Updated

A federal scientist said Tuesday his bosses ignored pleas to alert Gulf Coast hurricane victims about formaldehyde dangers in government-issued trailers and told him last year not to write e-mails about his warnings of potentially widespread health problems.

Christopher De Rosa, a top scientist at the Centers for Disease Control and Prevention's toxic substances agency, said his bosses told him that his warnings of a "pending public health catastrophe" could be misinterpreted if publicly released.

De Rosa's comments came Tuesday at a House Science and Technology subcommittee hearing on how the CDC and other agencies handled complaints about potentially high levels of formaldehyde in trailers issued by the Federal Emergency Management Agency to victims of hurricanes Katrina and Rita.

Committee Democrats have accused FEMA of manipulating scientific research to play down the dangers of high levels of formaldehyde found in the trailers. They say the CDC and its Agency for Toxic Substances and Disease Registry went along with misleading residents.

In mid-2006, FEMA enlisted the CDC's help in analyzing the results of air-quality tests on unoccupied trailers. But the CDC didn't start testing the air quality in occupied FEMA trailers — or study the possible health effects of long-term formaldehyde exposure — until late last year.

The CDC said in February that tests on hundreds of occupied FEMA trailers and mobile homes found formaldehyde levels that were, on average, about five times higher than what people are exposed to in most modern homes. The results prompted FEMA to step up efforts to move roughly 35,000 families still living in the trailers after the 2005 hurricanes Katrina and Rita.

Formaldehyde can cause respiratory problems and has been classified as a carcinogen by the International Agency for Research on Cancer and a probable carcinogen by the U.S. Environmental Protection Agency.

FEMA officials say the number of occupied trailers on the Gulf Coast, which peaked at more than 143,000 after the hurricanes, has dropped to about 34,000 as FEMA rushes to move people into safer housing.