Brominated Flame Retardants

Abstract Brominated flame retardants (BFRs) belong to a growing group of organohalogen chemicals. They can be highly persistent, can be bioaccumulative, and can cause adverse effects in humans and wildlife. Although some BFRs are banned or voluntarily withdrawn from usage by the manufacturer, emerging and existing BFRs continue to be used in industrialized countries. Because of the widespread use and large quantities of these chemicals in consumer products and household items, indoor contamination is proposed to be a significant source of human exposure. Other exposure routes are oral—via breast milk, fat-containing foods, hand-to-mouth activity, etc. Recent epidemiological studies clearly indicated that BFRs affect human health. The human health effects due to BFRs include cryptorchidism, alterations in thyroid hormone homeostasis, reproductive effects, and reduced development of children at school age that include psychomotor development index and IQ performance. Studies have also indicated that the infant daily exposure dose of polybrominated diphenyl ethers (PBDEs) via inhalation, accidental oral ingestion, and dermal absorption of house dust was significantly higher than that of adults. Many rodent studies have confirmed that developmental exposure to these compounds should be limited. Studies in rodents indicated that several BFRs are developmental neurotoxicants affecting the nervous system growth and function. Several studies have also confirmed that the BFRs are indeed endocrine disruptors, with the potential to disrupt male and female reproductive development and adult reproductive function by having antiandrogenic actions (males) and by altering steroidogenic activities. This has been demonstrated in several in vivo studies using rodent models and by in vitro systems to determine effects on receptor binding [androgen receptor (AR), constitutive activated/androstane receptor (CAR), and pregnane X receptor (PXR)] and on steroidogenesis. There is also increasing evidence in cell and animal models that BFRs may activate nuclear receptors and related pathways to modify adipogenesis or lipogenesis. These potential modes of action may also be relevant to humans. This is incredibly important to consider, as there have been several reports of adverse health consequences associated with increased PBDE exposure in humans in the last few years. Further research is needed to determine the long-term adverse consequences of exposures to the BFR described herein as well as a number of emerging replacement chemicals coming onto the market, as these compounds are known to bioaccumulate and can be transplacentally and lactationally transferred.