Environ. Sci. Technol. 2008, 42, 459–464
Hexabromocyclododecanes In Indoor Dust From Canada, the United Kingdom, and the United States MOHAMED ABOU-ELWAFA ABDALLAH,† S T U A R T H A R R A D , * ,† C A T A L I N A I B A R R A , † MIRIAM DIAMOND,‡ LISA MELYMUK,‡ MATTHEW ROBSON,‡ AND ADRIAN COVACI§ Division of Environmental Health and Risk Management, School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, United Kingdom, Department of Geography, 100 St George Street, University of Toronto, Toronto, Ontario, Canada M5S 3G3, and Toxicological Center, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium
Received September 21, 2007. Revised manuscript received November 8, 2007. Accepted November 9, 2007.
R-, β-, and γ-hexabromocyclododecane diastereomers (HBCDs) were measured in house dust from Birmingham, UK (n ) 31, median concentration ) 730 ng ΣHBCDs g-1); Amarillo/ Austin, TX (n ) 13, 390 ng g-1); and Toronto, Canada (n ) 8, 640 ng g-1). Concentrations in dust (n ) 6, 650 ng g-1) from UK offices were within the range for UK homes. Concentrations from each country were statistically indistinguishable. In one UK house dust sample, 110,000 ng g-1 was recorded-the highest recorded in indoor dust to date. While upper bound average UK dietary exposures for adults and toddlers, respectively, are 413 and 240 ng ΣHBCDs day-1, UK adults and toddlers daily ingesting, respectively, 50 and 200 mg of dust contaminated at the 95th percentile concentration are exposed, respectively, to 1100 and 4400 ng ΣHBCDs day-1. Normalized to body weight, this high-end exposure scenario estimate for toddlers is within the range reported elsewhere for occupationally exposed adults. While in commercial formulations γ-HBCD predominates (>80%), R-HBCD in dust constitutes 14-67% of ΣHBCDs (average 32%). Hence the predominance of the R-diastereomer in humans may arise partly from dust ingestion, and not solely to in vivo metabolism (when R-HBCD is formed from bioisomerization of other diastereomers), or dietaryexposure(whereR-HBCDpredominatesinmostfoodstuffs).
Introduction The manufacture and use of the commercial brominated flame retardant (BFR) formulations Penta-BDE and OctaBDE has been banned recently in the European Union (1). Furthermore, the Deca-BDE flame retardant formulation is the subject of ongoing EU risk assessment (2). This has created a need for alternative FR chemicals that will meet stringent fire safety regulations in both the short and long term. The alternative also must have properties that allow it to be added * Corresponding author e-mail:
[email protected]; fax: +44 121 414 3078. † University of Birmingham. ‡ University of Toronto. § University of Antwerp. 10.1021/es702378t CCC: $40.75
Published on Web 12/12/2007
2008 American Chemical Society
to plastics while not altering the physical characteristics of that material. One such chemical is hexabromocyclododecane (HBCD), which may be used as an alternative to the banned PBDE formulations (3). HBCD is a BFR used widely as an additive to expanded and extruded polystyrene foams for thermal insulation of buildings, and to a lesser extent to high-impact polystyrene used in enclosures for electronic equipment, such as televisions (4). In 2001, the world market demand for HBCD was 16,700 tonnes of which about 9,500 tonnes was consumed in Europe (5). It is an aliphatic, brominated cyclic alkane produced by bromination of cyclododecatri-1,5,9-ene (6). It has a complex stereochemistry, comprising a theoretical 16 stereoisomers, including 6 diastereomeric pairs of enantiomers, and 4 meso forms. The commercial formulations consist mainly of the R-, β-, and γ-diastereomers (each of which exist as enantiomeric pairs) with γ- predominant. HBCD has a low vapor pressure, very low water solubility, and a fairly high log KOW value of 5.6. Combined with its persistence, it can thus bioaccumulate in fatty tissues. Its persistence, exemplified by estimated halflives of 3 days in air and 2–25 days in water, also bestow potential for long-range transport (3). HBCDs can enter the environment by different pathways including emission during its production or manufacture of the flame-retarded materials and then final products, leaching from products, or following product disposal. Oral exposure to HBCD induces hepatic cytochrome P450 enzymes in rats and can alter the normal uptake of neurotransmitters in rat brain (7, 8). There are other indications that it can disrupt the thyroid hormone system and induce cancer through a nonmutagenic mechanism in humans (3). HBCD has been recognized by the UK Chemical Stakeholders Forum as a persistent, bioaccumulative, and toxic (PBT) chemical and is included on the OSPAR list of chemicals for priority action. While currently no specific regulatory actions are taken in the United States, HBCD has been identified for risk assessment in Canada, Australia, and Japan. Further regulatory/assessment activities in these countries will take place over the next few years (2), and most recently, it has been recognized as a PBT substance within the EU. Despite these concerns and the detection of HBCDs in human tissues (9, 10), relatively little is known about the magnitude of human exposure and the relative significance of different pathways. To date, measurements of dietary exposure are limited to a study that estimated UK upper bound average dietary intake in 2004 to be 413 ng ΣHBCDs/ day for a 70 kg adult and 240 ng ΣHBCDs/day for a 10 kg toddler (11). Likewise, while concentrations of HBCDs have been reported in a small number of studies of both domestic and office indoor dusts from Europe and the United States (12–15), no systematic estimate of the significance as a human exposure pathway that ingestion of indoor dust represents has yet been conducted. This is potentially important given the evidence of its relevance for another class of brominated flame retardants, namely PBDEs (16–20). In addition, there are no diastereomer-specific data on concentrations of HBCDs in indoor dust samples to date, save for the indicative values reported in NIST SRM 2585 ( (21); see Table 1). Furthermore, there exist to date relatively few measurements of individual HBCD diastereomers (as opposed to ΣHBCDs) in matrices pertinent to human exposure. This is of interest given that knowledge of the relative toxicity of the different diastereomers is sparse, and that the relative abundance of individual HBCD diastereomers shifts from predominantly γ- in the commercial formulations to predominantly R- in biota (3). Covaci et al. (3) suggested that VOL. 42, NO. 2, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Concentrations of HBCD Isomers in SRM2585 compared to the Indicative Values (21) average concentration (ng g-1) ( standard deviation (n ) 5) R-HBCD β-HBCD γ-HBCD
measured
indicative
19 ( 3.6 4.4 ( 0.4 125 ( 18
19 ( 3.7 4.3 ( 1.1 120 ( 22
this shift is the result of a “combination of factors such as variations in solubility, partitioning behaviour, uptake, and possibly selective uptake of individual isomers”, and identified a need for “research on how HBCDs are transferred from products into the environment”. While the observed predominance of R-HBCD in biota may be attributed to the fact that cytochrome P450 preferentially metabolizes the γ- and β-diastereomers, but not the R-diastereomer (22), there is evidence that the shift from the γ- to the R- may also occur via abiotic means. For example, while the γ-diastereomer predominates in the commercial formulations, the temperatures (160-220 °C depending on the application) required to incorporate the commercial formulation into treated products such as expanded or extruded polystyrene have been shown to effect a marked shift toward predominance of the R-diastereomer (23). Such a shift is reflected presumably in the treated products. Given the above, this study reports concentrations of the three principal HBCD diastereomers in indoor dust. These concentrations are used to provide a preliminary assessment of human exposure to HBCDs via dust ingestion. Given the observed order-of-magnitude differences between North American and European exposure via this pathway to Σtrihexa-BDEs (17), dust samples are examined from Toronto, Canada, Birmingham, UK, and Austin/Amarillo, TX. Furthermore, this study evaluates the extent to which the observed shift in diastereomer pattern thought to occur during incorporation of the commercial formulations into flame-retarded products is reflected in indoor dust.
Materials and Methods Sampling Methods. Dust samples were collected from living rooms in homes in each city (n ) 31, 8, and 13 in Birmingham, Toronto, and Amarillo/Austin, respectively) using a Nilfisk Sprint Plus 1600 W vacuum cleaner or equivalent Nilfisk model available in the country sampled. In addition, a small number (n ) 6) of offices were sampled in Birmingham, UK. Sampling was conducted in July-August 2006 (UK), September 2006 (Canada), and October 2006 (U.S.); the homes (and offices) selected in each city comprised a convenience sample of acquaintances of the authors. Sampling was conducted according to a clearly defined standard protocol by one of the research team. One m2 of carpet was vacuumed for 2 min in each location and in case of bare floors 4 m2 was vacuumed for 4 min. Samples were collected using nylon sample socks (25 µm pore size) that were mounted in the furniture attachment tube of the vacuum cleaner. After sampling, socks were closed with a twist tie, sealed in a plastic bag and stored at -20 °C. Before and after sampling, the furniture attachment was cleaned thoroughly using an isopropanol-impregnated disposable wipe. Analysis. The samples were sieved through a 500 µm mesh size sieve, weighed accurately then extracted using pressurized fluid extraction (Dionex Europe, UK, ASE 300). Dust samples (1 g) were loaded into precleaned 66 mL cells containing 1.5 g of Florisil and Hydromatrix (Varian Inc., UK) to fill the void volume of the cells, spiked with 13C-labeled R-, β-, and γ-HBCD (100 µL of a 0.25 ng µL-1 hexane 460
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solution-i.e., 25 ng of each diastereomer) as internal (or surrogate) standards (i.e., standards used for determination of analyte concentrations) and extracted with hexane/CH2Cl2 (1:1 v/v) at 90 °C and 1500 psi. The heating time was 6 min, static time 5 min, purge time 100 s, flush volume 50%, and the number of static cycles was 3. The crude extracts were concentrated to 0.5 mL using a Zymark Turbovap II then washed with 98% sulfuric acid. The hexane layer was transferred onto a Florisil column topped with sodium sulfate and then eluted with 30 mL of hexane/CH2Cl2 (1:1). The eluate was concentrated under a gentle stream of N2, solvent exchanged into methanol and d18-γ-HBCD was added as a recovery determination (or syringe) standard, used to determine the recoveries of internal/surrogate standards for QA/QC purposes. Separation of R-, β-, and γ- HBCD was achieved using a dual pump Shimadzu LC-20AB prominence liquid chromatograph equipped with SIL-20A autosampler and DGU-20A3 vacuum degasser. A Varian Pursuit XRS3 C18 reversed phase analytical column (150 mm × 2 mm i.d., 3 µm particle size) was used. A mobile phase of (a) 1:1 water/methanol with 2 mM ammonium acetate and (b) methanol at a flow rate of 150 µL min-1 was applied for elution of the target compounds; starting at 50% (b) then increased linearly to 100% (b) over 3 min; this was held for 5 min followed by a linear decrease to 65% (b) over 2.5 min and held for 3.5 min. The three diastereomers were baseline separated on the reversed phase C18 column with retention times of 9.4, 9.9, and 10.3 min for R-, β-, and γ- HBCD, respectively. Mass spectrometric analysis was performed using a Sciex API 2000 triple quadrupole mass spectrometer operated in the ES negative ion mode. Infusion experiments utilized the built-in Harvard syringe pump with a flow rate of 10 µL min-1. MS/MS detection operated in the MRM mode was used for quantitative determination of the HBCD isomers based on m/z 640.6f m/z 79, m/z 652.4f m/z 79, and m/z 657.7f m/z 79 for the native, 13C-labeled, and d18-labeled diastereomers, respectively. Recoveries (average ( standard deviation) of the three 13C-HBCD diastereomers were as follows: R-HBCD ) 82 ( 8, β-HBCD 88 ( 5, and γ-HBCD 83 ( 8%. No HBCDs could be detected in method blanks (n ) 6) for the dust analysis procedures consisting of sodium sulfate (1 g). Detectable, but very low concentrations (typically 0.1–0.5 ng ΣHBCDs g-1) were obtained for field blanks (n ) 6). These consisted of sodium sulfate (1 g) “sampled” using the vacuum cleaner and sock according to the standard protocol and treated as a sample. Concentrations in samples in each batch of 10 were thus corrected for the contamination detected in the associated field blank. Method detection limits (MDLs) for individual diastereomers were governed by the field blanks and were typically 0.1 ng g-1. The accuracy and precision of the analytical method was assessed via replicate analysis (n ) 5) of SRM 2585. The results obtained compared favorably with the indicative values reported elsewhere ( (21) and Table 1). In instances where particularly elevated ΣHBCDs concentrations were found (i.e., such that the internal standard “spiking” levels were inappropriately low), a fresh aliquot of the dust sample in question was analyzed using a smaller quantity of dust and a higher amount of internal standards. Statistical analysis of the data was conducted using Excel (Microsoft Office for Mac OS X) to generate descriptive statistics, with other statistical procedures (tests for normality of distribution, Kruskal–Wallis, ANOVA, and posthoc tests) conducted using SPSS version 13.0 for Mac OS X.
Results and Discussion All 3 HBCD diastereomers were detected and quantified in all dust samples. A statistical summary is given in table 2, with the concentrations of each HBCD diastereomer in each
TABLE 2. Summary of Concentrations (ng g-1) of HBCD Diastereomers in Indoor Dust in This and Other Studies location (reference) UK homes, n ) 31 (this study)
UK offices, n ) 6 (this study)
Canadian homes, n ) 8 (this study)
US homes, n ) 13 (this study)
Belgian offices and homes, n ) 23 (12) offices within EU, n ) 18 (13) UK offices and homes, n ) 10 (14) U.S. homes, n ) 17 (15)
statistical parameter/ diastereomer
r-HBCD
β-HBCD
γ-HBCD
ΣHBCDs
arithmeticmean σn median geometricmean minimum maximum arithmeticmean σn median geometricmean minimum maximum arithmeticmean σn median geometricmean minimum maximum arithmeticmean σn median geometricmean minimum maximum arithmeticmean minimum maximum minimum maximum arithmeticmean minimum maximum arithmeticmean minimum maximum
2800 12000 170 290 22 66000 250 250 100 120 15 630 340 210 300 250 25 670 260 460 80 110 17 1800
470 1500 66 81 9 7800 160 150 75 84 11 380 70 42 72 51 6 130 56 79 28 29 6 300
2800 7700 440 560 70 37000 1000 1000 470 540 65 2600 260 150 230 200 34 470 490 580 300 290 79 2000
6000 20000 730 1000 140 110000 1400 1400 650 750 90 3600 670 390 640 500 64 1300 810 1100 390 450 110 4000 4800
