When Flint, Mich., started taking water from the nearby Flint River in 2014, lead levels spiked in the water coming out of residents’ taps.
Now, chemical and microscopic analyses of the city’s water pipes reveal a pockmarked pattern that confirms the lead came from corrosion of the pipes. The analysis also allowed the researchers to estimate the amount of lead released into the city’s water system.
This study further highlights the hazards of lead accumulation and mobilization in water pipes, says Marc A. Edwards of Virginia Tech, who played an integral role in exposing the Flint water crisis but who was not involved with this new study.
“It just goes to show that we can forget these lead pipes are there, but the second we let down our guard, they can provide a horrible reminder of their danger to humans,” he says.
The research team, led by Terese M. Olson and Brian R. Ellis of the University of Michigan, Ann Arbor, collected 10-cm-long segments of lead water pipes from various locations in Flint and sampled the pipe scale—the about 300-µm-thick mineral layer that lines the pipe interior. They measured the concentration of various metals in the scale by inductively coupled plasma mass spectrometry and compared the values with metal concentrations in water pipes from other cities.
Flint’s mineral lining was depleted in lead and phosphate, indicating selective release of lead phosphates after pipe corrosion. When the city switched water sources in 2014, they did not treat the water with an orthophosphate corrosion inhibitor, which would have reduced or prevented this release, Ellis says.
Based on the scale comparisons, the team could calculate the amount of lead missing from Flint pipe samples. They determined that the pipes released about 2.7 g of lead per meter of service line over the course of the 1.5-year-long crisis, meaning that a lead pipe delivering water to a single Flint household would have released approximately 18 g of the neurotoxic metal (Environ. Sci. Technol. Lett. 2017, DOI: 10.1021/acs.estlett.7b00226).
Edwards says that this level of lead release was about one-third of the amount released during a similar event in Washington, D.C., from 2001 to 2006. The difference between the two events, he says, was “in large part because Flint consumers discovered the problem relatively early as scale started to chemically degrade and detach.”
Ellis cautions that it is hard to estimate people’s exposure to the lead release in Flint. “Once lead goes into solution, its fate is very complicated,” he says. His team is now searching for lead pipes in Flint that were shut off during the water crisis to obtain more accurate precorrosion measurements.