Research Concentrations of Polybrominated Diphenyl Ethers in Air and Soil on a Rural-Urban Transect Across a Major UK Conurbation STUART HARRAD* AND STUART HUNTER Division of Environmental Health and Risk Management, Public Health Building, School of Geography, Earth, and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, United Kingdom
Polybrominated diphenyl ethers (PBDEs) were measured in air (using PUF disk passive samplers) and soil samples taken at approximately monthly intervals over 1 year at 10 locations on a transect across the West Midlands of the UK. Concentrations in air are consistent with those detected elsewhere in Europe and the Great Lakes basin. Concentrations in soil fall within the range reported for rural woodland and grassland soils in the UK and Norway. In both air and soil, concentrations clearly decrease with increasing distance from the city center, supporting the existence of an urban “pulse”, indicating the West Midlands conurbation to be a source of PBDEs to the wider environment. Examination of seasonal trends revealed no evidence of a “spring pulse” in concentrations in air, with no summer peak in concentrations in air observed for 70% of sites. The PBDE congener pattern in air differs from that in soil, with ratios of congeners 47:99 higher in air than in soil. It is hypothesized that PBDEs volatilize from treated products indoors, before ventilating outdoors, where congener 99 undergoes preferential atmospheric deposition and accumulation in soil.
Introduction Polybrominated diphenyl ethers (PBDEs) are a group of brominated compounds widely used as flame retardants. In recent years, production and use of PBDEs has been in the guise of three formulations: penta (consisting primarily of BDEs 47 and 99 (37% each), alongside smaller amounts of other tetra-, penta-, and hexa-BDEs); octa (a mixture of hexa (10-12%), hepta- (44-46%), octa- (33-35%), and nona- (1011%); and deca (98% decabromodiphenyl ether (BDE 209) and 2% various nona-BDEs) (1, 2). Worldwide, PBDE production is dominated by the deca commercial formulation, with global demand in 2001 an estimated 56 100 t (3). This is similar to the 1999 estimate of 54 800 t (4). By comparison, 2001 global demand for the penta product was 7500 t (3), down slightly from 8500 t in 1999 (4). Production and use of commercial PBDE formulations in Europe was considerably less than that in North America; for example, in 2001, 7100 t of penta product was used in North America, compared to just 150 t in Europe (3). The uses for these commercial formulations are myriad: the penta product was * Corresponding author e-mail:
[email protected]; phone: +44 121 414 7298; fax: +44 121 414 3078. 4548
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employed principally to flame-retard polyurethane foams in carpet underlay, furniture, and bedding; the octa formulation was used to flame-retard thermoplastics such as high-impact polystyrene, and the deca product is used principally in plastic housings for electrical goods such as TVs and computers, as well as in textiles (1). As a result of concerns surrounding these contaminants owing to their presence in the diet and indoor air and dust (5-7), and human tissues (8), coupled with evidence relating to their potential adverse effects on human health (2, 9), several jurisdictions have banned the marketing and use of penta- and octa-BDEs. Furthermore, the main United States producer and the U.S. EPA, have reached a voluntary agreement to discontinue production of the penta- and octa-BDE mixtures. Despite this, there remain comparatively few data relating to their presence in outdoor air, with information relating to their concentrations in soil also restricted. With respect to outdoor air, while the limited (n ) 6) data reported by our group for Birmingham, U.K. (5), suggested concentrations to be in line with those reported for Chicago (10), othersagain limited (n ) 7)sdata from a Europe-wide study suggest the UK to be the focus of the most contaminated locations, with the highest contamination detected in major urban centers such as Manchester, Middlesborough, and London (11). There is only one substantial survey reporting concentrations of PBDEs in surface soils, revealing concentrations in UK grassland (n ) 16), and both UK (n ) 17) and Norwegian (n ) 21) woodland (i.e., rural) soils to be similar in magnitude to those detected for PCBs (12). Given this, we set out to study the atmospheric and edaphic behavior of PBDEs within the West Midlands conurbation (population 2.5 million), at the heart of which is Birmingham (population 1 million), the second most populous UK city. This study reports concentrations of a number of PBDE congeners in outdoor air (using PUF disk passive air samplers) and surface soil taken from 10 locations on a 79 km transect across the West Midlands. The direction of the transect corresponds with the prevailing wind direction (i.e., from the southwest (upwind) to the northeast (downwind) of the West Midlands) thereby affording a potential insight into the role of the heavily urbanized center as a source of PBDEs to the wider environment. By covering distances from Birmingham city center of 48 km southwest to 31 km northeast with intersite distances of 3-17 km, spatial variation between a range of rural, sururban, and urban locations could be studied. Samples of both air and soil were taken on an approximately monthly basis at each location, thereby facilitating elucidation of seasonal trends. While recognizing that other PBDE congeners such as BDE 49, 66, 75, and 85 etc. may be present in measurable quantities in air, we focused on BDEs 28, 47, 99, 100, 153, and 154. These congeners were selected for two principal reasons, specifically: (i) they have been identified as the most abundant in air (11) and soil (12), and (ii) they are the principal congeners monitored in previous comparable studies (10). Although decabromodiphenyl ether is being increasingly reported, it was not included in this study owing to the difficulties in achieving its reliable determination at the outset of the study (13). Our principal objectives were the following: (1) to significantly augment the worldwide database on concentrations of PBDEs in both outdoor air and topsoil; (2) to assess the spatial and seasonal variation of concentrations and congener profiles of PBDEs in outdoor air and topsoil within 10.1021/es0606879 CCC: $33.50
2006 American Chemical Society Published on Web 06/21/2006
FIGURE 1. Sampling locations.
TABLE 1. Sampling Site Information distance from city center site (km) 1 2 3 4 5 6 7 8 9 10 11
48 31 21 11 6 3 0 6 18 23 31
TABLE 2. Sampling Periods at All Sites and Air Temperatures at Site 6 Averaged over Each Sampling Period
site classification
site name
sample
period date
mean air temp. (°C)
rural rural rural suburban suburban urban urban (city center) urban rural suburban rural
Whitbourne Bishops Wood Chaddesley Wood West Heath Weoley Castle EROS Centenary Square Hodge Hill Kingsbury Water Park Tamworth Newton Regis
1 2 3 4 5 6 7 8 9 10 11
16/08/2003 - 06/10/2003 06/10/2003 - 07/11/2003 07/11/2003 - 10/12/2003 10/12/2003 - 19/01/2004 19/01/2004 - 19/02/2004 19/02/2004 - 26/03/2004 26/03/2004 - 23/04/2004 23/04/2004 - 17/06/2004 17/06/2004 - 30/07/2004 30/07/2004 - 01/09/2004 01/09/2004 - 15/10/2004
10.8 9.4 10.1 6.6 4.1 5.8 9.2 13.2 14.7 17.4 11.9
the West Midlands; and (3) to use these data to further understanding of the environmental sources and fate of PBDEs, in particular the significance of urban areas as source regions.
Experimental Section Sampling Strategy. Outdoor air and soil samples were collected from 10 sites within the West Midlands conurbation. Sampling sites were located on a southwest (upwind) to northeast (downwind) transect at intervals of between 3 and 17 km across the conurbation. Hence, a mix of rural, suburban, and urban sampling locations was studied. Figure 1 shows the location of each outdoor sampling location, with each number relating to a specific location for which relevant data are given in Table 1. Table 2 provides information on the average air temperature recorded at site 6 (meteorological information was not available for the other sites) and the dates of each sampling period (these were identical for all sites). For operational reasons, sampling at location 10 ceased
after 2 months and no data are reported for this site. At each location, 11 paired air and soil samples were taken. Air Sampling. Passive air samplers (i.e., PUF disks) were employed to provide a time-integrated sample over each sampling period. These have been used successfully in other studies (11, 14). To provide sufficient contaminant mass, four PUF disk samplers (each comprising one shelter each fitted with one PUF disk) were simultaneously deployed approximately 20 cm apart at a height of 1.5 m above the surface at each site and combined after sampling to provide 1 sample for analysis. Each PUF disk measured 14 cm in diameter and 1.2 cm in thickness, giving a surface area of 360 cm2, and density 0.01685 g cm-3. Disks were sheltered by two different size stainless steel housings (18 cm diameter, 1 L bottom housing and 23 cm diameter, 2 L top housing, respectively). Prior to deployment, disks were washed thoroughly in tap and distilled water sequentially to remove loose material, then extracted in hexane using a Soxhlet apparatus for 48 h to remove any target or interfering VOL. 40, NO. 15, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 3. Averagea(σn-1) Concentrations (pg m-3) of PBDEs in Air Samples in This and Other Studies Employing PUF Disk Samplers site/reference
28
47
99
100
153
154
ΣBDE
47:99 ratio
1 2 3 4 5 6 7 8 9 11 EROS (5)c Europe-wide (11) Ottawa (15) Great Lakes Basine (16) Asia (27) Toronto (14)
0.50 (0.52) 0.32 (0.31) 0.55 (0.35) 0.87 (0.50) 1.15 (0.89) 1.65 (0.60) 2.04 (0.77) 1.44 (0.63) 0.87 (0.41) 0.55 (0.32) nab
