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Study Details Americans' Chemical Exposure

Many Exposures Down, but Health Effects Uncertain

From the WebMD Archives

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.

Secondhand Smoke

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.

Phthalates

The study also shows low but relatively widespread exposure to phthalates, a class of chemicals found in cosmetics, plastics, and many plastic-coated food packages. The chemicals are known to affect hormone-producing organs and can cause liver and testicular damage in lab animals.

They find that half of adolescents between 12 to 19 years old had phthalates measurable in their urine, though researchers said they still don't know what the health effects are. More research is needed.

The report states that there is very limited scientific information available on potential human health effects of phthalates.

"We have reason now to look further" at the possible health effects of Americans' exposure to the chemicals, Gerberding says.

Mercury

Scientists pointed to an apparent overall drop in mercury exposure, though the toxin remains widely prevalent in the U.S. population. The metal is used in making electrical equipment (thermostats or switches). It is also combined with other substances in batteries, and while its use in pharmaceutical applications has been declining, it has been used as a preservative. It is also used in some countries outside of the U.S. in making cosmetic skin creams.

Yet most of the mercury in blood comes from the consumption of fish or shellfish.

The report shows no women of childbearing age approached levels known to affect newborns' nerve and brain development. Yet 6% of women had levels that were within a factor of 10 of those associated with harmful effects to the developing fetus.

Gerberding suggests that the figures would direct the CDC to encourage more research into defining safe levels of mercury in the blood.

Pesticides

The CDC also recorded falling levels of many pesticides, though levels of at least one industrial pesticide, DDE, were up since 2000 in all groups studied.

Meanwhile, an analysis released by the Pesticide Action Network of North America showed that 90% of people in the study harbored between five and 16 different pesticides in their bodies. On average, Americans show evidence of exposure to 10 to 11 different pesticides, according to the analysis.

"It just shows that we are carrying around a lot of pesticides and this is just the tip of the iceberg," Margaret Reeves, PhD, the group's senior scientist, tells WebMD.

Chemical manufacturers released a statement Thursday stressing that low levels of toxic exposure do not necessarily translate to increased disease risk.

"Just because people have an environmental chemical in their blood or urine does not mean that the chemical causes disease. Small amounts may be of no health consequence," a statement from the American Chemistry Council notes.

WebMD Health News

Sources

SOURCES: Third National Report on Human Exposure to Environmental Chemicals, CDC, July 21, 2005. Julie M. Gerberding, MD, director, CDC. Margaret Reeves, PhD, senior scientist, Pesticide Action Network of North America. American Chemistry Council.
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