Stung lung: volatile chemical may cut respiratory capacity.

A chemical in some air fresheners and pestcontrol products may slightly impair lung function in millions of people, a nationwide study suggests.

The compound, para-dichlorobenzene, is used to make mothballs, urinal deodorizers, and air-freshening blocks for household use. At room temperature, the strong-smelling chemical gradually changes from a solid to a gas.

Para-dichlorobenzene was previously detected in the blood of more than 95 percent of the participants tested in a U.S. study called NHANES III.

Scientists at the National Institute of Environmental Health Sciences in Research Triangle Park, N.C., looked for effects of the chemical and 10 other volatile organic compounds commonly detected in U.S. residents. Led by internist and epidemiologist Stephanie J. London, the team analyzed NHANES III data from 953 adult volunteers.

The researchers compared the recorded blood concentrations of each of the 11 chemicals to several measures of lung function, including forced expiratory volume in 1 second (FEV1). They also considered related factors, such as exposure to cigarette smoke.

The tenth of the study's participants who had the most para-dichlorobenzene in their blood--more than 4.4 micrograms per liter--had about 4 percent lower FEV1 values than did the tenth of participants with the lowest blood concentrations--averaging 0.1 [micro]g/1. That difference in FEV1 amounted to an average of 0.151. The average FEV1 of people in the study was 3.441, the researchers report in the August Environmental Health Perspectives.

While "it's not some huge effect," London says, "at the borderline [of healthy lung function], losing 4 percent of your FEV1 could be a problem"

FEV1 is low in people who have chronic obstructive pulmonary disease or who are regularly exposed to cigarette smoke. The FEV1 deficit associated with paradichlorobenzene exposure is on par with that linked to secondhand smoke, London says. One-quarter of the volunteers were smokers, and others had been exposed to secondhand smoke in various amounts. The link between para-dichlorobenzene and reduced lung function persisted even when the researchers took those factors into account.

"This is an interesting new finding that will need to be replicated," comments Ralph J. Delfino of the University of California, Irvine.

Delfino and London agree that pard dichlorobenzene may not be the culprit behind the reduced lung function that London's team reports. Rather, there may be other environmental hazards that are common in homes and workplaces that have products emitting para-dichlorobenzene, London says.