How much lead in water poses an imminent threat?
The water contamination crisis in Flint, Mich., has fueled concerns about how much lead is coming out of taps in homes across the USA.
But what amount of lead in drinking water poses an urgent health risk — the kind of threat that should cause consumers to immediately stop using their home's water for drinking and cooking?
The federal government has given water systems no recommendation on issuing a do-not-drink order, said Jim Taft, executive director of the Association of State Drinking Water Administrators.
If water samples show lead levels like those in Flint, "people need to stop drinking the water," Taft said. "But what is that number?"
That's difficult to answer because the amount of lead coming out of taps across a city can vary significantly depending on the amount of lead in each home's plumbing. Water is generally lead free leaving a system's treatment plant and becomes contaminated only as it approaches individual homes that have lead service lines or internal plumbing made with lead.
Newer homes without lead in their plumbing face no risk.
The U.S. Environmental Protection Agency and the Centers for Disease Control and Prevention both say no amount of lead in water is safe.
But neither agency answered the USA TODAY NETWORK's questions about when lead contamination in water poses an imminent health risk or when do-not-drink orders should be issued.
"At this time, EPA has not provided a broader guidance regarding a lead concentration that would trigger a do-not-drink order," the agency said in an emailed statement.
The EPA's current action level for lead in drinking water is part of a water treatment technique rule designed to serve as a warning sign for water systems that they need to address the corrosivity of their water. The more corrosive the water, the more lead that will leach from old plumbing.
Only when more than 10% of a system's tap water samples show lead concentrations above 15 parts per billion does an alert go out to customers.
But these notifications don't tell consumers to stop drinking the water. They advise of a potential risk and give ways to reduce exposures, such as letting taps run to clear stagnant water that has been sitting in pipes and may contain the most lead.
In Flint, the amount of lead found in in residents' water since the crisis erupted has varied from house to house with many showing no detectable levels of lead. At a few homes, lead levels reached 4,000 ppb to nearly 12,000 ppb.
As of earlier this month, regulators had conducted more than 14,800 tests at homes across Flint. About 1,100 testsshowed lead levels at greater than the EPA's 15 ppb action level with more than a third of them above 40 ppb, state data show.
From at least 2002 into 2004, archived webpages show the EPA’s website said a lead concentration of 40 ppb or more in drinking water was cause for “immediate action.” At that level, the water posed an “imminent and substantial endangerment to the health of children and pregnant women.”
A USA TODAY NETWORK review of EPA drinking water enforcement data found at least 125 water systems — run by schools, villages and businesses — that reported lead concentrations of 40 ppb or greater in more than 10% of their tap water samples during the past four years.
The EPA removed its online references to this 40 ppb danger level in 2004, amid growing publicity about another lead-water crisis in the water system in the nation's capital caused because of a change in disinfection chemicals that increased lead leaching.
In response USA TODAY NETWORK questions, the EPA acknowledged its website for several years displayed 40 ppb as a health-threat standard, but said it never was adopted formally.
“Use of a 17-year-old draft analysis that has not undergone scientific peer review is not the right approach to help build public understanding of lead risks in drinking water,” the EPA said in a statement.
The EPA refused to release the analysis voluntarily and told the USA TODAY NETWORK it would need to file a federal Freedom of Information Act, a process that often takes months or years.
Joel Beauvais, deputy assistant administrator of the EPA's Office of Water, emphasized: “EPA’s position is there is no safe level of lead exposure.”
The CDC, which declined to grant an interview, emailed a statement saying the agency recommends that pregnant women and children use bottled or filtered water if lead levels in their home's water exceed the EPA's 15 ppb action level. Children's developing brains and bodies are especially vulnerable to lead's toxic effects.
Yet some studies have found harm from consuming water when lead levels are above 5 ppb of lead, which is the maximum amount of lead contamination the U.S. Food and Drug Administration allows in bottled water.
Exposures to lead are cumulative.
Drinking lead-contaminated water adds to the body’s burden from other sources. Those include soil contaminated with old leaded gasoline and factory waste and dust from deteriorating lead-based paint, which is often found in older homes.
“When we looked at the relative contributions from lead in water, soil and dust, we estimate that water lead contributes about 20%,” said lead-poisoning researcher Bruce Lanphear at Simon Fraser University in British Columbia, who studied children exposed to lead in Rochester, N.Y.
Lanphear said his work has estimated that water with lead levels greater than 5 ppb were associated with a one-point rise in children's blood-lead levels.
Unlike other sources of lead exposure, contaminated water poses an increased threat because you are drinking it.
“You should assume you’re absorbing most of it,” Lanphear said. “It’s not like the house dust over there.
"This is what you put into your mouth or you’re cooking with. It’s a direct exposure,” he said.
Infant formula made with lead-contaminated water poses a significant risk, Lanphear said. In another study, Virginia Tech researcher Marc Edwards estimated that half of infants fed formula reconstituted with tap water containing 18 ppb of lead would have their blood-lead levels rise above the current CDC level of concern.
In December, experts on the EPA's National Drinking Water Advisory Council recommended that the agency develop a health-based "household action level" that would require water systems to notify local health officials when a home's lead test exceeded a certain level. But the council did not specify what that level should be.
The EPA has said it is studying this and many other recommendations from the council and expects to publish proposed revisions to drinking water regulations in 2017.
Contributing: Mark Nichols, USA TODAY. Follow Alison Young on Twitter: @alisonannyoung