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Galvanic Corrosion of Lead by Iron (Oxyhydr)Oxides: Potential Impacts on Drinking Water Quality Benjamin F. Trueman,† Gregory A. Sweet,§ Matthew D. Harding,§ Hayden Estabrook,† D. Paul Bishop,§ and Graham A. Gagnon*,† †
Department of Civil & Resource Engineering, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada Department of Mechanical Engineering, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada
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S Supporting Information *
ABSTRACT: Lead exposure via drinking water remains a significant public health risk; this study explored the potential effects of upstream iron corrosion on lead mobility in water distribution systems. Specifically, galvanic corrosion of lead by iron (oxyhydr)oxides was investigated. Coupling an iron mineral cathode with metallic lead in a galvanic cell increased lead release by 531 μg L−1 on averagea 9-fold increase over uniform corrosion in the absence of iron. Cathodes were composed of spark plasma sintered Fe3O4 or α-Fe2O3 or fieldextracted Fe3O4 and α-FeOOH. Orthophosphate immobilized oxidized lead as insoluble hydroxypyromorphite, while humic acid enhanced lead mobility. Addition of a humic isolate increased lead release due to uniform corrosion by 81 μg L−1 andupon coupling lead to a mineral cathoderelease due to galvanic corrosion by 990 μg L−1. Elevated lead in the presence of humic acid appeared to be driven by complexation, with 208Pb and UV254 size-exclusion chromatograms exhibiting strong correlation under these conditions (R2average = 0.87). A significant iron corrosion effect was consistent with field data: lead levels after lead service line replacement were greater by factors of 2.3−4.7 at sites supplied by unlined cast iron distribution mains compared with the alternative, lined ductile iron.
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INTRODUCTION Exposure to leadeven at low levelsis strongly linked with cognitive deficits in children.1 Lead in drinking water is correlated with lead in blood,2,3 and many jurisdictions regulate lead as a drinking water contaminant due to human health risks.4,5 The principal sources of lead in water systems are plumbing components: lead-soldered joints, brass fittings, and lead service lines. Appreciable levels of iron are often present in distributed drinking water, and iron is frequently correlated with lead.6−8 The presence of corroded iron distribution mains has been linked specifically with elevated lead release from lead service lines.9 While the mechanisms governing lead−iron interactions in drinking water systems are not well understood, both adsorption6−8 and electrochemical phenomena may be important.10 Lead adsorbs readily to the iron oxides and oxyhydroxides commonly found in iron corrosion scale.11,12 These may include magnetite (Fe3O4), goethite (α-FeOOH), hematite (αFe 2 O 3 ), maghemite (λ-Fe 2 O 3 ), and lepidocrocite (λFeOOH).13−16 Iron scales are known to release nanosize (
