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

-1
ranged from 0.56 to 7.72 ng·g lipid, which shows that concentrations continued to increase into the early
[36]
2000s, prior to regulatory action being taken on these chemicals . North American studies measuring
PBDEs (consistently including Σ28, 47, 99, 100, 153) in human milk during the early to mid-2000s found
concentrations to be higher than observed in Europe during a similar period (range 0.1-2,010 ng·g
-1
lipid) . Since HBCD has not been as widely studied as PBDEs, temporal trends were not readily established
[37]
in human milk globally [38,39] . In addition to differences in temporal patterns, concentrations of these legacy
BFRs vary among countries and regions.

The determination of PBDEs and HBCD in human milk is important because these data allow researchers
to determine maternal exposure via their milk concentrations. Additionally, human milk is often the sole
source of nutrition for infants and very young children, which means it represents an important dietary
exposure to BFRs for this demographic. Owing to the fact that infants and very young children are growing
and changing rapidly, BFR exposure during this phase of life may impact their development since these
compounds are associated with impacts on endocrine function and frequently related to thyroid function
disruption [13,40,41] . Although exposure at critical developmental stages may not result in immediate impacts,
PBDE exposure can lead to increased risk of disease at later life stages (e.g., diabetes, cancer,
neurobehavioural effects) [41-43] , and HBCD has also been associated with neurobehavioural impacts and
[40]
[13]
changes in sex-related hormones , resulting in effects on behaviour and memory .
Despite the presence of persistent organic contaminants, including BFRs, in human milk, the World Health
Organization (WHO) recommends that mothers feed children human milk exclusively for the first six
months, because of the presence of important nutritional constituents and positive health effects for the
mothers and their babies . In addition, breastfed infants are reported to have a lower incidence of obesity
[44]
[45]
later in life .

The present study, known as the Maternal-Infant Research on Environmental Chemicals (MIREC) study,
was undertaken across Canada between 2008 and 2011 to measure maternal concentrations of
environmental chemicals during pregnancy and in the milk following the birth of their babies . The work
[46]
described herein is focused on the measurement of PBDEs and HBCD in human milk.

EXPERIMENTAL
Study population and sampling
Participants for the MIREC study were recruited from across Canada to allow for a pan-Canadian
perspective on maternal environmental chemical concentrations. In addition to providing biomonitoring
data on the participants, this work supported the determination of infant dietary exposure via human milk
sampling. Research centres were identified as possible recruitment sites if it was determined that existing
frameworks for clinical obstetric research were in place prior to being associated with the MIREC study. In
advance of confirming any clinic as a MIREC recruitment site or study centre, each clinic was required to
obtain ethics board approval from their own research centre, Health Canada’s ethics board, and the ethics
board of the MIREC coordination centre in CHU Sainte Justine, Québec. Once a clinic was confirmed to be
a MIREC study centre, recruitment was undertaken during prenatal clinics . Study centres were
[46]
established in 10 cities (from six provinces) across southern Canada, from west to east: Vancouver (British
Columbia); Edmonton (Alberta); Winnipeg (Manitoba); Hamilton, Kingston, Ottawa, Sudbury and
Toronto (Ontario); Montréal (Québec) and Halifax (Nova Scotia).

Eligibility requirements were limited to women aged 18 or above, in the first 14 weeks of gestation, and
capable of communicating in either English or French . Among the women approached regarding the
[46]