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Page 2 of 17 Rawn et al. J Environ Expo Assess 2024;3:16 https://dx.doi.org/10.20517/jeea.2024.04

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was 7.66 ng·g lipid (median value 0.303 ng·g lipid). These data suggest that HBCD concentrations similarly
decreased in Canadian human milk between the early 2000s and sampling for the present study. Maternal age did
not impact the concentrations of these flame retardants in milk. Additionally, other maternal characteristics [e.g.,
the number of children a woman has had, pre-pregnancy body mass index (BMI), and education level] did not
impact concentrations of these brominated flame retardant concentrations.

Keywords: Polybrominated diphenyl ethers, hexabromocyclododecane, human milk, pan-Canadian study,
human biomonitoring

INTRODUCTION
Polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD) are both additive
brominated flame retardants (BFRs) that are mixed with polymers present in consumer products (e.g.,
textiles, electronics, etc.) to reduce flammability . By being added and mixed with the polymers, rather than
[1]
chemically bonded, they are more readily released to the environment throughout their lifecycle. PBDEs
were produced as three mixtures named according to the dominant contributors to the total PBDE
concentration: the penta-mix, dominated by the penta- and tetra-brominated congeners; the octa-mix,
which encompasses significant levels of the octa-, nona- and decabrominated congeners, and the deca-mix,
reported to comprise 92%-97% decabromodiphenyl ether (PBDE 209) . The penta-mix and octa-mix were
[2]
used in different applications (e.g., penta-mix - polyvinylchloride, unsaturated polyesters, rubber, paints,
lacquers, and textiles; octa-mix - acrylonitrile butadiene styrene, polyamide, poly butylene terephthalate,
polystyrene/high impact polystyrene). While the deca-mix was used for most purposes identified for the
other mixtures, it was also used in polyethylene cross-linked polyethylene, polyethylene terephthalate, and
polypropylene . The inclusion of PBDEs in these chemicals resulted in their presence in a wide variety of
[3]
consumer products such as televisions, computers, appliances, smoke detectors, conveyor belts, carpets,
[3]
textiles, furniture, and the seating upholstery in vehicles . HBCD was used as a replacement for PBDEs
[4]
primarily in building insulation (expanded and extruded polystyrene), although it was also used to a minor
extent in textiles .
[5]
Although persistence is a desirable quality for flame retardants in consumer products, this characteristic,
coupled with their application as additive BFRs, has contributed to their release into the environment
[6-8]
during product lifecycles and following disposal . Given that many of the products containing PBDEs and
HBCD are present within homes and workplaces, they are detected at elevated concentrations in indoor
dust and air relative to outdoor environments in global regions free of outdoor sources [9,10] . In addition, BFR
levels in the air and dust in offices have been related to the number of electronic devices present .
[6]
Subsequently, the release of BFRs during recycling of electronic/electrical waste and repair of electronic
equipment has been documented as leading to their elevated levels in air and dust where this activity is
performed [11,12] .

While both of these classes of BFRs are known to be persistent, they also accumulate in the tissues of living
organisms, particularly in the lipid tissues . As a result of the bioaccumulation potential, PBDEs and
[13]
HBCD have been monitored in many different organisms globally, and studies have shown that both of
these BFRs biomagnify through food webs [14-22] . In addition, PBDEs and HBCD have been reported in
human tissues/fluids throughout the world (e.g., serum, milk) for more than a decade [23-33] . Human milk
collected in Sweden over a period of 25 years (1972 to 1997) was analyzed to measure PBDEs and
highlighted a dramatic increase in ΣPBDE (Σ of PBDE 28, 47, 66, 85, 99, 100, 153, 154) concentration, from
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< 0.1 ng·g lipid in 1972 to ~4 ng·g lipid in 1997 [34,35] . Following this study, the same group analyzed a
limited number of human milk samples (n = 15) collected in 2000-2001 and found ΣPBDE concentrations