Transformation and toxicity assessment of two UV filters using UV/HO process.

The treatment of two typical UV filters benzophenone-4 (BP4) and benzophenone-9 (BP9) was evaluated in aqueous solutions by UV/HO process. High-resolution accurate mass spectrometry (HRMS) was used to identify the degradation intermediates. A total of 12 BP4 degradation products and 17 BP9 degradation products were identified. A series of OH-initiated reactions, including hydroxylation, dihydroxylation, decarboxylation, demethylation, and ring breaking, lead to the final mineralization of BP4 and BP9. The degradation mechanisms of BP4 and BP9 are also proposed, separately. Toxicity prediction and assessment indicate that the bio-toxicity of the intermediates is higher, even if the parent compounds are completely transformed. It is necessary to further assess the environmental risk of BP4, BP9 and their intermediates in engineered systems and ambient aquatic environments.