LOS ANGELES – Researchers have found that Californians have twice as much of flame-retardant chemicals in their blood and as much as 10 times more of them in their homes than anywhere in the country.

Older children and infants, who may be more susceptible to the harmful effects of the chemicals, can have several times as much as adults, it was reported Wednesday in the journal Environmental Science & Technology.

The chemicals, known as polybrominated diphenyl ethers, or PBDEs, have been widely used in California after a law was passed 30 years ago requiring furniture and bedding to withstand 12 seconds of contact with an open flame without igniting. Foam and similar materials contain as much as 12 percent PBDEs by weight.

The chemical is released from furniture in dust produced by abrasion and normal wear. Children can get larger doses because they come in contact with the fine dust on floors.

“The health effects are of particular concern for babies, children and pregnant women,” said environmental epidemiologist Ami Zota of the Silent Spring Institute in Newton, Mass., who led the study.

PBDEs have been shown in animals to cause thyroid hormone disruption and to interfere with developing reproductive and nervous systems.

The research team collected samples from 49 homes in the San Francisco Bay area cities of Richmond and Bolinas and 120 homes on Cape Cod and compared levels in those homes with published levels from Canada, Europe and several U.S. cities.

Levels in California homes were 10 times higher than those on Cape Cod, five times higher than those in Texas, six times higher than those in Washington, D.C., four times higher than those in Boston and 200 times higher than those in Europe, where the chemicals are used sparingly.