The temporary homes that sickened victims of the Gulf Coast hurricane have urged environmentalists take into consideration the indoor air-quality issue.

"In retrospect, we did not engage the formaldehyde issue as aggressively and as early as we should have," Howard Frumkin, director of the CDC's National Center For Environmental Health, told a Senate subcommittee, according to The Washington Post.

Investigation showed that formaldehyde levels in the trailers differ greatly. Apparently, four of the six most popular brands are among the most toxic, a federal study released Monday found, according to The Associated Press.

Air samples from trailers made by Gulf Stream, Keystone, Pilgrim and Forest River contained more than four times the formaldehyde levels that are found in newer U.S. homes, according to the study by the U.S. Centers for Disease Control and Prevention.

The Federal Emergency Managament Agency had provided 56,000 trailers to Katrina victims in 2005 and 2006, until their homes were restored. But last month FEMA evacuated the hurricane victims from 35,000 trailers, after tests revealed toxic levels of formaldehyde fumes.

The U.S. Centers for Disease Control and Prevention found average levels of 77 parts formaldehyde per billion parts of air, much higher than the 10 to 17 parts per billion concentrations seen in newer homes.

Formaldehyde is a colourless gas which can cause respiratory problems and has been classified by scientists as carcinogen.

Scientists have said that the problem was not to be generalizable to other travel trailers in the country. Heat and other factors may increase formaldehyde levels.

Last week, FEMA declared that it was making efforts to find safer alternatives to trailers and mobile homes.