Elevated Pb(II) Release from the Reduction of Pb(IV) Corrosion Product PbO2 Induced by Bromide-Catalyzed Monochloramine Decomposition

The stability of Pb(IV) corrosion product PbO2 has been linked to lead contamination in chloraminated drinking water. Recent studies have shown that autodecomposition of monochloramine (NH2Cl) can cause lead release from PbO2 via reductive dissolution. Bromide (Br(-)) is a known catalyst for NH2Cl decomposition. In this study, we investigated whether Br(-)-catalyzed NH2Cl decomposition could further enhance lead release from PbO2. Our results showed that Br(-_)catalyzed NH2Cl decomposition did accelerate the reduction of PbO2, and the rate was enhanced by the lower pH value, higher Br(-), and NH2Cl concentrations. A single linear correlation was found between the amount of NH2Cl decomposed and the amount of total Pb(II) released either in the absence or presence of Br(-), suggesting that Br(-)-catalyzed NH2Cl decomposition and NH2Cl autodecomposition may generate the same intermediate toward PbO2 reduction. The kinetics of total Pb(II) release can be successfully modeled by considering the overall rate of NH2Cl decomposition with NOH as the reactive intermediate responsible for PbO2 reduction. Our findings suggested that special attentions on lead contamination should be paid to systems with PbO2 scales and high Br(-)-containing source waters when switching disinfectant from free chlorine to monochloramine.