WASHINGTON — A federal scientist said Tuesday his bosses ignored pleas to alert Gulf Coast hurricane victims earlier about health risks from formaldehyde in government-issued trailers.

Christopher De Rosa, until recently one of the government's top toxicologists, told a House Science and Technology subcommittee hearing he repeatedly raised concerns early last year that the Centers for Disease Control and Prevention (CDC) was not adequately telling the public of the hazard.

As a result, tens of thousands of families displaced by hurricanes Katrina and Rita remained in the trailers without full knowledge of the risks, he said. "I stated that such clinical signs were a 'harbinger of a pending public health catastrophe,' " De Rosa said in written testimony, quoting one series of e-mails he wrote to superiors last summer. "[But] the only response I received was that such matters should not be discussed in e-mails since they might be 'misinterpreted.' "

Formaldehyde is commonly used in building materials. Prolonged exposure can lead to breathing problems and is believed to cause cancer.

The CDC initially said in February 2007 that, with proper ventilation, formaldehyde levels were safe in the short term. FEMA began citing the advisory as evidence the trailers were safe. De Rosa said he protested that the CDC should more aggressively address the matter.

It wasn't until February 2008 that the CDC released preliminary results from additional testing showing that Federal Emergency Management Agency (FEMA) trailers and mobile homes had formaldehyde levels that were, on average, about five times higher than in most modern homes.

The CDC urged people to move as quickly as possible, prompting FEMA to say it would rush to find new housing for some 35,000 families living in the trailers.

De Rosa's bosses Howard Frumkin and deputy director Thomas Sinks acknowledged the toxic-substances agency took too long to address the hazard but said there was no effort to silence De Rosa or mislead the public.

Frumkin said his agency is planning a five-year study of children who lived in the trailers in Alabama, Louisiana, Mississippi and Texas.