High levels of iron in distributed drinking water often accompany elevated lead release from lead service lines and other plumbing. Lead-iron interactions in drinking water distribution systems are hypothesized to be the result of adsorption and transport of lead by iron oxide particles. This mechanism was explored using point-of-use drinking water samples characterized by size exclusion chromatography with UV and multi-element (ICP-MS) detection. In separations on two different stationary phases, high apparent molecular weight (>669 kDa) elution profiles for Fe-56 and Pb-208 were strongly correlated (average R-2 = 0.96, N = 73 samples representing 23 single-unit residences). Moreover, Fe-56 and Pb-208 peak areas exhibited an apparent linear dependence (R-2 = 0.82), consistent with mobilization of lead via adsorption to colloidal particles rich in iron. A UV254 absorbance peak, coincident with high molecular weight Fe-56 and Pb-208, implied that natural organic matter was interacting with the hypothesized colloidal species. High molecular weight UV254 peak areas were correlated with both Fe-56 and Pb-208 peak areas (R-2 = 0.87 and 0.58, respectively). On average, 45% (std. dev. 10%) of total lead occurred in the size range 0.05-0.45 mu m. (C) 2016 Elsevier B.V. All rights reserved.