Lead in water linked to coagulant
It’s not just chloramines. Coagulants used in drinking-water facilities can create lead problems too.
High levels of lead in drinking water that poisoned a child in Durham, N.C., probably resulted from a change in the coagulant used to remove organic matter, says a corrosion scientist who tested the Durham water. The incident raises the specter of similar undetected problems in other parts of the U.S., says Marc Edwards, a corrosion engineer at Virginia Polytechnic Institute and State University. This case is especially vexing because Durham’s routine water-quality monitoring, which is required by the U.S. EPA’s Lead and Copper Rule, failed to detect the problem in 2004.
Since the 2004 Washington, D.C., lead crisis [316KB PDF]drew attention to lead in drinking water, a few cities that were once meeting the EPA action limit have developed problems. Durham joins Greenville, N.C., and Stafford, Va., on the list of cities where water-treatment changes enacted to reduce disinfection byproducts have unexpectedly raised lead levels. Until now, the prime suspect for these cases was a switch from free chlorine to chloramines for secondary disinfection—the established cause of D.C.’s problem.
Besides switching to chloramines, all three cities changed from alum or another nonchloride coagulant to ferric chloride to better remove organic matter and further reduce disinfection byproducts. This change increased the ratio of chloride to sulfate in the drinking water. When this ratio is >~0.58, galvanic corrosion occurs and erodes particles of solder, according to Edwards. This process takes place even when other aspects of the water chemistry—such as pH, alkalinity, and the use of a phosphate-based corrosion inhibitor—should prevent lead contamination of water, he says.
The chloride-to-sulfate ratio was first reported as an important factor in water corrosion in 1983 by scientists in the U.K. Edwards cited their work in a 1999 publication that indicated the ratio could be important at U.S. utilities. A 2005 American Water Works Association report [1.3MB PDF] made passing mention of the ratio. Even so, most corrosion scientists and utilities managers contacted by ES&T were unaware of the issue.
In Durham, a doctor spotted the child’s elevated blood lead level, >20 µg/dL, during a routine examination this spring. Public-health officials linked the boy’s poisoning to drinking water after they found >800 ppb of lead in tap water and no other source of lead in his mother’s apartment, according to Durham County health officer Marc Meyer.
Paint, dust, or soil—not water—are generally considered major sources of lead exposure. Lead solder, banned in the mid-1980s, could potentially be a significant source of lead in drinking water, according to Mary Jean Brown, head of the U.S. Centers for Disease Control and Prevention’s lead poisoning prevention branch. However, aging processes are thought to deposit various films or scales on top of the solder that protect it from corrosion. “If the aging process does not protect against this, then it would be new,” she says.
Plant managers say that the problem is new. After the switch to ferric chloride, Stafford plant manager Harry Critzer watched lead levels climb. After coagulants were changed, the lead levels quickly dropped below the action limit.
Greenville had a similar experience. “We switched to ferric chloride at about the same time as we switched to chloramines,” says Greenville plant manager Barrett Lasater. “At first, we thought it was a dissolved-lead problem, so we changed our corrosion inhibitor, but this didn’t have much of an effect. EPA, the state regulators, and other consultants didn’t know what it was. There is no literature. There are no guidelines.”
Most corrosion controls focus on soluble-lead leaching, but this is different. It’s about physical processes. “Because these are particles, it means that flow rate is important; the aerator is important,” Lasater adds.
Aerators on or off, a seemingly minor detail, could explain why the Durham health department found a problem that the water company missed. The health department sampled with the aerators on. The water company took them off. Although the aerator on/off issue was highlighted in a previous ES&T article about sampling in Washington, D.C., schools, where EPA Region 3 agreed to an “aerators off” sampling protocol, disagreement about how to sample still exists. “We want to get a real-world sample that reflects what people are drinking,” says Meyer, who advocates leaving the aerators on.
A Region 4 EPA spokesperson tells ES&T that the water utility sampled correctly and that the health department’s procedure “differed from what’s required by regulation,” but the spokesperson declined to explain the results. EPA’s proposed revisions to the Lead and Copper Rule, released on July 6, are silent on specific sampling issues. The proposals would require utilities to consult with state regulators when contemplating a treatment change that might lead to corrosion.
But on July 26, EPA Office of Water assistant administrator Benjamin Grumbles, in a letter to a Durham, N.C., newspaper, wrote, “The U.S. Environmental Protection Agency does not have stated guidelines concerning the removal of faucet aerators before testing for lead in drinking water. We were unaware that water-treatment facilities may be making such a recommendation. Since this matter came to our attention, we have begun looking into it to determine whether we need to provide supplemental guidance on the issue. We hope to make that determination soon.”
Lasater, who switched coagulant a few months ago, is waiting to see whether the change solves Greenville’s lead problem, and Durham’s water company is also expected to stop using ferric chloride. North Carolina’s experiences have raised awareness of water as a source of elevated blood lead, says Meyer. In Greenville, it took a year to determine that water was responsible for high lead levels in children. In Durham, it took a month. “Prior to Greenville, we didn’t sample water when we investigated a home. Now, it’s routine,” he says.
