Following the lead (Pb) contamination crisis in the Flint water supply, the State of Michigan instituted the Sentinel program to monitor water Pb levels (WLLs) in Flint houses. This paper will discuss the data collected and insights that might be gained from the Sentinel and other Pb monitoring programs in Flint. While there are concerns associated with the Sentinel program in terms of the representativeness of the sampling sites, the results provide insights into the changes in WWLs in Flint over time. As shown in Figure 1, there has been a significant decrease over time in the percentage of houses with Pb service lines (LSL) in which WLLs exceed the 15 ppb Action Limit set under the federal Lead and Copper Rule. However, in houses with copper service lines (CSL) there is no evidence of time dependence (based on the Runs Test). In 2017, the percentage of exceedances was greater in houses with CSLs (8.4%) than in homes with LSLs (5.9%). This difference is statistically significant (Z = -3.16, p = 0.0015 using the Mann-Whitney U Test). Overall, Pb concentrations &gt;15 ppb were observed in 7.6% of the homes with CSLs (Figure 2). Thus, even if all LSLs are replaced many people in Flint may still be exposed to significant levels of Pb in their drinking water. It is not clear that these results are generalizable to other cities. In Flint, phosphate has been added at a concentration of &gt;3 mg/L. In the US, where phosphate is added as a corrosion inhibitor, it is generally added at a concentration of 1 mg/L or less. Phosphate has been found to accelerate the galvanic corrosion of Pb from simulated soldered copper joints (Nguyen et al., 2011) so, in homes where the copper pipes were soldered with lead solder, it is possible that the elevated phosphate levels in Flint drinking water could have resulted in increased WLLs. Future work will investigate the impact of water chemistry on Pb levels in Flint drinking water.

Lead levels in copper and lead service lines in Flint, Michigan

255th National Meeting (2018)

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