Insight into the dynamic transformation properties of microplastic-derived dissolved organic matter and its contribution to the formation of chlorination disinfection by-products.

Microplastics (MPs) can cause adverse effects and pose potential threats to humans and the environment. In addition, dissolved organic matter leached from MPs (MP-DOM) is also a critical issue due to its ecotoxicity and potential to form disinfection by-products (DBPs) during the disinfection process of water treatment plants. However, limited information is available on the dynamic transformation of MP-DOM during UV irradiation and subsequent disinfection, which may further influence the formation of DBPs in MP-DOM. Herein, PSMPs-DOM were leached in aqueous solutions under UV irradiation and the samples were then chlorinated. PSMPs-DOM before and after chlorination were characterized by multiple spectral technologies and methods. With prolonged irradiation time, the aromaticity, molecular weight, humic-like substances and oxygen-containing functional groups of PSMPs-DOM increased, suggesting the continuous transformation of PSMPs-DOM. After chlorination, the aromaticity, molecular weight and humic-like substances of PSMPs-DOM decreased, among which the changes of C2 and oxygen-containing functional groups were more significant. Besides, the PSMPs-DOM formed under prolonged irradiation exhibited higher chlorine reactivity, owing to the more aromatic structures and unsaturated bonds. TCM, DCBM, DBCM and TBM were detected in all chlorinated PSMPs-DOM samples, while the PSMPs-DOM formed at the later stage of irradiation exhibited lower THMs formation potential. The correlation results showed that the conversion of humic-like substances in PSMPs-DOM affected the THMs formation potential, with photo-induced humic-like substance being a more dominant factor. This study provided more information on the relationship between the compositional transformation of MP-DOM and their potential to form DBPs, which may facilitate the assessment of potential toxicity associated with MPs-containing water, as well as the development of more effective water treatment methods.