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Mineralogical Evidence of Galvanic Corrosion in Drinking Water Lead Pipe Joints
Citation:
DeSantis, Mike, S. Triantafyllidou, M. Schock, AND D. Lytle. Mineralogical Evidence of Galvanic Corrosion in Drinking Water Lead Pipe Joints. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 52(6):3365-3374, (2018). https://doi.org/10.1021/acs.est.7b06010
Impact/Purpose:
This manuscript aims to inform the scientific community of the observational research conducted at the US EPA's AMSARC lab on galvanic lead corrosion, based on the first and only collection of actual excavated lead galvanic joints in North America. The specific goal of this work was to employ comprehensive visual and mineralogical characterization of pipe scales at galvanically connected lead-brass or lead-copper joints, excavated from different U.S. water distribution systems after long periods of service, in order to: (1) directly confirm the presence or absence of galvanic corrosion, (2) conclusively determine identify which metal in the galvanic cell actually behaved anodically (i.e., corroded) over time, and (3) evaluate identify mineral phases at the galvanic junction as opposed to the remaining pipe surface, to gain mechanistic insights on possible galvanic microlayer effects and associated implications.
Description:
The importance/longevity of galvanic corrosion as a mechanism of toxic lead release into drinking water has been under scientific debate in the U.S. for over 30 years. Visual and mineralogical analysis of 28 lead pipe joints, excavated after 60+ years from 8 U.S. water utilities, provided the first direct view of galvanic corrosion presence/extent in practice. Three patterns were observed: (1) no galvanic corrosion; (2) galvanic corrosion with lead pipe cathodic; (3) galvanic corrosion with lead pipe anodic. Pattern 3 is consistent with the order of increasing nobility found in empirical galvanic series (lead, brass, copper) and poses the greatest risk of Pb exposure. Pattern 2 is consistent with galvanic battery reversion, and was identified in water systems with well-developed Pb(IV) scales on their lead pipes. A variety of copper-sulfate minerals (Pattern 2), and lead-sulfate and/ lead-chloride minerals (Pattern 3) were identified in the galvanic zones, illustrating the migration of chloride and sulfate ions toward the sacrificial anode. Geochemical modeling confirmed the required pH drop from the bulk water level to pH 3.0-4.0 (Pattern 2) and pH<5.5 (Pattern 3) in order to form the identified minerals. Despite joints being over 60 years old, galvanic zones in Pattern 3 were active and possibly posed an important source of lead to drinking water.
URLs/Downloads:
DOI: Mineralogical Evidence of Galvanic Corrosion in Drinking Water Lead Pipe Joints
https://pubs.acs.org/doi/pdf/10.1021/acs.est.7b06010
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