Kinetics and mechanism of DBT degradation during chlorination and natural solar photochlorination.

Diethylhexyl butamido triazone (DBT), an emerging triazine-based ultraviolet filter widely employed in personal care products, is inevitably exposed to both solar irradiation and free chlorine in water. However, studies on its chlorination behavior remain limited. This first systematic investigation demonstrates that DBT exhibits high stability under chlorination in swimming pool water, yet undergoes rapid degradation under photochlorination. Moreover, the experimental batches were conducted over a period of seven-month under natural ambient weather conditions, providing robust evidence that photochlorination serves as a persistent and effective attenuation mechanism for DBT across a range of natural UV regimes, including those encountered in swimming pool water and real seawater. The water matrix exerts a dual and complex influence, simultaneously promoting and inhibiting DBT transformation, depending on the specific constituents present. Reactive chlorine species (RCS) and hydroxyl radicals (•OH) were identified as the dominant reactive species during photochlorination. The chlorination of DBT proceeds predominantly via electrophilic aromatic substitution, yielding mono-, di-, and tri-chlorinated derivatives. In contrast, photochlorination triggers a broader spectrum of reaction pathways, including chlorination, hydroxylation, carbon-nitrogen bond cleavage, and formation of chlorinated cleavage products. Acute toxicity assessment indicates that photochlorination transformation products are generally less toxic than those generated by chlorination.