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Introduction
The prevalence of neurodevelopmental disorders such as autism and Attention-Deficit/Hyperactivity Disorder (ADHD) has increased over the past four decades (Grandjean and Landrigan 2006; Newschaffer et al. 2005; Prior 2003; Rutter 2005; Visser et al. 2010), currently estimated to affect about 15% of children in the U.S. (Boyle et al. 2011; U.S. EPA 2013). This increase cannot be completely explained by genetics, improved diagnostics, or known environmental risk factors (Hertz-Picciotto and Delwiche 2009; Landrigan et al. 2012; NRC 2000; Newschaffer et al. 2005), although increased diagnosis and awareness of the disorders could play a role. Emerging science has identified the potential role of toxic environmental chemicals as being an underevaluated modifiable risk factor that may interfere with brain development in fetuses and children (Bennett et al. 2016). Environmental chemical exposures are widespread in the population, and modest associations characteristic of environmental risks can translate into adverse population-level effects (Bellinger 2012; Institute of Medicine 1981).
Polybrominated diphenyl ethers (PBDEs) are a group of synthetic chemicals used as chemical flame retardants to inhibit or resist the spread of fire (ATSDR 2004). PBDEs comprise 209 possible congeners, with the major congeners detected in human and environmental samples being BDE-47, BDE-99, BDE-100, and BDE-153 (Darnerud et al. 2001; Frederiksen et al. 2009; Hites 2004; Sjodin et al. 2008). PBDEs have been used in polyurethane foam and hard plastics and can be found in a variety of everyday products, such as upholstered furniture, cars, mattresses, building materials, textiles, and computers and other electronic equipment (ATSDR 2004; Birnbaum and Staskal 2004). Because they can be present in significant quantities in products (5–30% by weight) (Darnerud et al. 2001; World Health Organization 1994) and because they are additives rather than covalently bound to consumer products, there is higher potential for leaching, volatilization, or degradation, leading to consumer and environmental exposures (Darnerud et al. 2001; Gill et al. 2004; Watanabe and Sakai 2003). Human exposures are ubiquitous beginning in utero (Morello-Frosch et al. 2016; Woodruff et al. 2011b), which is a highly vulnerable period of human brain development (Grandjean et al. 2008), and PBDEs have been found pervasively in U.S. household dust samples (Darnerud et al. 2001; Frederiksen et al. 2009; Mitro et al. 2016). Levels of PBDEs measured in Americans are the...