Exposure to flame retardant chemicals is relatively ubiquitous among the general public, and research has demonstrated that these contaminants can pass from a mom to her baby through the placenta. During fetal development, the placenta is responsible for nutrient, waste and gas exchange, protection from the maternal immune system as well as pathogens, and it also serves as an endocrine organ. Thus, it is suspected that the placenta is a target of endocrine disrupting chemicals, such as flame retardants. Recently, we conducted a study that measured brominated flame retardant levels in human placental tissues from a group of women in North Carolina.
Our research group measured a suite of polybrominated diphenyl ether (PBDEs), 2,4,6-tribromophenol and thyroid hormone levels (T4, T3 and rT3) in each tissue sample. Significant associations were observed between the flame retardants and thyroid hormone levels in the placenta; however, the associations were opposite in direction depending on the sex of the fetus. Further, we found that concentrations were significantly higher in the placental tissues if the placenta was associated with a male infant, compared to a female infant (see Leonetti et al. 2016). In collaboration with a lab at NCSU, we have explored the toxicokinetics of a PBDE mixture using pregnant Wistar rats as a model. We sought to understand the tissue-specific accumulation of PBDEs in the placenta and the impact on thyroid hormone regulation. We found that PBDEs accumulated in the fetal portion of the placenta at 2-3 times higher concentrations than the maternal portion of the placenta. We also observed a significant effect on dam serum thyroid hormone levels but did not see any effects in the placenta or fetus (See Ruis et al. 2019).
The factors or variables driving this difference in flame retardant accumulation are unclear, but we are conducting further research to determine if this may be related to differences in metabolism, or differences in transport of the flame retardants and thyroid hormones across the placental barrier. We are currently exploring the effects of flame retardants on thyroid and estrogen regulation and metabolism using placental cell lines, animal models, as well as ex vivo human placental tissue. This research has been supported by a grant from the National Institute of Environmental Health Sciences (R01ES020430).