Polybrominated Diphenyl Ethers
CATEGORY: IARC probable, NTP reasonably anticipated, endocrine disruptor
USED IN: furniture, electronics
PBDEs are a complex group of chemicals that are structurally similar to the PCBs described above. They are used extensively as fire retardants in both consumer and industrial products (Costa, 2008). Major products containing PBDEs include polyurethane foam in furniture (penta-BDE) and electronic and plastic products (octa- and deca-BDEs) (Zota, 2008). Although both penta- and octa-BDEs have been banned in the European Union and have not been produced in the United States since 2004, products containing them remain throughout the world. PBDEs are found ubiquitously in the environment, detected in air, dust, soil and food as well as in many wildlife species. These chemicals have been found in human fat tissue, as well as in serum and breast tissue and milk (Costa, 2008; Darnerud, 2001; De Wit, 2002). PBDEs cross the placenta, resulting in exposures to developing fetuses (Frederiksen, 2010). Recent data indicate considerable geographic variability in exposures to the chemicals; people in California, with its particularly stringent furniture flammability standards, have much higher levels of PBDE exposures than do people in Massachusetts. Within the California cohort, having a lower socioeconomic status (SES) is associated with higher PBDE levels (Zota, 2008).
New data from young girls (ages 6 to 9) from California and Ohio support these findings. Although PBDEs were found in almost all samples tested, girls in California had significantly higher serum PBDE levels than did girls from Ohio, and young black girls had higher levels than either white or Hispanic girls (Windham, 2010).
PBDEs are endocrine-disrupting compounds, exerting effects on a number of hormonal systems, including the androgens, progestins and estrogens, though the major system affected by PBDEs is that of the thyroid hormone (Costa, 2008). Most studies of health outcomes after PBDE exposures have focused on neural development, given the prominent role of thyroid hormones (especially T4) in regulating brain development (Costa, 2007; Talsness, 2008).
Very few data directly address the possible effects of PBDEs on breast cancer risk. However, at least some PBDEs have been shown to be as effective as many of the other EDCs described in this section in promoting estrogenic-like proliferation of human breast cancer cells in vitro (Meerts, 2001). More recent data on MCF-7 human tumor cells indicate that penta-BDE enhances tumor-cell proliferation through estrogen-like effects on cell pathways that regulate programmed cell death, or apoptosis (Yu, 2009). Given the extensive overlap and interaction of estrogen- and thyroid-mediated responses in the regulation of breast cancer (Davis, 2009), PBDEs will be a class of chemicals of continued concern for scientists interested in understanding environmental links to breast cancer (Birnbaum, 2009).
