Photochemical fate of triphenyltin pesticides in engineered UV and UV-H2O2 treatment systems: Reaction kinetics, transformation products, and residual toxicity

Abstract

Triphenyltin hydroxide (TPTH) is an organotin fungicide that causes endocrine disruption and reproductive malformation in aquatic organisms. The objectives of this study were to determine the photodegradation kinetics, identify the transformation products, and measure the residual toxicity of TPTH during UV-254 and UV-H2O2 treatment. The quantum yield of TPTH was 0.18 ± 0.02 mol Ein⁻¹ for direct photolysis at 254 nm. The effects of pH (4−10), ionic strength (0.001–0.1 M), and photosensitizers (hydrogen peroxide, dissolved organic matter) on TPTH photodegradation were evaluated to simulate environmental conditions and treatment scenarios. Solution pH and ionic strength had a negligible influence on TPTH degradation kinetics. However, TPTH degradation was enhanced in the UV-H₂O₂ process due to reaction with hydroxyl radicals. The second-order rate constant for TPTH reaction with hydroxyl radicals was (7.81 ± 0.37)× 10⁸ M⁻¹ s⁻¹. The primary phototransformation products involved hydroxylation of the phenyl groups in TPTH. The toxicity of TPTH and its phototransformation products were measured using a novel bacterial growth inhibition assay with the potency equivalents approach, and the results indicated that both direct photolysis and advanced oxidation generated toxic products. Overall, this study highlighted the need for advanced treatment systems for organotin chemicals and careful consideration of the photoproduct toxicity.