Brominated and Chlorinated Flame Retardants in Tree Bark from

Dec 11, 2012 - Brominated and chlorinated flame retardants were measured in about 40 samples of tree bark from 12 locations around the globe. The anal...
0 downloads 11 Views 2MB Size
Download PDF
Article pubs.acs.org/est

Brominated and Chlorinated Flame Retardants in Tree Bark from Around the Globe Amina Salamova and Ronald A. Hites* School of Public and Environmental Affairs, Indiana University, Bloomington, Indiana 47405, United States S Supporting Information *

ABSTRACT: Brominated and chlorinated flame retardants were measured in about 40 samples of tree bark from 12 locations around the globe. The analytes were polybrominated diphenyl ethers (PBDE), Dechlorane Plus (DP), decabromodiphenylethane (DBDPE), hexabromocyclododecane (HBCD), hexabromobenzene (HBB), pentabromoethylbenzene (PBEB), pentabromobenzene (PBBz), and tetrabromo-p-xylene (pTBX). The highest concentrations of these compounds were detected at an urban site in Downsview, Ontario, Canada. Total PBDE and DP concentrations ranged from 2.1 to 190 ng/g lipid weight and from 0.89 to 48 ng/g lipid weight, respectively. Relatively high levels of DP (46 ± 4 ng/g lipid weight) were found at a remote site at Bukit Kototabang in Indonesia. The concentrations of total PBDE, DP, PBEB, and HBCD in the tree bark samples were significantly associated with human population in the nearby areas (r2 = 0.21−0.56; P < 0.05). In addition, the concentrations of total PBDE and DP were significantly associated (r2 = 0.40−0.64; P < 0.05). with the corresponding atmospheric concentrations of these compounds over a concentration range of 2−3 orders of magnitude.

■

INTRODUCTION Tree bark has been shown to effectively accumulate atmospheric pollution,1,2 and the measurement of persistent organic pollutant (POP) concentrations in tree bark has provided spatial patterns and identified local and regional pollution sources for several POPs. These include polychlorinated biphenyls,1,3−6 polycyclic aromatic compounds,7 polychlorinated dibenzo-p-dioxins,3,8 organochlorine pesticides,1,9 and polybrominated and polychlorinated flame retardants.1,2,10,11 Using tree bark as an atmospheric passive sampler for POPs is advantageous because it is relatively easy to collect and hence inexpensive compared to conventional high-volume active and even sorbent-based passive air sampling methods. Tree bark is a good sampling medium for POPs with high octanol−air partition coefficients because of its relatively high lipid content and large surface area. In addition, bark accumulates both vapor- and particle-phase POPs from the surrounding air,12,13 allowing the measurement of pollutants in these two phases simultaneously. Brominated and chlorinated flame retardants have been widely used in plastics, foam, wood, and textiles in a variety of consumer products for many years to slow the spread of fire and the combustion of these products. Polybrominated diphenyl ethers (PBDE) are the most widely used of these products. They are persistent and accumulate in the environment,14 and as a result, the production and use of these chemicals was restricted in North America and in the European Union.15−17 Another widely used brominated flame retardant is hexabromocyclododecane (HBCD), which is mainly used in upholstery textiles and in building insulation materials.18 HBCD has been found in the environment and humans, and thus, it too is being considered for production and use © 2012 American Chemical Society

restrictions under several national review, risk assessment, and monitoring programs.19 Perhaps because of these restrictions, the market demand for flame retardants has shifted toward nonregulated chemicals, such as decabromodiphenyl ethane (DBDPE), a chlorinated flame retardant Dechlorane Plus (DP), and perhaps even some “older” flame retardants, which were used decades ago. The latter include pentabromobenzene (PBBz), hexabromobenzene (HBB), pentabromoethylbenzene (PBEB), and tetrabromo-p-xylene (pTBX), which were apparently manufactured in the late 1980s but have recently been found in the environment.20−22 Because of their persistence, brominated and chlorinated flame retardants are distributed throughout the globe and are often found at remote places where they had never been used.23 International efforts, such as the Stockholm Convention, have attempted to address this global distribution of POPs by establishing of global monitoring networks.24 For example, the Global Atmospheric Passive Sampling (GAPS) network was established as a result of these efforts.25 GAPS was initiated in 2004 with about 55 sites on 6 continents, and it deploys passive polyurethane foam (PUF) disks to investigate the levels of POPs in the atmosphere. The study reported here was a collaboration with the GAPS network, and its goal was to measure the concentrations of brominated and chlorinated flame retardants in tree bark samples collected at several of the GAPS sites and to compare these results with the concentrations measured in GAPS PUF samples26,27 and to Received: Revised: Accepted: Published: 349

August 21, 2012 October 19, 2012 November 16, 2012 December 11, 2012 dx.doi.org/10.1021/es303393z | Environ. Sci. Technol. 2013, 47, 349−354

Environmental Science & Technology

Article

Table 1. Locations of Tree Bark Samples, Site Information, Concentrationsa (in ng/g Lipid Weight) of Total PBDE, DP, DBDPE, HBCD, HBB, PBEB, and PBBz (Average ± Standard Error), and Lipid Fraction (% ± Standard Error) location

country

latitude

longitude

Birkenes

Norway

58°23′ N

8°15′ E

Bukit Kototabang

Indonesia

00°12′ S

100°19′ E

Cape Grim

Tasmania

40°68′ S

144°70′ E

De Aar

South Africa Nepal

30°40′ S

24°00′ E

27°37′ N

85°33′ E

Canada

43°47′ N

79°28′ W

Canada

49°53′ N

81°34′ W

49°35′ N

15°05′ E

Malin Head

Czech Republic Ireland

55°22′ N

07°20′ W

Reykjavik

Iceland

64°08′ N

21°58′ W

Tula, American Samoa Whistler, British Columbia range

United States Canada

14°14′ S

170°34′ W

50°04′ N

122°57′ W

Dhulikhel Downsview, Toronto, Ontario Frasardale, Ontario Košetice

populationb

PBDEc

2390 12.2 ± 4.6 111 000 11.4 ± 1.8 3360 2.12 ± 0.53 51 500 6.02 ± 1.95 9810 8.16 ± 1.16 5 130 000 190 ± 46 7640 27.4 ± 4.7 699 7.51 ± 2.24 1820 11.2 ± 4.5 119 000 3.06 ± 0.22 413 3.72 ± 1.49 7700 4.89 ± 0.93 2.12− 190

DP 9.12 ± 4.89 46.1 ± 4.2 0.89 ± 0.21 3.13 ± 0.70 1.37 ± 0.36 48.4 ± 24.9 3.22 ± 0.92 4.36 ± 1.98 4.81 ± 1.15 1.02 ± 0.25 2.00 ± 0.82 3.03 ± 0.83 0.89− 48.4

DBDPE

HBCD

ndd

1.30 ± 0.50 1.39 ± 0.75 1.45 ± 0.78 0.66 ± 0.16 0.35 ± 0.10 21.3 ± 7.7 0.84 ± 0.13 1.65 ± 0.94 nd

nd nd nd nd 6.63 ± 2.47 1.39 ± 0.14 3.92 ± 0.68 nd nd nd nd 1.39− 6.63

0.62 ± 0.09 0.76 ± 0.65 0.27 ± 0.03 0.27− 21.3

HBB

PBEB

0.19 ± 0.11 0.08 ± 0.02 0.28 ± 0.10 0.05 ± 0.02 0.11 ± 0.02 0.72 ± 0.04 0.10 ± 0.23 0.11 ± 0.04 0.53 ± 0.29 0.06 ± 0.01 0.12 ± 0.02 0.02 ± 0.01 0.02− 0.72

0.15 ± 0.08 0.10 ± 0.05 0.04 ± 0.01 0.06 ± 0.03 0.04 ± 0.01 0.27 ± 0.07 0.15 ± 0.01 0.10 ± 0.02 0.11 ± 0.08 0.03 ± 0.01 0.01 ± 0.01 0.05 ± 0.01 0.01− 0.27

PBBz nd nd nd nd nd 0.25 ± 0.05 0.04 ± 0.01 0.11 ± 0.04 nd nd nd nd 0.04− 0.25

lipids 2.3 ± 0.5 1.8 ± 0.3 5.7 ± 0.7 2.5 ± 0.4 4.2 ± 0.3 3.1 ± 0.3 2.5 ± 0.2 3.3 ± 0.4 2.1 ± 1.0 9.3 ± 0.5 6.7 ± 1.5 5.2 ± 0.2 1.8− 9.3

a

Each concentration value is an average of 3−4 replicate samples collected at each site. bThe most recent official census population data was included. The World Gazetteer database (http://world-gazetteer.com) was used to retrieve the data. In cases where the census data was not available (some of the remote sites), the census data for the closest town was used. Toronto’s population data was used for Downsview, Ontario. cPBDE is the sum of the concentrations of BDE-28, 47, 99, 100, 153, 154, 183, 207, 208, and 209. dnd = not detected; those not detected or detected in only one or two of the 3−4 replicate samples were considered as not detected.

other available atmospheric data.1,2,13 The analytes of interest in this study are PBDE, both syn- and anti-DP, DBDPE, HBCD, HBB, PBEB, PBBz, and pTBX.

Soxhlet extraction thimble bedded with 25 g of granular anhydrous Na2SO4 (Fisher Chemical, Fair Lawn, NJ) and then covered with another 25 g of Na2SO4 to keep the bark from floating during extraction. The sample was spiked with known amounts of BDE-77, BDE-166, and 13C12-BDE-209 as recovery standards and then extracted with 400 mL of a 1:1 (v/v) mixture of hexane and acetone for 24 h. The extracts were then concentrated by rotary evaporation to 2 mL, and the solvent was exchanged with 75 mL of hexane twice. The extract was transferred into a 15 mL centrifuge tube, blown down with dry nitrogen to about 3 mL, and treated with 5 mL of concentrated H2SO4 (EM Science, Gibbstown, NJ) overnight. The organic layer was separated by centrifugation, the acid residue was back extracted twice with 3 mL of hexane each time, and the organic layers were combined. The concentrated extract was fractionated on a fully activated alumina (MP BioMedicals GmbH, Eschewed, Germany) column. The column was eluted with 25 mL of hexane followed by 25 mL of a 1:1 (v/v) mixture of dichloromethane and hexane. All targeted flame retardants eluted in the second fraction. The extracts were then concentrated by rotary evaporation to about 2 mL, and the second fraction was solvent exchanged to hexane twice. The extracts were transferred into 4 mL vials and further blown down with dry N2 to about 1 mL. BDE-118 was added as an internal quantitation standard to the final extracts. Throughout the extraction, cleanup, and analysis procedures, the analytes were protected from light by wrapping the containers with aluminum foil or by using amber glassware. The lipid concentrations were determined gravimetrically after Soxhlet extraction by transferring about 10% of the extract

■

EXPERIMENTAL SECTION Sampling Information. The names of the sampling sites and their longitudes and latitudes are given in Table 1. With the exception of the site at Downsview, Ontario, all of the sampling sites were at remote locations (see population, longitude, and latitude values in Table 1). The Downsview site is about 8 km north of central downtown Toronto, the largest city in Canada. All samples were collected at GAPS network sites during 2009−2010, inclusive. Bark samples were collected from fullgrown hardwood and coniferous trees with coarse bark such as pine, fir, and spruce. Trees with smooth bark, such as aspen and paper birch, were avoided. Bark samples were collected from 3 to 4 individual trees at each site. Trees closest to the GAPS samplers and located within about 50 m from one another were used wherever possible. A sample of bark (about 100 g) was collected from two different sides of each tree using a precleaned chisel at a height of 1.5 m; these two samples were combined. The cambium was not sampled so that the tree was not permanently harmed. The bark sample was wrapped in aluminum foil, sealed in a plastic bag, and kept at ambient temperature until the samples were shipped to the laboratory at Indiana University, where they were kept at −20 °C until extraction. Sample Analysis. The method described in Salamova and Hites1 was modified for this study. In brief, about 10 g of bark was cut into pieces of about 1 cm square using precleaned pruning shears. The sample was weighed and then packed in a 350

dx.doi.org/10.1021/es303393z | Environ. Sci. Technol. 2013, 47, 349−354

Environmental Science & Technology

Article

Figure 1. Tree bark sampling sites and the corresponding concentrations (ng/g lipid weight) of total PBDE (red), DP (green), HBCD (blue), HBB (purple), and PBEB (black). and = not detected.

■

RESULTS AND DISCUSSION Concentrations. The concentrations of total PBDE (reported as the sum of the 10 congeners listed above), DP (reported as the sum of the syn- and anti-DP conformers), DBDPE, HBCD (reported as the sum of α-, β-, γ-HBCD isomers), HBB, PBEB, and PBBz are given in Table 1. The reported average concentrations and standard errors for each target compound are from three or four bark samples collected at each site. The concentrations were normalized to the weight of bark lipids to account for differences in the tree species,28 and an average percent lipid for the samples at each site is also given in Table 1. Figure 1 shows the approximate locations of the sampling sites and the corresponding bark concentrations of total PBDE, DP, HBCD, HBB, and PBEB measured at each site. In general, the highest total PBDE concentrations were found at the two sites in Ontario, Canada: Downsview (190 ± 46 ng/g lipid weight) and Frasardale (27 ± 5 ng/g lipid weight). The lowest total PBDE concentrations were found at a very remote site at Cape Grim (2.1 ± 0.5 ng/g lipid weight), which is on the northwestern coast of Tasmania, Australia. The total PBDE concentrations measured at the urban Downsview site are generally lower than those previously measured at two urban sites in the United States: Chicago (mean 431 ng/g lipid weight) and Cleveland (mean 243 ng/g lipid weight).1 These three concentrations are all much lower than total PBDE concentrations measured in southern Arkansas (5700 ng/g lipid weight), where the United States PBDE manufacturing facilities are located,10 and Beijing, China (mean 780 ng/g lipid weight).2 Interestingly, the total PBDE concentration measured previously at a U.S. remote site (Eagle Harbor, Michigan, mean 19 ng/g lipid weight)1 is higher than the concentrations measured at the remote sites in this study. North America was the largest consumer of commercial PBDE products over the last several decades, a usage pattern that may have resulted in the elevated levels of these compounds observed in tree bark from the United States and Canada.

into a preweighed aluminum dish and evaporating the solvent at a room temperature to a constant weight.11 Instrumental Analysis. Just before analysis, the samples were further concentrated to about 100 μL. These samples were analyzed on an Agilent 7890 series gas chromatograph (GC) coupled to an Agilent 5975 mass spectrometer (MS) using helium as the carrier gas and operating in the electron capture negative ionization (ECNI) mode with selected ion monitoring (SIM). The mass spectrometer was operated with an ion source temperature of 200 °C and a quadrupole temperature of 106 °C. Injections (1 μL) were made in the pulsed splitless mode. The injection port was held at 285 °C. Rtx-1614 (15 m, 250 μm i.d., 0.1 μm phase thickness) fused silica capillary GC columns (Restek Corporation, Bellefonte, CA) were used for determination of all the target compounds. The GC oven temperature program was as follows: isothermal at 100 °C for 2 min, 25 °C/min to 250 °C, 3 °C/min to 270 °C, 25 °C/min to 320 °C, and held at 320 °C for 4 min. The total run time was 20.7 min. The GC to MS transfer tube was held at 280 °C. The samples were analyzed for the following PBDE congeners: 28, 47, 99, 100, 153, 154 (measured as the sum of BB-153 + BDE-154), 183, 207, 208, and 209. Other analytes included the syn- and anti-DP conformers, DBDPE, HBCD (measured as a sum of α-, β-, and γ-HBCD isomers), HBB, PBEB, PBBz, and pTBX. Selected ion monitoring of the two bromide ions at m/z 79 and 81 was used to detect the less brominated PBDEs, DBDPE, HBCD, HBB, PBEB, PBBz, and pTBX. The ions at m/z 486.8 and 488.8 were used for BDE207 to BDE-209, and m/z 494.6 and 496.6 were used for 13C12BDE-209. The ions at m/z 651.8 and 653.8 were used to detect the two conformers of DP. All compounds were quantitated with the internal standard method using BDE-118 as the internal standard. The details on the quality assurance and control and on materials used in the study are provided in the Supporting Information. 351

dx.doi.org/10.1021/es303393z | Environ. Sci. Technol. 2013, 47, 349−354

Environmental Science & Technology

Article

(0.11 ± 0.04 ng/g lipid weight). These are the first reports of HBB, PBEB, PBBz, and pTBX concentrations in tree bark. Correlation of Bark Concentrations with Human Population. It has been shown that atmospheric concentrations of various flame retardants track human population.20,31 This dependence is likely related to the heavy use of these flame retardants in homes and offices, the number of which obviously track the local population. Since it has previously been shown that bark concentrations of a variety of POPs are significantly related to the concentrations of these compounds in the atmosphere,1 we investigated the dependence of the bark concentrations measured in this study on human population. Figure 2 shows the dependence of total PBDE, DP, PBEB, and HBCD concentrations in tree bark on the nearby human

On average, about 80% of total PBDE concentrations comprise BDE-47, -99, and -209. The distribution profiles for these three congeners are shown in Figure S1 of the Supporting Information. Overall, BDE-47 and -99 are the most abundant congeners for all the sites, except Downsview and Frasardale in Canada and Dhulikhel in Nepal, where BDE-209 is the most abundant congener. Although DP concentrations vary over a large range (from 0.89 to 48 ng/g lipid weight), both the syn- and anti-DP conformers were detected in all the tree bark samples analyzed, suggesting that DP is a worldwide pollutant. Like PBDE, the highest concentrations of DP were detected at Downsview, Canada (48 ± 25 ng/g lipid weight). The large variability (rsd = 51%) of these DP concentrations is due to one sample with a high DP concentration (122 ng/g lipid weight) which is 5 times the mean of the other three samples. Surprisingly, a remote site in Bukit Kototabang, Indonesia, has DP concentrations (46 ± 4 ng/g lipid weight) similar to those at urban Downsview. DP concentrations measured at Downsview and Bukit Kototabang are similar to those previously measured at Sturgeon Point in the United States (mean 37 ng/g lipid weight), a site located within 50 km of the North American DP manufacturing facility in Niagara Falls, New York.1 However, these concentrations are all lower than those measured in tree bark collected near this production plant (mean 464 ng/g lipid weight).11 The lowest DP concentrations in this study were measured at Cape Grim in Tasmania (0.89 ± 0.21 ng/g lipid weight). This finding does not confirm surprisingly high atmospheric DP concentrations measured by the GAPS project at this site previously.29 An average fanti (the ratio of anti-DP to syn- + anti-DP concentrations) for all the bark samples was 0.83, which is close to that measured in the technical DP mixture (0.75).30 This finding suggests a similar fate for the two DP conformers in tree bark. Several other brominated flame retardants were detected in these bark samples. DBDPE was detected at three sites: Downsview (6.6 ± 2.5 ng/g lipid weight) and Frasardale (1.4 ± 0.1 ng/g lipid weight) in Canada and Košetice in the Czech Republic (3.9 ± 0.7 ng/g lipid). These DBDPE concentrations are similar to those previously reported for urban United States sites: Chicago (mean 5.7 ng/g lipid weight) and Cleveland (mean 2.5 g/g lipid weight).1 However, these values are lower than those found in Shenzheng, China (mean 1050 ng/g lipid weight), which is a major electronic manufacturing region in China.11 Traces of HBCD (measured as the sum of all isomers) were detected in the majority of the bark samples. Like PBDE, DP, and DBDPE concentrations, the highest HBCD concentrations were measured in bark samples collected at the urban Downsview site (21 ± 8 ng/g lipid weight). These levels are all much lower than those previously reported for HBCD in bark samples from China (mean 410 ng/g lipid weight).2 In addition, traces of HBB, PBEB, PBBz, and pTBX were detected in these samples. HBB and PBEB were detected in all of the samples, and like other flame retardants measured in this study, the highest concentrations of these compounds were found at the urban Downsview site in Canada (HBB: 0.72 ± 0.04; PBEB: 0.27 ± 0.07 ng/g lipid). Similarly to DBDPE, PBBz was only detected at Downsview (0.25 ± 0.05 ng/g lipid weight) and Frasardale (0.04 ± 0.01 ng/g lipid weight) in Ontario, Canada, and at Košetice in the Czech Republic (0.11 ± 0.04 ng/g lipid weight). pTBX was detected only at Košetice

Figure 2. Regression of the concentrations of (A) total PBDE, (B) DP, (C) PBEB, and (D) HBCD in tree bark (ng/g lipid weight) versus the local human population. The details of the regression lines are as follows: (A) PBDEs, r2 = 0.21, P = 0.024, or omitting the Marshall, Arkansas, outlier, r2 = 0.48, P = 0.0002; (B) DP, r2 = 0.24, P = 0.028, or omitting the Niagara Falls, New York, outlier, r2 = 0.42, P = 0.0027; (C) PBEB, r2 = 0.40, P = 0.0064; and (D) HBCD, r2 = 0.56, P = 0.0033.

population. For a full picture, we also included previously reported tree bark concentrations for these compounds from the studies of Salamova and Hites,1 Hu et al.,2 Zhu and Hites,10 Qiu and Hites,11 and Zhao et al.13 The most recent official census population data was used for the correlation (see Table 1). In cases where the census data was not available (some of the remote sites), the census data for the closest town was used. All four of these relationships are statistically significant with r2 values ranging from 0.21 (P = 0.024) to 0.56 (P = 0.0033), indicating that the concentrations of these compounds in bark track human population, which is in turn a surrogate for the consumption of flame retarded products. Overall, higher bark 352

dx.doi.org/10.1021/es303393z | Environ. Sci. Technol. 2013, 47, 349−354

Environmental Science & Technology

Article

concentrations are measured at urban locations; however, there are two outliers in these correlations that are worth discussing. The measured tree bark concentration of total PBDEs is well above the regression line for the sample collected at Marshall, Arkansas,10 see the black circle in Figure 2A. PBDEs were manufactured by Chemtura and Albemarle in El Dorado and Magnolia, Arkansas, respectively, which are located about 300 km south of the Marshall sampling site.10 If this outlier is omitted from the data set, the regression with population is very much better (r2 = 0.48, P = 0.0002 vs r2 = 0.21, P = 0.024), suggesting that the elevated total PBDE concentration at Marshall, Arkansas, is due to the nearby point sources of PBDEs rather than due to the population at this location. The regression of DP concentrations versus human population (see Figure 2B) is significant (r2 = 0.24, P = 0.028 vs r2 = 0.42, P = 0.0027 with the exception of the sample from Niagara Falls, New York, United States,11 which is very much above the regression line). The sole U.S. manufacturing facility of DP, OxyChem, is located in Niagara Falls, and perhaps this facility acts as a point source of DP.1,11 If this outlier is omitted from the data set, the regression improves, suggesting that, like the above outlier at Marshall, Arkansas, DP concentrations measured at the site in Niagara Falls are most probably due to the emissions from this nearby DP point source. The correlation of PBEB concentrations with population (see Figure 2C) was highly significant (r2 = 0.40, P = 0.0064) with high bark concentrations at the urban sites in Chicago and Cleveland. There are no apparent outliers in this regression, suggesting that PBEB concentrations at these sites are related to human population densities and the associated use of consumer products containing PBEB. However, because not much is known about the production and use of PBEB,32 it is not possible to be more conclusive. The correlation of HBCD concentrations with population (see Figure 2D) was also highly significant (r2 = 0.56, P = 0.0033), showing particularly high values for the samples collected at Beijing, China.2 This observation suggests that one or more point sources of HBCD are located in Beijing, which is not surprising considering China’s rapid industrial development. The correlation of HBB concentrations with human population was not statistically significant and is not included in Figure 2. There is not much known about the production and use of HBB; thus, it is difficult to interpret this result. Correlation with Atmospheric Concentrations. Figure 3 shows the relationship between the concentrations of total PBDE and DP in tree bark compared to the concentrations of these compounds in the atmosphere surrounding the tree. Atmospheric data for total PBDE and DP concentrations are mainly from the GAPS network (passive air sampling over a three month period),26,27 as well as from Salamova and Hites (active high-volume air sampling every 12 days over 2005− 2007),1 Hu et al. (active high-volume air sampling seasonally over 2008−2009),2 and Zhao et al. (estimated from bark−air partitioning coefficient).13 Corresponding bark data from the three latest studies1,2,13 have also been included. Both air and bark total PBDE concentrations feature similar BDE congener suites and include major congeners such as BDE-28, -47, -99, -100, -153, -154, -183, and -209. Both of these relationships are highly significant (r2 > 0.40, P < 0.021) and both cover 2−3 orders of magnitude. Interestingly, the site at Cape Grim, Tasmania, is a high outlier in both relationships because the high atmospheric concentrations of PBDE and DP reported by

Figure 3. The regression of the concentrations of (A) total polybrominated diphenyl ethers (PBDE) and (B) Dechlorane Plus (DP) in tree bark (ng/g lipid weight) versus the measured atmospheric concentrations (pg/m3). The details of the regression lines are: (A) PBDEs, r2 = 0.64, P = 0.0003; and (B) DP, r2 = 0.40, P = 0.021.

the GAPS network27,29 were not confirmed by our bark measurements for these compounds at this location. Bark−air partition coefficients for total PBDE and for DP were calculated using the average bark and atmospheric data from Figure 3 (only bark data from this study and the corresponding GAPS atmospheric data were used). For each bark−air concentration pair, the coefficient was calculated using the following:33 KBA =

CB CA

(1)

where CB is the concentration of a specific compound in tree bark (ng/g lipid weight) and C A is the atmospheric concentration of the same compound. To rectify the units in eq 1, we note that 1 m3 air weighs 1.2 kg at 25 °C. The common logarithms of KBA values were averaged over all the sites for total PBDE and DP. The log(KBA) values for total PBDE and DP were 6.0 ± 0.2 and 5.9 ± 0.2, respectively. These values are in good agreement with our previous estimates of log(KBA) values for total PBDE and DP (∼6)1 and with the log(KBA) value for total PBDE from Zhao et al. (∼8).13 In addition, our log(KBA) values are in good agreement with previously estimated log(KBA) values for other persistent organic pollutants, including polychlorinated biphenyls (∼8),13 polycyclic aromatic hydrocarbons (∼ 6),33 and toxaphene (∼6).9 Taken together with our previous findings,1 these results suggest that tree bark is an excellent passive sampler for the measurement of persistent organic compound concentrations in air. Using bark as a passive sampler is an easy and costeffective sampling method that can be particularly useful in tracing the sources of pollutants.

■

ASSOCIATED CONTENT

S Supporting Information *

Additional experimental details on the quality control and quality assurance results, the materials used in this study, and a figure on the PBDE congener distribution profiles. This 353

dx.doi.org/10.1021/es303393z | Environ. Sci. Technol. 2013, 47, 349−354

Environmental Science & Technology

Article

diphenyl ether and octabromodiphenyl ether). Official Journal L 042, 15/02/2003. (16) European Court of Justice. Cases C-14/06 and C-295/06, Judgment of the Court, 1 April 2008, Directive 200/95/EC and Commission Decision 2005/717/EC; 2008. (17) U.S. Environmental Protection Agency. Deca-BDE Phase-out Initiative. http://www.epa.gov/oppt/existingchemicals/pubs/ actionplans/deccadbe.html (accessed December 4, 2012). (18) HBCD Factsheet, Bromine Science and Environmental Forum (BSEF). http://www.bsef/library/library-2009/ (accessed December 4, 2012). (19) Vorkamp, K.; Bester, B.; Rigét, F. F. Species-specific time trends and enantiomer fractions of hexabromocyclododecane (HBCD) in biota from East Greenland. Environ. Sci. Technol. 2012, 46, 10549− 10555. (20) Salamova, A.; Hites, R. A. Discontinued and alternative brominated flame retardants in the atmosphere and precipitation from the Great Lakes basin. Environ. Sci. Technol. 2011, 45, 8698− 8706. (21) Venier, M.; Ma, Y.; Hites, R. A. Bromobenzene flame retardants in the Great Lakes atmosphere. Environ. Sci. Technol. 2012, 46, 8653− 8660. (22) Möller, A.; Xie, Z.; Cai, M.; Sturm, R.; Ebinghaus, R. Brominated flame retardants and Dechlorane Plus in the marine atmosphere from Southeast Asia towards Antarctica. Environ. Sci. Technol. 2012, 46, 3141−3148. (23) deWit, C. A. An overview of brominated flame retardants in the environment. Chemosphere 2002, 46, 583−624. (24) Stockholm Convention on Persistent Organic Pollutants (POPs); Interim Secretariat for the Stockholm Convention, United Nations Environmental Programme (UNEP) Chemicals, Geneva, Switzerland, October, 2001. http://www.pops.int (accessed August 13, 2012). (25) Pozo, K.; Harner, T.; Wania, F.; Muir, D. C. G.; Jones, K. C.; Barrie, L. A. Toward a global network for persistent organic pollutants in air: results from the GAPS study. Environ. Sci. Technol. 2006, 40, 4867−4873. (26) Koblizkova, M.; Genualdi, S.; Lee, S. C.; Harner, T. Application of sorbent impregnated polyurethane foam (SIP) disk passive air samplers for investigating organochlorine pesticides and polybrominated diphenyl ethers at the global scale. Environ. Sci. Technol. 2012, 46, 391−396. (27) Sverko, E. Determination of Dechlorane Plus and related compounds in the environment. Ph.D. Dissertation, McMaster University, Hamilton, Ontario, 2011. (28) Simonich, S. L.; Hites, R. A. Global distribution of persistent organochlorine compounds. Science 1995, 269, 1851−1854. (29) Sverko, E.; Tomy, G. T.; Reiner, E. J.; Li, Y. F.; McCarry, B. E.; Arnot, J. A.; Law, R. J.; Hites, R. A. Dechlorane Plus and related compounds in the environment: a review. Environ. Sci. Technol. 2011, 45, 5088−5098. (30) Hoh, E.; Zhu, L.; Hites, R. A. Dechlorane Plus, a chlorinated flame retardant, in the Great Lakes. Environ. Sci. Technol. 2006, 40, 1184−1189. (31) Salamova, A.; Hites, R. A. Dechlorane Plus in the atmosphere and precipitation near the Great Lakes. Environ. Sci. Technol. 2011, 45, 9924−9930. (32) Covaci, A.; Harrad, S.; Abdallah, M. A. E.; Ali, N.; Law, R. J.; Herzke, D.; de Wit, C. A. Novel brominated flame retardants: a review of their analysis, environmental fate and behavior. Environ. Int. 2011, 37, 532−556. (33) Simonich, S. L.; Hites, R. A. Vegetation-atmosphere partitioning of polycyclic aromatic hydrocarbons. Environ. Sci. Technol. 1994, 28, 939−943.

material is available free of charge via the Internet at http:// pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by the Great Lakes National Program Office of the U.S. Environmental Protection Agency (grant no. GL00E76601-0, Todd Nettesheim, project manager). We also thank Sum Chi Lee, Tom Harner, Ed Sverko, and the GAPS Network operators for their help with sampling and GAPS data.

■

REFERENCES

(1) Salamova, A.; Hites, R. A. Evaluation of tree bark as a passive atmospheric sampler for flame retardants, PCBs, and organochlorine pesticides. Environ. Sci. Technol. 2010, 44, 6196−6201. (2) Hu, J.; Jin, J.; Wang, Y.; Ma, Z.; Zheng, W. Levels of polybrominated diphenyl ethers and hexabromocyclododecane in the atmosphere and tree bark from Beijing, China. Chemosphere 2011, 84, 355−360. (3) Guéguen, F.; Stille, P.; Millet, M. Air quality assessment by tree bark biomonitoring in urban, industrial and rural environments of the Rhine Valley: PCDD/Fs, PCBs and trace metal evidence. Chemosphere 2011, 85, 195−202. (4) Meredith, M. L.; Hites, R. A. Polychlorinated biphenyl accumulation in tree bark and wood growth rings. Environ. Sci. Technol. 1987, 21, 709−712. (5) Hermanson, M. H.; Hites, R. A. Polychlorinated biphenyls in tree bark. Environ. Sci. Technol. 1990, 24, 666−671. (6) Hermanson, M. H.; Johnson, G. W. Polychlorinated biphenyls in tree bark near a former manufacturing plant in Anniston, AL. Chemosphere 2007, 68, 191−198. (7) Sturaro, A.; Parvoli, G.; Doretti, L. Plane tree bark as a passive sampler of polycyclic aromatic hydrocarbons in an urban environment. J. Chromatogr. 1993, 643, 435−438. (8) Clarkson, P. J.; Larrazabal-Moya, D.; Staton, I.; McLeod, C. W.; Ward, D. B.; Sharifi, V. N.; Swithenbank, J. The use of tree bark as a passive sampler for polychlorinated dibenzo-p-dioxins and furans. Int. J. Environ. Anal. Chem. 2002, 82, 843−850. (9) McDonald, J. C.; Hites, R. A. Radial dilution model for the distribution of toxaphene in the United States and Canada on the basis of measured concentrations in tree bark. Environ. Sci. Technol. 2003, 37, 475−481. (10) Zhu, L.; Hites, R. A. Brominated flame retardants in tree bark from North America. Environ. Sci. Technol. 2006, 40, 3711−3716. (11) Qiu, X.; Hites, R. A. Dechlorane Plus and other flame retardants in tree bark from the northeastern United States. Environ. Sci. Technol. 2008, 42, 31−36. (12) Wang, Q.; Zhao, Y.; Yan, D.; Yang, L.; Li, Z.; Huang, B. Historical records of airborne polycyclic aromatic hydrocarbons by analyzing dated corks of the bark pocket in a Longpetiole Beech tree. Environ. Sci. Technol. 2004, 38, 4739−4744. (13) Zhao, Y.; Yang, L.; Wang, Q. Modeling persistent organic pollutant (POP) partitioning between tree bark and air and its application to spatial monitoring of atmospheric POPs in mainland China. Environ. Sci. Technol. 2008, 42, 6046−6051. (14) Hites, R. A. Polybrominated diphenyl ethers in the environment and in people: a meta-analysis of concentrations. Environ. Sci. Technol. 2004, 38, 945−956. (15) Directive 2003/11//EC of the European Parliament and of the Council of 6 February 2003 amending for the 24th time Council directive 76/769/EEC relating to restrictions on the marketing and use of certain dangerous substances and preparations (pentabromo354

dx.doi.org/10.1021/es303393z | Environ. Sci. Technol. 2013, 47, 349−354