Sakrapport till Naturvårdsverkets Miljöövervakning:
Bromerade flamskyddsmedel i modersmjölk från förstföderskor i Uppsala - uppdaterad tidstrend 1996-2006
Avtalsnummer: 215 0616
Utförare: Livsmedelsverket
Programområde: Hälsorelaterad miljöövervakning Delprogram: Exponering via livsmedel
Undersökningar/uppdrag: Komplettering tidstrend bröstmjölk
Kompletterande analyser av bromerade flamskyddsmedel i modersmjölk från förstföderskor i Uppsala.
Sanna Lignell, Marie Aune, Per Ola Darnerud och Anders Glynn Livsmedelsverket
2008-03-28
SAMMANFATTNING
Under perioden 1996 till 2006 har Livsmedelsverket samlat in modersmjölk från
förstföderskor i Uppsala län. Ett av syftena med studierna är att undersöka hur halterna av vissa persistenta organiska miljögifter förändras med tiden. I denna rapport utvärderas eventuella tidstrender för bromerade flamskyddsmedel (polybromerade difenyletrar (PBDE) och hexabromcyklododecan (HBCD)). Tidstrender för PBDEer under den aktuella
tidsperioden har utvärderats tidigare (Glynn et al. 2007), och resultaten har nu kompletterats med analys av ytterligare 80 prover.
Bland PBDE kongenerna uppvisade BDE-47 den högsta medianhalten (1,5 ng/g fett) i modermjölk, följt av BDE-153 (0,57 ng/g fett), BDE-99 (0,32 ng/g fett) och BDE-100 (0,29 ng/g fett). Halterna av BDE-28, -66, -138, -154, -183 och HBCD låg under kvantifierings- gränsen i de flesta av proverna.
Inga generella trender observerades beträffande PBDEer i modersmjölk. Multipel linjär regression visade att medianhalterna av BDE-47 och BDE-99 har sjunkit (4,3 % respektive 7,5% per år), medan medianhalten av BDE-153 har ökat (4,9% per år) under den studerade tioårsperioden. Ingen signifikant trend kunde påvisas för BDE-100. En långsamt nedåtgående trend av summaPBDE-koncentrationerna (summan av BDE-47, BDE-99, BDE-100, BDE-153 och BDE-154) observerades. Denna nedåtgående trend är dock osäker eftersom den tid det beräknas ta för medianhalten att halveras (34 år) är betydligt längre än den tid som studien sträcker sig över (10 år).
I likhet med våra resultat har en studie av PBDE koncentrationer i poolade mjölkprover från kvinnor i Stockholmsområdet också visat att halterna av lägre bromerade kongener (t.ex.
BDE-47 och BDE-99) har minskat från mitten av 1990-talet, medan halterna av BDE-153 har
ökat (Fängström et al. 2008). Förklaringen till detta kan vara att användningen av lägre
bromerade PBDE kongener har minskat och/eller att BDE-153 är mer persistent i jämförelse
med t.ex. BDE-47.
Report to the Swedish Environmental Protection Agency, 2008-03-28 Sanna Lignell, Marie Aune, Per Ola Darnerud and Anders Glynn
Brominated flame retardants in mother’s milk from primiparae women in Uppsala County, Sweden – updated temporal trends 1996-2006
INTRODUCTION
In order to estimate the body burdens of persistent organic pollutants (POPs) among pregnant and nursing women, and to estimate the intake of these compounds by breast-feeding infants, the Swedish National Food Administration (NFA) has made recurrent measurements of concentrations of POPs in mother’s milk. Another purpose with the project is to investigate if there are temporal trends of POP concentrations in mother’s milk. Temporal trends of POPs, including brominated flame retardants, between 1996 and 2006 have been reported earlier (Glynn et al. 2007). At that point, the number of analysed samples from 1996 to 1999 was small, and in the present report, temporal trends of brominated flame retardants are updated with data from analysis of polybrominated diphenylethers (PBDE) and hexabromcyclo- dodecane (HBCD) in additional samples (N=80) collected in 1996-1999.
MATERIAL AND METHODS
Recruitment and sampling
The recruitment and sampling is described in detail in Lignell et al. (2006a) and Glynn et al.
(2007). Mother’s milk was exclusively sampled from primipara women in order to minimise
variation. A total of 335 women were recruited from 1996 to 2006. Mothers who were born in
non-Nordic countries (N=10) were excluded before the statistical analysis. Data on age,
weight, lifestyle, medical history, dietary habits, etc of the mothers were obtained from
questionnaires (Table 1). The mothers sampled milk at home during the third week after
delivery (day 14-21 post partum). The goal was to sample 500 mL from each mother during 7 days of sampling. During the sampling week, the mother’s milk was stored in the home freezer in acetone-washed bottles. Newly sampled milk was poured on top of the frozen milk.
Table 1. Personal characteristics of the participating primiparous mothers.
Variable n Mean Median Min Max
Age (years) 325 28.7 28.8 19 41
Pre-pregnancy body mass index (BMI) (kg/m2) 319 22.8 22.1 16 38 Weight increase during pregnancy (% of initial wt/week) 318 0.63 0.61 0.03 1.5
Weight reduction from delivery to sampling (%)a 310 9.5 9.4 -1.7 21
n %
Education max 3-4 years high school 132 41
1-3 years higher education 68 21
>3 years higher education 122 38 Smoking during pregnancy 49 15
aWeight reduction minus birth weight of the child in % of weight just before delivery.
Analysis
PBDEs (BDE-28, -47, -66, -99, -100, -138, -153, -154 and -183) and HBCD were analysed at the NFA using a method described in Atuma et al. (2000), with a few modifications. All samples were fortified with internal standards prior to extraction to correct for analytical losses and to ensure quality control. A number of control samples were analysed together with the samples to verify the accuracy and precision of the measurements. A total of 80 milk samples, collected between 1996 and 1999, were analysed. Together with the samples analysed earlier, PBDEs (BDE-47, BDE-99, -100, -153, -154) have been analysed in 276 samples and HBCD in 177 samples collected between 1996 and 2006. BDE-28, -66, -138 and -183 have not been analysed in all samples since these congeners were not included in the analytical method in the beginning of the study.
Calculations and statistics
Lipid adjusted mother’s milk concentrations were used in the statistical analysis since lipid- adjusted concentrations give a better estimate of the body burden than non-adjusted
concentrations (Lignell et al. 2004). In the case of concentrations below the limit of
quantification (LOQ), half of LOQ was taken as an estimated value in the calculations. The
distributions of the PBDE and HBCD analytical results closely followed a log-normal
distribution. Therefore all statistical analyses were performed on log transformed data.
Temporal trends were not established for BDE-28, -66, -138, -154, -183 and HBCD since the mother’s milk levels of these substances were low (levels below LOQ in 66-100 % of the samples).
Statistical analysis was performed in MINITAB 15
®Statistical Software for Windows.
Multiple linear regression was used to analyse associations between concentrations of PBDEs and sampling year. Independent variables (life-style factors) that have been shown to
influence POP levels in mother’s milk (Lignell et al. 2004, Lignell et al. 2006b) were included as explanatory variables in the model. The variables considered were age of the mother (years), pre-pregnancy BMI (Body Mass Index, kg/m
2) and body weight change during pregnancy as well as after delivery (Table 1). In the multiple regressions, observations with a standard residual >3 were excluded due to their large influence on the results. As a consequence of the logaritmic transformation, the associations between sampling year and PBDE concentrations are presented as percent change per year, and not as change in absolute levels.
RESULTS AND DISCUSSION
Among the PBDEs, BDE-47 showed the highest median concentration, followed by BDE- 153, BDE-99 and BDE-100 (Table 2). The levels of BDE-28, -66, -138, -154, -183 and HBCD were below LOQ in most samples.
There were no general trends regarding the PBDE congeners during the time period (Table 3,
Figure 1-2). Multiple linear regressions showed that the concentrations of BDE-47 and BDE-
99 decreased significantly, while the concentrations of BDE-153 increased. No significant
trend was shown for BDE-100. The concentrations of sumPBDE (sum of BDE-47, -99, -100,
-153 and 154) showed a slow but statistically significant decline. The uncertainty of this result
is however large since the estimated years needed for the adjusted mean concentration to be
halved in mothers milk from primiparous women (34 yrs) were much longer than the duration
of the study period.
Table 2. Concentrations of PBDEs and HBCD in mother’s milk samples from primipara women in Uppsala, Sweden, collected in 1996-2006 (ng/g lipid). Concentrations below LOQ were set to ½ LOQ in the calculations of mean, median and standard deviation (SD).
Compound N Mean Median SD Min Max % <LOQ BDE-28 196 0.12 0.11 0.07 <0.06 0.60 76 BDE-47 276 1.9 1.5 1.7 <0.4 16 1 BDE-66 196 0.09 0.09 0.05 <0.06 0.32 98 BDE-99 276 0.45 0.32 0.51 <0.12 5.2 16 BDE-100 276 0.36 0.29 0.40 <0.10 5.1 9 BDE-138 196 0.09 0.09 0.06 <0.06 0.55 100 BDE-153 276 0.64 0.57 0.45 <0.23 4.6 2 BDE-154 276 0.09 0.07 0.04 <0.06 0.94 88 BDE-183 167 0.10 0.10 0.05 <0.06 0.32 98 sumPBDEa 276 3.5 2.9 2.7 0.91 28 - HBCD 177 0.39 0.25 0.70 <0.20 7.8 66
asum of BDE-47, -99, -100, -153 and 154.
Table 3. Percent change in concentrations of PBDEs per year in mother’s milk from primiparae women living in Uppsala County 1996-2006. Temporal trends were adjusted for age, pre-pregnancy BMI, weight gain during pregnancy and weight loss after delivery.
Compound Change per year (%) R2 (%)a “half- time”b (years) p Mean SE
BDE-47 -4.3 1.1 7 16 <0.001
BDE-99 -7.5 1.2 13 9 <0.001
BDE-100 -1.2 1.2 2 56 0.324
BDE-153 +4.9 0.7 31 - <0.001
sumPBDEc -2.0 0.9 3 34 0.03
aCoefficient of determination for the whole regression model
bThe estimated time it takes for the concentrations to be halved in the population.
cincluding BDE-47, -99, -100, -153 and 154.
In contrast to other POPs (Glynn et al. 2006), there were only few significant associations between PBDE-levels and the explanatory variables included in the regression model. The regression model only explained 2-13 % of the variation in levels of BDE-47, BDE-99, BDE- 100 and sumPBDE. However, BDE-153 deviated from the other PBDEs in this aspect, and the BDE-153 levels were significant associated with age, BMI, weight gain during pregnancy and weight loss after delivery (the regression model explained 31 % of the variation in BDE- 153 levels).
Similarly to our results, a study by Fängström et al. (2008), based on PBDEs analyses of
pooled milk samples from mothers in the Stockholm region in 1980-2004, indicate that that
the concentrations of lower brominated PBDE congeners (e.g. BDE-47, BDE-99, BDE-100)
0,1 1,0 10,0 100,0
1996 1998 2000 2002 2004 2006 2008
year
BDE-47 in mother's milk (ng/g lipid)
0,1 1,0 10,0
1996 1998 2000 2002 2004 2006 2008
year
BDE-153 in mother's milk (ng/g lipid)
0,01 0,10 1,00 10,00
1996 1998 2000 2002 2004 2006 2008
year
BDE-99 in mother's milk (ng/g lipid)
0,1 1,0 10,0 100,0
1996 1998 2000 2002 2004 2006 2008
year
sumPBDE in milk (ng/g lipid)
Figure 1. Temporal trends (1996-2006) of PBDE concentrations in mother’s milk from primiparous
mothers living in Uppsala County, Sweden (N=276). Each point corresponds to the PBDE level in a milk sample from an individual woman. Note that the plots are based on raw data that have not been adjusted for life-style factors and that the y-axis has a log scale.
0 1 2 3 4
1995 1997 1999 2001 2003 2005 2007
year
concentration in milk (ng/g lipid)
sum PBDE sum PBDE BDE-47 BDE-47 BDE-153 BDE-153 BDE-99 BDE-99
Figure 2. Yearly median concentrations of sum PBDE, BDE-47, BDE-153 and BDE-99 in mother’s milk from primiparous mothers in Uppsala, Sweden (N=276). The lines represent regression lines obtained from multiple regression analysis including important life-style factors.
have decreased from the middle of the 1990’s while the concentrations of BDE-153 have increased (Figure 3). The explanation to these findings may be a reduced use of lower brominated PBDEs and/or a higher persistence of BDE-153 compared to BDE-47. By this time, it is not possible to establish any solid temporal trend for the PBDE congeners studied in mother’s milk from Uppsala. This makes it important to continue to sample mother’s milk for PBDE analysis in the future.
0,0 0,5 1,0 1,5 2,0 2,5
1980 1985 1990 1995 2000 2005 2010
year BDE-47 in mother's milk (ng/g lipid) Stockholm mothers
Uppsala mothers (present study)
0,0 0,5 1,0 1,5
1980 1985 1990 1995 2000 2005 2010
year
BDE-153 in mother's milk (ng/g lipid) Stockholm mothers
Uppsala mothers (present study)
Figure 3. BDE-47 and BDE-153 concentrations in human milk samples in the present study (yearly
median concentrations) and in a previous study on pooled milk samples from mothers in the Stockholm region (Fängström et al. 2008).
