Then, they set the final screening level for water based on a standard estimate for a 1-year-old child of about 22 pounds of body weight and consumption of a little more than a quart of water per day.
In an interview Friday, Webster explained that what the CDC's exercise actually does is set an estimated safe dose for daily exposure to the chemical of 0.1 milligrams per kilogram of body weight.
An average adult weighing about 150 pounds and drinking a little more than two quarts of water a day would get an exposure dose of about 0.03 milligrams per kilogram of body weight, Webster said. That amounts to three times lower than the level that the CDC considers as unacceptable under its screening level.
But for a 1-year-old child weighing 22 pounds and drinking about a quart of water per day, she said, the daily dose would be 0.1 milligrams per kilogram of body weight. That's right at the level the CDC set with its screening level.
"The people who are most vulnerable to any chemical exposure are the fetus, infants and young children," Webster said, and in this instance, children "will be closer to that maximum level considered safe by the CDC."
Webster said that it's also important to consider the levels of Crude MCHM in the water, something that Tomblin administration officials have emphasized are dropping to well below the 1-part-per-million number.
In a statement issued late Friday afternoon, Gov. Earl Ray Tomblin said, "My team's number one priority is the health and safety of those impacted by this crisis. My family is in the affected area. Many of the team's families and neighbors are in the affected areas.
"This crisis hits home," the governor said. "The efforts we are taking are for all of our families."
Still, while praising the state and CDC for issuing the bottled water advisory for pregnant women, outside experts say the advisory came too late and should have also included young children. The experts noted that the CDC calculation contained a wide variety of uncertainties that could mean the actual "safe" level is far different from what the agency estimated.
"I think the CDC tripped up when they delayed before issuing the pregnant woman warning," said Jennifer Sass, senior scientist with the Natural Resources Defense Council. "I would recommend that not only pregnant women, but also infants and children avoid the water as long as the chemical contaminants are detected. And, the public needs to know what the detection limit is, so an informed decision can be made about how long to wait after the chemicals are no longer detected."
Experts pointed to a variety of weaknesses in the CDC's approach. Most importantly, they said, it was based on little data. Also, rat studies based on high doses of chemicals can often mask adverse health effects that occur at lower levels.
"It's a very rough calculation," Webster said. "And each step has uncertainty associated with it. It is not an exact science."Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.