentation of the particles coated with the pesticide is relatively fast. Shortly after application distribution and solubilizing processes and metabolism are starting. Azocyclotin is quickly hydrolyzed to cyhexatin. According to its solubility cyhexatin is mainly sorbed to sediment and the layer of biota in direct contact with sediment. About 20% of the applied radioactivity was concentrated in this biota layer as cyhexatin. More mobile metabolites are concentrated in the water phase (water and biota of the water phase). For cyhexatin a DT50 value of 68 d and a DT90 value of 300 d could be calculated. Cyhexatin is mineralised, therefore no stable metabolites could be detected.