Nonsmoking adults are getting much less exposure to secondhand smoke than they used to--but children are still getting plenty. That's one of the conclusions of a report issued today by the U.S. Centers for Disease Control and Prevention (CDC) that documents levels of exposure to environmental chemicals. The study did not examine the chemicals' effects on health.
The first CDC report on environmental chemicals, issued 2 years ago, suggested that efforts to curb secondhand smoke were paying off in the overall population (ScienceNOW, 21 March 2001 ). In that study, researchers measured levels of 27 chemicals--including cotinine, a marker for secondhand tobacco smoke--in blood and urine samples from 3800 people participating in the CDC's National Center for Health Statistics general survey of health in the United States. Today's follow-up report expands the list of chemicals to 116 and breaks the volunteer population into groups by age, race, and sex.
In the case of cotinine, the breakdown revealed a key difference: Children have twice the levels of cotinine that adults have, the study found. That's because continine levels in adults have declined 75% since the early 1990s, but by only 58% in children. Secondhand smoke is associated with sudden infant death syndrome, ear infections, and respiratory infections, says Richard Jackson, deputy director of science for CDC. "If we had to pick something to really go after, that would be one I would argue is an extraordinarily high priority, and something people can actually do something about," says Jackson.
The report also reveals that some old bugbears are still hanging around. Although the pesticide DDT was banned in the United States in 1973, a chemical called DDE, formed when DDT breaks down, showed up in teenagers who were born in the 1980s. The study also found that Mexican-Americans had DDE levels three times higher than nonhispanic white or black Americans--possibly due to exposure at agricultural jobs or in Mexico, where DDT is banned but is probably still being used, Jackson says. CDC doesn't know, however, how the observed levels of DDE would affect health, Jackson says.
The report is "a marvelous addition" to what scientists know about American's exposure to environmental chemicals, says Linda Birnbaum, director of the environmental toxicology division of the Environmental Protection Agency. "It can help us understand the improvements that we have made, what our regulations have brought about," she says. It also gives a reference point for future studies, she says.
The Second National Report on Human Exposure to Environmental Chemicals 
Public health statement on DDT and DDE from the
Agency for Toxic Substances and Disease Registry 
American Chemistry Council statement on the CDC report