INSIGHTS TO THE SPECIATION AND DISTRIBUTION OF VANADIUM ASSOCIATED WITH DRINKING WATER IRON PIPE CORROSION FROM SYNCHROTRON-BASED μ-XRF MAPPING AND μ-XANES

The ingestion of vanadium (V) from drinking water is an emerging health concern and is on track to becoming a regulated contaminant. The extent of potential V associated with iron pipe corrosion, its speciation, and mechanism of inclusion are unknown. However, if present in corrosion products within distribution system or premise plumbing in appreciable concentrations, hydraulic or chemical disturbances may reintroduce V into the drinking water. This study assesses the extent of potential V reservoirs associated with iron corrosion products, its speciation and mechanism of inclusion, using synchrotron-based m-XRF mapping and m-XANES. Vanadium concentrations in the iron corrosion ranged from 35 to 899 mg L^-1. In-situ V K- and Pb L3-edge μ-XANES spectra were collected and identified mainly as vanadinite [Pb₅(V⁵⁺O₄)₃Cl] based on the normalized pre-edge peak positions ranging from 5469.48 to 5469.50 eV, which corresponds to a 4.48-4.50 eV offset from the 5465 eV K-edge position of V metal). Pre-edge intensities ranged from 0.988 to 1.063, and absolute derivative peak positions of the main edge from 16.45 to 16.49 eV. Linear combination fitting and PCA results indicated that vanadinte accounts for approximately 91 to 98% of the V present in the iron corrosion with the remaining amount identified as V(V) oxide. The presence of V(V) oxide suggests that the vanadate oxyanion forms or that vanadate ions are adsorbing to available Pb ions or onto the iron oxide/oxyhydroxide mineral surfaces composing the surface layer of the iron corrosion. Potential sources of the V were examined and it was determined that the most likely source for the vanadinite was a result of destabilization of lead pipe corrosion located upstream which also contained vanadinite. However this finding does not provide any insights into the ultimate source of the V. It is likely that persistent V reservoirs associated with iron drinking water pipe corrosion exist in numerous drinking water distribution systems. For a pipe with iron corrosion products with low V concentration, 100 mg kg^-1, as little as 0.0027% of a 0.1-cm thick 100-cm long section of that corrosion needs to be disturbed to increase V concentrations in the drinking water at the tap to levels above the 15 mg L^-1 notification level set by the State of California and could adversely impact human health.