When tap water in Flint, Michigan became smelly and discolored in 2014, researchers soon traced the contamination to a chemical reaction between the city’s new water supply and a protective “scale” inside the lead service lines.
But that was just the beginning of Flint’s problems. Now, researchers have shown that the average service line—the pipe that runs from a water main to an individual home—as it was stripped of its scale, released about 18 grams of lead from April 2014 to October 2015.
The study , conducted by researchers from the University of Michigan, confirms what was generally understood to be the cause of contamination, and predicts the amount of lead that made its way into people’s homes.
Many of Flint’s service lines are made of pure lead, and they corrode slightly as they’re used. The lead that’s released reacts with compounds dissolved in the water to form a protective scale on the inside of the pipe. The scale is made up of lead, aluminum, and magnesium silicate, as well as other elements. As long as the scale is intact, the pipes can deliver lead-free water.
But when the city of Flint switched its water supply from the Detroit Water and Sewage Department to the Flint River, it failed to add orthophosphate, which acts as an anti-corrosive, to the new water supply. As a result, the scale inside the pipes began to release its lead into the water.
The team collected short samples of service lines during spring and fall of 2016, and conducted chemical analysis of the scale. They found proportionally high levels of aluminum and magnesium, but depleted levels of lead.
Richard Luthy, a professor of civil and environmental engineering at Stanford University who was not involved in the study, said that the results confirm that the absence of orthophosphate was a significant contributor to the lead crisis in drinking water in Flint.
The team also used microscopy to get a visual image of the state of the scale, which showed the inner layer to be thinned out and fragmented.
“In most of these lead service lines, quite a bit of the scale that’s present in the lining of the pipe is comprised of lead,” said Terri Olson, an associate professor in the department of civil and environmental engineering at the University of Michigan and corresponding author of the study.
“It was kind of amazing to me that because there’s so much [lead] there, you could actually see a difference as a result of what happened,” Olson said.
Olson said the team is now looking for a service line in Flint that was not exposed to the untreated water, such as a house whose water was turned off during the contamination event. Such a line would provide a baseline to compare the findings with.
Luthy pointed out the need for more comprehensive study of cities with lead service lines to better assess factors such as the consistency in orthophosphate supply on lead release and the behavior of lead in particulate form. “In short,” he said, “there’s much to learn still about treatment chemicals and operations on leachable lead in old water systems.”