Impact of chlorine and UV/H2O2 on microplastics in drinking water†

Limited studies to-date have assessed the impacts of disinfectants (chlorine and ultraviolet (UV)/H₂O₂) on microplastics (MPs), with most employing dosages and fluences that are much higher than typically applied during drinking water treatment. Formation of hydroxyl, carbonyl, and carbon–chlorine bonds on the surface of MP particles, as well as the potential for fragmentation and changes to surface roughness have been linked to an increase in toxicity. Additional knowledge regarding physicochemical changes to MPs under conditions representative of drinking water disinfection will aid our understanding of potential risk. In this study, changes to virgin low-density polyethylene (LDPE) and high-density polyethylene (HDPE) fragments (2–125 μm) were examined following exposure to 6 mg L⁻¹ free chlorine over a two-week period. Relative changes to hydroxyl, carbonyl, carbon–oxygen, and carbon–chlorine indices were determined using Attenuated Total Reflectance Fourier Transform Spectroscopy (ATR-FTIR). Following exposure, particle size distributions remained consistent, indicating that MPs did not fragment as reported in earlier studies by others. Neither polymer type nor pH level exhibited an impact on fragmentation or bond indices that was statistically significant (P > 0.05). These findings suggest that neither chlorination nor UV/H₂O₂ adversely impact LDPE or HDPE.