WHAT CONTRIBUTES TO HUMAN BODY BURDENS OF HALOGENATED FLAME RETARDANTS?
Joo Hui Tay
What contributes to human body burdens of halogenated flame retardants?
An experimental approach
Joo Hui Tay ©Joo Hui Tay, Stockholm University 2018
ISBN print 978-91-7797-177-1 ISBN PDF 978-91-7797-178-8
Printed in Sweden by Universitetsservice US-AB, Stockholm 2018 Distributor: Department of Environmental Science and Analytical Chemistry (ACES) Cover illustration by Siao Hui Tay This thesis is dedicated to my parents.
Contents
Abstract……………………………………………………………………..III Svensk sammanfattning………………………………………….………….V List of papers………………………………………………………...…….VII Author contributions…………………………………………………..….VIII Abbreviations …………………………………………………...………….IX 1 Introduction ...... 1 1.1 Legacy and emerging halogenated flame retardants…………….1 1.2 External exposure………………………………………………..5 1.3 Internal exposure………………………………………………...6 2 Objectives ...... 7 3 Materials & methods ...... 8 3.1 Study design……………………………………………………..8 3.2 Sample extraction, cleanup and instrumental analysis.………….8 3.2.1 Food analysis……………………………………………... 8 3.2.2 Air, dust, hand wipe and serum analysis…………………. 9 3.3 QA/QC…………………………………………………………..9 3.4 Statistical analysis……………………………………………….9 3.5 Human exposure estimation……………………………………10 3.6 Estimating serum HFR concentrations from intake data……….11 4 Results and discussion...... 12 4.1 Dietary exposure………………………………………………. 12 4.2 Inhalation exposure……………………………………………. 13 4.3 Dust ingestion…………………………………………………..14 4.4 Dermal exposure………………………………………………. 15 4.5 Internal exposure……………………………………………….16 4.6 Total daily exposure……………………………………………17 4.7 Relative importance of different exposure pathways…………..19 5 Conclusions and future perspectives ...... 22 6 Acknowledgements…………………………………………………..25 7 References ...... 26
I II Abstract
Flame retardants (FRs) are chemicals added to a broad range of consumer products such as textiles, electrical and electronic equipment, furniture and building material to meet flammability requirements. Most of these chemicals are additives that can continuously leach out from the applied products during usage. FRs are studied because of their abundance in indoor environments and concerns about their impact on human health. The restrictions on many brominated FRs have resulted in a need for their replacement with a variety of emerging halogenated FRs (EHFRs). Humans are exposed to these chemicals mainly through dust and diet ingestion, but there is still insufficient data about the relative importance of other exposure pathways. In this thesis, a Norwegian cohort of 61 adults (age 20-66, 16 males and 45 females) was studied for their exposure to legacy and emerging HFRs. Duplicate diet, stationary air, personal air, settled dust, hand wipe and serum samples were collected from the participants and analyzed for polybrominated diphenyl ethers (PBDEs), hexabromocyclododecanes (HBCDDs) and EHFRs. External exposures via dietary intake, air inhalation, dust ingestion and dermal exposure (in pg/kg body weight/day) were estimated from the measured concentrations. The intake values were then compared to elucidate which of these exposure pathways were most important for the Norwegian cohorts’ exposure to specific HFRs. Dietary intake was the predominant exposure route for most of the PBDE congeners and EHFRs, whereas dust ingestion contributed significantly to the exposure of some less volatile HFRs. Inhalation exposure was negligible for most of the target HFRs except for those with higher volatility, such as tetrabromoethylcyclohexane (DBE- DBCH), 2-bromoallyl 2,4,6-tribromophenyl ether (BATE) and 1,2,3,4,5- pentabromobenzene (PBBz). Dermal exposure seems to be a significant exposure pathway for HBCDDs and tetrabromobisphenol A (TBBPA) but the relevance of hand wipes to represent total dermal exposure remains uncertain. Overall, the median and 95th percentile total intakes for all target HFRs did not exceed the regulatory reference doses (RfD). Estimated serum concentrations were calculated from total intakes from all exposure pathways using a one compartment pharmacokinetic model and these were compared to measured concentrations. The estimated median serum BDE-47 and BDE-153 concentrations were slightly over-estimated by a factor of 5.5 and 4.3, respectively whereas BDE-197 and -209 were under-estimated by 1 to 2 orders of magnitude compared to the measured concentrations. Statistical
III analysis suggested that age, number of electronic equipment at home, certain dietary habits, hand washing and house cleaning frequency were possible contributors to HFR exposure.
Keywords: halogenated flame retardants, air, dust, hand wipes, duplicate diet, serum, human exposure
IV Svensk sammanfattning
Flamskyddsmedel (FR) är kemikalier som inkorporeras i ett brett spektrum av konsumentprodukter, till exempel textilier, elektrisk och elektronisk utrustning, möbler och byggmaterial för att uppfylla gällande brandsäkerhetskrav. De flesta av dessa flamskyddsmedel binds inte kemiskt till materialet utan blandas bara in och kan därför kontinuerligt läcka ut från produkterna under användning. FR studeras bland annat därför att de förekommer i stor mängd i inomhusmiljöer och för att det finns en oro över deras inverkan på människors hälsa. Många bromerade FR har belagts med restriktioner vilket har skapat ett behov av ersättningsmedel för dessa, en rad olika så kallade framväxande halogenerade FR (EHFR). Människor utsätts för dessa kemikalier främst genom damm- och matintag, men det finns fortfarande otillräckliga data om hur viktiga andra exponeringsvägar kan vara. I det här arbetet studerades exponeringen för gamla och nya HFR hos en grupp om 61 vuxna personer (16 män och 45 kvinnor, ålder 20-66 år) i Norge. Från varje deltagare insamlades matprover (duplicate diet, dvs en exakt kopia av allt de åt och drack under ett dygn), luftprover från deras vardagsrum (stationär luft), luftprover från en provtagare de bar nära sina ansikten i ett dygn (personlig luft), dammprover från deras vardagsrum, handavtorkningsprov och blodserumprover. Proverna analyserades med avseende på polybromerade difenyletrar (PBDE), hexabromcyklododekaner (HBCDD) och EHFR och de uppmätta koncentrationerna användes till att beräkna den externa exponeringen för FR via födointag, inhalering av luft, intag av damm och upptag via huden (i pg/ kg kroppsvikt/ dag). Födointaget var den viktigaste exponeringsvägen för de flesta av PBDE-kongenerna och EHFR. För några mindre flyktiga EHFR bidrog dammintaget signifikant till exponeringen. Exponering via inhalering av luft var försumbar för alla HFR utom de mest lättflyktiga, dvs tetrabrometylcyklohexan (DBE-DBCH), 2- bromallyl 2,4,6-tribromfenyleter (BATE) och 1,2,3,4,5-pentabrombensen (PBBz). Exponering via hud verkar vara signifikant för HBCDD och tetrabrombisfenol A (TBBPA), men det är osäkert hur väl handavstrykningsprov representerar den totala dermala exponeringen. Sammantaget så överskred varken medianintaget eller 95e percentilintaget de regulatoriska referensdoserna (RfD) för någon av de HFR som ingick i studien. Uppmätta koncentrationer av HFR i serum jämfördes med de som erhölls genom beräkningar av summan av intag från alla exponeringsvägar
V med hjälp av en farmakokinetisk modell. För BDE-47 och -153 blev de beräknade mediankoncentrationerna i serum något överskattade (med en faktor 5,5 respektive 4,3). För BDE-197 och -209 underskattades mediankoncentrationerna med 10-100 gånger jämfört med de uppmätta koncentrationerna. Med hjälp av statistisk analys kunde faktorer såsom deltagarnas ålder, antal elektroniska apparater hemma, vissa kostvanor, handtvätts- och städningsfrekvens urskiljas som möjliga bidragsgivare till exponeringen för HFR.
Nyckelord: halogenerade flamskyddsmedel, luft, damm, handavstrykning, duplikatdiet, serum, humanexponering
VI List of papers
Paper I
F. Xu*, J.H. Tay*, A. Covaci, J.A. Padilla-Sanchez, E. Papadopoulou, L.S. Haug, H. Neels, U. Sellström and C.A. de Wit. 2017. Assessment of dietary exposure to organohalogen contaminants, legacy and emerging flame retardants in a Norwegian cohort. Environment International 102: 236-243.
* Shared first authorship
Paper II
J.H. Tay, U. Sellström, E. Papadopoulou, J.A. Padilla-Sánchez, L.S. Haug and C.A. de Wit. 2017. Human Exposure to Legacy and Emerging Halogenated Flame Retardants via Inhalation and Dust Ingestion in a Norwegian Cohort. Environmental Science & Technology 51(14): 8176-8184.
Paper III
J.H. Tay, U. Sellström, E. Papadopoulou, J.A. Padilla-Sánchez, L.S. Haug and C.A. de Wit. 2018. Assessment of dermal exposure to halogenated flame retardants: Comparison using direct measurements from hand wipes with an indirect estimation from settled dust concentrations. Environment International 115: 285-294.
Paper IV
J.H. Tay, U. Sellström, E. Papadopoulou, J.A. Padilla-Sánchez, L.S. Haug and C.A. de Wit. Serum concentrations of legacy and emerging halogenated flame retardants in a Norwegian cohort: Relationship to external exposure. (Manuscript)
Paper I & III reproduced with permission from Environmental International, Elsevier. Paper II reproduced with permission from Environmental Science & Technology, American Chemical Society.
VII Author contributions
I, J.H. Tay, made the following contributions to the papers presented in this thesis:
Paper I
Participated in the sampling campaign. Performed all the experimental work, including laboratory work and instrumental analysis together with F. Xu. Instrumental and data analysis of PCBs and OCPs was carried out with the help of A. Covaci. Responsible for data analysis of HFRs and statistical analysis of all compounds. Jointly led the writing of the manuscript with F. Xu.
Paper II
Involved in the sampling campaign. Responsible for all the experimental work, including laboratory work, instrumental, data and statistical analysis. Led the writing of the manuscript.
Paper III
Participated in the sampling campaign. Performed dermal exposure assessment with two different approaches and compared the results. Statistical analysis was carried out with the help of E. Papadopoulou. Led the writing of the manuscript.
Paper IV
Performed all the experimental work, including laboratory work, instrumental and data analysis. Statistical analysis was carried out with the help of E. Papadopoulou. Led the writing of the manuscript.
VIII Abbreviations
ABS Acrylonitrile-butadiene-styrene APS Aminopropyl silica Advanced tools for exposure assessment and bio- A-TEAM monitoring BATE 2-bromoallyl 2,4,6-tribromophenyl ether BDE Brominated diphenyl ether BDE-28 2,4,4'-tribromodiphenyl ether BDE-35 3,3',4-tribromodiphenyl ether BDE-47 2,2',4,4'-tetrabromodiphenyl ether BDE-49 2,2',4,5'-tetrabromodiphenyl ether BDE-66 2,3',4,4'-tetrabromodiphenyl ether BDE-77 3,3',4,4'-tetrabromodiphenyl ether BDE-85 2,2',3,4,4'-pentabromodiphenyl ether BDE-99 2,2',4,4',5-pentabromodiphenyl ether BDE-100 2,2',4,4',6-pentabromodiphenyl ether BDE-153 2,2',4,4',5,5'-hexabromodiphenyl ether BDE-154 2,2',4,4',5,6'-hexabromodiphenyl ether BDE-182 2,2',3,4,4',5,6'-heptabromodiphenyl ether BDE-183 2,2',3,4,4',5',6-heptabromodiphenyl ether BDE-184 2,2',3,4,4',5,6'-heptabromodiphenyl ether BDE-185 2,2',3,4,5,5',6-heptabromodiphenyl ether BDE-191 2,3,3',4,4',5',6-heptabromodiphenyl ether BDE-196 2,2',3,3',4,4',5,6'-octabromodiphenyl ether BDE-197 2,2',3,3',4,4',6,6'-octabromodiphenyl ether BDE-203 2,2',3,4,4',5,5',6-octabromodiphenyl ether BDE-206 2,2',3,3',4,4',5,5',6-nonabromodiphenyl ether BDE-207 2,2',3,3',4,4',5,6,6'-nonabromodiphenyl ether BDE-208 2,2',3,3',4,5,5',6,6'-nonabromodiphenyl ether BDE-209 2,2',3,3',4,4',5,5',6,6'-decabromodiphenyl ether BEH-TEBP Bis(2-ethyl-1-hexyl)tetrabromophthalate BFRs Brominated flame retardants BFs Field blanks BLs Laboratory blanks BMI Body mass index BTBPE 1,2-bis(2,4,6-tribromophenoxy)ethane CN cis-nonachlor
IX DBDPE Decabromodiphenylethane DBE-DBCH Tetrabromoethylcyclohexane DCM Dichloromethane DDC-CO Dechlorane Plus DecaBDE Technical DecaBDE mixture DF Detection frequency d-SPE Dispersive solid phase extraction ECNI Electron chemical negative ionization EHDPHP Ethylhexyl-diphenyl phosphate EHFRs Emerging halogenated flame retardants EH-TBB 2-ethylhexyl-2,3,4,5-tetrabromobenzoate EPS Expanded polystyrene ESI Electrospray ionization EtOAc Ethyl acetate FFQ Food frequency questionnaire FRs Flame retardants GC Gas chromatography GFF Glass fiber filter HBB Hexabromobenzene HBCDD Hexabromocyclododecane HCB Hexachlorobenzene HCDBCO Hexachlorocyclopentenyl-dibromocyclooctane HCH α-, β- and γ-hexachlorocyclohexane HFRs Halogenated flame retardants HIPS High-impact polystyrene IQ Intelligence quotient IRIS Integrated risk information system, USEPA KOA Octanol-air partition coefficient mLODs Method detection limits mLOQs Method quantification limits MLQ Method quantification limits used in paper I MS Mass spectrometer MW Molecular weight NaOH Sodium hydroxide NH2 Aminopropyl NRC National research council OBTMPI Octabromotrimethylphenylindane OCPs Organochlorine pesticides OctaBDE Technical OctaBDE mixture OPEs Organophosphate esters PBBz 1,2,3,4,5-pentabromobenzene PBDEs Polybrominated diphenyl ethers PBEB Pentabromoethylbenzene PBT Pentabromotoluene
X PC Personal computer PCA Principle component analysis PCBs Polychlorinated biphenyls PentaBDE Technical PentaBDE mixture PK Pharmacokinetic p,p’-DDE Dichlorodiphenyldichloroethylene p,p’-DDT Dichlorodiphenyltrichloroethane PUF Polyurethane foam QA/QC Quality assurance/quality control OxC Oxychlordane RfDs Reference doses SD Standard deviation SI Supporting information SPE Solid phase extraction SRM Standard reference material sumEHFR Sum of all detected EHFRs sumHBCDD Sum of α-, β- and γ-HBCDD stereoisomers sumOCP Sum of all detected OCPs sumOPE Sum of all detected OPEs sumPBDE Sum of all detected PBDE congeners sumPCB Sum of all detected PCB congeners SVOCs Semi-volatile organic compounds TBBPA Tetrabromobisphenol A TBCO 1,2,5,6-tetrabromocyclooctane TBCT Tetrabromo-o-chlorotoluene TBE-AE Allyl 2,4,6-tribromophenyl ether TBOEP Tri(butoxyethyl) phosphate TBP-DBPE 2,3-dibromopropyl 2,4,6-tribromophenyl ether TBX 2,3,5,6-tetrabromo-p-xylene TCEP Tris(2-chloroethtyl) phosphate TCPP Trichloropropyl phosphate TDCIPP Tris(1,3-dichloroisopropyl) phosphate TDI Tolerable daily intake TN trans-nonachlor TPHP Triphenyl phosphate BDE-17, 28, 47, 49, 66, 71, 77, 85, 99, 100, 119, 126, Tri-heptaBDE 138, 153, 154 and 183 UK United Kingdom US United States UPLC Ultraperformance liquid chromatography USEPA United States Environmental Protection Agency UV Ultraviolet v/v Volume/volume XPS Extruded polystyrene
XI XII 1 Introduction
1.1 Legacy and emerging halogenated flame retardants
Flame retardants (FRs) are chemicals added to various consumer products in order to slow down and/or inhibit the initial phase of a developing fire. There are three main families of flame-retardant chemicals, namely the inorganic, halogenated, and organophosphorus-based FRs. The focus of this thesis is on the halogenated FRs (HFRs) which include a large group of brominated FRs (BFRs) and one chlorinated FR, Dechlorane Plus (DDC-CO). The most widely produced and used BFRs include tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCDD) and polybrominated diphenyl ethers (PBDEs). The structures of these chemicals are shown in Figure 1.
(a) (b) (c) m + n = 1-10
Figure 1: Molecular structure of (a) PBDE, (b) HBCDD and (c) TBBPA.
PBDEs have been used as three different commercial mixtures: Penta-, Octa- and DecaBDE. The PentaBDE product was primarily used in polyurethane foam (PUF) for mattresses and cushioning, OctaBDE in hard plastics such as computer casings and monitors, while DecaBDE was used in high-impact polystyrene and other materials for electronic and electrical appliances, as well as in textiles1, 2. Commercial HBCDD consists of three diasteroisomers: α-, β-, and γ-HBCDD (approximately 10%, 10% and 80%, respectively) and it is mainly used in polystyrene foams and upholstered textiles3. TBBPA, the BFR produced in the highest volumes covering around 60% of the total BFR market4, is widely used as a reactive FR in printed circuit boards and as an additive FR in acrylonitrile-butadiene-styrene (ABS) plastics. Most of the FRs are additive but some (such as TBBPA) are covalently bound into materials during production. Additive FRs are more likely to leach from the finished product during use, and enter the environment through a number of pathways
1 including the recycling of wastes containing FRs and leaching from disposal sites. However, some of the reactive FR may not have polymerized and may migrate out of the material.
BFRs are known as endocrine disrupters5. The toxicity and human health risks associated with PBDEs, HBCDD and TBBPA have been reviewed1, 2, 6-8. High exposures to PBDEs have been found to be significantly associated with attention deficits, reduced fine motor coordination and cognition in early school age children as well as deficits in neurodevelopment and intelligence quotient (IQ) through prenatal and childhood exposure2, 9, 10. HBCDD exposure has been related to disruption of the reproductive system, developmental and behavioral effects in animals11. As a result of growing evidence of their harmful effects on ecosystems and human health, all three PBDE commercial formulations, as well as HBCDD have been included in the list for elimination under the Stockholm Convention for Persistent Organic Pollutants12. TBBPA is poorly absorbed from the gastrointestinal tract in animal studies and therefore the risk to the general population from TBBPA exposure is considered to be insignificant13. There are currently no global restrictions on the production and usage of TBBPA or its derivatives.
The restriction of high production volume FRs, such as PBDEs and HBCDD, has led to a market shift towards alternative FRs. These replacement substances are known as emerging HFRs (EHFRs). For example, 2- ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB) and bis(2-ethyl-1- hexyl)tetrabromophthalate (BEH-TEBP), the main brominated components of Firemaster 550, are produced by Chemtura as a replacement for PentaBDE in PUF applications14, 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) as a replacement for OctaBDE15, while DDC-CO is an alternative for the DecaBDE formulation16. The names, abbreviations and molecular structures of some important EHFRs, HBCDDs and PBDEs included in this thesis are listed in Table 1. The applications, uses and production volumes of several EHFRs are presented in the supporting information of paper II.
2 Table 1: Abbreviations, full names, CAS numbers, structures and log KOA of some important EHFRs, HBCDDs and PBDEs included in this thesis. Abbrevia- CAS MW log Full name Formula Structure tion number (g/mol) KOA
Allyl 2,4,6-tribromo- 3278-89- TBE-AE C9H7Br3O 370.87 5.59a phenyl ether 5
DBE- tetrabromoethylcyclo- 3322-93- C8H12Br4 427.8 8.01a DBCH hexane 8
2,3,5,6-tetrabromo-p- 23488- TBX C8H6Br4 421.75 8.82a xylene 38-2
2-bromoallyl 2,4,6-tri- 99717- BATE C9H6Br4O 449.8 9.65a bromophenyl ether 56-3
1,2,3,4,5-pentabromo- PBBz 608-90-2 C6HBr5 472.59 9.10c benzene
1,2,5,6-tetrabromocy- 3194-57- TBCO C8H12Br4 427.8 8.01c clooctane 8
tetrabromo-o-chloro- 39569- C7H3Br4 TBCT 442.17 9.08c toluene 21-6 Cl
PBT Pentabromotoluene 87-83-2 C7H3Br5 486.62 9.6a
Pentabromoethylben- PBEB 85-22-3 C8H5Br5 500.65 9.97a zene
2,3-dibromopropyl TBP- 35109- 2,4,6-tribromophenyl C9H7Br5O 530.68 11.1a DBPE 60-5 ether
HBB Hexabromobenzene 87-82-1 C6Br6 551.49 9.13a
3 octabromotrime- 1084889 C18H16 OBTMPI 867.52 17.8b thylphenylindane -51-9 Br8
Decabromodiphe- 84852- C14H4 DBDPE 971.2 19.2a nylethane 53-9 Br10
1,2-bis(2,4,6-tribromo- 37853- C14H8Br6 BTBPE 687.6 15.7a phenoxy)ethane 59-1 O2
2-ethylhexyl-2,3,4,5- 183658- C15H18 EH-TBB 549.93 12.3a tetrabromobenzoate 27-7 Br4O2
bis(2-ethyl-1- BEH- 26040- C24H18 hexyl)tetra-bromoph- 706.1 16.9b TEBP 51-7 Br4O4 thalate
13560- C18H12 DDC-CO Dechlorane Plus 653.7 14.8a 89-9 Cl12
3194-55- hexabromocyclodo- 6 C12H18 HBCDD 641.7 10.5a decane 25637- Br6 99-4
3,3'5,5'-tetrabrombi- C15H12 TBBPA 79-94-7 543.9 18.2a sphenol A Br4O2
2,2',4,4'-tetrabromodi- 5436-43- C12H6Br4 BDE-47 485.79 10.53d phenyl ether 1 O
2,2',4,4',5-pentabromo- 60348- C12H5Br5 BDE-99 564.69 11.31d diphenyl ether 60-9 O
2,2',4,4',5,5'-hexabro- 68631- C12H4Br6 BDE-153 643.58 12.1d modiphenyl ether 49-2 O
2,2',3,3',4,4',5,5',6,6'- 1163-19- BDE-209 decabromodiphenyl C12Br10O 959.17 18.4a 5 ether
a&b: EPI SUITE estimation17, 18; c: KOAWIN estimation19; d: Experimental data20
4 1.2 External exposure
Various sources and pathways are relevant for adult exposure to HFRs, such as food, ingestion of dust, inhalation of contaminated air as well as dermal absorption (Figure 2). Occupational exposure, in general, is limited to high exposure groups such as electronic dismantlers21, 22, thermal cutting workers23 and HFR manufacturing workers24. Being lipophilic and persistent organic compounds, HFRs accumulate preferentially in the lipid-rich tissues of organisms. Relatively high concentrations of HFRs have been found in fatty food items such as fish, meat, eggs and dairy products25-27, presenting an important exposure pathway to humans.
Body burden
Metabolism Bioavailability
Ingesstion Inhalation Dermal absorption
Consumer Diet Dust Indoor air Outdoor air Dust products
Figure 2: Overview of the human exposure pathways to HFRs. Figure adapted from Abdallah et al.28. Consumer products cover a wide range of products e.g. electronic equipment, textiles and furniture.
The significance of indoor exposures arises from the fact that most people spend a very high proportion of their total time indoors29. A considerable amount of literature has been published on contamination of indoor dust with these chemicals14, 30-33. These studies suggest that dust ingestion may constitute a significant part of the exposure to HFRs. The presence of HFRs in dust has been attributed to physical weathering and abrasion of HFR-treated consumer products34, 35, as well as leaching of HFRs from the application products36, 37, although the mechanism of transfer remains poorly understood. Indoor air concentrations of HFRs are in general higher than outdoor levels due to the presence of indoor sources (consumer products and building
5 materials), smaller space and weaker air circulation38, 39. Overall, inhalation has been considered as a minor source of exposure.
The importance of dermal absorption as a potential significant route of exposure for HFRs has not received sufficient attention until recently, but stronger correlations between PBDEs in hand wipes and serum (rather than dust) have been reported40, 41. Several dermal exposure assessments have focussed only on the dust contact transfer33, 42, but gaseous contaminants and direct contact with HFR-treated commercial products may also contribute significantly to the level of HFRs on the skin surface43, 44. Furthermore, fabrics such as clothing can act as a reservoir for semi-volatile organic compounds (SVOCs), leading to increased dermal uptake of these chemicals45, 46. Overall, dermal absorption of HFRs has not yet been completely elucidated. A few studies have produced estimates of HFR dermal absorption for children and adults through the skin wipe approach47, 48, but more data are needed for better understanding the significance of this pathway to overall human exposure.
1.3 Internal exposure
Similar to their bioaccumulation in the environment, lipophilic HFRs tend to accumulate in the lipids in the human body. Many studies have been performed to determine lipid-adjusted concentrations of HFRs in breast milk, blood serum and adipose tissue worldwide as an aggregated measurement of internal dose from all exposure sources and pathways. Geographical differences in the patterns and concentrations of PBDEs in biomonitoring samples have been observed49, proving that humans are subjected to widespread HFR exposure depending on regional fire regulations and subsequent FR usage patterns. Moreover, the presence of HFRs in placenta and cord blood samples confirms prenatal exposure50-52.
Only a few comprehensive studies have been carried out to investigate the associations between external exposure to HFRs from multiple media and internal concentrations in adults. In Germany, dietary exposure was reported as the predominant intake pathway for tri-heptaBDEs although correlations between dietary intake and plasma levels were not found53. The authors also did not find any significant association between air and dust concentrations with body burden. In contrast, Bramwell et al.54 reported significant correlations between levels of tri-heptaBDE in duplicate diet, indoor dust and serum, whereas BDE-209 in serum was found to be associated with workplace dust. To the best of our knowledge, no similar studies exist for EHFRs in adults or children.
6 2 Objectives
The overall aim of this thesis was to perform a comprehensive evaluation of different pathways of human exposure to HFRs. This was done by quantifying the external exposures from dietary intake, dust ingestion, air inhalation and dermal uptake determined from hand wipe samples (papers I-III) and the internal exposure from serum samples (paper IV) for a Norwegian cohort.
Paper I aimed at quantifying the levels of HFRs, organophosphate esters (OPEs), organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in 24-h duplicate diet samples from the studied cohort. The study also aimed to estimate daily dietary intakes for the individuals and to identify which food items might be contributing to dietary exposure to these contaminants.
Paper II aimed to estimate the exposure to HFRs through dust ingestion and air inhalation by quantifying indoor dust and air HFR concentrations. Another objective of this study was to evaluate the comparability of indoor stationary air from the home to personal air by performing simultaneous sampling of both air samples for a subsample of the participants. Possible indoor sources of exposure were investigated by correlating HFR concentrations in air and dust with the number of electronic equipment and/or type of materials in the households.
Paper III aimed to compare the performance of two different approaches for dermal exposure assessment, the direct and indirect methods via the measurement of hand wipe concentrations and uptake through dust contact, respectively. The associations between hand wipe measurements, living room dust concentrations, number of electronic equipment and personal behavior were investigated.
Paper IV aimed to assess the internal exposure via the measurement of serum HFR concentrations. The values were then compared to the estimated concentrations calculated from external intakes using a one compartment pharmacokinetic (PK) model.
7 3 Materials & methods
3.1 Study design
This study was conducted as part of the A-TEAM (Advanced Tools for Exposure Assessment and Biomonitoring) project, which aimed to enhance knowledge of external and internal human exposure to selected consumer chemicals (OPEs, perfluoroalkyl substances, phthalate esters and HFRs), based upon detailed study of a single, well-characterized human cohort. The study population (the A-TEAM cohort) consisted of 61 adults from Oslo, Norway (age 20-66, 16 males and 45 females). Sample collection was conducted during winter of 2013-2014, when the proportion of time spent indoors is at a maximum and ventilation is at its minimum. The sampling campaign was approved by the Regional Committees for Medical and Health Research Ethics in Norway (Case number 2013/1269). Approval for the chemical analyses carried out in Sweden was given by the Regional Ethics Committee in Stockholm, Sweden (Case number 2014/624-31/1). Details about dietary habits, indoor environment and other lifestyle characteristics of the participants were collected through questionnaires55. Air, dust, hand wipe and duplicate diet samples were collected from each participant and used to characterize external exposure pathways. Blood serum samples were collected for internal exposure evaluation. The sampling methods for each sample matrix are described in papers I (duplicate diet), II (stationary air, personal air and settled dust), III (hand wipes) and IV (serum).
3.2 Sample extraction, cleanup and instrumental analysis
3.2.1 Food analysis
Food analysis was performed at the Toxicological Center, University of Antwerp according to Xu et al.56 with some modifications. In short, freeze- dried food samples were extracted by ultrasonication, syringe filtration and followed by a multi-stage clean-up procedure involving Florisil, aminopropyl silica (APS), acid silica cartridges and dispersive solid phase extraction (d- SPE). PBDEs and EHFRs were analyzed with an Agilent 6890 Gas Chromatograph (GC) coupled to an Agilent 5973 Mass Spectrometer (MS) operated in the electron negative ionization (ECNI) mode. Detailed
8 information on chemical analysis of duplicate food samples can be found in paper I and its supporting information (SI).
3.2.2 Air, dust, hand wipe and serum analysis
Indoor air, personal air, settled dust and hand wipe samples were extracted by ultrasonication. Extraction of serum samples was performed according to Hovander et al.57 with some modifications. Air extracts (both indoor air and personal air) were fractionated according to Ionas and Covaci58, while the extracts of settled dust, hand wipe and serum samples were fractionated according to Sahlström et al.59 with some modifications. All fractions were further cleaned-up before instrumental analysis. PBDEs and EHFRs were analyzed with GC-ECNI-MS, while HBCDDs and TBBPA were analyzed using ultra performance liquid chromatography (UPLC) coupled to tandem- quadrupole MS using electrospray ionization (ESI) in negative mode, on the basis of a previously described method59. Detailed information about the fractionation scheme, clean-up and instrumental method used for each sample matrix can be found in papers II-IV and their respective SI.
3.3 Quality assurance/quality control (QA/QC)
All samples were analyzed in batches containing up to 20 samples. Each batch also included 3-4 field blanks (BFs) and/or 1-2 laboratory blanks (BLs), together with 1-2 QC samples (standard reference material (SRM) or in-house reference material), when available. At the University of Antwerp, a spiked food sample prepared in-house was used as reference material for food analyses. SRM 2585 (organic contaminants in house dust) from the National Institute of Standards and Technology (NIST; Gaithersburg, MD) was used as the QC sample for the dust analyses. For serum samples, SRM 1958 (organic contaminants in fortified human serum, NIST) was used. Blank correlation was performed by subtracting the mean amount detected in the BFs from the same batch. Method detection limits (mLODs) and method quantification limits (mLOQs) for analytes present in the blanks were set to the mean blank values plus 3 and 5 times the standard deviation of the blanks, respectively. For analytes not present in the blanks, mLOQ was defined as a signal/noise ratio of 10 and mLOD as one third of mLOQ.
3.4 Statistical analysis
Statistical tests were performed using IBM SPSS statistics 24 (Chicago, IL) and only when a compound was detected in at least 40% of the samples. For duplicate diet samples (paper I), non-detects and concentrations below the method limits of quantification (MLQ) were substituted with zero according to the general practice of censoring limits and reporting conventions for non-
9 detects at the Toxicological Center, University of Antwerp. For settled dust, stationary air, personal air, hand wipes and serum samples (papers II-IV), the non-detects and concentrations below the mLOD were replaced with the mLOD divided by the square root of 2. Concentrations above the mLOD but below the mLOQ were replaced with the mLOQ divided by the square root of 2. Dietary intake data from paper I were recalculated using methods for handling below-detection values as in papers II-IV prior to performing total daily exposure assessment and prediction of serum concentrations from intake data (paper IV). The distribution of HFR concentrations and the calculated exposures were highly skewed. Therefore, Mann-Whitney rank sum tests were used for comparison of the HFR concentrations in the study group, Spearman’s rank test for investigation of bivariate correlations in general, and Kruskal-Wallis test for comparing more than two subgroups of the study population. The significance was set at α = 0.05 in all the statistical analyses. In addition to the analysis of individual compound correlations, principal component analysis (PCA) was used in an attempt to elucidate underlying HFR patterns by using log-transformed data for settled dust and hand wipes. The relationship between concentrations of HFRs in serum with daily consumption of specific food categories (g/day), demographic information and household factors, as well as between masses of HFRs in hand wipes and household factors, were assessed using Spearman’s rank correlation test. Factors correlated with serum concentrations/hand wipe masses (p < 0.2) in the bivariate analysis were further considered for inclusion in multivariate linear regression models of log-transformed serum concentrations/hand wipe masses. Factors that were found to be significant (p < 0.05), after removing the highest p-values following a backward selection procedure, were retained in the final multivariable linear regression models.
3.5 Human exposure estimation
Each participant’s exposure to HFRs (pg/kg bw/d) from external media was estimated as below in order to estimate the relative importance of each exposure pathway. Detailed methodology and assumptions are presented in papers I-III.
ൈூ ൈிൈாி (ൌ (1 ݁ݎݑݏݕ݁ݔݎݐܽ݁݅ܦ ௐ
ൈூோൈிൈாൈாி (ൌ ೌ (2 ݁ݎݑݏݐ݅݊݁ݔ݈݄ܽܽ݊ܫ ௐ
ൈிൈூൈி (ൌ (3 ݁ݎݑݏݐ݅݊݁ݔݏݐ݅݊݃݁ݏݑܦ ௐ
10 ൈௌൈிൈாൈாி (ݓ݅݁ ൌ ೢ (4݄݀݊ܽ݃݊݅ݏݑ݁ݎݑݏݔ݈݁ܽ݉ݎ݁ܦ ௐ
ൈிൈௌൈൈிൈாൈாி (ݐܿ݊ݐܽܿݐ ൌ (5ݏݒ݅ܽ݀ݑ݁ݎݑݏݔ݈݁ܽ݉ݎ݁ܦ ௐ
݄݈݅݊ܽܽݐ݅݊ ݁ݎݑݏݕ݁ݔݎൌ ݀݅݁ݐܽ ݁ݎݑݏݐ݈݈ܽ݀ܽ݅ݕ݁ݔܶ
(6) ݁ݎݑݏݔ݈݁ܽ݉ݎ݁݀ ݐ݅݊ ݏݐ݅݊݃݁ݏݑ݀
Where,
Cf = concentration of HFRs in duplicate food samples (pg/g fresh weight food) 3 Ca = concentration of HFRs in air (pg/m ) Cd = concentration of HFRs in dust (pg/g) 2 Chw = surface area normalized mass of HFRs in hand wipes (pg/cm ) If = amount of food consumed within the last 24h (g/d) IR = inhalation rate (m3/d) DI = mean daily dust intake (mg/d) SA = hand skin surface area exposed per event (cm2/event) CF = conversion factor (1x10-3 g/mg) DA = amount of dust adhered to the skin (mg dust/cm2) AF= absorption fraction (unitless) ED = exposure duration in one day (t/24) EF = exposure frequency (event/day) BW = body weight (kg)
Exposure factors (i.e. inhalation rates, amounts of dust ingested, hand surface area estimation, amount of dust adhered to skin, absorption fractions) necessary for assessing exposure were taken from various sources60-68.
3.6 Estimating serum HFR concentrations from intake data
A simple, one-compartment, first order pharmacokinetic (PK) model by Lorber69 was used to estimate serum concentrations of HFRs from intake data. The values were then compared to biomonitoring data (measured serum concentrations). Detailed equations and assumptions are presented in paper IV.
11 4 Results and discussion
4.1 Dietary exposure
Concentrations of HFRs, OPEs and other organohalogen contaminants were determined in duplicate diet samples from the A-TEAM cohort (paper I) but several HFRs (DBE-DBCH, BATE, OBTMPI, HBCDDs, TBBPA, BDE-35, -49, -99, -203, -207 and -208) were not included in our analysis. Results revealed that BDE-209 was the predominant PBDE congener detected in duplicate diet samples with a median concentration of 0.045 ng/g ww, followed by BDE-47 (0.010 ng/g ww). BEH-TEBP was detected in 44% of the samples with concentrations up to 0.14 ng/g ww. Other HFRs were mostly below detection limits. The estimated median dietary intake of sumPBDE (sum of BDE-28, -47, -66, -85, -100, -153, -154, -183 and -209) was 1.3 ng/kg bw/d, which is in agreement with those reported in several European countries53, 70-72. Levels of BDE-47 in food were highly correlated to fish consumption, while BEH-TEBP levels were related to the consumption of meat and fruits. The presence of BDE-209 in food samples might be attributed to contamination from cooking utensils during the cooking process73 and/or dust particles adhering to the food. Dietary exposure to HFRs was considered minor in relation to other organohalogen contaminants, with estimated exposure values for sumHFR (sum of PBDEs and EHFRs) that were 1-2 orders of magnitude lower than those estimated for sumOPE (tri(butoxyethyl) phosphate (TBOEP), ethylhexyl-diphenyl phosphate (EHDPHP), tris(2- chloroethtyl) phosphate (TCEP), triphenyl phosphate (TPHP), tris(1,3- dichloroisopropyl) phosphate (TDCIPP) and trichloropropyl phosphate (TCPP)); sumPCB (sum of PCB-99, -101, -105, -118, -138, -153, -156, -170, -171, -177, -180, -183, -187, -194, -206 and -209) and sumOCP (oxychlordane (OxC), trans- and cis-nonachlor (TN and CN), hexachlorobenzene (HCB), α-, β- and γ-hexachlorocyclohexane (HCH), dichlorodiphenyldichloroethylene (p,p’-DDE) and dichlorodiphenyltrichloroethane (p,p’-DDT)) (Figure 3). However, due to the large amount of food intake per day, even a trace amount of contamination could make a substantial contribution to total daily intake.
12 100
80
60
40 ng/kg bw/day 20
0 sumPCB sumOCP sumPBDE sumEHFR sumOPE
Figure 3: Estimated median daily dietary exposure (ng/kg bw/d) to different organohanogen contaminants.
4.2 Inhalation exposure
In paper II, both stationary air and personal air sampling techniques were used to estimate human inhalation exposure to HFRs. EH-TBB was the most abundant HFR detected in stationary air samples (detection frequency, DF = 100%, median = 150 pg/m3), but it was detected in only 15% of the personal air samples. Tetrabromoethylcyclohexane (DBE-DBCH) and BDE-209 were measured frequently (DF >54%) in both samples but the levels were significantly higher in personal air (Figure 4). Higher levels of BDE-209 in personal air samples could be explained by the “personal cloud effect”74 as well as the presence of microparticles (fragments) of the HFR-treated consumer products in the air and dust. Similar results have been seen in a previous study75. DBE-DBCH is more volatile and therefore probably not as particle-associated. The exposure from the work environment, outdoor activities and time spent in transportation might play a more important role in individual’s inhalation exposure to DBE-DBCH. The estimated inhalation exposures for individual HFRs in our study for stationary air (0.47-26 pg/kg bw/d, excluding EH-TBB) were generally lower than those reported in the UK76 and a previous Norwegian study33 (SI of paper II). Our estimation of inhalation exposure using stationary air data may be an underestimate since our participants also spent time at their work environment and in their bedroom rather than only the living room. BDE-49 concentrations in indoor air were positively correlated with the total area of the home, number of desktops and personal computer (PC) screens, while 2-bromoallyl 2,4,6-
13 tribromophenyl ether (BATE) and TBBPA concentrations were positively related to the area of the living room.
Figure 4: Box-whisker plots of HFR concentration (pg/m3) detected in both personal air and stationary air samples. Y-axis is on a logarithmic scale.
4.3 Dust ingestion
Settled dust samples were predominated by less volatile HFRs such as BDE- 209, BEH-TEBP, HBCDDs, decabromodiphenylethane (DBDPE) and TBBPA (medians of 23-940 ng/g) (paper II). The concentrations of other more volatile HFRs (such as DBE-DBCH, EH-TBB, BDE-28, -35, -47, -49) were lower (medians of 0.50 to 25 ng/g). The results are consistent with studies that showed the HFRs with lower octanol-air partition coefficients 30, 33, 38 (KOA) tend to be less associated with dust particles . Median exposure to single BDE congeners (0.074-6.6 pg/kg bw/d, excluding BDE-209) for the Norwegian cohort was comparable to exposures found in studies from Germany and the UK but lower than that from a previous Norwegian study (SI of paper II). The calculated median exposure to BDE-209 (14 pg/kg bw/d) was lower than reported in the literature by several orders of magnitude due to our use of absorption factors in the estimation of dust ingestion exposure. However, our result was similar to that reported in Germany, where they used the same absorption factor approach (16 pg/kg bw/d) (SI of paper II). Concentrations of HFRs in dust were mostly associated with the number of electronic equipment (such as televisions, desktops, laptops etc) in the home. Principle component analysis (PCA) revealed two distinct groupings of HFRs according to the technical formulations of Penta- and DecaBDE, as well as a third group containing BDE-49 and HBCDDs (Figure 5).
14 Figure 5: (a) Two-component plot in rotated space without component 2, (b) Two-component plot in rotated space without component 1, extracted by factor analysis from data obtained from settled dust analysis.
4.4 Dermal exposure
In paper III, dermal exposure to HFRs was estimated from hand wipe measurements (direct approach) and compared with those estimated indirectly from dust contact (data from paper II). TBBPA was the most predominant HFR in hand wipe samples, contributing about 77 % to the total mass of HFRs (median = 570 ng), followed by α-, β-, and γ-HBCDDs (medians of 78, 33 and 53 ng, respectively) and BEH-TEBP (median = 7.7 ng). Levels of TBBPA in hand wipes were negatively associated with hand washing frequency, while lower DBE-DBCH and BDE-28 masses were related to higher house cleaning frequency. Other HFRs were mostly positively correlated with number of electronic appliances, size of home and number of cohabitants (SI of paper III). Positive and significant correlations were found between settled dust concentrations and hand wipe masses for many HFRs. PCA of the HFRs measured in hand wipes (SI of paper III) revealed groupings and patterns that were similar to the pattern in dust (Figure 5), suggesting their similar sources.
Daily dermal exposure for sumEHFR was estimated to be the highest, followed by sumHBCDD and sumPBDE with the hand wipe approach. However, dermal exposure via dust contact was estimated to be dominated by sumPBDE followed by sumEHFR and sumHBCDD. Reasonable agreement was found between the medians of direct (hand wipes) and indirect dermal exposure estimates (<10-fold deviation) for many of the individual EHFRs and PBDEs but 10 to 1000-times higher exposures were observed for TBBPA
15 and HBCDDs with the hand wipe approach (paper III). The inconsistency between the two types of exposure estimates for HFRs might be related to heterogeneous distribution of HFRs in dust depending on their usages and migration pathways (such as BDE-209 and HBCDDs)34, 77, as well as the impact direct skin contact with HFR-treated products has, which was not taken into account in the indirect approach. Due to the application of the fixed absorption fraction approach used in the present study, the dermal exposure for the various HFRs might be underestimated by at least 3- to 10-times. However, this could still be underestimated since the sampling may be missing already absorbed chemicals.
4.5 Internal exposure
BDE-209 was the most abundant HFR in serum samples with a median concentration of 1.5 ng/g lipid, followed by BDE-153, -197 and -47 (median of 1.0, 0.75 and 0.23 ng/g lipid, respectively). The median concentrations of individual BDE congeners detected in serum samples in this study were within the ranges found in the literature (paper IV). Positive and significant associations between BDE-47 and -153 in matched dust, hand wipe and serum samples were observed, indicating the dust from the living rooms could be a primary source of these BDE congeners. No correlation was found between the levels of PBDEs in indoor air and serum samples, suggesting inhalation as a minor pathway of exposure to these chemicals. On the other hand, BDE-153 levels in serum were related to participant age, indicating its persistency in the human body78.
Serum concentrations were estimated from external exposure using a simple, one-compartment, first order PK model (data from papers I-III) and compared to the measured serum data in paper IV (Figure 6). For BDE-47, - 153, -197 and -209, measured serum concentrations differed from estimated data by a factor of 0.18, 0.23, 84 and 13, respectively (observed to estimated ratio). As we did not detect BDE-153 in duplicate diet samples, the dietary intake was estimated solely from the mLOD. BDE-197 was not included in our food analysis, therefore a median dietary BDE-197 intake of 2.7 ng/day as reported by Sahlström et al.79 for a Swedish cohort of mothers was used in our calculation. The median serum concentration of BDE-197, however, was still underestimated by 2 orders of magnitude. These substantial differences suggest that dietary habits for our participants might be different from those of the Swedish mothers, and/or that exposure from other microenvironments
16 such as at work could play an important role in explaining the concentrations measured in serum.
Figure 6: Box-Whisker plots of concentration in serum (ng/g lipid) based on biomonitoring data (blue) and external exposure (red). Boxes represent 25th, 50th and 75th percentiles. A □ represent the mean. Whiskers indicate maximum and minimum values. All data sets are significantly different in a Mann- Whitney U test (p <0.05).
4.6 Total daily exposure
The estimated total daily exposure to various HFRs through dietary intake, inhalation, dust ingestion and dermal uptake compared to reference doses (RfDs) is presented in Table 2. Results showed that even when assuming a high-end scenario using 95th percentile concentrations, the HFR daily exposures are still some orders of magnitude below the RfDs. It is currently not possible to estimate the exposure risk for several EHFRs since no tolerable daily intake (TDI) or RfD values are available.
17 Table 2: Estimated daily exposure (pg/kg bw/d) to HFRs for adults in the Norwegian cohort compared to reference doses, where available. Total daily exposure (pg/kg bw/d) RfD 5th percentile median 95th percentile TBP-AE 0.16 0.18 1.4 α-DBE-DBCH 42 57 85 β-DBE-DBCH 10 14 28 BATE 1.3 1.8 5.4 PBBz 2.6 3.2 9.4 TBCT 2.5 3.4 4.3 PBT 6.6 9.2 18 PBEB 4.0 5.5 7.2 TBP-DBPE 13 18 23 HBB 0.17 0.50 5.6 EH-TBB 2.0x107 a 630 1200 1700 BTBPE 2.4x108 a 83 180 260 BEH-TEBP 2.0x107 a 170 290 1100 syn-DDC-CO 130 260 430 anti-DDC-CO 230 460 890 OBTMPI 0.19 0.27 1.1 DBDPE 3.3x108 a 3300 6500 9200 TBBPA 6.0x108 b 160 2700 17 000 α-HBCDD 180 560 3200 β-HBCDD 170 290 2000 γ-HBCDD 130 310 7500 BDE-28 66 130 220 BDE-35 0.38 0.70 1.8 BDE-47 1.0x105 c 77 250 1400 BDE-49 0.37 1.2 9.3 BDE-66 99 200 330 BDE-77 0.073 0.090 0.23 BDE-85 160 330 460 BDE-99 1.0x105 c 160 170 240 BDE-100 130 260 410 BDE-153 2.0x105 c 99 200 280 BDE-154 82 160 230 BDE-182 0.082 0.098 0.27 BDE-183 110 200 280 BDE-184 0.14 0.16 0.39 BDE-191 0.13 0.16 0.41 BDE-196 0.69 1.1 4.5 BDE-197 0.34 0.72 4.6 BDE-203 2.6 3.1 16 BDE-206 0.19 1.3 37 BDE-207 0.94 2.2 40 BDE-208 0.51 1.2 14 BDE-209 7.0x106 c 570 1300 10 000 sumPBDE 1800 3600 12 000 sumHBCDD 2.0x108 d 520 1200 13 000 sumEHFR 6800 12 000 26 000 a: RfD values used by Ali et al. 80 b: RfD value suggested by Wikoff et al. 81 c: RfD values by IRIS, USEPA 82-85 d: RfD value by NRC 86 The sums of PBDE, HBCDD and EHFR were calculated from individual results.
18 4.7 Relative importance of different exposure pathways
The relative importance of different exposure pathways (inhalation, dust ingestion, dietary intake and dermal uptake) to the total daily exposure of various HFRs for the A-TEAM cohort is shown in Figure 7 and Figure 8. Inhalation exposure was assessed using stationary air data, whereas dermal exposure was estimated using hand wipe samples. For TBP-AE, PBBz, DDC- CO, BDE-182, -184 and -191, dermal exposure via dust contact was used since no hand wipe results were available. As our duplicate diet samples were not analyzed for several HFRs including TBBPA and HBCDDs, the potential dietary exposure to these chemicals remains unknown. Median daily dietary HBCDD (sum of α-, β- and γ-isomers, 330 pg/kg bw/d) and BDE-99 (90 pg/kg bw/d) intake from a previous Norwegian study87, as well as dietary intake data for DBE-DBCH, BATE, PBBz, TBCT, PBT, PBEB, TBP-DBPE, BDE-197, -206, -207 and -208 as estimated by Sahlström et al.79 for a Swedish mother’s cohort were used for our calculations. Comparing the different exposure pathways suggested that dietary intake was the predominant route of exposure (up to nearly 100% of the total daily exposure) for most of the target PBDEs and several EHFRs (Figure 7). Inhalation was relatively important for more volatile HFRs, contributing to approximately 20-35% of the intake for PBBz, β-DBE-DBCH, BATE and PBT, but was negligible for other HFRs. Dust ingestion was, on the other hand, more significant for less volatile HFRs, where its contribution was up to 35% for BDE-207 and -208. The contribution of dermal uptake to total intake was relatively small for most of the HFRs (<10%) except for PBT and HBCDDs, where it contributed to 40-75% of the total daily exposure. However, our dermal exposure estimation might have underestimated the real exposure due to the application of a fixed absorption factor approach as well as the uncertainty regarding how hand wipe samples reflect initial dose and intake. Overall, dermal exposure is still poorly understood and therefore has the largest uncertainty compared to other estimations.
19 α-DBE-DBCH β-DBE-DBCH BATE PBBz TBCT PBT PBEB TBP-DBPE EH-TBB BTBPE BEH-TEBP syn-DDC-CO anti-DDC-CO DBDPE α-HBCDD β-HBCDD γ-HBCDD BDE-28 BDE-47 BDE-66 BDE-85 BDE-99 BDE-100 BDE-153 BDE-154 BDE-183 BDE-197 BDE-206 BDE-207 BDE-208 BDE-209
0% 20% 40% 60% 80% 100%
Dermal exposure Inhalation Dust ingestion Dietary intake
Figure 7: The relative importance of different exposure pathways for PBDEs, HBCDDs and EHFRs, comparing the medians of each intake route.
20 Dietary intake data for TBP-AE, HBB, OBTMPI, TBBPA, BDE-35, -49, -99, -77, -85, -182, -184, -191 and -196 were missing and therefore only inhalation, dust ingestion and dermal uptake pathways were investigated for these compounds (Figure 8). Both inhalation and dust ingestion contributed to about 45% of BDE-35, -49, -77, -182, -184 and -191. Dermal uptake was relatively minor for this group of chemicals, except for BDE-196 and TBBPA where the dermal uptake contributed to approximately 55% and 99% of total intake, respectively.
TBP-AE
HBB
OBTMPI
TBBPA
BDE-35
BDE-49
BDE-77
BDE-182
BDE-184
BDE-191
BDE-196
BDE-203
0% 20% 40% 60% 80% 100%
Dermal exposure Inhalation Dust ingestion
Figure 8: The relative importance of different exposure pathways for TBP- AE, HBB, OBTMPI, TBBPA, BDE-35, -49, -99, -77, -182, -184, -191 and - 196, comparing the medians of each intake route.
21 5 Conclusions and future perspectives
This comprehensive study of individual human exposure to HFRs via different environmental media contributes to deeper understanding of HFR exposure in a Norwegian cohort. Paper I showed that HFRs were not the main contaminants in food but the large amount of daily food consumption can still contribute substantially to the total daily intake of HFRs. Human exposure to various HFRs via inhalation and dust ingestion was assessed in paper II. Significant differences in concentrations and distribution patterns of HFRs were observed in stationary air compared to the corresponding personal air samples. However, the differences did not have a significant impact on the total daily intake of HFRs from air inhalation. Due to the slow turnover of HFR-treated consumer products in indoor environments, exposure to PBDEs through dust ingestion might remain important for many years. In paper III, dermal exposure through direct and indirect approaches was assessed and compared. Both methods gave comparable dermal exposure estimates for many individual HFRs but these values could still be underestimates as a result of several study limitations and uncertainties. Links between external and internal concentrations for many HFRs could not be established in paper IV due to low detection frequencies in serum samples as well as missing intake information. Overall, our results indicate that the exposure of this Norwegian cohort remains low compared to the available reference doses.
The main strength of our study design is the multi-pathway exposure analysis including multiple methods for assessment of exposure from each exposure pathway. However, there are still several aspects that need to be improved. Firstly, the study population was mainly recruited from the NIPH and thus not representative of the general Norwegian population. Statistical power in comparisons between genders is limited because our participants were predominantly female. For future studies, similar comprehensive studies for high risk groups such as children of different age groups will be valuable, since they are likely to be exposed to higher doses and have different uptake patterns than adults.
Secondly, the samples collected within the 24h period provided a snapshot of intake and are not completely representative of participants’ long term exposure. This may have limited our ability to detect relationships between external and internal exposure since most of our target HFRs are persistent, and hence their levels in serum reflect long-term exposure whereas our
22 external exposure media represents short-term exposure within a 24h period. A long term study, i.e. multiple 24h measurements at different time periods, could help to understand the seasonal variation of external exposure. Our duplicate diet method has the advantage of providing precise estimates of chemical concentrations in food including from food cooking, storing and packaging, but it can be a burden to the participant and expensive to be performed in a larger scale. The dilution effect of composite food also resulted in low detection frequencies for many HFRs. This problem can be improved by collection of several duplicate food samples segregated by eating events (breakfast, lunch, dinner and snacks). Or else different food types could be pooled together, for example all meats in one sample, fish in another, etc. Development of more sensitive analytical methods would be useful in detecting these contaminants at trace levels.
Collection of settled dust and stationary air samples in the present study was only done in the living room; therefore, the total exposure may be underestimated. Air and dust samples from different microenvironments (workplaces, cars etc.) should also be monitored as they could be important contributors to total intake. The personal air sampling approach may be more relevant for overall inhalation exposure but it has the drawback of being intrusive. Low detection frequencies in personal air samples could be improved by having a longer sampling period (e.g. 7 days) as well as higher sampling flow rate. Alternatively, a piece of silicone wristband cut and pinned on the lapel on a shirt collar could be used as a passive sampling device for inhalation exposure assessments as demonstrated in O’Connell et al.88. However, additional work is required to determine the silicone-air partition coefficients for HFRs.
Regarding dermal exposure, a wide research gap still exists. There is a need for additional dermal uptake and percutaneous penetration experiments covering a wider range of loads to span the range of expected exposures. Improved estimates of the fraction of HFRs absorbed by the skin could be used for future dermal exposure assessments. More information on how well hand wipe samples reflect true dermal uptake would help us to establish a greater degree of accuracy on dermal exposure assessment with this approach. A future study investigating the relative importance of dermal uptake via dust, air, direct contact with HFR-treated product and indirect uptake through clothing, either through mathematical modelling or experimental studies would be worthwhile.
Blood serum is among the most widely analyzed matrix for determination of the internal exposure to HFRs but a sufficiently large amount of sample would be needed in order to measure them in low concentrations. In future investigations, it might be possible to use other non-invasive matrices, such as hair, nails and sweat as biomarkers to assess human exposure to HFRs.
23 Development of highly sensitive and specific analytical methods for HFR determination in various biological matrices are therefore recommended.
24 6 Acknowledgements
I would like to acknowledge the people who have made this thesis possible.
First of all I would like to offer my sincerest gratitude to my supervisors, Cynthia de Wit and Ulla Sellström, as well as my external supervisor, Karine Elihn, who have supported me throughout my thesis with their patience, enthusiasm and knowledge. I truly appreciate all the helpful discussion throughout the project and I am grateful for the trust you have placed in me. I could not have imagined having better supervisors for my PhD study.
Dozens of people have helped and taught me a lot since I started at ITMo/ACESo. Special thanks to Leena for being a mentor in the lab. Not forgetting also Ulla E, Tomas, Oscar and Merle, for all the help with the analytical instruments. Thanks to all the nice people at ACESo/x/b for providing such a great working environment. Malte, my housemate for almost a year; Ellen, my writing companion; Li, Tong and Fangyuan for being such a great friend. And also the early lunch group members, thanks for all the great time and nice talks during lunch.
A special acknowledgement goes to my great T502 officemates: Lukas, Claudia, Ines and Bo S who have been supportive in every way: office fika, Swedish learning sessions, discussions (scientific and other) and the weekly Pilates training sessions, I’m going to miss those.
I would like to extend my appreciation to the A-TEAM crew for the wonderful experience including meetings, collaborations and trips. Special thanks to Adrian Covaci for hosting me during my secondment at University of Antwerp. Also Fenix, who I worked very closely for the food analysis and paper writing during my visit to Antwerp. Line, Lila and Juan from NIPH for valuable discussions and fast feedback on my manuscripts. And also Melissa, Stathis, Thuy, George, Somrutai, Ana, Katerina, Luisa, Aldreia, Gopal and Claudio for all the great moments we shared.
Last but not least, I would like to take this opportunity to thank my family: my parents and my siblings for helping me get through the difficult times in my life, and for all the unconditional support, care and love they provided.
25 7 References
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