Impact of Chlorine Disinfectants on Dissolution of the Lead Corrosion Product PbO2

Plattnerite (beta-PbO2) is a corrosion product that develops on lead pipes that have been in contact with free chlorine present as a residual disinfectant The reductive dissolution of PbO2 can cause elevated lead concentrations in tap water when the residual disinfectant is switched from free chlorine to monochloramine. The objectives of this study were to quantify plattnerite dissolution rates in the presence of chlorine disinfectants, gain insights into dissolution mechanisms, and measure plattnerite's equilibrium solubility in the presence of free chlorine. The effects of free chlorine and monochloramine on the dissolution rates of plattnerite were quantified in completely mixed continuous-flow reactors at relevant pH and dissolved inorganic carbon conditions. Plattnerite dissolution rates decreased in the following order no disinfectant > monochloramine > chlorine, which was consistent with the trend in the redox potential. Compared with experiments without disinfectant, monochloramine inhibited plattnerite dissolution in continuous-flow experiments. Although free chlorine maintained steady-state lead concentrations below the action level of 15 mu g/L in flow-through experiments, in batch experiments lead concentrations exceeded the action level for longer residence times and approached an equilibrium value that was several orders of magnitude higher than that predicted from available thermodynamic data.