The dangers of lead pipes in drinking-water systems are well established, but could the cure be even worse?
Quite possibly, say researchers at Washington University in St. Louis.
It turns out that the common practice of replacing old lead lines with new copper pipes using brass fittings spurs galvanic corrosion that may actually dramatically increase the amount of lead released into drinking water.
Photos: Joe Angeles/WUSTL
|Old lead water pipes are spliced with either a plastic or brass fitting to new copper pipes in Dan Giammar's lab at Washington University in St. Louis. Joining the dissimilar metals leads to galvanic corrosion that releases more lead into the water, Giammar (right) has found.|
“Work done in our laboratory shows galvanic corrosion in joined service lines is significant and lasts for a long time,” says Dan Giammar, PhD, of the university’s Department of Energy, Environmental & Chemical Engineering.
That means that lead-pipe removal programs underway at utilities nationwide may actually be increasing lead exposure for water customers.
Giammar has been working with 80- to 100-year-old lead water pipes that were dug out of the ground in Washington, D.C., and shipped to his lab in St. Louis. Some of those pipes have been cut and then joined with brass couplings to new copper pipe.
This setup mimics what happens if a utility company is replacing lead service lines and homeowners—as they typically do—decline to pay to have their sections replaced as well.
You might think the problem “would be half of what it was or—maybe—completely unchanged,” Giammar says.
Instead, Giammar found, immersing the dissimilar metals in a conducting liquid triggers galvanic corrosion, which then releases five times more lead than the original lead pipe did.
Case Study: Washington, D.C.
Lead pipes were outlawed in new construction in 1978, and lead levels in drinking water were regulated in 1991, when the Lead and Copper Rule was passed.
However, Giammar noticed, the lead levels in Washington D.C.’s drinking water began to rise in 2001.
After some study, he discovered that the difference was due to a change in the disinfectant added to the water.
“The lead pipe, in itself, is not much of a concern,” Giammar says. Pure lead (lead 0) is not particularly reactive or soluble, and lead lasts much longer than iron, which is why it was used for plumbing to begin with, the university reports in an article.
But when lead oxidizes (corrodes), the lead species that then form determine how much lead ends up in the water, the university says.
The lead comes from the piping, but whether it is released depends on the chemistry of the water running through the distribution system, Giammar found.
A strong oxidant in a disinfectant like pure chlorine (which the D.C. district had previously used) will keep the lead species stable, he discovered. But then the district switched to a weaker oxidant—chloramine—to improve the water quality.
|Giammar and doctoral students Yin Wang and Vrajesh Mehta studied pipes that had been dug up from water lines in Washington, DC, where lead levels had inexplicably increased.|
When that happened, “the pipe scale that had formed over years of chlorine treatment began to release lead into the water,” Giammar said.
The case is a reminder that tap water is a manufactured product, not a natural resource, Giammar says. Water leaving a treatment plant may have essentially no lead, but that could change by the time it reaches the faucet.
The Right Blend
One critical factor, he eventually discovered, was the water’s pH. “We knew pH would be an important variable,” he says. “You don’t want your pH to fall too low, especially for the lead carbonates, which dissolve at lower pH.”
“But we didn’t realize how important pH was. … In some cases, the pH made the difference between a lead concentration that met the drinking water standard and one that didn’t.”
The other important factor was phosphate. Adding phosphate could reduce dissolution rates, but is undesirable for health, cost and environmental reasons.
“It’s never going to be a one-size-fits-all solution, because the source-water compositions are different,” says Giammar. But the team’s report on the project (“Influence of Water Chemistry on the Dissolution and Transformation Rates of Lead Corrosion Products”) makes “some pretty strong recommendations.”