Has the Phase-Out of PBDEs Affected Their Atmospheric Levels

Sep 23, 2013 - Alternative Flame Retardant, 2,4,6-Tris(2,4,6-tribromophenoxy)-1,3 .... Environmental Science & Technology 2016 50 (1), 321-330 .... Mu...
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Has the Phase-Out of PBDEs Affected Their Atmospheric Levels? Trends of PBDEs and Their Replacements in the Great Lakes Atmosphere Yuning Ma, Amina Salamova, Marta Venier, and Ronald A. Hites* School of Public and Environmental Affairs, Indiana University, Bloomington, Indiana 47405, United States S Supporting Information *

ABSTRACT: Air and precipitation samples were collected every 12 days at five sites near the North American Great Lakes from 2005 to 2011 (inclusive) by the Integrated Atmospheric Deposition Network (IADN). The concentrations of polybrominated diphenyl ethers (PBDEs) and selected alternative brominated flame retardants [pentabromoethyl benzene (PBEB), hexabromobenzene (HBB), 1,2-bis(2,4,6-tribromophenoxy)ethane (TBE or BTBPE), decabromodiphenylethane (DBDPE), 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB), and bis(2-ethylhexyl)-tetrabromo-phthalate (TBPH)] were measured in these samples. The concentrations of almost all of these flame retardants were related to the number of people within a 25 km radius of the sampling site, except for HBB, the concentrations of which were relatively high at Sturgeon Point, and PBEB, the concentrations of which were relatively high at Eagle Harbor. The temporal trends of all of these concentrations were variable. For example, BDE-47 vapor phase concentrations were increasing with doubling times of 5−10 years at Sturgeon Point, Sleeping Bear Dunes, and Eagle Harbor, but these concentrations were slowly decreasing in all phases at Chicago. The most consistent trend was for TBE, which showed concentrations that were unchanging or decreasing in all phases at all sites. TBPH concentrations in particles and HBB concentrations in precipitation were rapidly increasing at most sites with doubling times of ∼2 years. The concentrations of DBDPE and BDE-209 were strongly and positively correlated, and the concentrations of TBB and TBPH were also strongly and positively correlated. The concentrations of TBB plus TBPH (representing Firemaster 550) and BDE-47, 85, 99, 100, 153, plus 154 (representing the withdrawn penta-BDE commercial mixture) were also strongly and positively correlated. These positive relationships indicate that the replacement of the deca-BDE commercial product by DBDPE and the penta-BDE product by Firemaster 550 have not yet become evident in the Great Lakes’ atmospheric environment.

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INTRODUCTION Brominated flame retardants (BFRs) slow the spread of fire in numerous commercial and consumer products.1 From about 1980 until 2004, polybrominated diphenyl ethers (PBDEs) were among the most widely used BFRs,2 but when their environmental persistence became apparent, their manufacturers voluntarily ceased production.3 In the United States, sales of the two major commercial PBDE products, penta- and octa-BDEs, stopped at the end of 2004,3 and the last major PBDE product, deca-BDE, will have been completely withdrawn from the market by the end of 2013.3 To replace these PBDE products, the flame retardant industry has turned to other brominated compounds. These include tetrabrominated aromatic esters, some of which might have adverse toxicological and ecological effects.4,5 One such replacement is Firemaster 550, which contains 2-ethylhexyl2,3,4,5-tetrabromo-benzoate (TBB), bis(2-ethylhexyl)-tetrabromophthalate (TBPH), and aromatic phosphate esters. Other highly brominated compounds such as 1,2-bis(2,4,6tribromophenoxy)ethane (TBE or BTBPE) and decabromodi© XXXX American Chemical Society

phenylethane (DBDPE) have also come into their own as replacements for PBDEs.6 A few monocyclic aromatic compounds, with lower production volumes, such as hexabromobenzene (HBB) and pentabromoethyl benzene (PBEB), have also found new flame retardant applications during this “flame retardant revolution.”6 More recently, organophosphorus flame retardants have reemerged on the market based on the presumption that they are less environmentally persistent than some of the previously used BFRs.6−8 Given this change in the compounds being used as flame retardants over the past few years, it is timely to measure the rates at which the concentrations of brominated flame retardants are changing (if at all) in the environment. We have made these measurements in the context of the Integrated Atmospheric Deposition Network (IADN), which Received: July 9, 2013 Revised: August 22, 2013 Accepted: September 5, 2013

A

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concentrations in samples collected in the Great Lakes region and in the east-central United States during 2002 to 2004.11 Those preliminary findings lead to the inclusion of about 35 PBDE congeners and other brominated and chlorinated flame retardants on the routine list of IADN analytes starting in 2005. Some of this data has been reported before. Venier and Hites reported the atmospheric PBDE, TBE, and DBDPE levels near the Great Lakes from 2005 to 2006 (inclusive),12 and Salamova and Hites reported the atmospheric levels of PBDEs, TBE, DBDPE, HBB, and PBEB in samples collected at the same sites from 2005 to 2009 (inclusive).13 In the study reported here, the atmospheric concentrations of 35 PBDE congeners (7, 10, 15, 17, 28, 30, 47, 49, 66, 85, 99, 100, 119, 126, 138−140, 153, 154, 156, 169, 180, 183, 184, 191, 196, 197, 201, 203−209) and 6 alternative brominated flame retardants (TBE, DBDPE, HBB, PBEB, TBB, and TBPH) were measured in about 1500 samples (see Table 1 for the exact numbers) collected at the five United States’ IADN sites around the North American Great Lakes from 2005 to 2011 (inclusive). By adding two more, full years of data (2010 and

has focused on the spatiotemporal trends of persistent organic pollutant atmospheric concentrations around the North American Great Lakes basin since 1990.9 The earlier analytes of interest to IADN included polychlorinated biphenyls, organochlorine pesticides, and polycyclic aromatic hydrocarbons, but flame retardants were preliminarily added to this list beginning in 1997. The first PBDE results for these locations were published by Strandberg et al., who analyzed 48 IADN samples collected between 1997 and 1999.10 Four years later, Hoh and Hites reported more atmospheric PBDE

Table 1. Average Concentrations (± Standard Error) and Detection Frequencies of the Flame Retardants Analyzed at the Five IADN Sitesa Chicago conc.

Cleveland %det

conc.

98 91 68 100 86 77 62

N1 = 190 13 ± 1 a 6.1 ± 0.4 a 1.3 ± 0.2 b 25 ± 2 a 1.3 ± 0.1 b 0.81 ± 0.12 b 0.37 ± 0.09 b

Sturgeon Point %det

conc.

97 81 56 100 93 77 14

N1 = 200 2.5 ± 0.2 b 2.7 ± 0.3 b 0.51 ± 0.07 c 7.3 ± 0.8 b 0.098 ± 0.007 d 5.3 ± 0.6 a 0.19 ± 0.02 b

Sleeping Bear Dunes %det

conc.

77 59 66 100 89 96 41

N1 = 203 2.9 ± 0.3 c 3.6 ± 0.4 b 0.79 ± 0.18 c 6.0 ± 0.6 bc 0.046 ± 0.005 e 0.19 ± 0.04 c 0.21 ± 0.04 b

Eagle Harbor

%det

conc.

%det

90 76 58 100 65 72 56

N1 = 206 2.1 ± 0.2 bc 2.9 ± 0.3 b 0.64 ± 0.11 c 4.7 ± 0.4 c 1.9 ± 0.2 a 0.16 ± 0.04 c 0.19 ± 0.06 c

71 54 45 100 74 65 23

Vapor (pg/m3) BDE-47 BDE-99 BDE-209 tot BDE PBEB HBB TBE

15 ± 1 a 5.6 ± 0.5 a 3.6 ± 0.5 a 32 ± 2 a 0.73 ± 0.04 c 0.67 ± 0.08 b 0.53 ± 0.05 a

Particle (pg/m3) BDE-47 BDE-99 BDE-209 tot BDE PBEB HBB TBE DBDPE TBB TBPH

N1 = 192, N2 = 105 4.8 ± 0.3 b 79 4.1 ± 0.4 b 90 12 ± 1 b 92 24 ± 1 b 100 0.076 ± 0.013 c 72 0.32 ± 0.04 a 67 1.3 ± 0.2 a 70 3.2 ± 0.5 ab 43 4.3 ± 0.3 a 90 5.3 ± 0.6 a 85

N1 = 193, N2 = 105 6.7 ± 0.4 a 82 9.4 ± 0.9 a 72 33 ± 5 a 95 52 ± 6 a 100 0.14 ± 0.02 b 84 0.40 ± 0.06 a 65 0.88 ± 0.08 a 88 5.2 ± 0.9 a 54 4.2 ± 0.5 a 70 8.0 ± 1.4 a 91

N1 = 199, N2 = 108 1.2 ± 0.1 c 52 1.8 ± 0.1 c 73 2.6 ± 0.2 c 63 7.9 ± 0.6 c 100 0.068 ± 0.028 d 20 0.23 ± 0.02 a 48 0.34 ± 0.07 c 81 1.8 ± 0.5 bc 17 0.69 ± 0.10 b 55 0.99 ± 0.13 b 81

N1 = 199, N2 = 115 0.82 ± 0.05 e 67 1.4 ± 0.1 d 78 1.9 ± 0.2 d 67 4.5 ± 0.4 e 100 0.044 ± 0.020 e 22 0.11 ± 0.02 b 47 0.56 ± 0.08 b 55 2.8 ± 0.9 c 23 0.42 ± 0.17 c 36 0.48 ± 0.10 c 53

N1 = 203, N2 = 115 1.1 ± 0.1 d 49 1.9 ± 0.3 c 46 1.1 ± 0.2 e 78 4.2 ± 0.4 d 100 1.0 ± 0.1 a 24 0.11 ± 0.02 b 46 0.20 ± 0.05 c 27 1.2 ± 0.4 c 8 0.80 ± 0.16 b 55 0.88 ± 0.15 b 63

Precip. (ng/L) BDE-47 BDE-99 BDE-209 tot BDE PBEB HBB TBE DBDPE TBB TBPH

N1 = 79, N2 = 24 14 ± 3 a 99 5.1 ± 1.2 a 97 2.1 ± 0.3 a 97 29 ± 5 a 100 0.0046 ± 0.0008 bc 63 0.93 ± 0.23 ab 76 0.085 ± 0.013 a 84 0.49 ± 0.07 ab 75 56 ± 12 a 96 3.2 ± 1.1 ab 96

N1 = 76, N2 = 22 1.3 ± 0.2 c 100 0.61 ± 0.13 b 100 5.5 ± 1.3 a 99 8.5 ± 1.5 b 100 0.0054 ± 0.0007 b 89 0.13 ± 0.03 c 86 0.061 ± 0.007 a 92 0.75 ± 0.18 a 74 10 ± 2 b 95 2.3 ± 0.7 ab 91

N1 = 81, N2 = 22 6.7 ± 1.4 ab 63 0.16 ± 0.02 d 86 0.54 ± 0.08 b 99 7.8 ± 1.5 c 100 0.0068 ± 0.0011 b 48 1.4 ± 0.3 a 77 0.028 ± 0.004 bc 75 0.41 ± 0.13 c 72 53 ± 11 a 100 6.7 ± 2.3 ab 100

N1 = 85, N2 = 25 6.8 ± 2.5 bc 82 0.99 ± 0.35 bc 85 0.54 ± 0.07 b 99 10 ± 3 c 100 0.0034 ± 0.0006 c 61 0.94 ± 0.30 abc 88 0.037 ± 0.005 b 75 0.29 ± 0.06 bc 68 31 ± 16 ab 88 24 ± 13 b 80

N1 = 80, N2 = 1.3 ± 0.3 c 0.23 ± 0.02 cd 0.44 ± 0.09 b 3.1 ± 0.5 c 0.020 ± 0.003 a 0.29 ± 0.05 bc 0.018 ± 0.003 c 0.15 ± 0.02 c 21 ± 5 ab 13 ± 4 a

N1 = 192

23 100 100 99 100 85 89 53 39 91 83

a

The concentrations are averaged over the years 2005−2011, inclusive. DBDPE, TBB, and TBPH were rarely detected in the vapor phase; hence, their concentrations are not reported here. ANOVA results for the log-transformed concentrations are given after the concentrations; the concentrations are not significantly different (P < 0.05) for those locations sharing the same letter. N1 is the sample size for the PBDEs, PBEB, HBB, TBE, and DBDPE. N2 is the sample size for TBB and TBPH. B

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method starting with the 2011 samples to further enhance the reliability of these data. The recovery of at least two out of the three recovery standards (BDE-77, BDE-166, and 13C12−BDE209) was between 70% and 130%. Field blanks were collected at every site seasonally. All the analytical standards except BDE118 were purchased from Wellington Laboratories, Guelph, ON. On average, the levels for all target analytes in the field blanks were 100 pg/m3). The overall average atmospheric concentrations (vapor + particle) in the Great Lakes region were ∼0.1−3 pg/m3 for PBEB, 0.3−5.5 pg/m3 for HBB, 0.4−1.8 pg/m3 for TBE, 1.2− 5.2 pg/m3 for DBDPE, 0.4−4.3 pg/m3 for TBB, and 0.5−8.0 pg/m3 for TBPH (Table 1). Atmospheric data against which these measurements can be compared are very limited. A few atmospheric concentrations of these compounds have been reported at remote oceanic or polar sites (SI Table S1). The overall levels of PBEB, HBB, TBE, TBB, and TBPH reported here were generally similar to those measured at other remote sites (SI Table S1). This is true even though two of these sampling sites were in the cities of Chicago and Cleveland. DBDPE levels in IADN samples are much lower than the reported concentrations of this compound in rural China (SI Table S1), suggesting higher DBDPE use in China than in North America. Spatial Trends. Because BDE-47, -99, and -209 were the three most abundant PBDE congeners found in all the samples, data for only those congeners are reported here along with the total concentration of all the 35 PBDE congeners measured. The average concentrations over the seven year time period, 2005−2011, for these PBDE congeners and for all of the other compounds (except for TBB and TBPH, which range from 2008 to 2011) measured in this study are given in Table 1. The average concentrations are listed for the vapor, particle, and precipitation phases at each site. Analyses of variance (ANOVA) of the logarithmically transformed concentrations were done on a compound-by-compound basis, and these results are given in Table 1. As expected, the atmospheric concentrations of almost all of these compounds were significantly higher in the cities (Chicago and Cleveland) and lower at the rural and remote sites (Sturgeon Point, Sleeping Bear Dunes, and Eagle Harbor). This is true for the vapor, particle, and precipitation phase samples, although the ANOVA is slightly ambiguous for the precipitation samples because of the relatively higher errors associated with these measurements. For the vapor and particle phases, this relationship can be parametrized as suggested by Venier and Hites, who used the square of the common C

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Cleveland.13 In this case, the size of the population gives only a partial description of the situation. These data suggest that more flame retardants are used or that more flame retardanttreated products are manufactured in the greater Cleveland area than in Chicago. The second anomaly is that two high outliers have been omitted from the plots in Figure 1: The first outlier is an average of 5.5 pg/m3 measured for HBB at Sturgeon Point, and the second outlier is an average of 2.9 pg/m3 measured for PBEB at Eagle Harbor. In fact, HBB concentrations were significantly higher in all three phases at Sturgeon Point, and PBEB concentrations were significantly higher in all three phases at Eagle Harbor. These anomalies for HBB at Sturgeon Point and PBEB at Eagle Harbor have been noticed before, and Venier et al. used potential source contribution function modeling to try to explain them. The conclusion of this modeling was that there may be local sources of these two compounds at these sites.14 Current results for HBB and PBEB are consistent with these previous results, although it is still not known what those local sources might be. DBDPE was introduced to replace the deca-BDE commercial mixture, which will be coming off the market at the end of 2013.3 In the atmospheric concentrations reported here, most of the DBDPE (like BDE-209) was associated with the particle phase and with precipitation. The DBDPE levels in these phases were similar to those of BDE-209 except for Cleveland, where the average concentration of BDE-209 was much higher than that of DBDPE. This observation further supports the suggestion that there are point or industrial sources of BDE-209 in the greater Cleveland area. Tian et al. measured PBEB, HBB, TBE, and DBDPE concentrations in atmospheric samples collected at a rural site in southern China.15 The reported geometric mean concentrations of these four compounds were 0.53, 3.1, 1.7, and 81 pg/m3, respectively. These concentrations are about a factor of 10 higher than those measured in Chicago and Cleveland for HBB and DBDPE, about the same as those measured in Chicago and Cleveland for TBE, and about the same as those measured in Eagle Harbor for PBEB. Although the southern China site has a slightly warmer climate, it is not at all obvious what Eagle Harbor and rural China might have in common that would account for this PBEB result. TBB and TBPH, the major components of Firemaster 550, were not consistently detected in vapor phase samples, but these two compounds were present in most of the particle phase samples from Chicago, Cleveland, and Sturgeon Point and in about half of the particle phase samples from the remote sites at Eagle Harbor and Sleeping Bear Dunes. Ma et al. reported that TBB and TBPH measured in 2008−2010 (inclusive) were more abundant at the urban sites than at rural or remote sites in the Great Lakes region.16 In the study reported here, data from the year 2011 were added, and a similar spatial trend for these compounds was analyzed on a site by site basis. TBB and TBPH concentrations in the particle phase were the highest in Chicago and Cleveland and the lowest at Sleeping Bear Dunes. Levels of TBB and TBPH in precipitation are reported here for the first time. These concentrations are not distinctly differentiated from one another by site, probably because of the relative high errors associated with these measurements. Our data suggests that TBB and TBPH tend to partition to the particle phase in the air and are washed out by precipitation.

logarithm of the population living and working within a 25 km radius of the sampling site as the independent variable and the logarithm of the concentrations as the dependent variable:12 log(Cv + p) = a0 + a1log 2(pop)

(1)

Figure 1 shows this relationship for the vapor plus particle phase concentrations for each of the compounds measured in

Figure 1. Concentrations of several brominated flame retardants in the atmosphere around the North American Great Lakes as a function of the number of people living and working within a 25 km radius of the sampling site. The population metric is the square of the common logarithm of the number of people. These populations are: Chicago 3 579 651; Cleveland 1 301 787; Sturgeon Point 68 361; Sleeping Bear Dunes 16 097; and Eagle Harbor 481.

this study. The relationships are significant at the probabilities given in each panel. All of these probabilities are significant at P ≤ 10%, and five are significant at P ≤ 5%. The strengths of these population-based predictions suggest that all of these flame retardants, the “old-timey” PBDEs and the emerging TBB and TBPH among them, have sources closely related to human population density. This finding is not surprising given that these chemicals are added to a variety of products that are commonly used in everyday activities such as furniture padding, consumer electronics, and vehicle interiors.2,5 There are two anomalies to this conclusion that should be specified: First, the concentrations of 7 out of the 10 compounds were higher at Cleveland than at Chicago even though the population was about one-third as high at Cleveland as at Chicago. This has been noticed before, and it has been suggested that this may be related to the presence of one or more point or industrial sources of flame retardants in or near D

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Temporal Trends. Another purpose of this study was to assess long-term temporal trends of PBDE and other flame retardant concentrations in the vapor, particle, and precipitation phases at each of the five sampling sites. Following procedures, developed in our laboratory for polychlorinated biphenyls and pesticides, the natural logarithms of the concentrations as a function of time were fitted by a harmonic regression17,18 ln(C) = a0 + a1sin(zt ) + a 2cos(zt ) + a3t

= 5) showed significant seasonality. These differences may be a result of lower overall concentrations of BDE-47 in the particle phase and in precipitation compared to the vapor phase. As expected,18 the vapor phase concentrations maximized in July and August, and the particle phase and precipitation concentrations maximized in February. Given that the goal of this paper is to look at long-term temporal trends, the a3 coefficients from eq 2 for all three phases and for all compounds have been used to calculate either halving times, if the concentrations were significantly decreasing, or doubling times, if the concentrations were significantly increasing [t = ln(2)/a3]. These times are shown in Figure 3 and in SI Table S5. It is apparent from these data that,

(2)

where C is the flame retardant’s atmospheric concentration in pg/m3; t is the time in Julian days starting from 1 January 2005; z = 2π/365.25 to fix periodicity to one year; a0 is the intercept that rectifies the units; a1 and a2 are the harmonic coefficients that describe seasonal variations; and a3 is the first-order rate constant in days−1, from which the halving or doubling times of a flame retardant’s concentrations can be calculated. Examples of these regressions for BDE-47 in the vapor phase and for BDE-209 in the particle phase are shown in Figure 2; all of the regression parameters for all compounds for all phases are given in the SI.

Figure 3. Halving (negative going bars) and doubling (positive going bars) times (in years) with standard errors for all the compounds analyzed in the vapor (red bars), particle (yellow bars), and precipitation (green bars) samples collected at the five IADN sites during 2005−2011 (inclusive). These times were calculated from the a3 coefficients in eq 2 if they were statistically significant (P ≤ 5%); if no bar is shown, the a3 coefficient was not significant or there were insufficient data for that compound in that phase to determine a regression.

Figure 2. Temporal regressions of BDE-47 concentrations in the vapor phase and BDE-209 concentrations in the particle phase (both in pg/m3) at the five IADN sites. If all four coefficients in eq 2 were statistically significant at P ≤ 5%, the resulting regression is shown as the solid red waveform. If only the a3 term was significant, this regression is shown as the dotted red straight line. If none of the terms were significant, no line is shown.

with a few exceptions, these concentrations are neither consistently increasing nor decreasing. The concentrations of BDE-47, which is usually the most abundant of the PBDE congeners, are decreasing with halving times of 5−9 years in the vapor and particle phases at Chicago and Cleveland but are increasing with doubling times of 7−11 years in the vapor phase and 2−4 years in precipitation at the other sites. BDE209 concentrations are not changing significantly at any site or

Some of these regressions (N = 13) showed statistically significant coefficients for the seasonality terms (a1 and a2) for some compounds in the vapor phase at some sites; for example, BDE-47 had a significant seasonality at Chicago and Cleveland (Figure 2, top left). On the other hand, only a few of the compounds in the particle phase (N = 4) or in precipitation (N E

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in any phase, except for the particle phase at Cleveland and Sturgeon Point, where the halving times are ∼5 years. Total PBDE (“tot BDE”) concentrations are increasing in one or the other phase at Sturgeon Point, Sleeping Bear Dunes, and Eagle Harbor but decreasing in the particle phase at Cleveland and in precipitation in Chicago. Overall, these data suggest that PBDEs are still persisting in the environment and are being removed from the environment slowly, if at all. PBEB concentrations are all decreasing with halving times of 5−10 years at all sites except at Eagle Harbor, the most remote site, where the highest PBEB concentrations were measured in all three phases. HBB concentrations are generally increasing in precipitation but decreasing in the vapor phase (with the exception of Sturgeon Point, where HBB concentrations were significantly higher in all three phases) both with times of 2−4 years. The one clear case is for TBE, the concentrations of which are unchanged or decreasing with halving times of ∼4 years in all three phases at all sites. For DBDPE and TBB, the data are too sparse to say much about the temporal trends of these compounds. For TBPH the concentrations at three of the five sites are increasing with a doubling time of ∼2 years. In general, the levels of most of those alternative flame retardants are now decreasing in the Great Lakes atmosphere, with the possible exception of TBPH in particles and HBB in precipitation. Previous work from our laboratory by both Venier and Hites12 and Salamova and Hites13 (the latter used pooled data for all the sites and phases together), concluded that the concentrations of the major PBDEs in the air over the Great Lake region were generally decreasing. The results shown in Figure 3 may indicate that this conclusion was premature; for example, the concentrations of total PBDEs at Eagle Harbor are now increasing in all the three phases when two more years’ of data are added. This is an unexpected result given that lower molecular weight PBDEs had been withdrawn from the market in 2004 and that BDE-209 will be withdrawn at the end of 2013.3 These results may indicate that the environment has some hysteresis, at least for PBDEs. It is also important to remember that when a material leaves the chemical marketplace (for example, the penta-BDE mixture in 2004), products manufactured using that chemical (for example, polyurethane foam) are still present (for example, in homes, schools, and businesses) long after that date. The environmental levels of these flame retardants will probably begin to consistently respond to market changes, especially at remote locations, when these manufactured products reach the end of their useful life and are permanently removed from the environment. It is also interesting that the vapor-phase concentrations of BDE-47 are decreasing in the cities but are increasing at the other three sites. This may indicate that there is a time lag between the withdrawal of the penta-BDEs from the market and the effect of this withdrawal on rural and remote atmospheric concentrations. Because cities are where most flame retardants are used, the effect of such a withdrawal from the market may be felt more quickly in the cities than in more remote regions. The concentrations of BDE-209, the commercial formulation of which (deca-BDE) will have been withdrawn from the market by the end of 2013,3 are already at a steady state at most sites over the period 2005−2011. Overall, the halving or doubling times of these, now classic, PBDEs are similar to those of polychlorinated biphenyls and some organochlorine pesticides.18

There are few data against which these temporal trend results can be compared. There have been a few short-term (1−2 year) trend studies reported for Point Petre (a rural site near Lake Ontario),19 Toronto,20 and the GAPS network,21 but the only study comparable to the one reported here is one in which PBDE atmospheric concentrations were measured from 2000 to 2010 at four sites in the United Kingdom.22 The total PBDE concentrations observed in that study were generally about 10 pg/m3 (the total of both the vapor and particle phases), which is similar to the Great Lakes results at the nonurban locations. In addition, these authors reported halving times at all four of their sites on the order of 2−4 years. The Great Lakes results are less consistent, depending on site and phase, and the halving times are generally slower. It remains to be seen if these differences reflect differences in the chemical management regulations in the United Kingdom as opposed to the United States and Canada or differences in the amounts of specific flame retardants used in Europe as opposed to North America. PBEB levels in the air were decreasing at all sites except for Eagle Harbor, which is puzzling. Given that nothing is known about the production or use history of this compound, it is difficult to interpret these results. Continued monitoring of these contaminants in the atmosphere may be needed to illuminated trends. The same problem applies to HBB, the concentrations of which show about equal numbers of increasing and decreasing trends. The consistent decreasing trends in all three phases for TBE, which came into the market in the mid-1970s and which is still being used in small amounts,11 may indicate that products made with TBE are not now impacting the environment.23 TBB and TBPH are products that are coming into their own on the flame retardant market, and Ma et al. reported that the Great Lakes atmospheric concentrations of TBB plus TBPH from 2008 to 2010 in the particle phase were increasing with doubling times of 1−2 years.16 In this study, one more year’s data were added, the vapor, particle, and precipitation phase concentrations were included, and TBB and TBPH concentrations were analyzed separately on a compound-by-compound and site-by-site basis. Both of these compound concentrations were decreasing in the particle phase at only Sleeping Bear Dunes with halving times of ∼1 year. The concentrations of TBPH in the particle phase were increasing with doubling times of 2−3 years at Chicago, Cleveland, and Sturgeon Point. This is a somewhat slower doubling time than previously reported for these compounds at these sites.16 TBB and TBPH have had different use histories, and this trend analyses may reflect these differences. For example, TBB was mostly used in foams, but TBPH was widely used in various specialized applications such as wire and cable insulation and coated fabrics.24 Among the alternative flame retardants reported here, the concentrations of TBPH were increasing most rapidly, perhaps indicating the current and heavy use of this compound in the commercial flame retardant market. No other studies on the long-term atmospheric temporal trends of TBB and TBPH have been reported. Overall, the halving or doubling times of the now classic PBDEs are longer than those of the emerging alternatives, indicating PBDE’s relative persistence in the environment. Correlations between Compound Concentrations and Relationships with Sources. This long-term data set of both discontinued and alternative flame retardants, covering a 7-year period, gives us a unique opportunity to look at how market shifts may have affected environmental levels. For example, F

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DBDPE had been introduced to the market as a replacement for BDE-209 in anticipation of its eventual withdrawal.6 Thus, it was thought that the concentrations of these two compounds should be negatively correlated; that is, as the environmental concentration of BDE-209 decreased, the concentrations of DBDPE would increase. This is just the opposite of what was observed here; Figure 4, top, shows that the relationship

fTBB =

[TBB] [TBB] + [TBPH]

(3)

where [TBB] and [TBPH] are the concentrations of TBB and TBPH in each sample.16 In Firemaster 550, this fraction is expected to be 0.77 ± 0.03, but for the data presented here, f TBB is 0.45 ± 0.02 (N = 207). This difference suggests that these two compounds may not all come from Firemaster 550. It is also possible, indeed likely, that these two compounds may have different environmental fates and that TBPH may be more persistent than TBB, which would tend to decrease f TBB. Interestingly, the ratio of TBB/TBPH showed a slight decrease as a function of year (r2 = 0.073, P < 0.001), which may indicate that the ratios of TBB/TBPH in the commercial product are changing or that other products containing TBB and TBPH have entered the market. Given the replacement of the penta-PBDE mixture by TBB and TBPH in the marketplace, it is instructive to look at the relationship of the commercial penta-BDE congener concentrations (here represented by the sum of BDE-47, 85, 99, 100, 153, 154 vapor and particle phase concentrations) as a function of the sum of the TBB and TBPH concentrations (in the particle phase). As with the BDE-209/DBDPE replacement, a negative relationship was anticipated, but the data showed the opposite (see Figure 4, bottom). The levels of the penta-BDEs were strongly and positively correlated with those of TBB + TBPH at the IADN sites. In general, this correlation analysis indicated that, like BDE-209/DBDPE, the replacement of the penta-BDE commercial mixture by Firemaster 550 has not yet become evident in the atmospheric environment.

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ASSOCIATED CONTENT

* Supporting Information S

Details of previous measurements of BFRs in the atmosphere, output of the regressions, and correlation plots are given. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected].

Figure 4. Scatterplot showing the pairwise correlations of the natural logarithms of the concentrations (in pg/m3) of BDE-209 vs DBDPE, TBB vs TBPH, and penta-BDEs vs the sum of TBB + TBPH at the five IADN sites. The color coded site legends are given at the very top. The regression lines (in red), the p-values, r 2 values, and the slopes are given in each plot.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Integrated Atmospheric Deposition Network Team for the operation of the network and laboratory support. This work has been funded by the U.S. Environmental Protection Agency’s Great Lakes National Program Office (Grant GL995656, Todd Nettesheim, project officer).

between these concentrations is strongly positively correlated, which may indicate that both of these flame retardants are still being used and share similar applications and sources and that DBDPE is not simply being substituted for BDE-209. Incidentally, a regression of the ratio of the BDE-209/ DBDPE concentrations in each sample vs year showed no relationship (r2 = 0.003), an observation that is consistent with this conclusion. As mentioned above, TBB and TBPH are major components of Firemaster 550, which replaced the penta-BDE commercial mixture. As expected, TBB and TBPH atmospheric concentrations were significantly correlated with one another (see Figure 4, middle); as the concentrations of one increase, the concentrations of the other also increase. We have previously defined f TBB as

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