Lead release from lead service lines and lead-containing materials in premise plumbing can pose severe risks to public health. Phosphate is commonly added to control lead release in tap water by forming low-solubility lead phosphate particles. Their aggregation behavior may affect their transport in pipes and thus Pb-removal efficiency. Using dynamic light scattering (DLS), the evolution of the sizes of lead phosphate particles in suspension was measured under various aqueous conditions typical of water supply systems. Parameters varied included the aqueous PO4/Pb ratios, ionic strength (IS), and pH in the absence/presence of substituting ions and natural organic matter (NOM). Zeta potentials of lead phosphate particles were also measured by DLS to understand the electrostatic interactions among particles. Under high aqueous PO4/Pb ratios (&gt; 1), the aggregation of lead phosphate particles was inhibited. This observation indicated that addition of excess phosphate may increase concentrations of particulate lead, thereby lowering dissolved lead concentrations, but maintaining high total lead concentrations. The presence of divalent cations (Ca2+ and Mg2+) promoted aggregation of lead phosphate particles at pH 7 due to cation adsorption that neutralized particle surface charges, suggesting that phosphate addition for lead corrosion control may be more efficient in harder waters. In contrast, the presence of anions (Cl-, F-, HCO3-) had no significant effect on the aggregation of lead phosphate particles though structural incorporation occurred. Aggregation of lead phosphate particles was retarded in the presence of natural organic matter (≥ 0.05 mg C/L humic acid and ≥ 0.5 mg C/L fulvic acid) at pH 7, primarily due to the steric repulsion caused by NOM adsorption onto the particles. Therefore, removal of organic carbon during water treatment to reduce formation of disinfection-by-products (DBPs) may have the additional benefit of minimizing the mobility of lead-containing particles. Our findings provide useful information for understanding the observed trends of total lead in drinking water after phosphate addition in both field and pilot-scale lead pipe studies, and for optimizing lead immobilization strategies.

Formation and aggregation of lead phosphate particles: Implications for lead immobilization in water supply systems

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.