Spatial Distribution of Old and Emerging Flame Retardants in Chinese

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Spatial distribution of old and emerging flame retardants in Chinese forest soils: Sources, trends and processes. Qian Zheng, Luca Nizzetto, Jun Li, Marie D Mulder, Ond#ej sanka, Gerhard Lammel, Haijian Bing, Xin Liu, Yishan Jiang, Chunling Luo, and Gan Zhang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/es505876k • Publication Date (Web): 08 Feb 2015 Downloaded from http://pubs.acs.org on February 18, 2015

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Environmental Science & Technology

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Spatial distribution of old and emerging flame retardants in

2

Chinese forest soils: Sources, trends and processes.

3

Qian Zhenga, Luca Nizzetto*b,c, Jun Lia, Marie D. Mulderb, Ondřej Sáňkab, Gerhard

4

Lammelb,d, Haijian Binge, Xin Liu a, Yishan Iiang a, Chunlin Luoa, Gan Zhang*a

5 6

a

7

Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China.

8

b

9

Brno, Czech Republic

State Key Laboratory of Organic Geochemistry, Guangzhou Institute of

Masaryk University, Research Centre for Toxic Compounds in the Environment,

10

c

Norwegian Institute for Water Research, Oslo, Norway

11

d

Max Planck Institute for Chemistry, Mainz, Germany

12

e

13

Institute of Mountain Hazards and Environment, Chinese Academy of Sciences,

14

Chengdu 610041, China

The Key Laboratory of Mountain Surface Processes and Ecological Regulation,

15 16 17

Contacts for correspondence:

18

Prof. Gan Zhang [email protected]

19

Tel. +86 20 8529 0805

20

Fax. +86 20 8529 0130

21

Dr Luca Nizzetto [email protected] and [email protected],

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Tel. +47 98215393

23

Fax. +47 22185200

24 25

ACS Paragon Plus Environment


26

TOC Art

27

28 29


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Abstract

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The levels and distribution of polybrominated diphenylethers (PBDEs),

32

novel brominated flame retardants (NBFRs) and Dechlorane Plus (DP) in

33

soils and their dependence on environmental and anthropological factors

34

were investigated in 159 soil samples from 30 background forested

35

mountain sites across China. Decabromodiphenylethane (DBDPE) was

36

the most abundant flame retardant (25-18000 pg g-1 and 5-13000 pg g-1 in

37

O-horizon and A-horizon, respectively), followed by BDE 209 (nd-5900

38

pg g-1 and nd-2400 pg g-1 in O-horizon and A-horizon, respectively). FRs

39

distributions were primarily controlled by source distribution. The

40

distributions of most phasing-out PBDEs, DP isomers and TBPH were in

41

fact correlated to a population density-based index used as proxy of areas

42

with elevated usage and waste of FR containing products. High

43

concentrations of some NBFRs were however observed in industrialized

44

regions and FR manufacturing plants. Strongly positive correlations were

45

observed between PBDEs and their replacement products suggesting

46

similar emission pattern and environmental behaviour. Exposure of

47

mineral sub-soils depended on precipitations driving leaching of FRs into

48

the soil core. This was especially evident for some emerging BFRs (TBE,

49

TBPH and TBB etc.) possibly indicating potential for diffuse ground

50

water contamination.

51



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1. Introduction

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Flame retardants (FRs) are a class of chemicals used to reduce

54

flammability in different kind of products. They are commonly added in

55

construction materials, furniture, electronics, etc.1 Brominated flame

56

retardants (BFRs) and chlorinated flame retardants (CFRs) are among the

57

most widely used.

58

BFRs are structurally heterogeneous.2,

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diphenylethers (PBDEs) were historically marketed as three different

60

commercial mixtures commonly referred to as Penta-BDE, Octa-BDE

61

and Deca-BDE.1 However, due to their persistence and bioaccumulative

62

properties some tetra-, penta-BDE, hexa-BDE and octa-BDE were added

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to the list of banned Persistent Organic Pollutants (POPs) under the

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Stockholm Convention.4 Restrictions on the use of PBDE congeners have

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paved the way for the use of “novel” BFRs (NBFRs).5, 6 Most commonly

66

used

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1,2-bis(2,4,6-tribromophenoxy)ethane

(TBE),

68

2-ethylhexyl-2,3,4,5-tetrabromobenzoate

(TBB),

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bis(2-ethylhexyl)-3,4,5,6-tetrabromo-phthalate

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hexabromobenzene (HBB) and pentabromoethylbenzene (PBEB).5,

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Despite the impelling demand for avoiding compounds with POP

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characteristics, some NBFRs were shown to have potential for long-range

73

atmospheric transport, persistence and bioaccumulation. 4, 8, 9

NBFRs

are:

3

Among them, polybrominated

1,2-bis(pentabromodiphenyl)ethane


(DBDPE),

(TBPH), 7

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Dechlorane plus (DP) belongs to the CFRs group and is common in

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electrical and electronic items such as wires and cables, as well as plastic

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roofing materials.10,

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bioaccumulative and potentially toxic.12

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Soils represent a principal receptor and environmental reservoir for many

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persistent semivolatile organic contaminants.13 Forest soils, in particular

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have been pointed out as effective accumulators of several hydrophobic

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and persistent substances due to the forest canopy effect in enhancing

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atmospheric depositions, elevated soil organic carbon (OC) content

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(representing the bulk capacity for storing these contaminants), and

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relatively

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remobilization.14-17 Researches on soils as environmental reservoirs of

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semivolatile contaminants have mainly focused on legacy POPs.18,

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Forest soils may also be important reservoirs of airborne old and

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emerging FRs20, 21, and high persistence in soils has been described for

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some NBFRs (e.g. the half-lives of TBE and HBB in soil are reported to

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be 8600 hours).22

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China has 134 million hectares of forested land including tropical,

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subtropical, temperate and boreal biomes23. Main forested areas in China

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are prevalently far away from major conurbations and therefore possible

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primary sources. Contaminant levels and distribution in these soils can

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therefore be regarded as indicators of background environmental

low

11

level

DP has been shown to be bioavailable,

of

disturbance,

which


could

prevent

19


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contamination expectedly reflecting the influence of major environmental

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drivers of distribution and distance from sources.24 Meteorological

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conditions

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distribution of semivolatile contaminants over large geographical scales.26

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The large land area, climate variability, topographic complexity,

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ecosystem diversity and expected elevated production, use and emissions

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of FRs make China an interesting case study and possibly an important

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region influencing global contamination and distribution pattern of these

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contaminants. 27

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Research on NBFRs and DP have traditionally mainly focused on air,

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sediment, water, sewage sludge and dust with very limited information on

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accumulation and levels in soils. 5, 8, 28-31 The scope of this study was to i)

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identify the levels and spatial distribution of target compounds in

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background forest soils along a range of environmental and

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anthropological gradients, ii) explore co-linearity between the distribution

111

of the target compounds, and iii) assess possible influences of

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environmental and geographical variables (namely: precipitation, altitude,

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soil OC content, and exposure to /distance from primary sources) on

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contaminant distribution.

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2. Experimental section

116

2.1 Monitoring design

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Thirty mountain sites across major accessible mountainous areas of China

(temperature

and

precipitation

patterns),25


influence

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were chosen (shown in Figure S1). In each site 1 to 4 sampling locations

119

were chosen along the same aspect on the altitudinal transect. In total,

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159 forest-soil samples including O-horizon (77) and A- horizon (82)

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were collected at 82 locations between 16 May 2012 and 15 March 2013.

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Major transects included: latitude ranging from 21˚ to 53˚; altitude

123

ranging from 200 m to 3800 m; the yearly mean temperature ranging

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from 6 °C to 21 °C and mean yearly precipitation ranging from 245 mm

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to 2129 mm. Geo-referenced datasets of elevation, yearly mean

126

temperature and precipitation (0.5' resolved) were obtained from

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WorldClim. Details on sampling location characteristics are presented in

128

Table S2.

129

2.2 Sampling of soil

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In each sampling location, three small trenches located at about 5 m apart

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from each other were excavated. Vegetation litter was carefully removed

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and the soil layers were classified based on colour and structure of the

133

material present in each horizon. Samples from the O- (humus) and A-

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(topsoil) horizons were collected separately from each trench, folded in

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aluminium foil, placed in polyethylene zip-bags, cooled and transported

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to the laboratory. The samples were then freeze dried and stored at -20 °C

137

until chemical analysis began.

138

2.3 Chemical Analysis

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In order to remove stones, each dry sample was sieved to exclude



140

structures larger than 2 mm. The samples were mixed by pooling together

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equivalent amounts of sample from the three trenches in order to create

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aggregated samples of the O-horizon and A-horizon (separately),

143

reflecting average conditions of the sampling location. Sample extraction

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and preparation were consistent with those described in a previous

145

study.32 Details are reported in the supplementary information (SI)

146

available on line. Total Organic Carbon (TOC) in soil samples was

147

determined with an elemental analyzer (CHNS Vario Ei III, Elementar)

148

after removal of carbonates with HCl as described somewhere else.33

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2.4 QA/QC

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10 procedural blanks and 20 repeated analysis of an individual sample

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were included in the running list to assess potential laboratory derived

152

contamination and ensure repeatability of analysis. The Instrument

153

Detection Limit (IDL) ranged from 0.09 to 0.36 pg (injected) and Method

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Detection Limit (MDL) 1.1 - 28.6 pg g-1, depending on substance

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(Further details are reported in Text S1.2 in the supplementary

156

information available on-line). 20ng PCB 198 and PCB 209 recovery

157

standards were added to each sample prior to extraction to monitor

158

quantitative analysis performance. Obtained recoveries were respectively

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82% ± 4.9% and 85% ± 3.7% (variance is expressed here as standard

160

error). Results reported in the study are expressed on a dry weight basis

161

(pg g-1 dry wt) and not corrected for recovery results.


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2.5 Atmospheric back trajectories analysis and Index of Potential

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Source Influence

164

In a primary sources controlled scenario, FRs concentrations will be

165

highest close to emission sources. Similarly to other parts of the world,34

166

previous assessment of FRs (such as PBDEs) distribution in soils and

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other environmental compartments in China evidenced the existence of

168

an urban-rural gradient with highly populated urban and industrial

169

districts representing the areas with highest density atmospheric

170

sources.35,

171

overlap.37 For this reason population count is an adequate proxy for

172

describing potential sources from FRs usage, wasting and manufacturing.

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A few important industrial plants manufacturing or processing NBFR can

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however be also found in areas with intermediate population density. In

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order to track the possible influence of use/related primary sources from

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high density urban areas on background soil contamination, air mass back

177

trajectories (BT) and a numerical index of potential source influence

178

(IPSI) in the regional domain were computed. We elaborated the concept

179

of IPSI in a previous paper38 (details are also reported in text S2 of the

180

present paper). In short, IPSI combines data on population density

181

distribution (as proxy of source distribution) and BT density calculated

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for each sampling location considering a full year of simulations (twice a

183

day). BT density is used by IPSI to weigh the influence of potential

36

In China, industrial and major urban clusters closely



184

sources in a given area for an individual sampling location based on how

185

often this area was upwind of the sampling point.

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3. Results and Discussion

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3.1 Summary of BFRs and DPs concentration results.

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All sixteen selected compounds were analyzed in all the samples. Table

189

S3 reports data of individual compounds in the O-horizon and A-horizon.

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The concentrations of target compounds in O-horizon were generally

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higher than those in A-horizon by an average factor of 5.4, possibly

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reflecting the more direct exposure to atmospheric deposition of the

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superficial O-horizon. (Table S3 reports details of soil characteristics).

194

The mean concentrations of the total PBDEs (∑8PBDEs) in the O- and

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A-horizon samples were 920 pg g-1 (3-6300 pg g-1) and 220 pg g-1 (not

196

detected-2500 pg g-1 ), respectively. As expected from previous results,

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BDE 209 was the most abundant PBDE congener in these samples,33, 39

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accounting for more than 60% of ∑8PBDEs, followed by BDE 47 and

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BDE 99. The concentrations of BDE 209 were in the range of nd-5900 pg

200

g-1 and nd-2400 pg g-1 in O and A-horizon, respectively. These values are

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much lower than those reported for agricultural soils in southern China

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(39.8-95.2 ng g-1)40 and soils in proximity of e-waste recycling areas

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(28.8-468 ng g-1).41 They are nevertheless much higher than forest soil

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concentrations measured in Sweden (15-750 pg g-1).42 Such elevated

205

values can be linked to the higher consumption of PBDEs in China


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(30,000t in 2005) which experienced a sharp increase during last several

207

years.43 The concentrations of other PBDEs (∑7PBDEs excluding

208

Deca-BDE) in O- and A-horizon were 3-800 pg g-1 and nd-320 pg g-1,

209

respectively. ∑7PBDEs in A-horizon was comparable to that observed in

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other locations in background soils, including Kuwait (24.7-296 pg g-1),34

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UK (73.5-285 pg g-1 ),44 and Brazil (434 pg g-1),39 somehow lower

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compared to that found in mountain soils in Italy (710 ± 830 pg g-1),45

213

however higher than that in the Tibetan Plateau soils.20, 21

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NBFRs and DP datasets of the soil compartment are very limited.

215

DBDPE was the FR with the highest concentrations measured in this

216

study. It ranged 25-18000 pg g-1 (mean 2643 pg g-1) and 5-13000 pg g-1

217

(mean 660 pg g-1) in O- and A-horizon, respectively. The present data are

218

lower than data reported for agricultural soils in southern China (28.1 ng

219

g-1)40. DBDPE predominance in environmental samples was also

220

previously shown in air samples at a rural site of China.36 Such a behavior

221

can be related to the large success of this product in the market. DBDPE

222

market is currently increasing at a yearly rate of 80% in China and

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globally.5 Some studies however have reported DBDPE concentrations

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lower than BDE 209 in sewage sludge samples in Europe2, 16 and air

225

samples in Chinese e-waste area.36 This discrepancy might be attributed

226

to several factors including: regional and temporal variability in FR usage

227

and emissions and type of samples.



228

The remaining set of NBFRs was present at generally lower

229

concentrations. TBB: nd-1400 pg g-1 (mean 250.5 pg g-1) and nd-1600 pg

230

g-1 (mean 184.0 pg g-1), TBPH: 4.0-643.7 pg g-1 (mean 131.7 pg g-1) and

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5.5-526.4 pg g-1(mean 68.9 pg g-1), TBE: nd-330 pg g-1 (mean 48.5 pg g-1)

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and nd-240 pg g-1 (mean 22.9 pg g-1), HBB: nd-340 pg g-1 (mean 46.0 pg

233

g-1) and nd-42 pg g-1(mean 7.2 pg g-1), and PBEB showed the lowest

234

concentrations in the range of nd-92 pg g-1 (mean 6.8 pg g-1) and nd-70 pg

235

g-1 (mean 9.0 pg g-1) in O-horizon and A-horizon, respectively. The

236

detection frequencies varied among different compounds (details are

237

given in Table S3).

238

Both anti-isomer and syn-isomer of DP were detected in 100% of the

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samples, demonstrating the currently broad distribution of this FRs in the

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Chinese markets. The concentrations of anti-isomer and syn-isomer were

241

5-680 pg g-1 and 4-390 pg g-1 in O-horizon and 3-220 pg g-1 and 2-170 pg

242

g-1 in A-horizon, respectively. Concentrations measured in the selected

243

forest soils were lower than those previously measured in urban, rural and

244

remote surface soils of Northern China (nd-8.45 ng g-1 and nd-3.76ng g-1

245

for anti-DP and syn-DP, respectively).28

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3.2 Spatial Trends in superficial soils

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High spatial variability of FR concentrations was observed during this

248

survey. For DBDPE, the differences between the highest and lowest

249

concentrations were up to a factor of 2300. In contrast, PBEB and the


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major components of PBDE congeners (i.e., BDE 28, BDE 153 and BDE

251

183) showed a considerably lower variability, due to the lower usage

252

volume or possibly current regulation. Figure 1 shows the spatial

253

variations of target compounds in O-horizons. Overall, high levels of

254

many FRs were mainly found in the Southeast China. For instance, the

255

highest average concentrations of BDE 47, BDE 99 and TBPH were

256

measured in site 21; while, anti-DP, syn-DP, BDE 209 and TBE showed

257

peaking concentrations in site 23. Site 21 and 23 are both in the

258

Guangdong province, already reported as one of the important e-waste

259

recycling and the most urbanized/ industrialized regions in South China36,

260

41, 46

. Some interesting and informative outliers were found too. DBDPE

261

displayed the highest average concentration in site 10 (Figure 1c) in

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Shandong Province, due to important DBDPE production facilities are

263

located in this area, 5, 8 while two outliers for TBB and HBB were located

264

in site 6 and 7 (Figure 1a) in Hebei province, also an important industrial

265

area. In China, 600 tons/year of HBB are produced in Shandong

266

province,5 and as expected high concentration could be found in site 10.

267

Unfortunately, there is no production or usage information publically

268

disclosed for TBB.5, 8 As far as we know, TBB combined with TBPH was

269

used in Firemaster BZ-54, Firemaster 550 (in a 4:1 ratio) and DP-45 (91%

270

TBPH together with 2−6% TBB by weight).47 The ratios of TBB to

271

TBPH in samples in Northern China averaged 5.2 (in contrast with



272

diagnostic ratios observed in the Southern part averaging 0.55), indicating

273

different sources or fate in these sub-regions as well as the northern

274

samples probably been more affected by proximity to manufacture related

275

sources. The high consumption of Firemaster 550 in Northern China,

276

especially in Hebei province appears to be related to the peculiar type of

277

manufacturing district present here which includes oil, coal, metallurgical,

278

mechanical and electronics industry. The considerably lower ratio value

279

found in Southern China suggests that manufacturers in this area may

280

have used different FR formulations (such as DP-45, neoprene and

281

polyvinylchloride (PVC)31) with a relatively higher level of TBPH.

282

Moreover, TBB has been reported to be more vulnerable to

283

photodegradation with a half-life twice shorter than TBPH.47, 48 Warmer

284

climate and higher solar radiation in Southern China might accelerate

285

degradation and result in lower ratios observed in the soils of this region.

286

In general, the presence of these outliers highlights the strong influence of

287

local production point sources for the exposure of background mountain

288

soils. These data indicate that the current emission control measures

289

applied during industrial production and processing in China may be

290

insufficient to prevent off-site exposure to FRs at the sub-regional level.

291

In summary, spatial distribution of flame retardants in background soils in

292

China appears to be dependent on source distribution and sensitive to the

293

typology of sources (e.g. e-waste facilities and manufacturing facilities as


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well as highly populated areas where the majority of FR containing

295

products are used). 49

296

In order to provide a more quantitative assessment of this hypothesis, we

297

statistically explored the interaction between concentrations of FRs in the

298

O-horizon and the results for IPSI. IPSI values for different sampling

299

sites ranged between 1 and 37 following a slightly negatively skewed

300

distribution, with most frequently observed values around 25 (Figure 1).

301

Consistently, the highest IPSI values are observed in the Southeast (in

302

particular sites 21-23). Most of the target compounds in the O-horizon

303

showed high levels in locations with a high IPSI. Nearly all the FRs (with

304

the exception of PBEB, HBB and TBB) showed positive correlation with

305

IPSI with correlation coefficients (Spearman) typically ranging between

306

0.1 and 0.5 (with exception of BDE 28: r=0.08 and BDE 209: r=0.06)

307

(Table S6). These relationships were statistically significant (p

Spatial Distribution of Old and Emerging Flame Retardants in Chinese

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