In a study that may help explain "sick building syndrome," federal officials say tests have found indoor air in new buildings has levels of harmful chemicals 100 times greater than outdoor air.

The Environmental Protection Agency study, the first major U.S. assessment of air pollution in public buildings, noted Thursday that chemical concentrations in new structures were highest in the initial months after construction ended and could remain elevated as long as six months.Altogether more than 500 chemicals were detected in 10 buildings sampled in the five-year study, including four homes for elderly people, three office buildings, one hospital, one school and an institute for governmental studies.

The buildings examined were in Washington; Worcester and Cambridge, Mass.; Fairfax, Va.; Martinsburg, W.Va.; and the Research Triangle Park in North Carolina. Three of the buildings were newly constructed.