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Page 6 of 17 Hammel et al. J Environ Expo Assess 2024;3:8 https://dx.doi.org/10.20517/jeea.2023.51

Breast milk
Levels
BFRs have only previously been reported in breast milk in Denmark in two studies collecting samples
[52]
between 1997 and 2002, which included PBDEs in milk and placenta samples and PBDEs and HBCDDs
[53]
in milk ; NBFRs had not previously been measured in breast milk from Denmark. In the current study, we
measured 19 PBDE congeners, 3 HBCDD diastereomers, 5 NBFRs, and 2 DP isomers. Of these chemicals, 8
PBDEs, 2 HBCDD diastereomers, and 4 NBFRs were detected in over 65% of the breast milk samples
[Tables 1 and 2]. Overall, the most abundant BFR measured in breast milk was BDE-153. It had a median
concentration of 0.79 ng/g lipid and was detected in all samples [Table 1], which could be expected given
that the half-life of BDE-153 is among the longest of the PBDE congeners . This was, however, not
[54]
observed in Danish breast milk collected 5-10 years earlier where BDE-47 was the dominating
congener [52,53] . BDE-47 was the congener with the second highest median concentration in our study
(median = 0.61 ng/g lipid), followed by BDE-209 (median = 0.53 ng/g lipid), which were detected in 100%
and 95% of the samples, respectively. PBDE congeners 99, 100 and 154 were also detected in more than 95%
of the samples, but with median concentrations < 0.25 ng/g lipid. However, the high detection frequency of
BDE-154 may have been affected by the co-elution of BB-153, which was more frequently detected in the
corresponding blood samples where the two BFRs were quantified separately . These concentrations were
[42]
[53]
lower than in those sampled in Denmark 5-10 years earlier with the exception of BDE-209 . However, the
levels were similar to those measured in a large-scale study in Norway between 2003 and 2005, although the
concentration of BDE-209 in this study was slightly higher (Norwegian study median = 0.32 ng/g lipid) .
[55]
The concentrations were also comparable to breast milk samples collected in Sweden around the same time
period . Finally the ∑ PBDE is within the range of other European countries for the same sampling period
[56]
6
as reported by the World Health Organization (WHO), though the number of participating countries was
low. The observations also match the decreasing trend observed in Western Europe since the year 2000 .
[57]
Of the HBCDD diastereomers, α-HBCDD was detected in all samples and was the most abundant
diastereomer (median = 0.24 ng/g lipid), with γ detected in 65% and β detected in only 6% of samples
[Table 2]. α-HBCDD was also the most abundant non-PBDE flame retardant that was measured in the
breast milk samples if disregarding BEH-TEBP that was only analyzed in five samples. α-HBCDD has also
previously been the dominant HBCDD diastereomer in diastereomer-specific analyses of breast milk [58,59] .
Compared to a previous Danish study conducted between 1997 and 2002 (n = 435), our study observed
slightly lower concentrations of α-HBCDD . Although it is difficult to determine trends in a region from
[53]
just two time points, data suggest that HBCDD concentrations could have decreased in Denmark in the
2000s, which is in line with Swedish studies indicating decreasing concentrations in the same time
[37]
period . Other studies examining breast milk samples in Europe from the mid to late 2000s detected
similar albeit slightly higher concentrations, including a cohort of Norwegian women and studies
[60]
[57]
conducted in Ireland , as well as the recent WHO/UNEP overview . However, other studies conducted in
[61]
the UK showed substantially higher concentrations of HBCDDs [62,63] , whereas HBCDDs were not detected in
a study on breast milk from Sweden, possibly related to a GC-MS method, which is less sensitive than the
commonly applied LC-MS/MS method [56,64] .

Detected in nearly all samples (DF = 91%), the most abundant NBFR in our study was DPTE
(median = 0.11 ng/g lipid) [Table 2]. DPTE was the main component of the BFR mixture Bromkal 73-5PE
that was manufactured until the mid-1980s [65,66] . Although production past the 1980s is unknown, it has been
measured in house dust, in addition to Arctic air, seawater, and biota, indicating persistence,
bioaccumulation, and long-range transport [12,67,68] . Previous studies conducted in the Netherlands, China,