One part in a million.
That's about one inch in 16 miles, or 1 minute in two years, or one drop in 13 gallons.
That's how much crude MCHM, the material that contaminated the water supply of 300,000 West Virginians, is considered safe. But how that number came about took a lot of guesswork, as no one really knows how much MCHM in the human body is safe.
The Centers for Disease Control and Prevention came up with that number after reviewing the existing literature on how MCHM affects lab animals.
With hundreds of chemicals in use, the CDC has extensive knowledge of how only a relatively few affect the human body. MCHM is one of those that the CDC just doesn't know much about, according to Dr. Vidas Kapil, chief medical officer of the National Center for Environmental Health at the CDC.
"It's not unusual to be faced with this type of a situation," he said in an interview with The State Journal and WOWK-TV.
The CDC relied on studies provided by Eastman Chemical Co., which manufactured the MCHM that was stored at the river terminal operated by Freedom Industries along the Kanawha River in Charleston.
Kapil said the CDC reviewed the studies and found the level at which there was no observable effect on lab animals. From that the researchers divided the dosages again and again to come up with a conservative estimate on what would be the allowable limit for human consumption. The result was 1 part per million in drinking water.
"We try to be conservative when we do this type of extrapolation," Kapil said.
The number was based on a child weighing 22 pounds. When asked about how much an adult could consumer, Kapil said the number would be about the same, as an adult has more mass but also consumes more water than a child.
The CDC provided its recommendation to West Virginia American Water Co. and the state agencies that had been monitoring the water situation.
Kapil stressed that the CDC does not set policy; it only makes recommendations.
West Virginia American Water spokesperson Laura Jordan said when the company and the interagency task force received the CDC's suggestion, they adopted it. Once concentrations in the system dropped below 1 ppm, the company began lifting the "do not use" order in certain areas.
The decision that water was safe was a consensus, but the final decision when people in particular zones could drink, cook with or bathe in the water depended as much on the water system as on the quality of the water, Jordan said. The water company would not release a zone until it was confident it had enough water for the flushing that would be done there, she said.
After it issued its recommendation and the water company told people the water was safe, the CDC decided that pregnant women probably should not drink it.
"It's really just an abundance of caution," Kapil said.
The CDC normally advises pregnant women to limit their exposure to chemicals, especially chemicals the agency knows little about, he said.
And one thing the agency does not know is how MCHM reacts with chlorine that is present in treated drinking water, Kapil said.
According to the safety data sheet provided by Eastman Chemical, crude MCHM is a mixture of chemicals. From 68 to 89 percent of MCHM is 4-methylcyclohexanemethanol. Another 4 to 22 percent is 4-(methooxymethyl)cyclohexanemethanol.
There's 4 to 10 percent water, 5 percent methyl 4-methylcyclohexanecarboxylate, 1 percent dimethyl 1,4-cyclohexanedicarboxylate, 1 percent methanol and 1 to 2 percent 1,4-cyclohexanedimethanol.
The MSDS gives first aid measures in case of inhalation, eye contact, skin contact and ingestion. It lists specific end uses as gasoline blending and in uses as an industrial chemical. It provides data on acute toxicity levels for oral and dermal contact, but no data was available for toxicity related to inhalation.