ATLANTA -- Americans have lower levels of lead and secondhand-smoke byproducts in their bodies than they did a decade ago, according to a government study that is being called the most extensive examination ever of exposure to environmental chemicals.
The Centers for Disease Control and Prevention attributed the decline to such things as stricter regulations on harmful chemicals, bans on smoking in the workplace, and programs to reduce children's exposure to lead paint.
The CDC took blood and urine samples from 2,500 people in 1999 and 2000 and tested for 116 chemicals, including metals, pesticides, insect repellents and disinfectants.
In the early 1990s, 4.4 percent of children ages 1 to 5 had elevated levels of lead, but that dropped to 2.2 percent in 1999-2000, the study found.
To gauge the effect of secondhand smoke, the CDC tested for cotinine, a product of nicotine after it enters the body, in nonsmokers. Levels dropped by 75 percent for nonsmoking adults and 58 percent for children in 1999-2000 compared with the early 1990s, the CDC said.
But blacks had more than twice the cotinine levels of whites or Mexican-Americans, the CDC said. And cotinine levels for children were twice as high as levels for nonsmoking adults.
CDC officials believe children's exposure to secondhand smoke may be high because public health efforts in the 1990s primarily focused on reducing secondhand smoke in adult areas, such as in the workplace. In addition, CDC officials said, children may absorb more from their environment than adults.
"What we are looking at now is that we have now a group we need to specifically target and think of new things to do to reduce their exposure" to secondhand smoke, said Dr. Jim Pirkle, deputy director of science for the CDC's environmental health center.
The CDC called the study the most extensive assessment ever of Americans' exposure to environmental chemicals, and both an environmental group and a chemical industry group praised it.
CDC officials said more research is needed on specific chemicals and their effects. Most of the chemicals in the 260-page report had never been studied before in the human body, though they have been toxic in animal studies.
But "just because a chemical can be measured doesn't mean it causes disease," said Dr. Richard Jackson, director of the CDC's National Center for Environmental Health.
CDC officials hope to use the study as a baseline for other environmental exposure studies and as an indicator of what needs to be done next.
The CDC found that levels of some chemicals considered harmful have been on the decline inside the body -- possibly because of regulation -- such as lead, dioxin and the banned insecticide DDT.
But the CDC found that levels of DDE, a product of DDT, were three times higher in Mexican-Americans than non-Hispanic whites or blacks.
Environmental activists and chemical industry officials both said the report would be helpful.
"We think it's important and valuable data that will help guide both industry and regulators and other stakeholders as we consider development of new products and the safety and re-evaluation of existing products," said Jay Vroom, president of CropLife America, which represents pesticide manufacturers.
Kris Thayer, senior scientist for the Environmental Working Group, said: "We desperately need this information if we're going to piece together possible health effects in humans."