In the meantime, though, outside experts expressed serious concerns with the CDC number.
Denison, whose group works for tougher regulation of toxic chemicals, blogged that the federal agency's figure had a "questionable basis" and that West Virginia officials were trusting "shaky science."
Among other concerns, Denison said that LD50 numbers for the lethality of a chemical should not be used to develop this sort of screening level, and the formula used did not take into account potential effects of longer-term, chronic exposure to the chemicals.
"Now let me be clear," Denison wrote. "I am not saying that the level of 1 ppm is unsafe. I am saying that we have no way of knowing whether it is safe. The data needed to make that assessment simply do not exist for this chemical."
'No observed adverse effects'
When the CDC finally started talking to the media and the public, the agency's explanation of how it arrived at the 1-ppm number had changed.
Starting with interviews, a media briefing, and a website posting, the CDC said it had used a different starting point than the LD50 number Cseh initially relied upon.
Dr. Vikas Kapil, chief medical officer for CDC's National Center for Environmental Health, told reporters Jan. 16 the agency used what's called a "no observable adverse effects level," or a NOAEL. That figure, 100 milligrams per kilogram, came from a 1990 Eastman study of 4-MCHM, the main component of Crude MCHM.
Using it, CDC officials again applied three uncertainty factors -- one for variation between animals and humans, one for vulnerable populations, and a third to try to account for how little was known about Crude MCHM's potential toxicity. They came up with the same end result: 1 part per million.
The CDC's use of the LD50 study for such an important screening level -- one impacting 300,000 people -- had been questioned in the public health community. The use instead of the NOAEL figure would deflect at least some of that criticism.
What remains unclear, though, is when exactly the CDC and other federal agencies or state officials obtained the 1990 Eastman study where they got the NOAEL number.
While the NOAEL study was older than the LD50 study -- it was from 1990 -- the NOAEL study was not listed on Eastman Chemical MSDS sheets published in 2005 and 2011.
In an interview, Cseh said he obtained the information sometime after 9:30 p.m. on Friday, Jan. 10, and didn't finish reviewing the material until the following day.
But Burden, the CDC press officer, was still talking only about the LD50 study in an email message late Saturday afternoon. And as late as early in the morning on Sunday, Jan. 12, Cseh sent an email message to state officials that still referenced only the LD50 number's use in developing the screening level, according to records obtained under the Freedom of Information Act.
Barbara Reynolds, another CDC press officer, said the initial recommendation of 1 ppm was based on "the limited science available" on the night of Jan. 9.
"The next day, this recommendation was validated by additional scientific studies including" the NOAEL, Reynolds said in a written response to Gazette-Mail questions. "A subsequent review by a Federal Interagency workgroup further validated the 1 ppm recommendation."
Also unclear, though, is exactly when and how the CDC obtained the Eastman studies.
Cseh said in his interview that he obtained them late on the night of Friday, Jan. 10. But at the time, he said, they were still considered proprietary work from Eastman, and the CDC could not make them public. In her email to the Gazette-Mail, Tierney also said that the Eastman study "is not publicly available."
"It is Eastman proprietary information," Tierney said.
But in an email Sunday, Jan. 12, when asked about any studies the CDC had obtained from Eastman, agency spokeswoman Burden said, "Eastman provided no studies or information to our agency. The information that is referenced in the response we sent you including studies that have been conducted in the past is available in the literature in the public domain."
Eastman posted its MCHM studies on its website -- releasing them publicly for the first time -- on the evening of Jan. 16, hours after Rep. Henry Waxman, D-Calif., wrote to the company asking for the studies to be released.
A 'clearly daunting task'
Even once the CDC started using the NOAEL number in their screening level calculations, experts from the public health community continued to criticize what they had done.
In a post for her group's blog, Natural Resources Defense Council senior scientist Jennifer Sass argued that the agency could have done the math differently, and come up with a more protective screening level.
Sass explained that the Eastman study used four chemical doses: No chemical (control), 25, 100, and 400 milligrams per kilogram body weight per day fed to each rat. Eastman's authors said the mid-dose of 100 milligrams per kilogram had no effect, and therefore should be used to calculate a "safe" level for people.
"But that's not what the data shows," Sass wrote. Male rats had body weight decreases at all dose levels, including the low dose of 25 and the mid dose of 100, she wrote.
"The effect showed a dose-response trend, increasing with increasing dose, but the trend was not statistically significant," Sass wrote. In female rats, the low- and mid-dose groups weighed 'slightly more than controls' but no specific measurements were reported and we are to trust the study authors that it was not statistically significant."
Sass wrote, "It is hard to get statistical significance in studies like this where so few rats are tested at each dose, given the natural variation between individual animals.
"In statistical-ese, we say that the study is underpowered -- its ability to detect an effect is very poor because the sample size is so small," Sass wrote. "So, when such a study actually finds an effect, like this body weight decrease, despite its lack of power, it suggests a treatment-related effect.
"The chemical company may 'overlook' the effect at low doses, but government scientists charged with protecting the public's safety shouldn't be so dismissive of the toxic effects seen at the mid- and low-dose."
Sass said if the CDC had used the low-dose figures from the Eastman study, the agency would have come up with a screening level far lower - 0.025 parts per million, or about 40 times more protective than the 1 ppm level.
Denison, the EDF scientist, said state and federal officials "were faced with the clearly daunting task of having exceedingly limited information to go on as they tried to assess and communicate about the risks of a chemical contaminating the tap water of hundreds of thousands of people.
"But instead of forthrightly acknowledging the enormous uncertainties, they instead rushed to establish a 'safe' level using that inadequate information, took many days to come clean about how they had derived the level, repeatedly claimed erroneously that the level provided a large safety margin, and then as new uncertainties arose -- more than one chemical actually leaked, exposure by inhalation during bathing had not been considered, the distinctive odor of the chemical was still being detected in homes and schools even after following the correct flushing procedure -- they continued to claim they had taken into account all contingencies," Denison said. "The result is a situation where, a month after the spill, there are still far more questions than there are answers."
Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.