Understanding the Role of Particulate Iron in Lead Release to Drinking Water

Lead service lines (LSLs) are a major source of drinking water lead, and high iron levels are frequently observed along with elevated lead release. A model distribution system, dosed with orthophosphate, was used to evaluate the effect of corroded iron distribution mains on lead release from recovered LSLs. Lead release was higher by 96 mu g L-1, on average, from LSLs supplied by corroded iron compared to the inert reference material (PVC). This effect may be explained by deposition of semiconducting iron oxide particles within LSLs. When galvanic cells with lead and magnetite (Fe3O4) electrodes were short-circuited, lead release increased 8-fold and a current averaging 26 mu A was observed. In effluent from LSLs with an upstream iron main, colloidal lead and iron occurred in the same size fraction possibly due to release of colloidal particles from LSL corrosion scale enriched with iron. Under these circumstances, high molecular weight (>669 kDa) Pb-208 and Fe-56 elution profiles, observed via size-exclusion chromatography, were highly correlated (average R-2 = 0.97). Increasing orthophosphate from 0.5 to 1.0 mg L-1 (as PO43-) accompanied an average reduction in lead release of 6 mu g L-1 month(-1) but did not significantly reduce the effect of an upstream iron main.