On Tuesday a federal scientist said he alerted his bosses about severe health risks from formaldehyde in government-issued trailers given to Hurricane Katrina victims. Christopher De Rosa, who until recently was one of the government's top toxicologists, told a congressional panel that he repeatedly raised concerns early last year that the Centers for Disease Control and Prevention was not adequately informing the public of the hazard. Three of 32 mobile homes tested for use in Arkansas had levels high enough to put people at an increased risk of cancer and respiratory illnesses. Formaldehyde, well known as a preservative and embalming fluid, is commonly used in building materials. Prolonged exposure can lead to breathing problems and is also believed to cause cancer. It wasn't until February of this year that the Center for Disease Control released preliminary results from more testing showing that Federal Emergency Management Agency trailers and mobile homes had formaldehyde levels that were, on average, about five times higher than in most modern homes.