Study Details Americans' Chemical Exposure
Many Exposures Down, but Health Effects Uncertain
July 21, 2005 -- American children's exposure to secondhand smoke and blood lead levels are declining. But the vast majority of Americans are still exposed to at least some potentially dangerous environmental chemical.
"This is the most extensive assessment ever of Americans' exposure to environmental chemicals; it shows we are making tremendous progress, and that's good news," says CDC Director Julie Gerberding, MD, in a news release. But she says many changes remain.
New data from a large federal study shows that children's blood lead levels continue to decline.
Average blood lead levels in 1- to 5-year-old children dropped from 2.23 to 1.70 micrograms per deciliter between 2000 and 2002.
Still, nearly 2% of children of this age had more than 10 micrograms per deciliter of lead in their blood -- the amount regulators consider a risk for lead's detrimental effects on brain development. This percentage has decreased from 4.4% in the early 1990s, according to the report.
The study computes national averages in samples of several thousands of Americans but did not take into account geographical locations that could greatly affect exposure levels.
Officials say they are encouraged by the apparent drop. They attribute the drops in lead levels and the reductions in the percentage of children with high blood lead levels to the removal of lead from gasoline several decades ago and to nationwide programs designed to remove lead-based paint from houses and buildings.
Lead poisoning can impede brain development in young children. Officials did not interpret the study's results as evidence that lead is no longer a danger to U.S. children.
"We still don't know what is a safe level," says Gerberding. The CDC conducted the study of 148 industrial chemicals and toxins in the American population.
Researchers also recorded falling levels of cotinine, a blood marker indicating exposure to secondhand smoke.
Gerberding says the CDC found an "astonishing reduction" in the chemical, suggesting that laws limiting smoking in buildings are having a positive effect.
Compared with average levels in 1988-1991, cotinine levels measured in 1999-2002 have decreased 68% in children, 69% in teens, and nearly 75% in adults, according to a news release.
But the drops were largely limited to whites. Some populations remain at risk. The study shows that blacks have levels twice as high as whites and Mexican-Americans.
Researchers take the results to mean that blacks are either being exposed to more secondhand smoke or that they metabolize nicotine differently than do whites, she says.
They also find that while levels of cotinine are decreasing, levels in children were twice as high as adults.