Decabrominated Diphenyl Ethers (BDE-209) in Chinese and Global Air

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Decabrominated diphenyl ethers (BDE-209) in Chinese and global air: Levels, gas/particle partitioning, and long-range transport: Is long range transport of BDE-209 really governed by the movement of particles? Yi-Fan Li, Li-Na Qiao, Nanqi Ren, Ed Sverko, Donald Mackay, and Robie W. Macdonald Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 15 Dec 2016 Downloaded from http://pubs.acs.org on December 15, 2016

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Environmental Science & Technology

1

Decabrominated diphenyl ethers (BDE-209) in Chinese and

2

global air: Levels, gas/particle partitioning, and long-range

3

transport: Is long range transport of BDE-209 really governed

4

by the movement of particles?

5 6

Yi-Fan Li1,2*,, Li-Na Qiao1, Nan-Qi Ren1, Ed Sverko1,2, Donald Mackay3, Robie W.

7

Macdonald4

8 9

1

Arctic Environment Research Group, International Joint Research Center for

10

Persistent Toxic Substances (IJRC-PTS-AERG), State Key Laboratory of Urban

11

Water Resource and Environment, School of Municipal and Environmental

12

Engineering, Harbin Institute of Technology, Harbin 150090, China

13

2

IJRC-PTS-NA, Toronto, M2N 6X9, Canada

14

3

Trent University, Peterborough, ON. K9J 7B8, Canada

15

4

Institute of Ocean Sciences, Department of Fisheries and Oceans, P.O. Box 6000,

16

Sidney, BC, V8L 4B2, Canada

17 18 19 20 21

________________________ * To whom correspondence should be addressed. E-mail: [email protected].

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This article contains supporting information online at www.pnas.org/

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1

ACS Paragon Plus Environment


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TOC Figure

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26 27

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Abstract

29

In this paper, we report air concentrations of BDE-209 in both gas- and

30

particle-phases across China. The annual mean concentrations of BDE-209 were from

31

below detection limit (BDL) to 77.0 pg·m-3 in the gas-phase and and 1.06-728 pg·m-3

32

in the particle-phase. Among the 9 PBDEs measured, BDE-209 is the dominant

33

congener in Chinese atmosphere in both gas and particle phases. We predicted the

34

partitioning behavior of BDE-209 in air using our newly developed steady state

35

equation, and the results matched the monitoring data worldwide very well. It was

36

found that the logarithm of the partition quotient of BDE-209 is a constant, and equal

37

to -1.53 under the global ambient temperature range (from -50 to +50°C). The

38

gaseous fractions of BDE-209 in air depends on the concentration of total suspended

39

particle (TSP). The most important conclusion derived from this study is that,

40

BDE-209, like other semivolatile organic compounds (SVOCs), cannot be sorbed

41

entirely to atmospheric particles; and there is a significant amount of gaseous

42

BDE-209 in global atmosphere, which is subject to long-range atmospheric transport

43

(LRAT). Therefore, it is not surprising that BDE-209 can enter the Arctic through

44

LRAT mainly by air transport rather than by particle movement. This is a significant

45

advancement in understanding the global transport process and the pathways entering

46

the Arctic for chemicals with low volatility and high octanol-air partition coefficients,

47

such as BDE-209.

48

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49 50

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Introduction Poly brominated diphenyl ethers (PBDEs), an important group of brominated

51

flame

retardants

(BFRs),

52

pentabromodiphenyl

53

(ComOctaBDE), and decabromodiphenyl ether (ComDecaBDE)1. These PBDE

54

formulations have been widely applied to products used in daily life. For example,

55

ComPentaBDE was added to flexible polyurethane foam, which is used as cushioning

56

in upholstered furniture; ComOctaBDE was added to acrylonitrile butadiene styrene;

57

and ComDecaBDE was added to the high-impact polystyrene components in

58

electronic equipment2, 3.

ether

derive

from three major commercial

(ComPentaBDE),

octabromodiphenyl

products: ether

59

PBDEs’ high production volume, widespread use, and environmental persistence,

60

have led to their ubiquitous presence in the environment. PBDEs are developmental

61

neurotoxicants, which at sufficient exposure lead to neurochemical and hormonal

62

deficiencies4-6. As a result, ComPentaBDE and ComOctaBDE were regulated in

63

Europe and the Unites States in 2002 and 2003, respectively7, and added to the list of

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persistent organic pollutants (POPs) under the Stockholm Convention at the 4th

65

Conference of the Parties (COP-4) held in May 2009. ComDecaBDE, with BDE-209

66

as the major compound, remains as the only commercial PBDE product still being

67

produced and used, which has been detected in many regions,8, 9 including remote

68

areas.10 Historically, ComDecaBDE has been produced in the largest volumes of any

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commercial PBDE (1.3 million t in 1970-2010 globally; 11 30,000 t in China in 200512

70

and 15,000 t in 2006,13 which has undoubtedly led to a large accumulated load in the

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environment presenting poorly understood risks14. Human exposure of PBDEs in

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houses15 and industrial plants16 has drawn more attention. The air inhalation of both

73

gaseous and particle-bound PBDEs and dust ingestion in indoor environment are

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exposure pathways. What’s more, the indoor air is a significant source of PBDEs to

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outdoor air.17

76

It is widely believed by those monitoring the atmosphere18-21 and by modelers22-26

77

that BDE-209 in air is almost entirely sorbed on particles due to its low vapor

78

pressure (PL) and high octanol-air partition coefficient (KOA). As a consequence,

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BDE-209 has been viewed strictly as a particulate component in the atmosphere,

80

which then dominates perspectives on relevant atmospheric processes and modeled

81

outcomes of its environmental fate (e.g., degradation, long-range transport)22-24, 27, 28.

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In a previous study29, we developed an equation to calculate the gas/particle (G/P)

83

partition quotient (log KP) for PBDEs, including BDE-209, using steady state rather

84

than thermodynamic equilibrium. The steady-state equation predicts that, under

85

steady state, the logarithm of the G/P partition quotient for PBDE congeners reaches a

86

constant value (-1.53) once the logarithm of the octanol-air partition coefficient (log

87

KOA) reaches a threshold value (=12.5), which contradicts the outcome of assuming

88

that equilibrium states apply30. Having the largest value of KOA among all PBDE

89

congeners at the same temperature, BDE-209 provides the greatest contrast between

90

steady state and equilibrium partitioning behavior and we are, therefore, particularly

91

interested in the partitioning behavior of this compound.

92

The main objectives of this work are (1) to investigate the levels of BDE-209 in

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93

the ambient atmosphere in both gas- and particle-phases, especially the gas-phase, by

94

taking advantage of our extensive monitoring program China-POPs SAMP-II across

95

China21 (Supporting Information (SI), Section S1) and other programs worldwide; (2)

96

to analyze the gas-particle partitioning of this compound in air; and (3) to evaluate

97

long-range atmospheric transport (LRAT) of BDE-209 to answer the question “Is long

98

range atmospheric transport of BDE-209 really governed by the movement of

99

particles?”

100

101

Materials and Methods

102

Monitoring

103

The annual mean concentrations of BDE-209 and for 9 PBDE congeners

104

(BDE-17, -28, -47, -99, -100, -153, -154, -183, and -209) in both gas- and particle

105

phases at the 15 sampling sites (Figure SI S1) from September 2008 to August 2009

106

from the China-POPs SAMP-II data set are depicted in the Supporting Information

107

(Table SI S1). In a previous study21, BDE-209 was reported only for the

108

particle-phase, given the widely-held belief that this compound was entirely sorbed in

109

the particle-phase and also because the instrument used in that study (Varian CP-3800

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gas chromatograph coupled with an electron capture detector (GC/ECD)) having high

111

detection limits for BDE-209 (0.72 pg·m-3). Here, we have requantified BDE-209

112

captured in polyurethane foam (PUF) using Agilent 6890-5975B gas chromatography

113

mass spectrometry (GC-MS) in electron capture negative ionization mode. A DB-5

114

MS capillary chromatographic column (15 m × 0.25 mm × 0.10 µm, J&W Scientific)

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was used to separate BDE-209 from other chemicals. The concentrations of BDE-209

116

of particle phase in 200 samples which were randomly chosen from more than 700

117

samples under SAMP-II were re-measured using GC-MS and the results were

118

compared to the concentrations of BDE-209 in the same samples that were

119

determined by GC-ECD. The results of comparison indicated that more than 80

120

percent of data pairs are within the range of standard error of ± 20% (Figure SI S2).

121

Therefore, both data measured by GC-MS and GC-ECD were considered acceptable;

122

and thus we use BDE-209 in gas phase measured in GC-MS and in particle phase

123

measured in GC-ECD in the present study.

124

Details of the sample collection, instrumental analysis, and quality assurance and

125

quality control can be found in Yang et al.21 and Li et al.29, and is presented in SI,

126

Section S2.

127

Methods

128

Gas-particle partitioning

129

Partitioning of atmospheric semi-volatile organic compounds (SVOCs) between

130

gas- and particle-phases is usually presented by the partition quotient, KP (m3·µg-1),

131

given by Yamasaki et al31 and Li et al29:

132

KP = (CP / TSP) / CG

(1)

133

where CG and CP are concentrations of gas- and particle- phases (in pg·m-3 of air),

134

respectively, and TSP is the concentration of total suspended particle in air (µg·m-3). It

135

is important to note that the partition quotient, KP, defined in Equation (1) is termed

136

the partition coefficient under equilibrium, KPE, when CG and CP are under

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equilibrium conditions, and the partition coefficient under steady state, KPS, when CG

138

and CP are under steady state conditions29.

139 140 141

The particle phase fraction of a chemical (φP = CP/(CG+CP)) is related to KP as follows:

φP = KP TSP / (1+ KP TSP)

(2)

142

Several gas-particle partitioning adsorption/absorption models have been

143

developed to describe the phase distribution of SVOCs in the global

144

atmosphere. Based on equilibrium conditions, the dominant absorption processes

145

between gas and particle phases, and equivalence of octanol to organic matter in

146

particles, Harner and Bidleman30 derived the following equation to calculate the

147

equilibrium partition coefficient, KPE, for nonpolar SVOCs as

148

log KPE = log KOA + log fOM -11.91

(3)

149

where fOM is the organic matter content of the particles and KOA is octanol-air partition

150

coefficient, which is a function of temperature T (in K)32

151

logKOA (t) = A+B/T

(4)

152

where parameters A and B for PBDEs are listed in Table SI S4. Unfortunately, these

153

two parameters are not yet available for BDE-209.

154

Another useful model of G/P partitioning is based on poly-parameter linear free

155

energy relationships (pp-LFERs).25, 26 This model can be used to both non-ionic polar

156

and nonpolar chemicals by taking both the absorption and adsorption processes into

157

account. It was found that, for the nonpolar SVOCs, such as PCBs and DDTs,

158

the pp-LFER-based model is similar to the Harner-Bidleman model 26, and

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both approaches were suggested to be appropriate for multimedia models with a

160

sorptive capacity dominated by organic matter. It was also pointed out, however, that

161

practical application of the pp-LFER-based model to a wide range of chemicals

162

(PBDEs for example) is currently limited by data gaps in measured parameters

163

(Abraham solvation parameters) needed for solving the model. The relationships

164

between the solvation parameters and meteorological parameters, such as temperature,

165

are also unclear. Thus we do not discuss this model in the present work.

166

In our previous work29, we developed an equation to calculate the partition

167

coefficient under steady state, KPS, by including the wet and dry deposition of

168

particles in studying the G/P partition of PBDEs:

169

log KPS = log KPE + log α

(5a)

170

where log KPE is designated the equilibrium term, given by Equation (3), and log α is

171

the non-equilibrium term, given by

172

log α = -log(1+4.18x10-11 fOMKOA)

(5b)

173

Therefore, we have two predicted partition coefficients: partition coefficient KPS

174

under steady state when the system is in steady state but not equilibrium state and

175

partition coefficient KPE under equilibrium when the system is in both steady state and

176

equilibrium. Equation (5a) indicates that the equilibrium is just a special case of the

177

steady state when log α = 0, or the wet and dry deposition of particles can be ignored.

178

Threshold values of log KOA and temperature T

179

An important result from Equation (5a) is the identification of two kinds of

180

threshold values of log KOA, log KOA1 (=11.4) and log KOA2 (=12.5), and

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temperature,29 which produce three partitioning domains: The EQ (equilibrium)

182

domain when log KOA < log KOA1 or t > tTH1; the NE (non-equilibrium) domain when

183

log KOA ≥ log KOA1 or t ≤ tTH1; and the MP (maximum partition) domain when log

184

KOA ≥ log KOA2 or t ≤ tTH2. These two kinds of threshold values are related by the

185

following equations: 29

186

tTH1(°C) = B/(log KOA1 – A) – 273.15

(6a)

187

tTH2(°C) = B/(log KOA2 – A) – 273.15

(6b)

188

where parameters A and B for PBDEs are listed in SI Table SI S4 for various PBDE

189

congeners.

190

The partitioning behaviour of a given PBDE congener mainly depends on the

191

octanol-air partition coefficient (KOA), which is a function of ambient temperature.

192

Equations (3) and (5) imply obvious differences in G/P partition coefficients between

193

log KPS and log KPE when log KOA ≥ log KOA1, which become larger when the values of

194

log KOA increases (shown in Figure SI S3). One appealing result is that, while Equation

195

(3) predicts the linear relationship between log KPE and log KOA, Equation (5) leads to a

196

conclusion that when log KOA ≥ log KOA2 the logarithm of G/P partition coefficient at

197

steady state (log KPS) levels off, reaches a constant value (log KPSM = -1.53), and is

198

apparently independent of log KOA and accordingly the temperature.

199

log KOA of BDE-209

200 201 202

The temperature dependence of KOA was calculated using33 log KOA(T) = log KOA0 + ∆UOA/[2.303R(1/T – 1/T0)]

(7)

where KOA0 is the value at reference temperature T0 (for example, 298.15 K), T is

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203

average temperature of each sampling event, R is the universal gas constant (8.314

204

J·mol-1·K-1), and ∆UOA is internal energy of phase transfer between octanol and air in

205

J·mol-1. Comparing Equation (7) to Equation (4) leads to the formulas for A and B B =∆UOA/(2.303R)

(8a)

A = log KOA0 - BO / T0

(8b)

206 207

Results

208

BDE-209 concentrations in China

209

The annual mean concentrations of BDE-209 and for 9 PBDE congeners (BDE-17,

210

-28, -47, -99, -100, -153, -154, -183, and -209) in both gas- and particle phases at the

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15 sampling sites from September 2008 to August 2009 from the China-POPs

212

SAMP-II data set are provided in Table SI S1. Concentration data of BDE-209 in gas

213

phase at Guangzhou site is not available due to the missing of the gas samples at this

214

site. The concentrations of BDE-209 in the gas-phase were in the range of 10.2-77.0

215

pg·m-3 for urban sites, 8.30 pg·m-3 for suburban site, and BDL (below detection limit)

216

for the remote/rural sites, whereas concentrations in the particle-phase according to the

217

three site types were in the range of 10.7-728 pg·m-3, 46.4 pg·m-3, and 1.06-6.20

218

pg·m-3, respectively. The mean percentages of gas-phase BDE-209 to total gas-phase

219

∑9PBDEs were 49.7% with a range from 23.7% in Nanchang to 81.0% in Beijing,

220

while those for particle-phase were higher, 84.6% with a range from 72.8% in Dalian

221

to 95.0% in Beijing. Similar to what was observed for the particle-phase, the

222

concentrations of 9 PBDE congeners in gas-phase were also dominated by BDE-209 at

223

most sites. 11



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224

Data available for BDE-209 in both gas- and particle-phase in air elsewhere in

225

China (See Table S5, SI) are comparable to the results obtained in this study. For

226

example, it was reported that air concentrations of BDE-209 at 6 urban and 11 rural

227

sites in North China in 2010 were 4.0 ± 6.1 pg·m-3 for gas-phase and 37 ± 69 pg·m-3

228

for particle-phase34. BDE-209 air concentrations at rural sites in Yunnan, China in

229

2006 were 2.17 ± 2.46 pg·m-3 for gas-phase and 15.90 ± 10.46 pg·m-3 for

230

particle-phase35. Air concentrations of BDE-209 in both gas and particle phases were

231

measured in Shanghai in 2011, 6.72 and 65.8 pg·m-3 for gas and particle phase,

232

respectively, at urban sites, and 13.2 and 3.86 pg·m-3 for gas and particle phase,

233

respectively, at rural sites, indicating almost 2 times higher concentrations in the

234

gas-phase but one order of magnitude lower in particle phase at rural sites compared

235

to urban sites36. In our study, BDE-209 concentrations at the Shanghai suburban site

236

were 8.30 pg·m-3 for gas phase and 46.4 pg·m-3 for particle phase.

237

BDE-209 concentrations in other countries

238

Air concentrations of BDE-209 in Europe and North America were quite low. In

239

Europe, 4.3-52 pg·m-3 for gas-phase and 9.5-46 pg·m-3 for particle-phase in the City

240

of Izmir in 2004-200537, and 3.0-150 pg·m-3 for gas-phase and 15-100 pg·m-3 for

241

particle-phase in the Izmir Bay, Turkey in 2005 were observed38 . In downtown Paris,

242

France, 4.61 ± 6.26 pg·m-3 for gas-phase and 21.79 ± 38.68 pg·m-3 for particle-phase

243

were found in 2008-200939. Even lower concentrations, 0.12 ± 0.04 for gas-phase and

244

1.98 ± 1.28 pg·m-3 for particle-phase, were measured at a French coastal site in

245

2007-200840. Air concentrations of BDE-209 similar to those found in Europe were

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also observed in North America. In urban centers of Chicago and Cleveland,

247

BDE-209 was around 2-4 pg·m-3 for gas-phase and 13-60 pg·m-3 for particle-phase,

248

but only < 1 pg·m-3 and 2-3 pg·m-3 respectively at rural sites in 2005-200941. Even

249

lower concentrations of BDE-209 were measured at remote sites, around 0.2-0.5

250

pg·m-3 for gas-phase and ~1 pg·m-3 for particle-phase in 2004-200941, 42, which is

251

comparable to concentrations observed in Canadian Arctic air with higher

252

concentrations in gas-phase (0.83 ± 0.94 pg·m-3) than those in particle-phase (0.20 ±

253

0.15 pg·m-3) in 2007-200843.

254

Gas-particle partitioning of BDE-209

255

Two descriptors, the octanol-air partition coefficient (KOA) and subcooled vapor

256

pressure (PL) have been employed to describe the partitioning behavior of SVOCs. In

257

a previous study29, the descriptor KOA was used for calculating the partition

258

coefficient of PBDE congeners under steady state (Equation (5)). The values for log

259

KOA for BDE-209, however, are lacking and only the value at 25 oC has been

260

estimated: 15.27 by Wania and Dugani22, 14.98 by Cetin and Odabasi37, 16.8 by

261

Schenker et al.44, and 15.24 by Zhang et al.45. Here, we estimate the values of log KOA

262

for BDE-209 as a function of temperature using the log KOA0 value of 15.2722 and the

263

∆UOA value of 80 000 J·mol-1

264

BDE-209, which are 1.25 and 4179, respectively.

23

in Eq. (8), and calculated the values of A and B for

265

Log KOA values for BDE-209 are much higher than the other eight PBDE

266

congeners (14.2 at +50°C to 20.0 at -50°C. As discussed in the previous section, the

267

values of log KPS reach the MP domain with log KPSM = -1.53 when log KOA > log

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KOA2 (= 12.5). Figure 1 presents ranges of log KOA for BDE-209 and other 8 PBDE

269

congeners in the ambient temperature range of -50 − +50°C (those for other

270

temperature ranges, -50 − 0°C, -30 − +30°C, and 0 − +50°C, are displayed in Figure

271

SI S4). It is clear that among all 9 BDE-congeners, BDE-209 is the only one that is

272

within the MP domain over the entire environmentally relevant temperature range of

273

-50°C − +50°C.

274

275 276 277

Figure 1.

278

Figure 1. The range of log KOA for 9 PBDE congeners (BDE-17, -28, -47, -99, -100,

279

-153, -154, -183, and -209) in the ambient temperature range of -50°C − 50°C. It is

280

obvious that only BDE-209 is within the MP domain in this temperature ranges.

281 282

The first and second temperature threshold values, tTH1 and tTH2, are also

283

calculated using Equation (6) for the 9 PBDE congeners. As presented in Figure 2,

284

while the threshold values of log KOA1 and log KOA2 are constants for all PBDE 14


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285

congeners, the threshold values of tTH1 and tTH2 differ. These two temperature threshold

286

values also produce three domains; the EQ domain when t > tTH1, the NE domain when

287

t ≤ tTH1, and the MP domain when t ≤ tTH2. As an example, with a tTH1 = +11 oC and tTH2

288

= -6 oC, BDE-47 is in the EQ domain when t > +11oC; in the NE domain when t ≤

289

+11oC; and in the MP domain at t ≤ -6 oC. For BDE-209, tTH1 = 139 oC and tTH2 = 98 oC,

290

once again indicating that BDE-209 is within the MP domain in the realistic ambient

291

temperature range from -50°C to +50°C.

292

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293 294

295 296

Figure 2.

297

Figure 2. The first and second threshold temperatures, tTH1 and tTH2 for the 9 PBDE

298

congeners, which divide the temperature space into the three domains (EQ, NE, and

299

MP). The light-blue shaded area indicates the ambient temperature range from -50°C

300

to +50°C. The figure clearly indicates that BDE-209 is within the MP domain under

301

this temperature range.

302 303

The steady state G/P partitioning theory for PBDEs leads to an important

304

prediction for BDE-209; namely, the logarithm of the measured partition quotient (log

305

KPM) at any ambient temperature and at any site except the sites with strong BDE-209

306

emissions (such as e-waste sites or manufacturers of Deca-BDEs) is a constant (=

307

-1.53). In a complex environmental system, however, we cannot expect that the

308

measured values of log KPM should be exactly equal to -1.53. In order to derive steady 16


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309

state Eq. (5), several assumptions have to be made; for example, the annual rainfall

310

was assumed to be 0.5 m·yr-1 and fOM was set equal to 0.1.29 Real environmental

311

conditions, however, may not be the same as those we assumed. Other factors, such as

312

sampling and analytical artifacts, measurement error, and wind speed, could also

313

affect the partitioning behavior of BDE-209. Thus the real values of log KPM could

314

deviate from -1.53. Taking into consideration of these factors, we define a maximum

315

partition range (MPR) as -0.5 ≥ log KPM ≥ -2.5 in our study, within which, the

316

observed and the predicted partitioning coefficients are within one order of magnitude

317

accuracy. Accordingly, we expect that the values of log KPM for BDE-209 should

318

mainly be in the MPR, and would not depend on log KOA and the ambient

319

temperature.

320

Here, the monitoring data, both from the China POPs SAMP-II program and

321

other sources, are used to verify this important prediction for BDE-209 in the

322

atmosphere worldwide.

323

The values of log KPM of BDE-209 in all 15 sampling sites, analyzed as functions

324

of temperature between -22°C and 38°C, as presented in Figure 3, show that the

325

majority (97.7%) of the values of log KPM are within the MPR, with their regression

326

line almost coinciding with the line of log KP = -1.53. The values of log KPM do not

327

change with temperature (the slope = -0.001 and R = 0.0245 with confidence of 95%).

328

These prediction results are obviously superior to those predicted by the

329

Harner-Bidleman Equation, which overestimates the values of log KPM for BDE-209

330

by ~2 orders of magnitude at 35oC and ~7 orders of magnitude at -20oC.

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331

The relationship between log KPM and temperature for BDE-209 at each sampling

332

site (Figure SI S5a) also indicate that most values of log KPM are within the MPR at

333

each sampling site and the Li-Ma-Yang Equation can predict 97.7 ± 3.8% (from

334

87.8% to 100%) of the observed partitioning quotients within one order of magnitude

335

accuracy across these 11 sampling sites. The regression lines for the 11 sampling sites

336

have slopes ranging from -0.029 to 0.0179 and a regression coefficient R from 0.081

337

to 0.521 with confidence of 95%, suggesting no or weak dependence of log KPM on

338

temperature. Thus, for BDE-209, there may be failure to approach equilibrium

339

conditions, as indicated by the levelling-off of the measured log KP values as shown

340

in Figures 3 and SI S5a.

341 342

Figure 3.

343

Figure 3: The values of log KP as function of temperature for BDE-209 from

344

China_POPs SAMP-II. The red line indicates the maximum partition value of -1.53

345

m3/µg. The relationship between log KP with temperature as predicted by the

346

Harner-Bidleman model (Eqs. (3) and (4)) is also included for comparison. 18


Page 19 of 34


347 348

The relationship between log KP and log KOA is also important for verifying the

349

steady-state theory. The temperature range under China POPs SAMP-II is from -22°C

350

to 38°C, corresponding to the range of log KOA from 15.4 to 17.9 for BDE-209, which

351

is much higher than log KOA2 (=12.5). As shown in Figure SI S5b, similar to what we

352

observed in the relationship between log KP and temperature, most values (97.7%) of

353

log KPM at all sites versus log KOA are within the MPR and do not change with log

354

KOA (the slope = 0.024 and R = 0.0374 with confidence of 95%).

355

The steady-state conditions found for BDE-209 at other sites appear to apply

356

widely based on findings reported in the open literature as discussed below.

357

However, to make comparisons we have had to assume reasonable values for TSP

358

(µg/m3) at most sites: 30 in summer and 50 in winter in Izmir Bay, Turkey and Zurich,

359

Switzerland, 50 in summer and 100 in winter in downtown Paris, France, 100 in

360

Tengchong, China, and 10 through whole year in Alert, Canada.

361

BDE-209 and other 6 PBDE congeners (BDE-28, -47, -99, -100, -153, and -154)

362

were determined at four sites (1 suburban, 2 urban, and 1 industrial) in the City of

363

Izmir, Turkey in summer and winter in 2004-2005 with a temperature range of 1.8 -

364

22.4oC37. Calculated partition coefficients of log KPS using Eq. (5) closely match the

365

monitoring data (Figure SI S6), and the log KPM values for BDE-209 at the 4 sites

366

were very close to the values of log KPSM (-1.53), from -1.56 to -1.37 (-1.50 ± 0.09).

367

Similar measurements of BDE-209 in air sampled at Izmir Bay, Turkey in July and

368

December, 200538 (Figure SI S7), show that all the log KPM values are within the

19



369

Page 20 of 34

MPR with the values from -2.04 to -0.67 (-1.70 ± 0.38).

370

The G/P partitioning behavior was estimated for BDE-209 in Zurich, Switzerland

371

measured in 2010 and 2011 with a temperature range from -5 to 30 oC24 (Figure SI

372

S8). The log KPM values match our prediction well all the log KPM values are within

373

the MPR with the values from -2.15 to -0.50 (-1.44 ± 0.36).

374

G/P partitioning behavior was studied for BDE-209 measured in downtown Paris,

375

France in 2010 with a temperature range of 1.3 to 22.5 oC39. The partition quotient log

376

KPM calculated using Eq. (1) well match our predictions (Figure SI S9), 85.2% of the

377

measured log KPM values are within the MPR with the values from -2.25 to 0.22

378

(-1.12 ± 0.59).

379

G/P partitioning behavior was calculated for BDE-209 using both the gas- and

380

particle-phase concentration at rural sites in Yunnan, China in 2006,35 and the results

381

are presented in Figure SI S10. All the measured log KPM values are within the MPR

382

with the values from -2.49 to -0.49 (-1.12 ± 0.41).

383

The Arctic provides a particularly good location to test the steady state theory due

384

to the low temperature and, thus, high values for log KOA, not only for PBDEs but also

385

for other SVOCs. According to steady-state calculations, BDE-209 in Arctic air

386

should be in MP domain, with a constant of log KPSM (-1.53). This prediction agrees

387

well with monitoring data collected in 6 years from 2006 to 201246 over a sampling

388

temperature range of 14.4 to -41.6 oC (Figure SI S11). Indeed, this remarkable dataset

389

shows that the majority (87.2%) of the measured log KPM values are within the MPR

390

with the mean value of -1.74 ± 0.63 (from -2.97 to 1.36).

20


Page 21 of 34


391

Particle phase fraction

392

Another important parameter, the particle-phase fraction, φP, has often been used

393

to describe the partitioning behavior of SVOCs in air. The prediction that 100% of

394

BDE-209 is sorbed to particles due to its very high octanol-air partition coefficient

395

23,24

396

steady-state conditions, the φP for BDE-209 as a function of TSP is not 100% but

397

varies from 12.9% when TSP = 5 µg·m-3 to 85.5% when TSP = 200 µg·m-3. The

398

monitoring data illustrated here in Figure 4 are consistent with these predicted values

399

for both φP and φG. It is interesting to note that the values of φG tend to be lower in

400

populated regions with high TSP than in the remote regions with low TSP, with Arctic

401

air providing the lowest TSP/highest φG values.

is not consistent with our estimated partitioning values (Figure 4). Under

402

21



Page 22 of 34

403

100

Particle-phase

90

φ P and φ G (%)

80 70 60 50 40 30

Gas-phase

20 10 0 0

20

40

60

80 100 120 140 160 180 200 -3

TSP (µg m ) 404 405

Figure 4.

406

Figure 4: The gas and particle phase fractions of BDE-209 in air as a function of TSP.

407

The solid lines are values predicted by Equation (2), and the open symbols are

408

monitoring data. Diamonds: Arctic46 (average for 6-year data); Triangles: Izmir Bay

409

and Izmur City37,38; Squares: Zurich24; Circles: China (This study. TSP = 100 µg·m-3,

410

average for 90-110 µg·m-3; TSP = 150 µg·m-3, average for 140-160 µg·m-3; and TSP

411

= 200 µg·m-3, average for 190-210 µg·m-3).

412 413

22


Page 23 of 34


414

Discussions

415

In this paper, we have theoretically analyzed partitioning behavior of BDE-209 in

416

air and compared that with monitoring data worldwide. This comparison clearly

417

indicates that the proportion of BDE-209 in gas phase under ambient temperature

418

ranges is far higher than those have been assumed or reported in the literatures.

419

Comparison of the results by equilibrium and steady-state equations indicates that

420

BDE-209 is under steady state, not at equilibrium under any ambient temperature

421

conditions. In these cases, the logarithm of its partition quotient is a constant (-1.53).

422

The BDE-209 gaseous and particulate phase fractions in air, however, are not

423

constants, but depend on the values of TSP.

424

The issue of artifacts. A higher fraction of gas phase BDE-209 and lower

425

fraction in the particle phase in monitoring data than those predicted by equilibrium

426

calculations have been noted by others24. A sampling artifact in which very fine

427

particles pass the filters and end up on the PUFs has been proposed as a possible

428

explanation. Thus, the fraction of PBDEs quantified in the PUFs may partly be

429

contributed by fine particulates. This sort of artifact may contribute to gas-phase

430

measurements. On the other hand, it was recognized that fiber filters commonly used

431

to collect aerosols for various analyses also collect gaseous organic chemicals during

432

sampling. This sort of artifact may favorite to particle-phase measurements47.

433

According to the comparisons provided here, however, the departure of G/P partition

434

quotients of PBDEs from the equilibrium is mainly due to the wet and dry deposition

435

of particles, not the artifacts. The influence of the artifacts to the G/P partition of

23



Page 24 of 34

436

SVOCs has been possibly overemphasized. Thus, the steady state equation (Equation

437

5), not the equilibrium equation (Equation 3), should be used in calculating the G/P

438

partition quotients for PBDEs, including BDE-209 discussed in the present study.

439

G/P partitioning behavior for other chemicals with high log KOA values. The

440

most appealing result from the steady-state equation (5) is the existence of the PM

441

Domain for PBDEs, in which the logarithm of G/P partition coefficient at steady state

442

(log KPS) equals a constant value (log KPSM = -1.53) when log KOA ≥ log KOA2, or t ≤

443

tTH2. This was also observed for other SVOCs.

444

Previously, we reported the partitioning behavior of non-PBDE brominated flame

445

retardants

(NBFRs),

such

as

l,2,5,6,9,10-hexabromocyclododecane

(HBCD),

446

decabromodiphenylethane (DBDPE), and 1,2-bis(2,4,6-tribromophenoxy)-ethane

447

(BTBPE), indicating that the values of log KPM of most samples fall into the MPR

448

range48 (90.5% for HBCD, 87.5% for BTBPE, and 100% for DBDPE) (see Figures

449

SI S12). The mean values (±SD) of log KPM are -1.11 ± 0.52 for HBCD, -1.16 ± 0.45

450

for BTBPE, and -1.45 ± 0.51 for DBDPE. In addition, four alternative halogenated

451

flame retardants, namely 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (EHTBB), bis

452

(2-ethylhexyl) tetrabromophthalate (BEHTBP), syn-dechlorane plus (syn-DP) and

453

anti-dechlorane plus (anti-DP) based on samples from Harbin, China, from 2008 to

454

2013 collected over a temperature range of -30°C to 29°C. The values of logKOA of

455

EHTBB, BEHTBP, syn-DP and anti-DP were 12.3, 16.9, 14.8, and 14.8 at 25°C,

456

respectively (estimated by KOAWIN in EPI Suite v4.1), close to, or above, the

457

second threshold value for PBDEs (log KOA2=12.5)36. Variation of log KPM for these 4

24


Page 25 of 34


458

chemicals with temperature (Figures SI S13) shows that most samples fall into the

459

MPR range (100% for EHTBB and BEHTBP, 85.0% for syn-DP, and 85.7% for

460

anti-DP). The mean values (±SD) of log KPM are -1.40 ± 0.23 for EHTBB, -1.53 ±

461

0.40 for BEHTBP, -1.29 ± 0.63 for syn-DP, and -1.06 ± 0.71 for anti-DP. It is clear

462

from these figures that the steady-state behavior of air-borne BDE-209 would also

463

apply to these seven flame retardants. On the other hand, the predicted log KPE by

464

Equation (3) are much higher than the monitoring data by 4-7 orders of magnitudes.

465

Long range transport of BDE-209 is governed by the movement of air, not

466

particles. BDE-209 has been considered as a nonvolatile BFR, sorbed almost entirely

467

to the particles in the atmosphere based on its very high octanol-air partition

468

coefficient or low vapor pressure 22, 49. This point of view has a profound influence on

469

projections of the environmental fate (e.g., LRAT) of this compound. As a particulate,

470

it has been suggested that BDE-209 would not distribute widely through the

471

atmosphere despite intense use in the industrialized world 22, 50, and would be difficult

472

to transport to the Arctic via LRAT50.

473

Monitoring data, however, show another story. Gouin et al.18, Hoh and Hites51,

474

and Cahill et al.52 identified BDE-209 in atmospheric particle samples collected at

475

various sites in North America, which included some sites far away from populated

476

and industrial centers. More importantly, BDE-209 was also found in Arctic air

477

particulates by Wang et al.53, in ice cores from Holtedahlfonna, Svalbard, Norway at

478

concentrations many times greater than the more volatile BDE-4950, and, most

479

significantly in the context of this paper, a high proportion of BDE-209 was found in

25



480

Page 26 of 34

the gas phase in Arctic air46.

481

These observations suggest that BDE-209 widely distributes through the

482

atmosphere and enters the Arctic through LRAT. This puzzling phenomenon was

483

explained by the proposal that LRAT must occur for BDE-209 by the movement of

484

particles, not air,22,23 and this particle transport could travel great distances, especially

485

during the Arctic haze seasons54.

486

According to the data and calculations provided here, particulate transport is not

487

actually required for BDE-209 to enter the Arctic. Even though it has high log KOA

488

properties, a significant proportion of BDE-209 remains in the gas phase, especially at

489

low TSP concentrations. From a global perspective, gaseous BDE-209 is abundant in

490

air (87.1% when TSP = 5 µg·m-3 to 14.5% when TSP = 200 µg·m-3 from our equation),

491

and is the dominant congener presented in gas phase in many populated areas, like

492

China. Similar to other SVOCs, gas phase BDE-209 is subject to LRAT with the

493

result that there is a general migration from warmer to colder areas leading to eventual

494

accumulation in Polar Regions55, 56. Furthermore, without further evaluation, it is

495

risky to assume that other toxic chemicals with high KOAs are entirely constrained to

496

the atmospheric particulate phase.

497

Associated content

498

Supporting Information

499

The Support Information: Sampling and analytical method details; The predicted and

500

monitored G/P partition coefficients of PBDEs as functions of log KOA and ambient

501

temperature; The log KP of other chemicals; Statistics of concentrations for ∑

26


Page 27 of 34


502

9PBDEs and BDE-209 in gaseous and particulate phases (pg·m-3); and Concentrations

503

for BDE-209 at gas- and particle-phases in different cities and places worldwide

504

(PDF)

505

Author Information

506

Corresponding Author

507

*Phone: +86 0451 86289130; e-mail: [email protected].

508

Acknowledgment

509

This work was supported by the National Natural Science Foundation of China (No.

510

21577030 and 41671470), the Independent Project of State Key Laboratory of Urban

511

Water Resource and Environment (HIT) (No. 2016DX09), and the HIT Environment

512

and Ecology Innovation Special Funds (No. EEISF1601). The air monitoring at the

513

three background/rural sites, a component of the International Polar Year (IPY)

514

Project (#327), was financially supported by the Government of Canada Program and

515

International Joint Research Center for Persistent Toxic Substances (IJRC-PTS-0805),

516

China. Wen-Long Li and Li-Na Qiao from IJRC-PTS of Harbin Institute of

517

Technology measured the BDE-209 in PUFs collected under China POPs SAMP-II

518

Program using Agilent 6890-5975B GC-MS. YFL thanks Hayley Hung from

519

Environment and Climate Change of Canada for providing PBDE data at Alert Station

520

and valuable comments and suggestions and Chongguo Tian from Yantai Institute of

521

Coastal Zone Research, China, for helpful discussion.

522

27



Page 28 of 34

523

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