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Treatment Strategies for Lead in Drinking Water
Citation:
Schock, M. Treatment Strategies for Lead in Drinking Water. Presented at 2013 AAAS Annual Meeting, Boston, MA, February 14 - 18, 2013.
Impact/Purpose:
Invited presentation at the American Academy for the Advancement of Science annual meeting in the session "Lead: The Global Poison -- Humans, Animals, and the Environment". The central topic is the science of lead in drinking water, how it occurs, and what can and can't be done through water treatment.
Description:
Lead pipes are capable of lasting hundreds of years. Conservatively, there are over 12 million, still serving drinking water in the US. Probably, this is a substantial underestimate. Leaded solder joining copper pipe abounds. Leaded brasses have dominated the materials used for faucets, shut-off valves, water meters and other in-line plumbing devices. All of these sources combine to contribute lead to the water, the amount depending specifically on the alloys, design, amount of lead, and water quality. Lead has accumulated over time in the scales of interior plumbing from upstream lead sources (such as lead service lines). The scope of the lead contamination of drinking water is widely underestimated by the frequent use of sampling and monitoring plans that are not designed to accurately detect the spatial and temporal variation within a dwelling or building. Drinking water treatment strategies for lead may be condensed into 3 approaches, in approximate order of effectiveness: (1) immobilization of protective PbO2 scales on the pipe surface; (2) immobilization by the formation of divalent lead orthophosphate compounds on the pipe surface; (3) immobilization of lead by the formation of divalent lead hydroxycarbonate scales at very high pH. A fourth mechanism for limiting lead release, though accidental, is the coating of the surface with precipitates and scales that inhibit the diffusion and release of lead into the water. The success of treatment strategies is limited by: lead chemistry itself; the physical nature of the pipe and device surfaces; the background water chemistry; hydraulic flow patterns within the water lines; physical disturbances of the lead pipes; and the expense of simultaneously complying with other Safe Drinking Water Act regulations. Physical disturbances of lead pipes are inevitable. Water systems replace meters, valves, and distribution system water mains. Such activities can increase lead release from pipes by a factor of 2 or (often) more, for many years. Many thousands of undetected disturbances occur yearly. Research has yet to identify what treatments or operational procedures can mitigate the severity of lead release consequences of these disturbances. The best OCCT allows at least a consistent background amount of lead exposure (2-15 µg/L) under the best of circumstances. Treatment is at best a temporary ‘band-aid’ of varying effectiveness. As long as lead pipes remain, a massive reservoir of lead exists, that invisibly can contaminate the water of thousands to millions of vulnerable people.
