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The abandoned e-waste recycling site continued to act as a significant source of polychlorinated biphenyls: An in situ assessment using fugacity samplers Yan Wang, Chunling Luo, Shaorui Wang, Zhineng Cheng, Jun Li, and Gan Zhang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b01620 • Publication Date (Web): 18 Jul 2016 Downloaded from http://pubs.acs.org on July 18, 2016

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Environmental Science & Technology

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The abandoned e-waste recycling site continued to act as a significant source of

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polychlorinated biphenyls: An in situ assessment using fugacity samplers

3 4

Yan Wang†, Chunling Luo‡, *, Shaorui Wang‡, Zhineng Cheng‡, Jun Li‡, Gan Zhang‡

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†

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School of Environmental Science and Technology, Dalian University of Technology,

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Dalian 116024, China

9

‡

10

Key Laboratory of Industrial Ecology and Environmental Engineering (MOE),

State Key Laboratory of Organic Geochemistry, Guangzhou Institute of

Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China

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* Corresponding author. E-mail: [email protected]; Tel.: +86-20-85290290; Fax:

13

+86-20-85290706

14 15

1

ACS Paragon Plus Environment


16

ABSTRACT

17

The recycling of e-waste has attracted significant attention due to emissions of

18

polychlorinated biphenyls (PCBs) and other contaminants into the environment. We

19

measured PCB concentrations in surface soils, air equilibrated with the soil, and air at

20

1.5-m height using a fugacity sampler in an abandoned electronic waste (e-waste)

21

recycling site in South China. The total concentrations of PCBs in the soils were

22

39.8−940 ng/g, whereas the concentrations in air equilibrated with the soil and air at

23

1.5-m height were 487−8280 pg/m3 and 287−7380 pg/m3, respectively. The PCB

24

concentrations displayed seasonal variation; they were higher in winter in the soils

25

and higher in summer in the air, indicating that the emission of PCBs from the soil

26

was enhanced during hot seasons for the relatively high temperature or additional

27

sources, especially for low-chlorinated PCBs. We compared two methods (traditional

28

fugacity model and fugacity sampler) for assessing the soil–air partition coefficients

29

(Ksa) and the fugacity fractions of PCBs. The results suggested that the fugacity

30

sampler provided more instructive and practical estimation on Ksa values and trends in

31

air-soil exchange, especially for low-chlorinated PCBs. The abandoned e-waste

32

burning site still acted as a significant source of PCBs many years after the

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prohibition on open burning.

34 35

Keywords: Polychlorinated biphenyls; Fugacity sampler; Air-soil exchange; E-waste

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2


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38 39

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1. INTRODUCTION

41

Although polychlorinated biphenyls (PCBs) have been banned for several

42

decades, they continue to be of significant concern because they are ubiquitous and

43

highly persistent in the environment and can cause numerous harmful health eﬀects 1.

44

PCBs are a group of synthetic organic chemicals formerly used in various industrial

45

and commercial applications that are also present in electronic waste (e-waste). They

46

can be released from the dismantling of e-waste, which has been recognized as an

47

important source of these contaminants 2.

48

The increasing demand for electronic products and the short lifespan of those

49

products have led to a proliferation of outdated electronic devices and waste. The

50

annual amount of global e-waste is estimated at ~50 million tons 3, and approximately

51

80% of this e-waste is disposed in developing countries such as China due to the low

52

labor costs and lax environmental regulations

53

has released a variety of toxic contaminants and caused serious environmental

54

problems

55

frequently detected in the environment around e-waste recycling sites, suggesting

56

severe contamination and risk to ambient ecosystems 5, 12-14. Moreover, the pollutants

57

can be re-released into the atmosphere from contaminated soils under certain

58

conditions, such as high temperature, and undergo both long- and short-range

59

atmospheric transport. This re-emission of pollutants from soils is becoming a major

60

source of atmospheric pollution

61

contamination caused by e-waste recycling

4-7

. The process of dismantling e-waste

6, 8-11

. High concentrations of PCBs and other contaminants have been

15

. Although numerous studies have focused on 1, 4, 16, 17

, information regarding the

4


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interface exchange of PCBs and other contaminants in this contaminated areas is still

63

lacking, especially for in situ field measurements.

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The warm climate in subtropical regions can increase the volatilization of PCBs

65

and other organic contaminants from primary sources (such as e-waste or ashes) and

66

secondary sources (such as contaminated soils), enhancing the interface exchange of

67

PCBs among various environmental media and the potential for long-range

68

atmospheric transport

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warm regions, especially in major e-waste recycling areas, are still poorly understood.

70

Due to increasingly stringent environmental laws and regulations, many old open

71

burning sites have been abandoned, but the environmental fate of e-waste

72

contaminants in those sites remains unknown. The present study addresses this

73

knowledge gap using fugacity samplers to quantify the in situ air-soil exchange of

74

PCBs in a subtropical abandoned e-waste contaminated area.

18

. However, the environmental fate and impact of PCBs in

75 76

2. MATERIALS AND METHODS

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2.1. Sampling.

78

Sampling was conducted in the town of Longtang, Qingyuan City, Guangdong

79

Province, South China [23°34′N, 113°0′E]. The studied area is under the influence of

80

subtropical monsoon climate with an average annual precipitation of 2000 mm. This

81

area was formerly among the most active e-waste recycling areas in subtropical

82

regions, and has been heavily contaminated by e-waste recycling activities.

83

Uncontaminated soils have been brought in and mixed with e-waste contaminated 5



84

soils and nearby soils in 2007. Despite the fact that most e-waste burning activities

85

have been banned and protection measures have been taken, high concentrations of

86

contaminants can still be detected in the ambient environment.

87

The samples were collected simultaneously at two clearing without vegetation:

88

an abandoned e-waste burning site (BS) and a nearby site (~50 m away) covering by

89

outside soil without e-waste burning activities (NBS). A fugacity sampler15, 19 was

90

used to collect the air that had equilibrated in situ with the surface soil. The chamber

91

of this sampler, covering an area of 1 m2, was located at 3−5 cm above the soil surface

92

to force a laminated flow of the equilibrated air parallel to the soil surface (Figure S1

93

in Supporting Information, SI). Air first passed through a glass fiber filter (GFF;

94

47-mm dia.), and then through a polyurethane foam (PUF, 2-cm dia., 9-cm length). To

95

limit disturbance by sampling, a relatively low flow rate of 8−10 L/min was used to

96

obtain an air sample of 12−14 m3 within 24 h. Ambient air samples were also

97

collected at a height of 1.5 m using a sampler with a GFF and PUF identical to those

98

used to collect the soil-equilibrated air. The sampling rate was also 8−10 L/min, which

99

was similar to that for the sampling of soil-equilibrated air.

100

Topsoil samples were collected after the air sampling by carefully collecting

101

samples from the soil surface layer (0−1 cm). Each topsoil sample was a composite of

102

three sub-samples collected under the sampler, which accounted for approximately 50%

103

of the total surface soil under the sampler. The surface soil of 0−5 cm layer at the

104

non-burning site in summer was analyzed, because the topsoil (0−1 cm) was disturbed

105

and covered by loose sandy soils with relatively low concentrations (Total PCBs: 39.8 6


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ng/g). Before the sampling in summer, there was a heavy rain lasted for 5 days with a

107

precipitation of ~290 mm. Therefore, the disturbance may due to uncontaminated soil

108

brought in by runoff during rainy season. To determine the concentrations of organic

109

pollutants in the surface soil, the top 0−5 or 0−10 cm layer is commonly collected 20,

110

21

111

contact with the air, is subject to air–soil partitioning

112

implied that the soil below 1 cm may also participate in the air-soil partitioning of

113

organic pollutants for those sites with loose sandy soil on top. More details are shown

114

in S1 in the SI.

; but previous studies suggested that only the top 0−1 cm layer, which is in direct 19, 22

. However, our study

115

Meteorological data were also monitored using a wireless weather station. The

116

physicochemical characteristics of the samples were measured simultaneously,

117

including air temperature (Air T), soil temperature (Soil T), soil total organic carbon

118

fraction (TOC), and soil total nitrogen fraction (TN). All sampling was conducted

119

during 9–11 December 2011 in winter and 28–29 June 2012 in summer. The average

120

temperatures during the winter and summer sampling periods were 10 °C and 25 °C,

121

respectively.

122 123

2.2. Sample Extraction and Analysis

124

Approximately 10 g freeze-dried topsoil (or PUF sample) was spiked with

125

surrogate standards (2, 4, 5, 6-Tetrachloro-m-xylene (TCMX), PCB30, PCB198, and

126

PCB209) and extracted with dichloromethane (DCM) and activated copper in a

127

Soxhlet apparatus for 48 h. The extract was concentrated to ~0.5 mL using a rotary 7



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evaporator after solvent exchanged with hexane. The extracts were purified with a

129

multi-layer silica gel/alumina column filled with anhydrous Na2SO4, 50% (w/w)

130

sulfuric acid silica gel, neutral silica gel (3% deactivated), and neutral alumina (3%

131

deactivated) from top to bottom with an eluent of 20 mL hexane/DCM (1:1, v/v).

132

After concentration to ~50 µL using a gentle stream of nitrogen,

133

PCB141 was added as the internal standard prior to instrumental analysis for the

134

quantification of PCBs.

13

C12-labelled

135

Twenty-six PCB congeners (indicator PCBs: PCB28, 52, 101, 138, 153, 180;

136

dioxin-like PCBs: PCB77, 105, 114, 118, 156, 189; and other PCBs: PCB37, 44, 60,

137

70, 74, 82, 87, 128, 158, 166, 170, 179, 183, 187) were detected using an Agilent

138

GC7890-5975MSD operated in electron impact ionization and selected ion mode with

139

a 50-m Varian capillary column (CP-Sil 8 CB, 50 m, 0.25 mm, 0.25 µm). The initial

140

oven temperature was set at 150°C for 3 min, raised to 290°C at a rate of 4°C/min,

141

and then held for 10 min. The temperatures of the MSD source and quadrupole were

142

230°C and 150°C, respectively. More details were shown in our previous study 2.

143 144

2.3. QA/QC

145

A procedural blank, a spiked blank, and a field blank (PUF plug and glass fiber

146

filter) sample were analyzed with each batch of 10 samples to assess the potential

147

sample contamination. No target compounds were detected in any of the blanks. The

148

average surrogate recoveries for TCMX, PCB30, PCB198, and PCB209 in all samples

149

were 71.5 ± 12.7%, 76.9 ± 13.8%, 98.8 ± 6.9%, and 101 ± 5.9%, respectively. The 8


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repeatability was evaluated by analyzing three soil sample replicates, which showed

151

that the relative standard deviations were within 0.45−9.7%. Method detection limits

152

were 0.005−0.02 ng/g for soil sample and 0.2−1.0 pg/m3 for air sample.

153 154

2.4. Calculation of Fugacity.

155

Fugacity can be used to determine the potential of a particular chemical to escape

156

from one matrix to another 23. The air fugacity (fa, Pa) of the PCBs was calculated as

157

follows: 24, 25

158

fa = Ca R T

159

where Ca is the PCB concentration in the air (mol/m3), R is the gas constant

160 161

(1)

(8.314 Pa m3/mol/K), and T is the average absolute air temperature (K). Two methods can be used to determine the soil fugacity of PCBs 25. First method:

162

the calculated soil fugacity (fs) can be obtained using the soil fugacity capacity and the

163

measured PCB concentration in soil 15, 26:

164

fs = Cs R T/Ksa= Cs R T/(0.411 ρs φtoc Koa)

(2)

165

where Cs is the PCB concentration in soil (mol/m3), ρs is the soil density

166

(assumed to be 2.5 kg/L), φtoc is the total soil TOC, Ksa is the soil–air partition

167

coefficient, and Koa is the octanol–air partition coefficient, which is strongly

168

temperature dependent. The Koa of the PCB congener was taken from the results of

169

Mackay et al. 27.

170

This assessment is easy to perform because it requires little field-monitoring time

171

and relies largely on calculations based on the soil concentrations of the compound, 9



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soil density, and soil TOC. However, this method also requires the octanol-air

173

partition coefficient, which is temperature dependent. Therefore, it is unsuitable for

174

emerging organic pollutants with unknown/variable properties, or for unstable

175

systems with varied concentrations or environmental parameters (e.g., temperature or

176

organic carbon content).

177

Second method: the measured soil fugacity (ffs) of PCBs was determined by

178

analyzing the concentration of PCBs in air (Csa) that had been equilibrated in situ with

179

the soil surface

180

fugacity sampler was calculated as follows:

19

. The measured soil fugacity based on the measurement of the

181

ffs = Csa R T

(3)

182

Because this method directly measures the concentration in the air in situ

183

equilibrated with the soil, it provides more reliable results during the whole sampling

184

period regardless of variable environmental parameters, which is appropriate for

185

unstable systems.

186

The fugacity fraction (ff) can be used as an indication of the direction of the air–

187

soil exchange of semi-volatile organic compounds 15. The ff is deﬁned as the ratio of

188

soil fugacity to the sum of the soil and air fugacities:

189

ff = fs/(fs + fa)

(4)

190 191

3. RESULTS AND DISCUSSION

192

3.1. PCBs in Soil and Ambient Air.

193

The PCB concentrations in the soils, soil-surface air (equilibrated with the soil), 10


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and ambient air are shown in Table 1. The total concentrations of PCBs in the

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e-waste-contaminated soils were 473 ng/g in winter and 537 ng/g in summer, whereas

196

in the nearby soils, they were 940 ng/g in winter and 198 ng/g (0–5 cm soil layer) in

197

summer. The relatively low concentration of PCBs in the nearby soil in summer may

198

because the topsoil was disturb by the rainfall and subsequent runoff during the rainy

199

season. The rich rainfall may wash away the topsoil with relatively high concentration

200

of PCBs but left the sandy soil with low concentration, or the topsoil may be

201

attributed to the coverage by the less contaminated sandy soil brought in by the runoff

202

during the rainy season. The total PCB concentrations in the air equilibrated with the

203

e-waste contaminated soils were 590 pg/m3 in winter and 7940 pg/m3 in summer,

204

whereas in the air equilibrated with the nearby soils, they were 487 pg/m3 in winter

205

and 8280 pg/m3 in summer, respectively. However, the total PCB concentrations in

206

the ambient air located at 1.5 m above the ground of the e-waste contaminated site

207

were 377 pg/m3 in winter and 7380 pg/m3 in summer, while in the ambient air above

208

the reference site they were 287 pg/m3 in winter and 6600 pg/m3 in summer. The PCB

209

concentrations in the soil and air varied markedly with season, especially in the air.

210

Significantly higher concentrations of PCBs in the air in summer than in winter

211

(p=0.016) indicated relatively high emissions of PCBs in this e-waste recycling area

212

due to the high temperatures or due to additional sources in summer (e.g. occasional

213

open burning in the nearby region). Despite the different sampling layers of soils, the

214

PCB concentrations were slightly lower than those (320−4000 ng/g) measured 5 years

215

ago 2. This area has been seriously polluted by several decades’ intensive e-waste 11



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open burning activities. However, the levels of contamination have declined since the

217

government banned the open burning of e-waste in fields in this area. The studied

218

e-waste-contaminated site is a former open burning site that was abandoned, and

219

uncontaminated soils have been brought in and mixed with existing contaminated

220

soils in 2007. Therefore, the observed decline in the concentrations of PCBs and other

221

contaminants in the soils may mostly due to the mixture with clean soil rather than the

222

natural degradation. The ambient air concentrations of PCBs were also lower than

223

those (gas plus particle, 7825–76330 pg/m3) measured in the nearby region by Chen et

224

al. 1, where e-waste recycling activities continue. However, the concentrations of

225

PCBs in the air were still significantly higher than levels (29−1050 pg/m3) in the air

226

across China 28 and were also slightly higher than those (271−4655 pg/m3) in the air at

227

25 km from the studied e-waste site 1, especially during the high-temperature period

228

in summer. Relatively high concentrations of PCBs in the air indicate that primitive

229

e-waste dismantling remains the main emission source of PCBs in this area.

230 231

3.2. Variation in Gradient of PCB Profiles

232

The compositions of different PCB homologue groups in soil and air are shown

233

in Figure 1. The PCB profiles differed between the soil and air. PCBs in the soils

234

showed relatively high compositions of highly chlorinated PCBs, especially for hexa-

235

and hepta-CBs, whereas PCBs in the ambient air had relatively high compositions of

236

low-chlorinated PCBs (e.g., tri- and tetra-CBs). However, low-chlorinated PCBs in

237

the air equilibrated with the surface soil (i.e., airsoil) were higher than those in the soil, 12


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but lower than those in the ambient air. The compositions of low-chlorinated PCBs

239

increased, while the compositions of high-chlorinated PCBs decreased from the soil

240

surface to the air at 1.5-m height.

241

The composition of PCB homologue groups also varied with season. Emissions

242

of low-chlorinated PCBs (tri- and tetra-CBs) from contaminated soil or e-waste

243

residue increased due to the high temperatures in summer, resulting in slightly higher

244

compositions of low-chlorinated PCBs in the ambient air in summer than in winter.

245

However, the PCB profiles of airsoil varied widely with season. The airsoil in the NBS

246

site had a relatively high percentage of tri-CBs in summer compared with that in

247

winter, whereas the airsoil in the BS site had a relatively high percentage of penta-CBs

248

in summer. The seasonal variation in PCB profiles in the airsoil indicated a potential

249

influence of temperature on the emission of PCB homologues from soil in this area.

250

The PCB profiles in soils also varied with season. However, the potential influences

251

were diverse, including the temperature-driven emission, heavy rainfall, and other

252

disturbance.

253 254

3.3. Soil-Air Partitioning of PCBs

255

The soil-air partition coefficient (Ksa) is a key parameter for estimating the

256

transport of organic pollutants between soil and air. The soil-air partition coefficient

257

was traditionally predicated using the octanol-air partition coefficient

258

Equation 2). This calculation depends on various physical-chemical parameters

259

including soil density, soil organic carbon fraction, and Koa, among which Koa is 13


15, 29

(see


260

significantly temperature dependent. Therefore, the calculated Ksa mostly depends on

261

variations in temperature. Nowadays, a fugacity sampler can be used to measure the in

262

situ soil-air partition coefficient (Measured Ksa = Cs/Csa) because the chamber of this

263

sampler allows sufficient time (~62.5–83.3 min) for the PCBs to reach equilibrium

264

between the air and soil surface

265

environmental variations into account, especially the variable temperature. Previous

266

studies suggested that only the top 0−1 cm layer, which is subject to air–soil

267

partitioning, should be used for the assessment of Ksa 19. However, for the comparison,

268

we estimated the measured Ksa values using the PCB concentrations in the soils of

269

both 0–1 cm and 0–5 cm layers. Figure S2 (SI) showed that the measured Ksa values

270

using the concentrations in the 0–1 cm layer soils were generally comparable at NBS

271

and BS sites (except those at the NBS site in summer), whereas the Ksa values using

272

the concentrations in the 0–5 cm soils differed significantly at these two sites for the

273

heterogeneity of 0–5 cm soil. It suggested that using the concentrations in the 0–1 cm

274

layer soils can obtain more reliable Ksa values than using the concentrations in the 0–5

275

cm layer. Since the 0–1 cm layer soil at the NBS site in summer may be disturbed by

276

heavy rainfall, the PCB concentrations in the 0–5 cm layer were used instead for

277

acquiring the Ksa values (Figure S2b, SI).

19, 25

. This measurement also takes most of the

278

The calculated and measured Ksa values of PCBs using Koa and fugacity samplers

279

respectively are compared in Figure 2. Several of the measured Ksa values were

280

slightly higher than the calculated Ksa values, indicating a difference between the

281

traditional method and the fugacity sampler in determining Ksa. This implied that the 14


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traditional calculated method may underestimate the true value of Ksa. Previous

283

studies

284

both absorption into soil organic carbon and adsorption to mineral surface. These

285

processes can be influenced not only by the soil composition, but also the temperature

286

and relative humidity. Therefore, when calculating the Ksa, temperature and humidity

287

should be involved in the predictive equations.

30, 31

also suggested that soil−air partitioning is a complex process involving

288

The measured Ksa values varied with time of sampling, with significantly high

289

Ksa values in winter in the low temperatures than in summer (t test, p=2.22×10-13 for

290

NBS; p=8.79×10-14 for BS). Low temperatures in winter can decrease the emission of

291

PCBs from the soil, resulting in a relatively low concentration of PCBs in the air.

292

Moreover, the varied soil properties (composition and organic carbon), temperature,

293

and relative humidity during different sampling periods may also influence the

294

measured Ksa values. However, the measured Ksa values were comparable at BS and

295

NBS sampling sites during the same sampling period. The paired-samples t test

296

showed that the difference between the measured Ksa values at NBS site and BS site

297

was insignificant (p=0.09 in winter; p=0.741 in summer). Moreover, significant

298

correlations (Table S1, SI) were found among those Ksa measured at different

299

sampling sites and during different periods, suggesting that the variation of measured

300

Ksa was caused by certain environmental parameters, such as soil properties,

301

temperature, or humidity. The Ksa values of polycyclic aromatic hydrocarbons (PAHs)

302

and PCBs measured by Cabrerizo et al.

303

indicating that soil organic matter content, redox potential, nitrogen content, and

19

varied with sampling sites as well,

15



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32

304

temperature may influence the soil-air partitioning of organic pollutants

.

305

Davie-Martin et al. 31 discovered that temperature, relative humidity, and soil type can

306

significantly influence the measured Ksa values based on the measurement by a

307

solid-phase fugacity meter. We also found significant correlations between log Ksa and

308

log TOC or between log Ksa and reciprocal temperature for most PCB congeners

309

(Table S2, SI), which confirmed that soil TOC and temperature were two factors

310

influencing the measured Ksa value. Thus, the soil properties and environment

311

parameters, including the organic carbon, particle size composition, soil texture, soil

312

porosity, temperature, and relative humidity, can affect the value of Ksa. These soil and

313

environment parameters are significantly variable during the sampling period, of

314

which the influences are difficult to be tracked. Given that the Ksa of organic

315

pollutants can be influenced by numerous parameters, the use of an in situ fugacity

316

sampler can provide a more instructive method on estimation the Ksa value than the

317

traditional method can for taking all variations into consideration.

318 319

3.4. Assessment of Air-Soil Exchange of PCBs

320

Similar to Ksa, we can use either the traditional fugacity model or the fugacity

321

sampler to assess the trend of air-soil exchange of PCBs by calculating the fugacity

322

fractions (see Equation 4). The calculated and measured ff values of PCBs are shown

323

in Figure 3. For the uncertainties, equilibrium was considered to be reached at a

324

calculated ff of 0.25–0.75 and a measured ff of 0.33–0.67 25 (See S2 of SI). Generally,

325

the measured ff values differed significantly from the calculated ff values not only in 16


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their values (p=1.8×10-17 for NBS and p=1.4×10-16 for BS) but also in their air-soil

327

exchange trends, especially for the low-chlorinated PCBs. For the traditional method,

328

low-chlorinated PCBs (tri- to hexa-CBs) were significantly emitted from the soil into

329

the air, whereas hepta-CBs (except PCB180) were generally in equilibrium between

330

the air and soil at both the BS and NBS in winter. In summer, PCBs in the BS and

331

NBS soils all volatilized into the air, except for PCB179, 183, and 189 at NBS. For

332

the measurement method, PCBs were generally in equilibrium between the air and

333

soil at both the BS and NBS in winter. In summer, PCBs were generally transported

334

from the air into soil in the NBS. However, low-chlorinated PCBs (tri- to tetra-CBs)

335

were generally in equilibrium between the air and soil, whereas high-chlorinated

336

PCBs (penta- to hepta-CBs) volatilized into the air from the BS soil. The greatest

337

difference between the results of the traditional method and those of the fugacity

338

sampler were observed in the low-chlorinated PCBs (tri- to tetra-CBs). The calculated

339

results showed higher emission trends than the measured results for the

340

low-chlorinated PCBs, suggesting that the traditional method may overestimate the

341

soil fugacity of low-chlorinated PCBs.

342

The traditional method has several disadvantages. First, it relies largely one

343

calculations based on the measured air and soil concentrations, soil properties (i.e.,

344

soil density and TOC), and the octanol–air partition coefficient. Because Koa is

345

temperature dependent and varies with literatures, it is unsuitable for estimating the

346

exchange of organic compound in an unstable system with varied concentrations or

347

environmental parameters, as well as for organic compounds whose Koa is unknown 17



25

. Moreover, previous studies30,

31

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348

or uncertain

suggested that temperature and

349

relative humidity should also be involved in the calculation of Ksa, which makes this

350

method even more uncertain. By contrast, the assessment using a fugacity sampler

351

relies largely on in situ measurements, thereby providing more reliable results than the

352

traditional method for taking the varied environment parameters into account. Second,

353

the traditional method using the concentration of extractable PCBs in soils may

354

slightly overestimate the proportion of PCBs that participate in the air-soil partition

355

process, especially for the low-chlorinated congeners. Some of the extractable PCBs

356

in soils are not activated and exchangeable, and do not participate in the air-soil

357

exchange process because they are strongly attached to organic matter

358

also be proved by the different fugacity fractions and exchange trends predicted by

359

these two methods. Third, the amount of compound involved in the partitioning

360

process in surface soil (0−5 cm) should be used as the concentration for calculating

361

soil fugacity, but it is difficult to collect the soil sample appropriately. Furthermore,

362

the traditional method is unsuitable for assessing the trend in the exchange of the

363

compound among more than two matrices, especially in the presence of plants

364

Although, the assessment using a fugacity sampler can provide more reliable results,

365

this method also has some disadvantages. For instance, (1) this fugacity sampler is

366

expensive and difficult to set-up; (2) the sampling is time-consuming, and need

367

powder source; (3) it is unsuitable for a large number of sampling at a high spatial

368

resolution. Therefore, we recommend using the fugacity sampler for more practical

369

assessment of the air-soil partitioning of organic pollutants at the unstable hotspots, 18


32

. This can

25

.

Page 19 of 28


370

such as the e-waste contaminated area.

371

The measured fugacity fractions of PCBs using the fugacity sampler suggest that

372

PCB congeners were generally in equilibrium between the air and soil in winter at

373

both the abandoned e-waste burning site and the nearby area. However, in summer,

374

the relatively high-chlorinated PCBs were generally volatilized from the soil into the

375

air at the abandoned burning site, and were deposited into the soil in the nearby area,

376

whereas the low-chlorinated PCBs were in equilibrium between the air and soil at the

377

burning site, but they were also deposited into the soil in the nearby area. Our results

378

show that even after more than five years since the ban on open burning of e-waste in

379

this area, as well as the implementation of various simple treatments such as covering

380

the contaminated soil with soil brought from outside this area, the abandoned burning

381

site still acted as an emission source of PCBs during warmer seasons. By contrast,

382

emissions from the contaminated soil were low in the area in winter. Tian et al. 33 and

383

Chen et al.

384

contaminated environmental compartments (e.g. soil, water, and e-waste residues)

385

was an important factor controlling the PCB concentrations in air at the e-waste site in

386

warmer seasons.

1

also suggested that temperature-driven volatilization from local

387 388

3.5 Environmental Implications of the Abandoned E-waste Recycling Site

389

China is one of the world’s largest dumping and recycling sites of e-waste due to

390

its less stringent environmental regulations. The town of Longtang, Qingyuan City,

391

has been one of the most active e-waste recycling areas in China since the early 1980s. 19



392

Due to the heavy pollution caused by primitive e-waste recycling activities, open

393

burning of e-waste in Qingyuan has been banned since 2007, leaving numerous

394

abandoned e-waste contaminated sites in fields in this area. Despite the fact that the

395

local government has taken various measures to control the emission of pollutants,

396

such as covering the burning site with clean soil or centralizing e-waste recycling

397

within a small factory, gradual diffusion of pollutants from the contaminated soils into

398

the air is still taking place. Although, the data obtained in this study was limited, the

399

results of two different prediction methods in this study both suggest that even many

400

years after the prohibition of open burning, these abandoned burning sites continue to

401

act as significant sources of PCBs and other pollutants, especially during the warmer

402

seasons. Greater attention should be paid to monitoring and managing these

403

abandoned e-waste recycling sites to avoid the further transport of and secondary

404

contamination by these pollutants to nearby regions or even globally.

405 406

ACKNOWLEDGMENTS

407

This study was supported by the National Natural Science Foundation of China

408

(Nos. 21307133, 41125014, and 41322008), the Fundamental Research Funds for the

409

Central Universities of China (No. DUT16RC(4)15).

410 411

ASSOCIATED CONTENT

412

Supporting Information Available. Details on soil sampling and uncertainty of

413

fugacity fraction. Figure S1 Scheme of the fugacity sampler for the in situ assessment 20


Page 20 of 28

Page 21 of 28


414

of the air-soil exchange. Figure S2 Measured log Ksa using the PCB concentrations in

415

the 0−1 cm and 0−5 cm layer soils at NBS and BS sites. Table S1 Correlation

416

coefficient matrix for Ksa values measured at NBS and BS sites. Table S2 Correlation

417

coefficient matrix for log TOC, reciprocal temperature, and measured log Ksa.

418 419

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420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451

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27. Mackay, D., Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals. 2006. 28. Zhang, Z.; Liu, L.; Li, Y.-F.; Wang, D.; Jia, H.; Harner, T.; Sverko, E.; Wan, X.; Xu, D.; Ren, N.; Ma, J.; Pozo, K., Analysis of polychlorinated biphenyls in concurrently sampled Chinese air and surface soil. Environ. Sci. Technol. 2008, 42, (17), 6514-6518. 29. Hippelein, M.; McLachlan, M. S., Soil/air partitioning of semivolatile organic compounds. 1. Method development and influence of physical-chemical properties. Environ. Sci. Technol. 1998, 32, (2), 310-316. 30. Hippelein, M.; McLachlan, M. S., Soil/air partitioning of semivolatile organic compounds. 2. Influence of temperature and relative humidity. Environ. Sci. Technol. 2000, 34, (16), 3521-3526. 31. Davie-Martin, C. L.; Hageman, K. J.; Chin, Y.-P.; Rouge, V.; Fujita, Y., Influence of Temperature, Relative Humidity, and Soil Properties on the Soil-Air Partitioning of Semivolatile Pesticides: Laboratory Measurements and Predictive Models. Environ. Sci. Technol. 2015, 49, (17), 10431-10439. 32. Cabrerizo, A.; Dachs, J.; Moeckel, C.; Ojeda, M.-J.; Caballero, G.; Barcelo, D.; Jones, K. C., Ubiquitous net volatilization of polycyclic aromatic hydrocarbons from soils and parameters influencing their soil-air partitioning. Environ. Sci. Technol. 2011, 45, (11), 4740-4747. 33. Tian, M.; Chen, S.-J.; Wang, J.; Zheng, X.-B.; Luo, X.-J.; Mai, B.-X., Brominated Flame Retardants in the Atmosphere of E-Waste and Rural Sites in Southern China: Seasonal Variation, Temperature Dependence, and Gas-Particle Partitioning. Environ. Sci. Technol. 2011, 45, (20), 8819-8825.

518 519

23



520

Table and Figures

521

Table 1 PCB concentrations in the surface soils, air equilibrated with the soil (airsoil),

522

and ambient air during different seasons.

523 524 525 526 527

Figure 1 Composition of different PCB homologue groups. (Soil-air means the air equilibrated with the surface soil.) Figure 2 Measured logKsa versus predicted logKsa for PCBs of two sampling sites during different seasons.

528

Figure 3 Measured and calculated fugacity fractions of PCBs during winter and

529

summer. (The dotted lines show the uncertainty of fugacity fraction. According

530

to the uncertainty, the measured fugacity fraction between 0.33 and 0.67 (blue

531

lines) is considered as equilibrium, while the calculated fugacity fraction

532

between 0.25 and 0.75 (yellow lines) is considered as equilibrium.)

533 534

24


Page 24 of 28

Page 25 of 28


535

Table 1 PCB concentrations in the surface soils, air equilibrated with the soil (airsoil),

536

and ambient air during different seasons.

537 Air (pg/m3) Winter NBS b BS c

538 539 540 541

189

Airsoil a (pg/m3)

Summer NBS

PCB28

104

PCB37

21.6 24.7

663

PCB52

27.1 40.1

787

PCB44

19.4 31.1

PCB74 PCB70

Winter

BS

151

Summer

BS

NBS

Winter

BS

NBS

Summer

BS

(0-1cm) (0-1cm)

NBS

BS

(0-5cm)d (0-1cm)

265

6630

3690

214

82.2

22.0

32.7

306

25.5 32.9

191

267

84.5

21.9

27.4

48.2

512

48.8 79.3

306

414

29.6

28.8

9.84

24.5

566

238

35.4 57.3

57.0

135

27.1

22.9

9.87

22.5

8.51 9.00

272

313

10.9 14.1

187

372

12.9

12.2

6.78

16.8

13.3 16.0

534

267

22.2 30.3

99.0

264

24.2

21.8

13.3

41.2

PCB60

9.28 9.61

312

120

14.0 17.1

59.0

88.8

15.0

15.5

4.51

12.0

PCB77

4.02 2.93

114

47.6

3.83 4.38

36.7

61.5

12.1

4.34

3.02

8.87

PCB101

11.2 13.2

281

434

31.7 24.8

356

1210

40.7

37.0

11.5

44.0

PCB87

7.10 6.61

91.5

92.6

13.4 11.4

124

243

22.1

18.5

6.33

24.5

PCB82

2.57 2.34

21.7

13.7

3.23 3.66

4.61

30.0

5.70

4.22

1.30

4.93

PCB118

10.2 8.86

156

118

15.7 12.2

79.0

362

58.2

45.8

18.3

74.1

PCB114

3.97 2.68

9.40

6.78

3.04 2.87

4.10

14.2

3.02

1.36

0.63

2.46

PCB105

3.46 2.81

64.8

36.9

5.95 4.46

24.8

107

26.8

18.10

10.3

34.9

PCB153

10.9 6.62

81.5

50.6

31.3 12.1

28.7

192

83.7

47.5

9.99

30.7

PCB138

4.52 2.94

112

65.9

9.13 4.48

34.2

265

32.4

22.3

16.7

57.1

PCB158

0.50 0.33

11.5

9.08

1.01 0.50

5.90

28.4

3.60

2.48

1.48

4.26

PCB166

0.85 0.57

1.19

3.45

0.80 0.53

2.85

6.49

1.75

1.19

0.08

0.40

PCB128

2.24 1.05

21.7

11.7

2.99 1.66

7.50

48.2

13.1

9.37

4.20

15.4

PCB156

2.10 0.74

11.7

7.27

3.52 1.62

4.98

21.2

10.5

6.20

3.27

12.7

PCB179

2.00 0.79

10.9

6.88

8.87 1.10

4.64

14.3

16.2

2.64

0.64

0.95

PCB187

4.84 1.40

21.6

15.7

16.0 1.87

9.39

28.3

55.5

7.62

2.86

3.39

PCB183

2.70 0.95

12.0

6.46

7.10 1.00

5.37

10.6

26.4

4.49

1.47

2.17

PCB180

7.22 1.53

28.0

20.2

14.6 3.45

12.9

42.6

88.4

21.8

7.87

10.2

PCB170

3.20 1.02

15.5

8.90

5.84 1.80

7.29

18.7

29.8

12.3

3.70

7.35

PCB189

0.25 0.22

1.22

0.36

0.78 0.23

0.81

0.80

2.28

0.62

0.24

0.54

ΣPCBs

287

6600 7380

487

8280

7940

940

473

198

537

377

2400 4670

NBS

Soil (ng/g)

590

a

The air equilibrated with soil surface. NBS means the non-burning site. c BS means the burning site. d Soil below 1 cm may also participate in the air-soil partitioning. b

542 543 25



544

Figure 1 Composition of different PCB homologue groups. (Soil-air means the air

545

equilibrated with the surface soil.)

546

547 548 549

26


Page 26 of 28

Page 27 of 28


550

Figure 2 Measured logKsa versus predicted logKsa for PCBs of two sampling sites

551

during different seasons.

552 553 554 555

27



556

Figure 3 Measured and calculated fugacity fractions of PCBs during winter and

557

summer. (The dotted lines show the uncertainty of fugacity fraction. According to the

558

uncertainty, the measured fugacity fraction between 0.33 and 0.67 (blue lines) is

559

considered as equilibrium, while the calculated fugacity fraction between 0.25 and

560

0.75 (yellow lines) is considered as equilibrium.)

561

562 563 564 28


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The Abandoned E-Waste Recycling Site ... - ACS Publications

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