Lead is a potent neurotoxin and drinking water represents an important route of exposure, especially where legacy lead pipe is widespread. Orthophosphate is often used to control lead solubility within distribution systems, but polyphosphates may form coordination complexes with lead, increasing solubility. We used size-exclusion chromatography (SEC) with multi-element detection to compare the speciation of lead below 0.45 µm in two water systems dosing different ortho-polyphosphate blends. In one system, polyphosphate reverted almost completely to orthophosphate during distribution; in the other, it did not. Under the influence of polyphosphate, lead and iron were present as dissolved species strongly associated with phosphorus. Moreover, experiments with sodium hexametaphosphate confirmed our ability to detect lead as a coordination complex using SEC. In the absence of polyphosphate, lead and iron were present as colloidal particles. Treatment with orthophosphate alone appeared to reduce lead solubility, as estimated using paired sample profiles collected at 17 single-unit residences. Increasing orthophosphate from 0.5 to 1.0 mg PO4 L-1 accompanied decreases in lead levels of 38% (95% CI: 15 – 51%) within eight months. Furthermore, analysis of recovered lead pipe corrosion scale was consistent with the presence of an insoluble lead phosphate compound: hydroxypyromorphite (Pb5(PO4)3OH).

Effects of ortho- and polyphosphates on lead speciation in drinking water

255th National Meeting (2018)

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