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Evaluating the Efficacy of System Flushing for Reducing Exposure to Pb Through School Drinking Water in Vermont

Background on Health Effects of Lead

Health effects of lead exposure include irreversible developmental neurotoxicity, disruption of the hormone and reproductive systems (Sanborn et al.), and gastrointestinal and cardiovascular issues. Even at low levels, lead has been known to decrease IQ scores. Lead exposures occur through various means, including from dust and soil contamination from earlier use of lead-based paint and leaded gasoline. The EPA estimates that ~20% of lead exposure is through drinking water. While no level of lead exposure is considered to be safe for anyone, exposure of children to lead is particularly concerning. Children absorb into their bodies a higher fraction of ingested lead and the detrimental effects of developmental exposures can be irreversible (Ellenhorn et al.). Because developing children spend much of their time at school, exposure to lead through drinking water in schools is an important issue (Edwards and Best; Laidlaw et al.). Ultimately, it is the amount of lead in a person’s blood that is considered the best indicator of potential health concerns. Vermont considers blood lead levels >5 ug/dL (micrograms per deciliter) to be elevated. Steady progress is being made on reducing the number of children with elevated levels. Between 2006 and 2017, the fraction of 1-2 year olds with elevated blood lead dropped from ~19-20% to 4-5%.

Overview

Beyond simply testing for Pb in school drinking water, my group was itching to know what can be done to remove Pb from water when we find it. A series of approaches are available, ranging from the upstream approaches that eliminate the sources of Pb (removal of Pb pipes, of pipes connected with Pb-based solder, replacing Pb-containing fixtures) to downstream approaches that remove the Pb before it is consumed (installation of water filters certified to remove Pb). “Flushing” is an additional means of trying to reduce Pb exposure that has been employed, especially by financially-strapped schools/districts. This method refers to flushing water through a building’s water system, typically on a Monday morning or perhaps every morning of the week, by simply turning on every faucet in the building and letting it run for some period of time (2-15 minutes is common). This approach is based on what we know about how stagnation time — the time the water sits in a water system in contact with pipes/solder/fixtures — relates to the concentration of Pb in the water. In short, the longer the stagnation time, the more Pb can dissolve (if it is present) and reach higher concentrations in the water. Flushing in the morning means that the water school children and staff may consume will have been sitting in the pipes for a shorter amount of time (shorter stagnation time) and will have had lesser opportunity to accumulate Pb.

In this project, we examined whether flushing, which theoretically should help, actually works. We asked such questions as, “In cases where a source of Pb is present, does flushing reduce Pb in water to below VT’s action level?” “How quickly after flushing do Pb levels rebound in the water?” “How much do they rebound … by lunchtime? or by the end of the school day when student clubs, athletics teams, and staff members may still be using the building?”