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Research Article

Materials and Methods Top

Sample collection. Individual breast milk samples from U.K.-resident women, donated anonymously and without criteria (i.e., no prior selection or bias), were obtained with appropriate ethical approval. A total of 54 samples were collected between late 2001 and January 2003 from the maternity units of hospitals based in the Lancaster (northwest England; n = 27, via a neonatal unit) and London (southeast England; n = 27, via a milk bank) regions. Donor ages ranged from 24 to 34 years, and milk samples (~100 mL from a single expression; in a small number of cases, samples expressed on different days were donated) were collected by manual expression into sterile collection bottles. Samples were immediately frozen and stored at -20°C before analysis.

Donors originating from Lancaster completed simple lifestyle questionnaires; such information was not available for London samples. Lancaster samples were donated within the first month of parturition, several being donated within the first 2-3 days. From the information obtained on Lancaster samples, it was noted that all but two donors were nonsmokers, and cumulative past lactation ranged from 0 to 21 months. All consumed meat, a healthy amount of fresh fruit, and low amounts of alcohol (five donors, 1-2 units/day; one unit is defined as 7.9 g ethanol). Lifestyle data thus collected were not found to correlate with the levels of contaminants measured (data not shown). In the absence of more details, it is difficult to comment on similarities or differences between the two cohorts originating from the London or Lancaster regions. However, experience would suggest that no marked differences in range of socioeconomic class, outlets through which food might be sourced, age, or parity would exist. Although the London cohort would be envisaged to be a more heterogeneous population with an input from foreign donors, this was not expected to have an overwhelming influence.

Extraction of milk for PBDE and PCB/OC analyses. All solvents were of HPLC or glass-distilled grade. Silica gel (0.063-0.200 mm; Merck, Poole, U.K.) and Na₂SO₄ were heated at 450°C overnight and stored in sealed containers. Standards were purchased from Promochem (Welwyn Garden City, U.K.) and QMx (Thaxted, U.K.).

After thawing, milk samples that originated from a single expression were centrifuged at 3,000 rpm for 15 min. After separation of the milk-fat layer from the aqueous phase, a mixture of milk fat (0.5 g), Na₂SO₄ (5 g), and hexane (50 mL) was boiled for 10 min and allowed to cool before lipid determination. Evaporated to 5 mL, these mixtures were applied to 25-mm inner-diameter columns containing 15 g acidified silica gel (2:1 silica gel:acid by weight) and eluted with hexane. Eluted samples were evaporated to 1 mL under a gentle stream of nitrogen and applied to gel permeation chromatography columns packed with Biobeads S-X3 (Biorad Laboratories, Hercules, CA, USA) and eluted with hexane:dichloromethane (1:1 by volume). ¹³C₁₂-labeled PCB and dioxin recovery standards (added at the beginning of the procedure) and internal standards (added at the end of the procedure) in dodecane were incorporated when subsequent gas chromatography-mass spectrometry (GC-MS) analysis was carried out on whole milk-fat extracts but were excluded when extracts were generated for subsequent ¹H-NMR spectroscopy.

Gas chromatography for PBDE analysis was performed on a Finnigan Trace GC2000 series gas chromatograph equipped with a 30-m DB-5MS 0.25-mm inner-diameter capillary column (J&W Scientific, Stockport, U.K.) fitted with a retention gap (2 m long, 0.53 mm inner diameter). Sample aliquots (2 µL) were injected by a Thermoquest AS2000 autoinjector (Finnigan, Hemel Hempstead, U.K.), with the injection port at 270°C, in splitless mode, with 100 kPa pressure surge. The carrier gas was helium at a flow rate of 1 mL/min. The oven temperature program was as follows: 80°C for 2 min, 25°C/min to 200°C, 4°C/min to 315°C, and 315°C for 10 min. The quadrupole TRACE mass spectrometer (Finnigan) was set in selected ion recording mode, in negative ion chemical ionization (CI-) mode, using ammonia as the reagent gas, a source temperature of 200°C, interface temperature of 315°C, and electron energy of 70 eV. The following PBDE congeners, chosen because of their reported occurrence in environmental samples, were screened: PBDE congeners 17, 28, 32, 35, 37, 47, 49, 71, 75, 85, 99, 100, 119, 153, and 154. Of these, congeners 28, 47, 99, 100, 153, and 154 were regularly detected in the milk samples.

Gas chromatography for PCB and OC analysis was performed on a Fisons GC8000 series gas chromatograph (Fisons, Manchester, U.K.) equipped with a 50-m CPSil8 0.25-mm inner-diameter capillary column (Chrompak, Walton-on-Thames, U.K.), fitted with a retention gap as for PBDE analysis. Sample aliquots (2 µL) were injected, with the injection port at 250°C, in splitless mode. The carrier gas was helium with a flow rate of 1 mL/min. The oven temperature program was as follows: 100°C for 2 min, 20°C/min to 140°C, 4°C/min to 200°C, 200°C for 13 min, 4°C/min to 300°C, and 300°C for 10 min. The quadrupole MD800 mass spectrometer (Fisons) was set in selected ion recording mode, in electron impact positive ion ionization (EI+) mode, with a source temperature of 250°C, interface temperature of 300°C, and electron energy of 70 eV. A screen for the following PCB congeners and OC pesticides was carried out: PCB congeners 18, 22, 28, 31, 41/64, 44, 49, 52, 54, 60/56, 70, 74, 87, 90/101, 95, 99, 104, 105, 110, 114, 118, 123, 132, 138, 141, 149, 151, 153, 155, 156, 157, 158, 167, 170, 174, 180, 183, 187, 188, 189, 194, 199, 203; ɑ-HCH, ß-HCH, ɣ-HCH, ƍ-HCH, hexachlorobenzene (HCB), ɑ-chlordane, ɣ-chlordane, o,p´-dichlorodiphenyldichloroethane (DDD), p,p´-DDD, o,p´-dichlorodiphenyldichloroethylene (DDE), p,p´-DDE, o,p´-DDT, and p,p´-DDT. The following were regularly detected in the milk samples: PCB congeners 41/64, 44, 49, 60/56, 70, 74, 87, 90/101, 95, 99, 105, 110, 114, 118, 138, 149, 151, 153, 156, 157, 158, 167, 170, 180, 183, 187, 189, 194, 203; ɑ-HCH, ß-HCH, ɣ-HCH, HCB, p,p´-DDD, o,p´-DDE, p,p´-DDE, and p,p´-DDT.

A seven-point calibration was used for quantifying all PBDEs, PCBs, and OCs. Detection limits were defined as three times the standard deviation of the levels found in the analytical blanks or the instrument detection limit in the absence of detectable levels in the blanks.

Quality assurance/quality control. Milk samples were analyzed in batches of six. Along with each batch a blank sample was included, and with every third batch an in-house reference material (a butter sample) was also extracted. This reference material had been analyzed on 12 separate occasions before these analyses and was considered a useful determinant of the reproducibility and rigorous nature of the analytical procedure employed.

A control chart was employed to identify the mean and warning limits (defined as plus two times the standard deviation of the average concentration found in the 12 reference material samples previously analyzed) of the reference materials analyzed throughout the study. The comparison quantity was defined as the sum of the levels of PBDE-47, PBDE-99, PBDE-100, PBDE-153, and PBDE-154 in the reference butter sample. Seven reference material samples were analyzed during the course of this study, and the value of the sum of the five PBDEs never exceeded the warning limits.

Recoveries ranged from 50 to 119%, with an average of 90%. Extracted milk fat ranged from 29 to 85% of centrifuged milk fat fresh weight (mean, 55%). Centrifuged milk fat fresh weight ranged from 0.7 to 5.7% (mean, 2%) of whole milk fresh weight.

¹H-NMR spectroscopy. Extracts in hexane were transported to Imperial College (London) for analysis. Extracts of milk samples containing the lowest contaminant levels (n = 7, all from Lancaster) were compared with extracts of milk samples containing the highest levels (n = 7, all from London). These two sets of samples were chosen on the basis of the sum of all contaminants. To these, an equal volume of CDCl₃ (99.9% deuterium; Sigma, Poole, U.K.) was added, and samples were purged with nitrogen gas. To ensure the removal of hexane, this purge process was repeated twice. Then samples were reconstituted in 500 µL of CDCl₃ and transferred into 5-mm NMR tubes. ¹H-NMR spectra were recorded on a Bruker DRX600 NMR spectrometer, at 300 kelvin, with a 5-mm inverse probe using a standard one-dimensional pulse sequence [RD-90°-t₁-90°-t_m-90°-acquisition]. The recycle delay (RD) was 3 sec; mixing time, t_m, 150 msec; t₁, 3 µsec. The 90° pulse length was adjusted to approximately 10 µsec. Transients (128) were collected into 32,768 data points for each spectrum with the spectral width of 12 kHz.

Data reduction and principal components analysis. All free induction decays were multiplied by an exponential function equivalent to a 1 Hz line-broadening factor before Fourier transformation. NMR spectra were then phase and baseline corrected before being divided into 245 buckets, over the chemical shift range 0.2-10 ppm, using AMIX (Bruker Analytik, Rheinstetten, Germany). Each bucket was 0.04 ppm wide, and the area in each region was integrated. The regions ƍ6.8-ƍ7.5 ppm and 1.5-2.5 ppm containing residual solvents (chloroform and water, respectively) were discarded. The value of each bucket was normalized relative to the total sum of the spectral integral before principal components analysis (PCA), which was carried out with the software Simca-P 8.0 (Umetrics, Umeå, Sweden).

Results Top

PBDE congener levels in milk-fat extracts obtained from U.K. breast milk samples (n = 54) obtained between late 2001 and January 2003 are shown in Table 1. ΣPBDE levels ranged from 0.1 to 69 ng/g lipid, with a geometric mean of 6.6 ng/g lipid (median, 6.3 ng/g lipid). PBDE-47 (geometric mean, 3 ng/g lipid; median, 2.7 ng/g lipid; 45% of ΣPBDE content) was always the most abundant congener present in breast milk. As a percentage of ΣPBDE content, other congeners were found in the following order: PBDE-153 (21%) > PBDE-99 (14%) > PBDE-100 (9.0%) > PBDE-154 (7%), respectively. Making up much smaller proportions of ΣPBDE levels were PBDE congeners 28, 32, 35, 17, and 71.

Published levels of ΣPBDE congeners in breast milk are shown in Table 2. Selected congeners have been included in the ΣPBDE values presented in Table 2 to facilitate comparisons with the results of different studies. Compared with European and Japanese milk samples, markedly higher (~10-fold) levels appear to occur in U.S. milk samples. Current ΣPBDE levels in U.K. milk samples, although not as high as those found in U.S. milk samples, are still much higher than in milk samples from other European countries and Japan. As a consequence of stringent fire regulations since 1988, the United Kingdom has seen the use of larger quantities of the pentaBDE mixture than many of her European counterparts. The United Kingdom is currently the fourth largest PBDE producer in the world, with an output of ~25,000 metric tons annually (Alaee et al. 2003).

PCB levels in milk-fat extracts obtained from U.K. breast milk are shown in Table 3. ΣPCB levels ranged from 26 to 530 ng/g lipid, with a geometric mean of 150 ng/g lipid (median, 180 ng/g lipid). The most commonly occurring PCB congeners were found to be present in the following order: PCB-153 > PCB-138 > PCB-180 > PCB-170 > PCB-118 > PCB-187 > PCB-99 > PCB-156. PCB-153 constituted some 26%, PCB-138 some 20%, and PCB-180 some 13% of ΣPCB levels. A comparison of the results from this study with previously reported U.K. levels (Table 4) suggests that ΣPCB levels are currently decreasing, probably as a consequence of bans imposed on the use of these contaminants.

Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

Total HCB levels ranged from below the detection limit to 180 ng/g lipid (geometric mean, 17 ng/g lipid; median, 18 ng/g lipid), whereas ΣHCH (defined as the sum of ɑ-, ß-, and ɣ-HCH) levels ranged from 1.2 to 1,500 ng/g lipid (geometric mean, 16 ng/g lipid; median, 18 ng/g lipid; Table 3). ΣDDX (p,p´-DDT and its metabolites) levels ranged from 24 to 2,300 ng/g lipid, giving rise to a geometric mean of 160 ng/g lipid (median, 160 ng/g lipid). The most commonly occurring isomers were p,p´-DDE (geometric mean, 150 ng/g lipid; median, 150 ng/g lipid; range, 20-1,600 ng/g lipid) and p,p´-DDT (geometric mean, 6.2 ng/g lipid; median, 6.2 ng/g lipid; range, 1.1-760 ng/g lipid). Of two milk samples that exhibited exceptionally high ΣDDX levels, one also exhibited exceptionally high ΣHCH levels and the other exhibited exceptionally high ΣHCB levels (data not shown). Table 4 again demonstrates that levels in U.K. breast milk of p,p´-DDE, HCB, and ß-HCH have been falling for some time.

Geometric means, medians, and ranges of various contaminant concentrations in milk-fat extracts obtained from breast milk samples originating from the London region (n = 27) and the Lancaster region (n = 27) are compared in Table 5 and Figure 1A, B. The data were log-transformed, and a t-test was used to investigate differences in contaminant levels between the samples from London and those from the Lancaster region. Significantly higher (p < 0.0001) levels of PBDE-47 were found in London milk samples compared with those originating from Lancaster, but no differences were found in ΣPBDE and the levels of four other PBDE congeners (Table 5, Figure 1B). With regard to PCBs and OCs, significantly higher (p < 0.05) levels of PCB-138, PCB-153, PCB-180, ΣPCB, p,p´-DDE, ΣDDX, HCB, ß-HCH, and ΣHCH were found in milk samples from London (Table 5, Figure 1A). Breast milk samples originating from London tended to exhibit higher geometric mean levels for all the contaminants analyzed in comparison with Lancaster levels (Figure 1A, B).

Figure 1.

A comparison (London vs. Lancaster) of the geometric mean levels of (A) PCBs and OCs and (B) PBDEs in breast milk samples obtained from U.K.-resident women.

¹H-NMR spectra showed that the major chemical constituents of extracts analyzed in this study were lipids (data not shown). Taking into account the remaining, unidentified NMR signals, seven of the milk-fat extracts shown to contain the lowest contaminant levels (all from the Lancaster region) were compared with seven extracts shown to contain the highest levels (all from the London region). NMR with pattern recognition methods gave rise to a multivariate PCA score plot (Figure 2) in which each point represents an individual extract. The observation that clustering occurred based on contaminant levels highlights the differences in the chemical composition of these two groups of milk-fat extracts. Excellent separation for the two groups of extracts was clearly evident along the first principal component, thus implying that the chemical constituents of both groups are significantly different.

Figure 2.

PCA score plots of milk-extract samples; t[1] and t[2] are first and second principal components, respectively. Black squares represent sample extracts containing the lowest contaminant levels (n = 7, all from Lancaster). Blue circles represent sample extracts containing the highest contaminant levels (n = 7, all from London). 
*Two sample extracts closely aligned together.

Discussion Top

The occurrence of PBDE-47 in breast milk (Meironyté et al. 1999), human blood plasma (Klasson-Wehler et al. 1997), and human adipose tissue (She et al. 2000) has been reported. In Sweden, a PBDE congener pattern consisting of PBDE-47 > PBDE-99 > PBDE-153 > PBDE-100 > PBDE-154 in terms of relative content has been noted, whereas others have reported the presence of equal levels of PBDE-99 and PBDE-153 (Darnerud et al. 1998; Meironyté et al. 1999). Other studies from Japan, Sweden, the United States, and now the United Kingdom (present study) have found PBDE-153 to be present at higher levels than PBDE-99 (Meironyté et al. 2003; Ohta et al. 2000; She et al. 2002).

Estimates of market demand for major brominated flame retardants suggest that some 58% of world market volume occurs in Asia, followed by the Americas (26%) and then Europe (14%) [Bromine Science and Environmental Forum (BSEF) 2001]. Of three commercial PBDE mixtures--pentaBDE, octaBDE and decaBDE--the latter is the most commonly found in Europe in recent years with approximately 7,600 metric tons of decaBDE in current use (BSEF 2001; Hardy 2002b). PBDE congeners 47, 99, 100, and 153 are all components of pentaBDE. It has been tentatively suggested that since 1970 a cumulative sum of 3,000 metric tons of pentaBDE may have been manufactured in the United Kingdom (Alcock et al. 2003).

That lower brominated PBDEs are still present in U.K. milk samples (Table 1) suggests historical use of the pentaBDE product still plays a role in determining current congener patterns. It has been hypothesized that in sand, soil, or sediment decaBDE photodegrades and may to a minor degree give rise to lower brominated congeners (Sellström et al. 1998; Söderström et al. 2004). Diet may be an important route of exposure to PBDEs, particularly through the consumption of fish (Lind et al. 2002). Whether diet is the dominant route of uptake remains to be ascertained.

As PBDEs are used in indoor environments, the potential for transfer via inhalation of indoor dusts is a possibility. Foam from furniture and cars in the United Kingdom is likely to have been treated with the technical pentaBDE mixture profile in the past (Wilford et al. 2003), and the possibility of PBDEs volatilizing from foam has been previously demonstrated (Wilford et al. 2003). The pattern of PBDE congeners in U.K. breast milk suggests higher PBDE-47, PBDE-100, PBDE-153, and PBDE-154 levels but lower PBDE-99 levels (Table 1). Indoor dust samples from two U.K. parliamentary buildings (Santillo et al. 2001) and from houses in the United Kingdom (Santillo et al. 2003) exhibited similar patterns. PBDE patterns in fish from the U.K. North Sea (Thomas et al. 2003) also gave rise to a closely matching profile. U.S. data suggest a similar profile for foam (Hale et al. 2002) but a different indoor dust pattern (Rudel et al. 2003).

London (population > 10 million) contrasts markedly with Lancaster, a semirural town (population ~100,000). Pearson correlations of the logged ΣPCB, ΣPBDE, ΣHCH, ΣDDX, and HCB levels were examined. ΣPCB significantly correlated with ΣPBDE (p < 0.01), ΣHCH (p < 0.05), ΣDDX (p < 0.01), and HCB (p < 0.01). ΣDDX also significantly correlated with ΣPBDE (p < 0.01), ΣHCH (p < 0.01), and HCB (p < 0.01), whereas ΣPBDE correlated well with ΣHCH (p < 0.05) and HCB (p < 0.05). PBDE congeners significantly correlated (p < 0.01) as follows: PBDE-47 with PBDE-99, PBDE-100, PBDE-153, and PBDE-153; PBDE-99 with PBDE-100, PBDE-153, and PBDE-154; and PBDE-153 with PBDE-154. Such correlation may indicate that humans are exposed to PBDEs predominantly via diet, as with PCBs. Higher breast milk PCB levels are associated with urban regions (Vartiainen et al. 1998). Contaminant levels absorbed in food may reflect ambient contamination (Kalantzi et al. 2001). The fact that ¹H-NMR spectroscopy further demonstrates these regional differences suggests that this method may have future potential as a chemical fingerprinting methodology of biologic fluids such as breast milk.

We ascertained current contaminant levels in milk-fat extracts obtained from U.K. breast milk samples obtained from two sources: a milk bank in the southeast and a neonatal unit in the northwest. Breast milk has been hypothesized to be a surrogate tissue to monitor in vivo exposures to breast epithelial cells (Martin et al. 2001). Epidemiologic studies (Stellman et al. 2000) and experimental studies in rodents (Schiestl et al. 1997) suggest a role for OCs and PCBs in cancer causation. Others suggest a lack of association between exposure to OCs or PCBs and breast cancer risk (Gammon et al. 2002; Zheng et al. 2000), whereas individual dioxin-like PCBs may increase risk (Demers et al. 2002). Breast cancer incidence in these areas of the United Kingdom is 68 per 100,000 in the southeast versus 64 per 100,000 in the northwest (Great Britain Department of Health 1998). However, any such associations with breast cancer incidence or, indeed, any other disease is difficult in the context of such a small sample size (n = 54) and in the absence of prospective follow-up.

Lifetime exposures to OCs, PCBs, or PBDEs will vary considerably (Angulo et al. 1999), and the effects of fluctuating levels of endocrine modulators remain to be ascertained (Kalantzi et al. 2004; Yared et al. 2002). Rather than inducing DNA damage themselves, such agents may enhance the susceptibility of target cells to other xenobiotics (Davis et al. 2002). Endocrine disruptors may bind with the aryl hydrocarbon receptor, increasing transcription of CYP1A1 (Behnisch et al. 2001). Such differential regulation by xenoestrogen mixtures could dramatically enhance toxicity (Coumoul et al. 2001) and may also modulate cell cycle events (Dohr and Abel 1997).

Despite the presence of contaminants in U.K. breast milk, it must be emphasized that breast-feeding is protective to the neonate (Dundaroz et al. 2002; Oddy 2001) and also appears to confer a protective effect against breast cancer in the mother (Grover and Martin 2002). The value of this resource is that it potentially allows us to noninvasively analyze ongoing exposures. This work shows for the first time the presence of PBDEs in U.K. breast milk obtained from two different locations and also points to significant regional differences in contaminants in this biologic fluid. Future work is required to ascertain the underlying reasons for these regional differences and also the biologic effects of such exposures.

Correction Top

Values in the tables and in the corresponding text in the original manuscript published online were incorrect and have been corrected here.

Supplemental Material Top

(3.1 MB) PDF.

References Top

1. Abbott DC, Collins GB, Goulding R. 1972. Organochlorine pesticide residues in human fat in the United Kingdom 1969-71. Br Med J 2:553–556. Find this article online
2. Abbott DC, Collins GB, Goulding R, Hoodless RA. 1981. Organochlorine pesticide residues in human fat in the United Kingdom 1976-7. Br Med J 283:1425–1428. Find this article online
3. Abbott DC, Goulding R, Holmes DC, Hoodless RA. 1985. Organochlorine pesticide residues in human fat in the United Kingdom 1982-1983. Hum Toxicol 4:435–445. Find this article online
4. Alaee M, Arias P, Sjodin A, Bergman A.. 2003. An overview of commercially used brominated flame retardants, their applications, their use patterns in different countries/regions and possible modes of release. Environ Int 29:683–689. Find this article online
5. Alcock RE, Sweetman AJ, Prevedouros K, Jones KC. 2003. Understanding levels and trends of BDE-47 in the UK and North America: an assessment of principal reservoirs and source inputs. Environ Int 29:691–698. Find this article online
6. Angulo R, Martinez P, Jodral ML. 1999. PCB congeners transferred by human milk, with an estimate of their daily intake. Food Chem Toxicol 37:1081–1088. Find this article online
7. Behnisch PA, Hosoe K, Sakai S. 2001. Bioanalytical screening methods for dioxins and dioxin-like compounds: a review of bioassay/biomarker technology. Environ Int 27:413–439. Find this article online
8. Branchi I, Capone F, Alleva E, Costa LG. 2003. Polybrominated diphenyl ethers: neurobehavioral effects following developmental exposure. Neurotoxicology 24:449–462. Find this article online
9. Breivik K, Alcock R, Li YF, Bailey RE, Fielder H, Pacyna JM. 2004. Primary sources of selected POPs: regional and global scale emission inventories. Environ Int 128:3–16. Find this article online
10. BSEF. 2001. Major Brominated Flame Retardants Volume Estimates. Total Market Demand by Region in 2001. Brussels:Bromine Science and Environmental Forum. Available: http://www.bsef-site.com/docs/BFR_vols_2​001.doc [accessed 12 April 2004].
11. Collins GB, Holmes DC, Hoodless RA. 1982. Organochlorine pesticide residues in human milk in Great Britain, 1979-1980. Hum Toxicol 1:425–431. Find this article online
12. Coumoul X, Diry M, Robillot C, Barouki R.. 2001. Differential regulation of cytochrome P450 1A1 and 1B1 by a combination of dioxin and pesticides in the breast tumor cell line MCF-7. Cancer Res 61:3942–3948. Find this article online
13. Darnerud PO, Atuma S, Aune M, Cnattingius S, Wernroth M-L, Wicklund-Glynn A. 1998. Polybrominated diphenyl ethers (PBDEs) in breast milk from primiparous women in Uppsala country, Sweden. Organohalogen Compounds 35:411–414. Find this article online
14. Darnerud PO, Eriksen GS, Johannesson T, Larsen PB, Viluksela M. 2001. Polybrominated diphenyl ethers: occurrence, dietary exposure, and toxicology. Environ Health Perspect 109: suppl 149–68. Find this article online
15. Davis C, Bhana S, Shorrocks AJ, Martin FL. 2002. Oestrogens induce G₁ arrest in benzo[a]pyrene-treated MCF-7 breast cells whilst enhancing genotoxicity and clonogenic survival. Mutagenesis 17:431–438. Find this article online
16. Demers A, Ayotte P, Brisson J, Dodin S, Robert J, Dewailly É.. 2002. Plasma concentrations of polychlorinated biphenyls and the risk of breast cancer: a congener-specific analysis. Am J Epidemiol 155:629–635. Find this article online
17. Dohr O, Abel J.. 1997. Transforming growth factor-beta1 coregulates mRNA expression of aryl hydrocarbon receptor and cell-cycle-regulating genes in human cancer cell lines. Biochem Biophys Res Commun 241:86–91. Find this article online
18. Duarte-Davidson R, Jones KC. 1994. Polychlorinated biphenyls (PCBs) in the UK population: estimated intake, exposure and body burden. Sci Total Environ 151:131–152. Find this article online
19. Duarte-Davidson R, Wilson SC, Jones KC. 1994. PCBs and other organochlorines in human tissue samples from the Welsh population: II--milk. Environ Pollut 84:79–87. Find this article online
20. Dundaroz R, Aydin HI, Ulucan H, Baltaci V, Denli M, Gokcay E. 2002. Preliminary study on DNA damage in non breast-fed infants. Pediatr Int 44:127–130. Find this article online
21. Gammon MD, Wolff MS, Neugut AI, Eng SM, Teitelbaum SL, Britton JA, et al. 2002. Environmental toxins and breast cancer on Long Island. II. Organochlorine compound levels in blood. Cancer Epidemiol Biomarkers Prev 11:686–697. Find this article online
22. Great Britain Department of Health. 1998. Nutritional Aspects of the Development of Cancer. Report on Health and Social Subjects No. 48. London:Her Majesty's Stationery Office.
23. Grover PL, Martin FL. 2002. The initiation of breast and prostate cancer. Carcinogenesis 23:1095–1102. Find this article online
24. Hale RC, La Guardia MJ, Harvey E, Mainor TM. 2002. The potential role of fire retardant-treated polyurethane foam as a source of brominated diphenyl ethers to the US environment. Chemosphere 46:729–735. Find this article online
25. Hallgren S, Darnerud PO. 2002. Polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs) and chlorinated paraffins (CPs) in rats-testing interactions and mechanisms for thyroid hormone effects. Toxicology 177:227–243. Find this article online
26. Hardy ML. 2000. . A comparison of the properties of the major commercial PBDPO/PBDE product to those of major PBB and PCB products. Chemosphere 46:717–728. Find this article online
27. Hardy ML. 2002. . The toxicology of the three commercial polybrominated diphenyl oxide (ether) flame retardants. Chemosphere 46:757–777. Find this article online
28. Harris CA, O'Hagan S, Merson GHJ. 1999. Organochlorine pesticide residues in human milk in the United Kingdom 1997-8. Hum Exp Toxicol 18:602–606. Find this article online
29. Hites RA. 2004. Polybrominated diphenyl ethers in the environment and in people: a meta-analysis of concentrations. Environ Sci Technol 38:945–956.; doi: 10.1021/es035082g Find this article online
30. Jakobsson K, Thuresson K, Rylander L, Sjodin A, Hagmar L, Bergman A.. 2002. Exposure to polybrominated diphenyl ethers and tetrabromobisphenol A among computer technicians. Chemosphere 46:709–716. Find this article online
31. Kalantzi OI, Alcock RE, Johnston PA, Santillo D, Stringer RL, Thomas GO, et al. 2001. The global distribution of PCBs and organochlorine pesticides in butter. Environ Sci Technol 35:1013–1018. Find this article online
32. Kalantzi OI, Alcock RE, Martin FL, Thomas GO, Jones KC. 2003. Polybrominated diphenyl ethers (PBDEs) and selected organochlorines in human breast milk samples from the United Kingdom. Organohalogen Compounds 61:9–12. Find this article online
33. Kalantzi OI, Hewitt R, Ford KJ, Cooper L, Alcock RE, Thomas GO, et al. 2004. Low-dose induction of micronuclei by lindane. Carcinogenesis 25:613–622.; doi: 10.1093/carcin/bgh047 Find this article online
34. Klasson-Wehler E, Hovander L, Bergman A.. 1997. New organohalogens in human plasma--identification and quantification. Organohalogen Compounds 33:420–425. Find this article online
35. Laug EP, Kunze FM, Pitchett CS. 1951. Occurrence of DDT in human fat and milk. Arch Ind Hyg 3:245–246. Find this article online
36. Lind Y, Aune M, Atuma S, Becker W, Bjerselius R, Glynn A, et al. 2002. Food intake of the brominated flame retardants PBDEs and HBCD in Sweden. Organohalogen Compounds 58:181–184. Find this article online
37. Lindon JC, Holmes E, Nicholson JK. 2003. So what's the deal with metabonomics? Anal Chem 75:384A–391A. Find this article online
38. Martin FL, Cole KJ, Weaver G, Hong GS, Lam BC, Balaram P, et al. 2001. Genotoxicity of human breast milk from different countries. Mutagenesis 16:401–406. Find this article online
39. McDonald TA. 2002. A perspective on the potential health risks of PBDEs. Chemosphere 46:745–755. Find this article online
40. Meironyté D, Aronsson A, Ekman-Ordeberg G, Bergman A, Norén K.. 2003. Human prenatal and postnatal exposure to polybrominated diphenyl ethers, polychlorinated biphenyls, polychlorobiphenylols, and pentachlorophenol. Environ Health Perspect 111:1235–1241.; doi: 10.1289/ehp.5946 Find this article online
41. Meironyté D, Norén K, Bergman A.. 1999. Analysis of polybrominated diphenyl ethers in Swedish human milk. A time-related trend study, 1972-1997. J Toxicol Environ Health 58:329–341. Find this article online
42. Nicholson JK, Lindon JC, Holmes E. 1999. "Metabonomics": understanding the metabolic responses of living systems to pathophysiological stimuli via multivariate statistical analysis of biological NMR spectroscopic data. Xenobiotica 29:1181–1189. Find this article online
43. Norén K, Meironyté D.. 2000. Certain organochlorine and organobromine contaminants in Swedish human milk in perspective of past 20-30 years. Chemosphere 40:1111–1123. Find this article online
44. Oddy WH. 2001. Breastfeeding protects against illness and infection in infants and children: a review of the evidence. Breastfeed Rev 9:11–18. Find this article online
45. Ohta S, Ishizuka D, Nishimura H, Nakao T, Aozasa O, Shimidzu Y, et al. 2000. Real situation of contamination by polybrominated diphenyl ethers as flame retardant in market fish and mother milk of Japan. Organohalogen Compounds 47:218–221. Find this article online
46. Rahman F, Langford KH, Scrimshaw MD, Lester JN. 2001. Polybrominated diphenyl ether (PBDE) flame retardants. Sci Total Environ 275:1–17. Find this article online
47. Rudel RA, Camann DE, Spengler JD, Korn LR, Brody JG. 2003. Phthalates, alkylphenols, pesticides, polybrominated diphenyl ethers, and other endocrine-disrupting compounds in indoor air and dust. Environ Sci Technol 37:4543–4553.; doi: 10.1021/es0264596 Find this article online
48. Ryan JJ, Patry B. 2000. Determination of brominated diphenyl ethers (BDEs) and levels in Canadian human milks. Organohalogen Compounds 47:57–60. Find this article online
49. Santillo D, Johnston P, Brigden K. 2001. Presence of Brominated Flame Retardants and Organotin Compounds in Dusts Collected from Parliament Buildings in Eight Countries. Greenpeace Research Laboratories Technical Note 03/2001. Exeter, UK:Greenpeace Research Laboratories. Available: http://www.greenpeace.to/html/commreps.h​tm [accessed 12 April 2004].
50. Santillo D, Labunska I, Davidson H, Johnston P, Strutt M, Knowles O. 2003. Consuming Chemicals: Hazardous Chemicals in House Dust as an Indicator of Chemical Exposure in the Home. Greenpeace Research Laboratories Technical Note 01/2003. Exeter, UK:Greenpeace Research Laboratories. Available: http://www.greenpeace.to/html/commreps.h​tm [accessed 12 April 2004].
51. Schecter A, Pavuk M, Päpke O, Ryan JJ, Birnbaum L, Rosen R. 2003. Polybrominated diphenyl ethers (PBDEs) in U.S. mothers' milk. Environ Health Perspect 111:1723–1729.; doi: 10.1289/ehp.6466 Find this article online
52. Schiestl RH, Aubrecht J, Yap WY, Kandikonda S, Sidhom S. 1997. Polychlorinated biphenyls and 2,3,7,8-tetrachlorodibenzo-p-dioxin induce intrachromosomal recombination in vitro and in vivo. Cancer Res 57:4378–4383. Find this article online
53. Sellström U, Söderström G, de Wit C, Tysklind M.. 1998. Photolytic debromination of decabromodiphenyl ether (DeBDE). Organohalogen Compounds 35:447–450. Find this article online
54. She J, Petreas M, Winkler J, Visita P, McKinney M, Kopec D.. 2002. PBDEs in San Francisco Bay Area: measurements in harbor seal blubber and human breast adipose tissue. Chemosphere 46:697–707. Find this article online
55. She J, Winkler J, Visita P, McKinney M, Petreas M.. 2000. Analysis of PBDEs in seal blubber and human breast adipose tissue samples. Organohalogen Compounds 47:53–56. Find this article online
56. Söderström G, Sellström U, de Wit CA, Tysklind M. 2004. Photolytic debromination of decabromodiphenyl ether (BDE 209). Environ Sci Technol 38:127–132.; doi: 10.1021/es034682c Find this article online
57. Solomon GM, Weiss PM. 2002. Chemical contaminants in breast milk: time trends and regional variability. Environ Health Perspect 110:A339–A347. Find this article online
58. Stellman SD, Djordjevic MV, Britton JA, Muscat JE, Citron ML, Kemeny M, et al. 2000. Breast cancer risk in relation to adipose concentrations of organochlorine pesticides and polychlorinated biphenyls in Long Island, New York. Cancer Epidemiol Biomarkers Prev 9:1241–1249. Find this article online
59. Strandman T, Koistinen J, Vartiainen T.. 2000. Polybrominated diphenyl ethers (PBDEs) in placenta and human milk. Organohalogen Compounds 47:61–64. Find this article online
60. Thomas GO, Moss S, Hall AJ, Jones KC. 2003. Absorption of PBDEs and PCBs by grey seals (Halichoerus grypus). Organohalogen Compounds 62:232–235. Find this article online
61. U.K. MAFF (Ministry of Agriculture, Fisheries and Food). 1983. Polychlorinated Biphenyl (PCB) Residues in Food and Human Tissues. The 13th report of the Steering Group of Food Surveillance. London:Her Majesty's Stationery Office.
62. Vartiainen T, Jaakkola JJK, Saarikoski S, Tuomisto J. 1998. Birth weight and sex of children and the correlation to the body burden of PCDDs/PCDFs and PCBs of the mother. Environ Health Perspect 106:61–66. Find this article online
63. Viant MR, Rosenblum ES, Tieerdema RS. 2003. NMR-based metabolomics: a powerful approach for characterizing the effects of environmental stressors on organism health. Environ Sci Technol 37:4982–4989.; doi: 10.1021/es034281x Find this article online
64. WHO. 1993. Environmental Health Criteria 140, Polychlorinated Biphenyls and Terphenyls. Geneva:World Health Organization. Available: http://www.inchem.org/documents/ ehc/ehc/ehc140.htm [accessed 12 April 2004].
65. Wilford BH, Thomas GO, Alcock RE, Jones KC. 2003. Polyurethane foam as a source of PBDEs to the environment. Organohalogen Compounds 61:219–222. Find this article online
66. Yared E, McMillan TJ, Martin FL. 2002. Genotoxic effects of oestrogens in breast cells detected by the micronucleus assay and the comet assay. Mutagenesis 17:345–352. Find this article online
67. Zheng T, Holford TR, Tessari J, Mayne ST, Owens PH, Ward B, et al. 2000. Breast cancer risk associated with congeners of polychlorinated biphenyls. Am J Epidemiol 152:50–58. Find this article online