Air pollution: no place like a mobile home.

A mobile home may feel cozy, but its tight construction seals in air pollutants better than most conventional homes. Adding to the problem, the pressed wood products typically used in mobile homes give off noxious formaldehyde gas. Many mobile home residents have complained of "sick building syndrome." Now researchers suggest that even those who don't complain may experience health effects -- and at lower levels of formaldehyde than previously documented.

Scientists at California's Indoor Air Quality Program in Berkeley monitored formaldehyde levels for two one-week periods in more than 500 mobile homes and collected health information from more than 1,000 uncomplaining occupants. The study found a strong statistical association linking eye, skin and upper-respiratory irritation with exposures to formaldehyde just below the 0.1 parts per million (ppm) level that the Environmental Protection Agency (EPA) has considered a threshold for irritation.

"This is the first study to show irritating effects at such a low level," says Kai-Shen Liu, who led the study.

The research team measured from 0.01 ppm to 0.46 ppm formaldehyde in the homes' air, then calculated weekly exposures. Though j mobile-home residents averaged 9.9 ppm-hour (the concentration times the number of hours exposed in a week), some homebodies inhaled more than twice the weekly 20 ppm-hour federal worker-exposure standard.

Burning eyes proved the best indicator of irritation, and its incidence rose linearly with increasing low-formaldehyde concentrations, Liu's team reports in the just released August ENVIRONMENTAL HEALTH PERSPECTIVES. Overall, persons with chronic respiratory and allergy problems experienced a higher rate of symptoms, suggesting that formaldehyde exacerbates existing respiratory conditions, the researchers say.

A variety of chemicals can pollute indoor air (SN: 9/28/85, p.198). Although the State of California scientists can't prove what caused the irritation, "I'm pretty sure it's formaldehyde," says Liu. "No other chemical we know of is so uniformly found in mobile homes."

This study could widely influence safety standards for formaldehyde exposure, according to James A. Frazier of the National Academy of Sciences in Washington, D.C. In fact, EPA has already cited it in a June report that summarizes recent research and attempts to reassess formaldehyde health risks.

Irritation alone can lead to disease, Frazier notes. Formaldehyde impairs the upper-respiratory tract's mucous-based defense system, which protects against foreign particles and bacteria. "By definition, irritation is an inflammation process," Frazier says. "Anytime you inflame, you're susceptible to an invasion of bacteria, and to other chemicals." He adds that formaldehyde is also a suspected carcinogen and that no one knows at what levels it might induce cancer.

Liu says that with 10,000 mobile homes sold annually in California alone, many people nationwide may suffer formaldehyde irritation. Joseph A. Cotruvo, who directs EPA's health and evaluation division, however, downplays the study's significance: "We're talking small percentages of people and mild effects."

Formaldehyde isn't all that threatens air quality in mobile homes. Another study reports that particulates and carbon monoxide emitted by kerosene space heaters exceeded EPA's outdoor air standards in four of the eight mobile homes surveyed. Moreover, heaters in five homes spewed mutagenic organic compounds. Judy L. Mumford of EPA in Research Triangle Park, N.C., and her team report their findings in the October ENVIRONMENTAL SCIENCE & TECHNOLOGY.

EPA has yet to set an safety standards for indoor air qualty. Cotruvo told SCIENCE NEWS the agency has plenty of scientific data showing indoor pollution requires action, but it needs new legislation to better define the roles EPA and other agencies should take.