PbO2 corrosion scales drive phenolic micropollutant transformation, lead release, and toxic halogenated byproduct formation.

Micropollutant-corrosion scale interactions in drinking water distribution networks (DWDNs) pose significant risks to water safety. Our study systematically investigated the transformation of phenol and bisphenol A (BPA) mediated by PbO2, a dominant component of lead pipe scales, in model aqueous solutions without added disinfectants. The transformations exhibited staged kinetic behavior and were therefore described using piecewise apparent pseudo-first-order fitting, with reaction rates strongly dependent on pH and electronic effects, and optimal conditions varying between compounds (e.g., low pH for phenol, pH 6.0 for BPA). Matrix constituents exhibited contrasting impacts: divalent cations and phosphate inhibited reactions, whereas halide ions, particularly iodide, dramatically accelerated transformation via the formation of reactive iodine species. Alarmingly, the transformation of phenols led to the reduction of PbO2 and subsequent release of Pb2+, a process significantly enhanced by iodide. High-resolution mass spectrometry showed that halides fundamentally altered transformation pathways, shifting from hydroxylation and ring cleavage to halogenation and C-O-C coupling. Furthermore, toxicity assessments revealed that iodinated intermediates, especially dimers and quinones, possessed substantially higher toxicity and bioaccumulation potential than the parent compounds. This work demonstrates that while PbO2 scales contribute to micropollutant breakdown, they also promote lead release and the generation of more hazardous halogenated byproducts when halides are present, highlighting critical challenges for water quality management in aging DWDNs.