Blood levels of dangerous chemicals recorded in CDC baseline screenings

Study of 3,000 people shows reduced exposure to tobacco smoke


PHILADELPHIA -- The push to limit smoking in public places has led to a 75 percent drop in the blood levels of a tobacco-linked carcinogen in the American population.

The decline since 1991 marks a "dramatic reduction in exposure" to environmental tobacco smoke, according to officials at the federal Centers for Disease Control and Prevention.

"It shows that the national effort to provide clean indoor air ... is working," said Terry Pechack, of the CDC Office of Smoking and Health.

The finding was the most striking in the CDC's first comprehensive evaluation of human exposure to dangerous chemicals.

The study, based on blood and urine samples from 3,000 adults and children around the country, also found that average Americans have traces of uranium, pesticides and heavy metals in their bodies.

"We live in a world that has exposures" to chemicals, said Richard Jackson, director of the CDC National Center for Environmental Health.

Jackson stressed that "the presence of a chemical in the blood or urine doesn't necessarily mean it will cause a disease."

The study creates the first baseline measurements of key environmental pollutants and provides a standard against which public health researchers and environmental groups can measure real-life exposures.

The CDC tested for 27 chemicals -- including heavy metals, pesticide traces and phthalates, a group of industrial chemicals found in consumer products ranging from vinyl flooring to perfume.

The survey, done in 1999, found the presence of 23 of the chemicals in the study group.

In all cases the chemicals were found in very small, trace amounts well below levels known to cause health problems.

The screening was done as part of the CDC's National Health and Nutrition Examination Survey -- a continuing national health survey of the U.S. population.

Each year an additional 25 chemicals will be added to the screening, Jackson said, until the CDC is testing for 100 toxic substances.

The study, Jackson said, is "a major step toward assessing in the U.S. population which environmental chemicals are present in blood and urine samples, who is exposed, trends in exposure over time, and whether interventions to reduce exposure are working."

Because this was the first year of testing for most of the chemicals, the CDC officials said they could not say if there was any trend.

The two exceptions were lead and cotinine, which had been screened for in earlier health surveys. Cotinine is created in the human body when nicotine breaks down. It is considered the best measure of exposure to tobacco smoke.

The average levels of cotinine in the surveyed population dropped from 0.20 nanograms per milliliter of blood to 0.05 nanograms between 1991 and 1999.

These measures are microscopic. Two-tenths of a nanogram is equal to a few fractions of a billionth of an ounce and a milliliter of blood is less than an eyedropper full.

CDC officials expressed concern that cotinine levels for teen-agers averaged 40 percent higher than for the general population. The levels for African-Americans averaged nearly 100 percent higher.

Lead exposures also showed a marked drop between 1994 and 1999 for the key population -- children younger than 6 -- according to the study data.

Lead impairs nerve and brain development in young children. The CDC has said that children with more than 10 micrograms of lead in a deciliter of blood are at risk.

When a study was conducted between 1991 and 1994, it found the average blood lead level for children at 2.7 micrograms per deciliter.

The average level for children in the 1999 study was down to 2.0 micrograms per deciliter.

"The good news is that blood lead levels continue to decline among children overall," said Eric Sampson, head of the Centers for Disease Control's Environmental Laboratory.

But Sampson said that other data shows that many children are still living in environments that place them at "high risk for lead exposure."

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