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Rawn et al. J Environ Expo Assess 2024;3:16 https://dx.doi.org/10.20517/jeea.2024.04 Page 11 of 17

Temporal trends
Both of the BFRs examined in the present study have been previously measured in Canadian human milk.
The prior work from our laboratory did not include PBDE 209 because it was not consistently present and,
at the time, it was thought to be a minor contributor to overall PBDE concentrations . Total PBDE
[28]
concentrations previously were reported as a total of seven congeners (Σ28, 47, 99, 100, 153, 154, 183) with
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concentrations ranging from 0.552 to 596 ng·g lipid (median 2.99 ng·g lipid; geometric mean 3.54 ng·g
lipid) for samples collected from across southern Canada in 1992 and from 0.841 to 956 ng·g lipid (median
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22.1 ng·g lipid; geometric mean 25.2 ng·g lipid) for the 2002 collection . Median/geometric mean ΣPBDE
[28]
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concentrations (19.9 and 21.1 ng·g lipid, respectively) in human milk collected from Hamilton, Ontario, in
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2005 indicated that PBDE concentrations had stabilized . The sum of concentrations for these same seven
[28]
congeners in the present study, 2008-2011 collection, as part of the MIREC study, ranged from 0.473 to
257 ng·g lipid (14.6 and 15.5 ng·g lipid, median and geometric mean, respectively), suggesting that PBDE
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concentrations in human milk began to decline relative to concentrations observed in 2002.
While ΣPBDE concentrations appear to be declining, not all individual congeners follow this trend. A
comparison of the previous data from our laboratory (1992, 2002 and 2005) with the data from the present
work does show similar patterns for several of the congeners considered. The lowest median concentrations
of PBDE 47, 99, 100, and 154 were observed in 1992, followed by increased concentrations in 2002, and
appeared to stabilize by 2005, followed by a decline observed in the present work [Table 4]. Median PBDE
28 concentrations increased between 1992 and 2002, reaching the highest concentration observed in 2005,
followed by a decline, while a comparison of the median PBDE 183 concentrations over time did not show a
clear trend. In contrast to the other congeners investigated, the median PBDE 153 concentration
determined in human milk from the present study was higher than the values reported in 1992, 2002 or
2005, although the results from 2002 and 2005 suggested the beginning of a decline [Table 4]. This
variability in temporal trends among PBDE congeners is consistent with what has been reported for human
milk collected in Sweden , although the pattern observed is similar to that observed in the serum of
[50]
Swedish mothers where a decrease in PBDEs 47, 99, and 100 was observed and an increase in PBDE 153 was
determined .
[51]

An additional study that measured PBDE concentrations (Σ four congeners: 47, 99, 100, and 153) in human
milk from two discrete communities in Canada (Kingston, Ontario in 2003/2004 and Sherbrooke, Québec in
[52]
2008/2009) has also been reported . PBDE concentrations ranged from 2.7 to 108 ng·g lipid and 2.9 to
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119 ng·g lipid, with median concentrations of 11 and 15 ng·g lipid in Kingston and Sherbrooke,
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respectively . The Σ47, 99, 100, and 153 congeners in the present study had a wider concentration range
[52]
than those observed in the two cities (0.02-251 ng·g lipid), albeit with only slightly elevated median
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(13.7 ng·g lipid) and geometric mean (14.7 ng·g lipid) concentrations than those reported for Kingston
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and Sherbrooke. The Canadian data over time suggest that PBDE concentrations peaked in Canadian
human milk during the early 2000s. These observations are consistent with the timing of the reviews of
tetra-, penta-, hexa- and heptabrominated diphenyl ethers as part of the Stockholm Convention, which
[53]
listed them as persistent organic pollutants in 2009 .
HBCD was determined previously in human milk from one community in northern Canada (Nunavik) at
two time points (1989-1991 and 1996-1999) and one location in southern Canada (Hamilton, Ontario) in
2005 . The early HBCD analysis of milk from Nunavik measured α-HBCD alone [0.1-0.6 ng·g lipid (1989-
[28]
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[28]
1991) and 0.1-13.3 ng·g lipid (1996-1999)] . In contrast, the analysis of samples collected from Hamilton
in 2005 involved the determination of α-, β- and γ- isomers. ΣHBCD concentrations in those samples ranged
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from 0.1-28.2 ng·g lipid, with median and geometric mean concentrations of 0.7 and 0.6 ng·g lipid,
respectively. The results of the pan-Canadian samples collected in the present study ranged from below the