Identification of Vanadinite (Pb5(V5+O4)3Cl) Formation in Lead Pipe Corrosion by-Products by XANES and μX-Ray Diffraction

Vanadium is beneficial or toxic to humans, depending on its concentration and oxidation state. Vanadyl (V⁴⁺) and vanadate (V⁵⁺) are the most toxic ions and may combine in natural and drinking waters to form a wide range of solids depending on the redox potential and pH. Ingestion of vanadium from drinking water is only recently being considered a potentially serious threat to human health. Vanadium accumulation, up to 1% by weight has been reported for corrosion deposits in lead drinking water pipes from numerous United States public drinking water systems (DWS), indicating a potential reservoir for human exposure if mobilized. This study presents the first detailed examination of vanadium speciation from twenty-one lead pipe corrosions by-products from eight municipal DWS. Six DWS use surface waters and two ground water as their sources. Vanadium concentrations for the samples determined by ICP-OES range from <40 to 8500 ppm. Bulk XANES, on eight samples, identified the presence of vanadinite (Pb₅(V⁵⁺O₄)₃Cl). Additionally μXRD or μXANES analyses on three in-situ lead pipe corrosion by-products indicated the presence of vanadinite and its location. Vanadinite appears to be mainly concentrated at the surface or near-surface portion of the corrosion by-products. Hydraulic dislodgement of scale pieces or chemical breakdown resulting from water treatment changes, could mobilize vanadium and provide an unexpected and unmonitored detrimental human exposure event. The results of this study suggest that treatment processes, redox potential, and pH present in the distribution system are likely to play a key roles in the formation of vanadinite in drinking water pipe scales, as well as the presence of lead premise piping. Thus, it is imperative to further investigate the presence, speciation, and concentration of vanadium in corrosion by-products in order to assess the chemical and physical factors controlling the formation and release of vanadium into drinking water.