CHARLESTON, W.Va. -- Federal health officials on Thursday defended their recommended 1-part-per-million threshold for acceptable levels of "Crude MCHM" in West Virginia drinking water, but also said they continue to gather data on the chemical's potential health impacts.
"This is a dynamic and evolving event," said Dr. Vikas Kapil, chief medical officer for the U.S. Centers for Disease Control and Prevention's National Center for Environmental Health.
Kapil said the CDC stands by its initial recommendation -- made in the absence of any regulatory standards or established public-health guidance -- but that the agency is searching for additional information that might help scientists refine their work.
"As we get additional information, we will be able to use that information as it becomes available," Kapil said. "However, we stand by the 1-part-per-million screening level that we have recommended."
Kapil made his statements during a conference call with local and national reporters, as the CDC faced increasing pressure to explain how it came up with the figure being used by state and local health officials in West Virginia.
However, agency officials also conceded that it's "almost as if we're learning as we go" in dealing with a chemical spill last Thursday that fouled the drinking water supply that serves nearly a third of a million West Virginians.
Other toxic-chemical experts continued to question the CDC's figures, to advise West Virginians that the number might not be as conservative as the agency would have residents believe and that the lack of data reflects a far broader problem.
"As much as this stinks, this is the way it works for almost all chemicals," said Laura Vandenberg, an assistant professor of environmental health at the University of Massachusetts at Amherst.
In Charleston and across a nine-county region, state officials and West Virginia American Water have been clearing residents since Monday night to resume drinking, bathing and cooking in water from their taps. Water company officials have given residents a zone-by-zone go-ahead to flush out their home plumbing systems based on water samples showing less than 1 part per million of MCHM, a coal-cleaning chemical also known as 4-methylcyclohexanemethanol.
Officials with the administration of Gov. Earl Ray Tomblin have backed the move, saying they trust the CDC recommendation, which Bureau for Public Health Commissioner Letitia Tearney said is based on one study result, called an LD50, that determined at what level of the chemical half of the exposed experimental rats would die.
Late Wednesday evening, though, the state Department of Health and Human Resources, acting on the CDC's advice, recommended that pregnant women not drink tap water until there is no MCHM, the chemical that leaked into the Elk River last week, detectable in the water.
Thursday morning -- after refusing repeated interview requests since last week -- the CDC made Kapil available for an interview with The Charleston Gazette. In that interview, Kapil stressed that the new recommendation to the state was made out of an "abundance of caution" and said pregnant women who have been drinking the water since "do not use" orders began to be lifted on Monday should not expect adverse effects.
"We would not expect that, at the levels we're talking about, that we would expect any adverse health effects, either for the mom or their baby or their unborn babies," Kapil said.
Kapil told the Gazette that the new advisory was not made because of newly discovered information.
"It's really just out of an abundance of caution. Exposure during pregnancy and reproductive toxicology is a challenge," Kapil said. "We often don't have a lot of reproductive toxicology information available on those exposures."
In a letter Wednesday to DHHR Secretary Karen Bowling, though, CDC Director Dr. Thomas Frieden specifically noted, "since making the initial calculation, scientists have obtained additional animal studies about MCHM. These are currently being reviewed.
"At this time, the scientists continue to recommend 1 ppm as a protective level to prevent adverse health effects," Frieden wrote. "However, due to limited availability of data, and out of an abundance of caution, you may wish to consider [an] alternative drinking water source for pregnant women until the chemical is at non-detectable levels in the water distribution system."
Richard Denison, a biochemist with the Environmental Defense Fund, has been following the West Virginia situation and writing about the CDC's risk-assessment efforts on his organization's blog.
Writing late Wednesday, Denison noted that the CDC letter made it appear that the newly obtained studies played some role in the federal agency's recommendation and the state's action. That, Denison said, "raises the question as to whether the new animal studies suggest a potential for developmental toxicity or a related effect.
"Clearly something prompted the issuance of the advisory," Denison wrote. "This new development, I believe, lends even greater weight to the need for immediate public release of available studies and the methodology."
Denison and some other critics had focused on the fact that initial reports from the state were that the CDC had used only the LD50 study, a move that would have, among other things, considered what level would be lethal, but did not examine other adverse health effects.
On Thursday, though, Kapil disclosed the existence of another study used by the CDC. He said that it resulted in a figure called the No Observable Adverse Effects Level, or NOAEL. That figure shows the maximum amount of chemical in which there are no biological or health effects visible in the test animals, which Kapil thought were either rats or guinea pigs.
The NOAEL for Crude MCHM is 100 milligrams per kilogram of body weight, Kapil said.
To that number, toxicologists at the CDC applied three safety factors, to try to account for uncertainty. The first safety factor accounts for the variation between animals and humans.
The second accounts for variation within humans, as some populations -- the elderly, children, those with pre-existing conditions -- could be more vulnerable.
The third safety factor accounts for how little information is available on Crude MCHM.