Colloidal lead in drinking water: Formation, occurrence, and characterization

Abstract

Lead colloids—particles between 0.001 and 1 µm—present unique challenges for maintaining drinking water quality. Most of the published literature on lead in drinking water adopts a threshold for soluble lead of <0.45 µm, yet strong evidence of lead colloids occurring below this threshold has been reported across North America and Europe. This highlights the potential to misclassify colloidal lead as soluble. Remedial actions taken to reduce soluble lead concentrations can differ from those used to target colloidal lead, and in some cases may exacerbate the problem. Concentrations of colloidal lead are difficult to measure and to predict from water quality data. Nevertheless, advances in analytical techniques have allowed for more precise identification and characterization of lead colloids and their interactions with other compounds in drinking water. Analytical cost or expertise may be a barrier to utilizing some of these techniques. A critical analysis, weighing practicality and data quality, of the strengths and weaknesses of these methods is presented. This review identifies and discusses four key factors that promote colloidal lead formation and mobility in drinking water: natural organic matter, adsorption of lead to colloidal iron particles, precipitation with orthophosphate, and complexation or dispersion by sequestrants. This review also summarizes previous observations of lead colloids originating from the corrosion of drinking water distribution system and premises plumbing components and evaluates the use of colloidal analysis as a diagnostic tool. Despite the challenges and need for further research, colloidal analysis is a useful tool to inform better lead mitigation strategies.