A new analysis by the California Environmental Protection Agency and the Seattle-based research group Northwest Environment Watch compared the PBDE levels in the breast milk of 40 Pacific Northwest mothers with the levels of another toxin and chemical cousin, PCB.

Polybrominated diphenyl ethers, or PBDEs, are used as a flame retardant while polychlorinated biphenyls, or PCBs, are a class of chemicals used in insulating fluids for electrical equipment before they were banned in the late 1970s after studies indicated they cause cancer.

The analysis of breast milk samples showed that 30 percent of the mothers tested in the Northwest study had higher levels of PBDEs than PCBs.

The analysis, released Thursday at the "Dioxin 2005" international conference in Toronto, suggests that PBDE contamination may be surpassing the level of PCB contamination in humans and the environment.

"The comparison with PCBs suggests that toxic flame retardants have emerged as a major environmental health concern," said Clark Williams-Derry, research director for Northwest Environment Watch.

The breast milk samples from Northwest women were analyzed in the California EPA's Hazardous Materials Laboratory in Berkeley, Calif. It is one of several studies under way on breast milk contamination.

Some of the data from the study was originally released by Northwest Environment Watch in 2004, but the comparison of contamination levels was just completed, researchers said.

The 40 mothers in the Northwest study are from Oregon, British Columbia, Montana and Washington state.

Overall, they had levels of PBDEs 20 to 40 times higher than levels found in women from Europe and Japan