Recent lead (Pb) release events in Flint, Michigan exposed the risk that historic lead services lines (LSLs) in drinking water distribution systems impose to public health. The absence of orthophosphate shifted Pb equilibrium and resulted in its release. With the continual drive to incorporate alternative drinking water sources, chemical matrix effects can lead to Pb instability in drinking water distribution systems. This study aimed to acquire a fundamental understanding on the effect of changing water chemistry parameters including carbonate and phosphate concentration, pH and the presence of bromide on reactivity and speciation of Pb minerals. For LSLs, cerussite (PbCO3), hydrocerussite (Pb3(CO3)2(OH)2), pyromorphite (Pb5(PO4)3Cl), and hydroxylpyromorphite (Pb5(PO4)3OH) are the predominant minerals while hypochlorous acid (HOCl) and hypobromous acid (HOBr) are oxidants of interest. Experiments were conducted at 5g/L of oxidant measured as Cl2 and 5.0-5.5 g/L of solids to obtain a molar ratio of 3:1 Cl2 to Pb and always ensure an oxidant residual. Experiments were run up to 5 days, sampling frequently to obtain time dependent speciation. Mineral characteristics were determined using x-ray absorption spectroscopy (XAS), XRD, SEM and EDS. XRD and linear combination of XAS showed that HOCl and HOBr both readily oxidized PbCO3 and Pb3(CO3)2(OH)2 to plattnerite (β-PbO2) and scrutinyite (α-PbO2), with HOBr oxidation occurring at rates up to an order of magnitude faster. Using kinetic modeling, rate constants for each reaction were derived. This research provides valuable insight to understanding and predicting lead surface chemistry in drinking water distribution systems while proposing strategies to help prevent another lead release event.

Effects of changing water chemistry on lead minerals: Implications on lead control in drinking water distribution systems

2019 Fall National Meeting

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