Flame retardants called polybrominated diphenyl ethers, or PBDEs, can further break down into pentabromodiphenyl ether, or penta BDEs.

A study, published online in Environmental Science & Technology, said California's unique furniture flammability standard -- requiring furniture to be fire resistant to an open flame for 12 seconds, has led to increased exposure to penta-BDE.

Penta-BDE production in the United States ended in 2004, however, furniture treated with the chemical is present in homes and most states haven't banned the use of flame retardant penta-BDE in imported furniture.

Chemical ingredients of the flame retardant penta-BDE were found in the dust of California homes at up to 10 times the levels found elsewhere in the United States and 200 times higher than in Europe, the study said.

The most contaminated California homes had levels higher than have been detected in household dust previously. The researchers also found double the amount of penta-BDEs in the blood of California residents compared to the nationwide average. Animal studies show PBDEs cause thyroid hormone disruption and affect developing reproductive and nervous systems.

The study was conducted by Silent Spring Institute in collaboration with other U.S. researchers.