Unraveling the Influence of Natural Organic Matter on Lead Release in Drinking Water Distribution Systems

Abstract

Lead release in drinking water distribution systems remains a critical public health challenge, governed by chemistry of corrosion scales and their interactions with bulk water chemistry. Parameters such as pH, dissolved inorganic carbon, residual disinfectants, aluminum residuals, and corrosion inhibitors exert direct control over the solubility, transformation, and stability of lead-bearing components. Natural organic matter (NOM)—a heterogeneous assemblage of compounds produced by biological and geochemical processes—further complicates these processes. NOM can enhance metal mobilization through surface complexation, colloid stabilization, and modification of corrosion product surfaces. This thesis investigates the role of NOM on lead in drinking water systems with emphasis on its characterization, its influence on corrosion scales, and its effects on lead release under variable chemical conditions. NOM from Southern Ontario, Canada, riverine and lacustrine sources was analyzed using complementary techniques like liquid chromatography–organic carbon detection (LC-OCD), fluorescence excitation–emission matrix (FEEM) spectroscopy, and solid-state 13C NMR. These methods identified distinct compositional differences between riverine and lacustrine NOM. Such compositional contrasts can be translated into differential affinities for forming complexes with corrosion products and varying propensities to generate mobile colloids. A series of bench-scale galvanic corrosion cells simulating partial lead service line replacement were used to assess the effects of NOM type , NOM concentration, pH, dissolved inorganic carbon (DIC), residual aluminum, and orthophosphate on lead release under chloraminated conditions. Two-level factorial or half-fractional designs were used for experimental design. Statistical analyses, generalized additive mixed models (GAMM) and factorial analysis, were employed to evaluate the influence of studied factors and their combined impacts on lead release. These analyses consistently demonstrated that higher pH and DIC reduced total and dissolved lead release, while NOM enhanced dissolved lead mobilization. While aluminum had minimal impact in NOM-free conditions, its presence under NOM-rich conditions reduced lead concentrations. NOM also diminished the effectiveness of orthophosphate in reducing lead concentration, even under elevated pH. Corrosion scales were analyzed to identify mineral phases and morphologies. Scale analysis confirmed the predominance of smaller hydrocerussite and/or cerussite in the presence of NOM. Collectively, these findings provide mechanistic insight into the interplay between NOM, water chemistry, and corrosion control strategies. This research advances understanding of NOM–metal interactions and supports the development of more resilient strategies for managing lead in drinking water systems.