PentaBDE was found in 17 percent of the couches. The chemical was phased out in the United States in 2005 after studies showed it was building up rapidly in human breast milk. In the tests of couches purchased prior to 2005, PentaBDE was the most common flame retardant, at 39 percent.
Tris was found in 24 percent of sofas purchased before 2005. But in couches bought after that, it was found in 52 percent, showing that it has become increasingly popular since PentaBDE was phased out.
Before 2005, PentaBDEs and Tris, also known as TDCPP, were the only flame retardants used in U.S. furniture, Stapleton said. Since then, chemical companies have developed several replacements, and scientists have struggled to keep pace with studying their health risks.
"Today, we know of at least six different mixtures being used as flame retardants in furniture," Stapleton said. "And we know less about the health effects of these flame retardants compared to PBDEs and TDCPP."
Firemaster 550, made by Chemtura, was found in 18 percent of couches tested. In February the U.S. Environmental Protection Agency put two of Firemaster 550's key ingredients on a list for review due to potential health concerns.
Mixtures of different kinds of chemicals were found in 13 percent of couches from 2005 or later. One is known as TBPP, which the authors say is the first report of its use as a flame retardant.
"This study highlights the fact that there are several new flame retardant chemicals replacing PBDEs in consumer products, most of which we have little to no human health data, which is concerning," said Lesliam Quirós-Alcalá of the University of California, Berkeley, who studies flame retardants in house dust but was not part of the new study.
PentaBDE and other brominated flame retardants known as PBDEs have been linked in some studies of people and animals to impaired neurological development, reduced fertility, early onset of puberty and altered thyroid hormones. Most recently, a study published this month found that prenatal and childhood exposures were linked to disabilities in attention, coordination and cognition in a cohort of school-age children.
By December, the last PBDE mixture in consumer products, DecaBDE, is scheduled for phase-out, but PBDEs will linger in older couches and in people.
"Given their environmental, and biological persistence, they are likely to join the legacy POPs [persistent organic pollutants], like PCBs and DDT, in being with us for the foreseeable future," said Linda Birnbaum, director of the National Institute of Environmental Health Sciences and National Toxicology Program.
Flame retardants are semi-volatile and do not stay in cushions. Toddlers and young children who crawl on the floor are highly exposed through dust. Research from Stapleton's lab has linked levels of PentaBDEs on toddlers’ hands to the blood levels in their bodies.
Birnbaum said dust tainted by the couches and other household items is “a major route of exposure to people."
Low-income families face disparately high residential exposures to the banned compounds PBDEs compared to newer flame retardants. That's due to the presence of older, deteriorated or poorly manufactured furniture treated with PBDEs.
"Low-income families may keep their furniture for longer, prolonging exposure to phased-out chemicals," Quirós-Alcalá said.
Concentrations of the chemicals in couches averaged 4 to 5 percent by weight, but some couches had over 11 percent.
Ironically, these levels of flame retardants may not stop a house fire. "There is growing evidence that at the concentrations used in products, they are not protective against fires," Birnbaum said.