Recently, there have been some new studies looking at the impact of serum levels of polybrominated diphenyl ethers (PBDEs) in expectant mothers, and health outcomes for their babies. PBDEs are common flame retardants found in household furnishings, appliances, textiles, paints, and electronics including televisions, cell phones, and computers. PBDEs are found to have similar effects as polychlorinated biphenyls (PCBs), including estrogenic effects that adversely affect neurodevelopment. One longitudinal cohort study out of Berkeley looked at the association of maternal PBDEs and newborn birth weights and found there was a link between increased levels of PBDEs and lower weights for infants. However, when controlled for maternal weight, the relationship appeared less than significant.
Another study out of McMaster University in Ontario, Canada also examined serum maternal levels of PBDEs in association with birth weight, and also included umbilical cord samples of various cogeners of the flame retardant. After parsing out the different chemical compounds and their specific relation to infant birth weight, it was found that low infant birth weight was specifically associated with the presence of PBDE-99. Study results, in comparison to other research assessing similar issues in the U.S., Europe and Asia, suggested that Canadian women have a higher exposure to these chemicals, with unclear causation. Of note, researchers from the McMaster study point out that socioeconomics seem to come into play here: that women of higher socioeconomic status had higher levels of the PBDEs than those of lower socioeconomic status. The postulation: the more “stuff” a woman/family can afford to buy/keep in the home environment (products which are treated with/contain flame retardant chemicals) the greater her exposure. This particular study was actually part of a larger investigation, The FAMILY (Family Atherosclerosis Monitoring In Early Life) Study, a longitudinal cohort study designed to identify prenatal and early life determinants of obesity, allergy, dyslipidemia, diabetes, and cardiovascular disease risk indicators in the offspring.
This review goes into further detail regarding PBDEs and their neurotoxic effects, as well as from which sources they are consumed (such as when the chemicals, having emulated from PBDE-laden products, end up in household dust and are then breathed in). Based on animal studies, (which, of course, are used to inform human-based studies) in vitro PBDE exposure (especially the brominated kind) is found to result in thyroid, cerebral structural and functional changes, as well as spontaneous behavioral changes. How do alterations in thyroid hormone and function affect the developing fetus? From the review:
In humans, thyroid hormone production starts at approximately 10 weeks of gestation and increases with the development of the fetal hypothalamic–pituitary–thyroid axis (reviewed by Howdeshell 2002). However, transplacental transfer of maternal thyroid hormones to the fetus is critical for neurodevelopment. Impaired psychomotor development and visuospatial processing have been revealed in children born to mothers with (subclinical) hypothyroidism (Haddow et al. 1999; Pop et al. 1999). Prenatal and postnatal hypothyroidism are associated with behavioral deficits in humans as well as animal models (reviewed by Zoeller and Rovet 2004).
Iodine deficiency, a common condition worldwide (reviewed by Walker et al. 2007), is an additional risk factor to increase the sensitivity to adverse effects from thyroid-disrupting chemicals. Because of the strict temporal regulation. To read a well-written “in layman’s terms” account of what PBDEs are and why we should be concerned about them, check out this blog post at O Ecotextiles. You might find this to be a helpful article to pass onto your expectant clients and students.