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Page 8 of 17 Hammel et al. J Environ Expo Assess 2024;3:8 https://dx.doi.org/10.20517/jeea.2023.51

Although BEH-TEBP was only measured in a subset of five samples due to degradation in the standard
clean-up procedure, the concentrations were among the highest of any BFR measured in the breast milk
samples (median = 0.78 ng/g lipid). High levels despite moderate detection frequency were also observed for
milk samples collected in Norway, Slovakia, and the Netherlands around the same time , which
[71]
collectively calls for inclusion of this compound in future studies, despite the analytical challenges, as it
could be an important pathway of exposure for infants.

The levels of syn- and anti-DP detected here were slightly lower than previously observed across Europe
[71]
[72]
but higher than in Canada . However, the literature on NBFRs in human milk is still very limited and thus
limits the comparison of our results to others; a recent review of contaminants in human milk by Chi et al.
[73]
included several groups of flame retardants but not any of the NBFRs investigated here .

Intramatrix correlations
In general, PBDEs, particularly the lower molecular weight congeners and congeners of the commercial
PentaBDE mixture, were highly correlated in breast milk [Table 3]. Likewise, the two diastereomers of
HBCDD (α and γ) were also highly correlated (r = 0.64, P < 0.0001). DPTE in breast milk was positively and
s
significantly correlated with BTBPE and anti-DP, but not with the HBCDD diastereomers. Anti-DP was
further moderately correlated with the two HBCDD diastereomers, whereas BTBPE was correlated with
BDE-28. α-HBCDD was also positively correlated with BDE-28, -47, -99, and -100 (r = 0.34-0.47, P < 0.05,
s
Table 3). Given their concurrent use as flame retardants, this indicates that HBCDDs and PBDEs could have
similar routes of exposure or sources.

Relationship with age
Several of the BFR compounds in breast milk were positively associated with the mother’s age. Two NBFRs
(BTBPE and anti-DP), α-HBCDD, and BDE-154 concentrations increased by almost 10% per one-year
change in the mother’s age [Figure 1]; however, for BDE-154 it is worth noting that it co-elutes with BB-
153, which is very persistent and its use dates back further than the PBDEs.

Dust
Among the PBDEs, the dust samples were dominated by BDE-209 (median: 432 ng/g), followed by BDE-99
(median: 19.2 ng/g) and BDE-47 (median: 13.7 ng/g) [Table 1], as previously observed in other European
[16]
studies . The median level of the ΣHBCDDs was comparable to BDE-209, though the maximum values
were not as pronounced for ΣHBCDDs. DBDPE was also found in high levels though not as high as BDE-
209, which at the time of sampling was still in use in some applications. Substantial amounts of EH-TBB,
BTBPE, and BEH-TEBP were also detected. Although median levels in the literature span many orders of
magnitude , the medians and ranges in the current study were very similar to levels reported by
[13]
Sahlström et al., who sampled a similar population in Sweden two years later, particularly for the PBDEs .
[74]

Intermatrix correlations of breast milk
Dust
Of the BFRs analyzed in both breast milk and house dust, three of the seven PBDEs in paired samples were
significantly correlated (r = 0.35-0.42, P < 0.05; Table 4), i.e., BDE-28, -47, -99. They are all lower molecular
s
weight PBDEs and prominent congeners of the Penta-BDE commercial mix. This suggests that house dust
could be a recent source of exposure together with toxicokinetic processes, which may favor the transfer to
and accumulation of lower brominated molecules in milk, despite higher exposure to BDE-209 . Positive
[75]
and significant correlations between milk and house dust have been observed previously for PBDE
congeners, although the strength of correlation varied by congener in different geographical regions.
Significant associations between breast milk and house dust have been observed in Sweden for
[56]
BDE-47 and -99 , in the U.S. for summed PBDEs , and in New Zealand for BDE-209 , but not in a study
[77]
[76]
[78]
performed in Australia .