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Diagnostic Sampling to Reveal Hidden Lead and Copper Health Risks
Citation:
SCHOCK, M. R., A. M. Sandvig, F. Lemieux, AND M. K. DESANTIS. Diagnostic Sampling to Reveal Hidden Lead and Copper Health Risks. Presented at 15th Canadian National Conference and 6th Policy Forum on Drinking Water, Kelowna, BC, CANADA, October 21 - 24, 2012.
Impact/Purpose:
To inform the public.
Description:
Lead, copper and other metallic contamination sources in premise drinking water plumbing systems, are unevenly distributed and are usually hidden from thought, view, or both. Many sampling protocols exist, each with some set of implicit assumptions governing its applicability to the specific question at hand. Consequently, misleading and erroneous conclusions are frequent consequences of applying the wrong sampling strategy. Sampling errors are common in assessing corrosion control effectiveness and determining where peak exposures to lead and copper would be encountered, typically systematically under-representing high concentrations. Lead and copper corrosion chemistry differ in significant ways. While they often are thought of together in terms of plumbing contamination, key differences in the most important variables and plumbing system characteristics must be considered when assessing exposure risk and treatment effectiveness. For lead, sequential sampling of water of different stagnation times is critical to identifying the location and relative contribution of the various lead-containing plumbing components and devices, which range from soldered joints to faucets, shut-off valves, meters, flow regulators, and pipes. Using sequential sampling and multi-element analysis, different scenarios will be presented using real data from different water systems and corrosion control approaches, illustrating varying levels of lead threat depending on the premise plumbing configuration and lead corrosion control mechanism. Data show that typical first liter sampling protocols often miss very high lead levels present in contact with lead service line piping, effectively hiding elevated lead levels consumers would likely encounter under normal usage conditions. An important knowledge gap is created for public health professionals investigating sources of children’s lead exposure in houses, apartment buildings, schools and day care centers. This protocol also gives misleading indications of treatment performance (i.e. reductions in lead levels) for lead service lines. Sequential or selected multiple samples are very helpful in diagnosing the presence of PbO2 lead pipe scales without necessarily excavating pipes, and assuring simultaneous control of lead release from in-line devices as well as lead piping. Copper corrosion and release contrasts with lead most importantly by undergoing dramatic scale solubility changes over months to years in waters of high bicarbonate content, and by needing much longer stagnation times to reach equilibrium in the presence of common drinking water oxidants. Opposite to lead, where Pb(IV) is much less soluble than Pb(II), Cu(II) is far more soluble than Cu(I), and is prone to release at levels of health concern. Though copper occurrence in premise plumbing tends to often be more linearly uniform (simplifying sampling in some respects), the water quality, scale aging, and stagnation behavior create a set of complications that largely diverge from the criteria for optimum lead sampling. Case study and research data are used to illustrate key concepts for copper monitoring, showing how common sampling misconceptions can systematically underestimate high levels of copper, and result in potentially adverse health outcomes.