UV-induced effects on toxicity of model disinfection byproducts

UV (Ultraviolet)-based treatment has been demonstrated to be effective for removal of some disinfection byproducts (DBPs) and to be beneficial for reduction of genotoxicity and cytotoxicity in chlorinated water. However, to a large extent, UV-induced effects on chemistry and toxicology have been treated as a black box, in the sense that little or no UV dose-dependent behavior has been reported. To address this issue, the effects of UV₂₅₄ irradiation on 1,4-dibenzoquinone (BQ), 2,6-dichloro-1,4-benzoquinone (DCBQ), and chlorocreatinine (Cl-Cre) as model DBPs were examined, both in terms of photodegradation and cytotoxicity. These compounds have been identified as DBPs that are relevant in swimming pool settings; however, these compounds will be relevant in other water treatment settings, including drinking water production and wastewater reuse. UV₂₅₄ irradiation was shown to promote photodecay of all three compounds. However, for BQ and DCBQ, the corresponding cytotoxicity of the UV-irradiated samples remained essentially unchanged, even when the compound was completely photodegraded. These results indicate that the photodegradation products of BQ and DCBQ carry similar cytotoxicity as their respective parent compounds. On the other hand, UV₂₅₄-irradiation of Cl-Cre yielded a decrease in cytotoxicity that correlated with photodechlorination of Cl-Cre. These experiments also demonstrated a reduction in cytotoxicity in connection with photodechlorination of an N-chlorinated organic compound. Overall, the results of these experiments indicate the importance of defining products of UV photodecay processes, both in terms of chemistry and toxicity; these attributes are expected to be important in many UV-based applications, including potable water production, water reuse, and recreational water settings.