Pb Release from End-Use Plumbing Components

摘要

The Seattle School Board adopted a policy in 2004 that limits acceptable lead (Pb) levels to 10 μg/L at drinking water sources in Seattle public schools. Several possible sources of Pb were identified in school piping systems including brass components and fittings in end-use plumbing. Field and laboratory studies were therefore conducted to determine Pb release from new end-use plumbing components and fittings installed at drinking water sources (primarily fountains) in Seattle Public Schools. Field studies were conducted by collecting sequential small-volume samples at 16 sources in 3 schools to assess the relative contributions of the various end-use components and fittings to lead in drinking water at the tap. Results indicated that most of the lead contained in first-draw 250-mL samples originated in the first 50 mL drawn from the source. Laboratory studies utilized stagnation and flow-through testing procedures on new enduse components and fittings with local tap water to determine Pb release as a function of cumulative contact time. Laboratory results showed elevated Pb levels during early testing, followed by a general decline in Pb levels with repeated exposures attributed to passivation of exposed brass surfaces. Periodic spikes in Pb observed for some components (I.e., bubbler heads and brass shutoff valves) were attributed to the movement of the valves during sample collection and possible release of machining residuals and metal particulates, or dezincification of brass materials. Field and laboratory testing results are significant because new end-use plumbing components typically had been installed in Seattle Public Schools immediately after purchase, without pre-conditioning. Results from this study were used to help identify likely causes of high Pb levels in water samples and develop mitigation measures, such as pre-conditioning of end-use plumbing components, so that drinking water sources can be used immediately after being retrofitted with new components and fittings in Seattle Public Schools.