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Excess lead: its evolving definition.

Excess lead: Its evolving definition

Last year the Centers for Disease Control (CDC) revised downward its definition of "an excessive absorption of lead" by children, the most susceptible population -- from 30 micrograms ([mu]g) of lead per deciliter (dl) of blood to 25 [mu]g/dl (SN: 2/16/85, p.103). But already experts within the Environmental Protection Agency (EPA) and its panel of outside advisers are recommending reducing that level further -- perhaps by 60 percent. Such a move would increase the percentage of U.S. children defined as carrying an excessive body burden of lead from 25 percent to more than 88 percent, explains Ellen Silbergeld, a lead toxicologist with the Environmental Defense Fund in Washington, D.C. Moreover, she adds, it would put 77 percent of adults in that category.

Based on a wealth of new studies, an internal EPA staff report has proposed to the agency that it consider any blood-lead levels above 10 [mu]g/dl as excessive, according to Ronnie Levin, one of the report's authors. And, notes EPA spokesperson Dave Ryan, EPA's Clean Air Science Advisory Committee of outside experts "has recommended that U.S. blood-lead levels be reduced below 10 [mu]g/dl."

Among the studies prompting a possible redefinition of excessive lead, Silbergeld says, are those by researchers with the U.S. Public Health Service and at Harvard University, showing that blood pressure in men increases as blood lead increases from 10 to 20 [mu]g/dl. A study published in the March 1986 PEDIATRICS reported an apparent "linear relationship" between elevated blood lead -- going down to 7 [mu]g/dl -- and diminished height in children, according to Joel Schwartz of EPA, one of the authors. Moreover, notes Schwartz, there are studies showing IQ deficits among children whose blood-lead levels are under 20 [mu]g/dl. Finally, a study has correlated both lower birthweight and slower childhood neuromotor development for blood lead below 10 to 15 [mu]g/dl (SN: 9/13/86, p.164).

Officials at the Atlanta-based CDC, which issues the lead guidelines independently of any other agency, are less convinced that the new studies prove "clear adverse health effects" below 25 [mu]g/dl, according to Vernon Houk, head of CDC's Center for Environmental Health. However, he adds, "I have not reviewed recently all of that [low-dose] data." Within the next year, though, he plans to convene a panel to review the data "and see if we need to make changes" in the CDC guidelines.
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Title Annotation:revised definition of lead-poisoning
Author:Raloff, Janet
Publication:Science News
Date:Nov 22, 1986
Words:417
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