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Occurrence and Source Effect of Novel Brominated Flame Retardants (NBFRs) in Soils from Five Asian Countries and Its Relationship with PBDEs Wen-long Li, Wan-Li Ma, Zifeng Zhang, Liyan Liu, Wei-Wei Song, Hongliang Jia, Yong-sheng Ding, Haruhiko Nakata, Nguyen Hung Minh, Ravindra Kumar Sinha, Hyo-Bang Moon, Kurunthachalam Kannan, Ed Sverko, and Yi-Fan Li Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b03207 • Publication Date (Web): 03 Sep 2017 Downloaded from http://pubs.acs.org on September 3, 2017
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Occurrence and Source Effect of Novel Brominated Flame
2
Retardants (NBFRs) in Soils from Five Asian Countries and Its
3
Relationship with PBDEs
4
Wen-Long Lia, Wan-Li Maa, Zi-Feng Zhanga, Li-Yan Liua, Wei-Wei Songa,
5
Hong-Liang Jiab, Yong-Sheng Dingc, Haruhiko Nakatad, Nguyen Hung Minhe,
6
Ravindra Kumar Sinhaf, Hyo-Bang Moong, Kurunthachalam Kannanh, Ed Sverkoa,
7
and Yi-Fan Lia,b,i*
8 9
a
International Joint Research Center for Persistent Toxic Substances (IJRC-PTS),
10
State Key Laboratory of Urban Water Resource and Environment, School of
11
Environment, Harbin Institute of Technology, Harbin 150090, China
12
b
University, Dalian 116026, China
13 14
c
IJRC-PTS, College of Environmental Science and Engineering, Shanghai Maritime University, Shanghai, 200135, China
15 16
d
IJRC-PTS, Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan
17 18
IJRC-PTS, College of Environmental Science and Engineering, Dalian Maritime
e
Dioxin laboratory, Center for Environmental Monitoring (CEM), Vietnam Environmental Administration (VEA), 556 Nguyen Van Cu, Long Bien, Ha Noi,
19
Vietnam
20 21
f
22
g
IJRC-PTS, Department of Zoology, Patna University, Patna 800 005, Bihar, India IJRC-PTS, Department of Marine Sciences and Convergent Technology, Hanyang
23
University, 55 Hanyangdaehak-ro, Sangnok-gu, Ansan city, Gyeonggi-do 426-791,
24
Republic of Korea
25
h
Wadsworth Center, New York State Department of Health, Department of
26
Environmental Health Sciences, School of Public Health, State University of New
27
York at Albany, Empire State Plaza, P.O. Box 509, Albany, New York 12201-0509, United States
28 29
i
IJRC-PTS-NA, Toronto, M2N 6X9, Canada
30 31
*Corresponding author: IJRC-PTS, School of Environment, Harbin Institute of
32
Technology, 202 Haihe Rd, Nangang District, Harbin 150090, Heilongjiang, China.
33
Tel. +86-451-8628-9130. E-mail:
[email protected] 1
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Word count: (Text) 5479 + 2 (Table)*300 + 3 (Figures)*300 = 6979.
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TOC:
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ABSTRACT: This paper presents the first comprehensive survey of 19 novel
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brominated flame retardants (NBFRs) in soil samples collected across five Asian
44
countries. High variability in concentrations of all NBFRs was found in soils with the
45
geometric mean (GM) values ranging from 0.50 ng/g dry weight (dw) in Vietnam to
46
540
47
urban/rural/background locations, the GM concentrations of ∑19NBFRs decreased in
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the order of Japan > South Korea > China > India > Vietnam. Correlations among
49
different NBFR compounds were positive and statistically significant (p < 0.05),
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suggesting that they originate from similar sources. Evidences for simultaneous
51
application between polybrominated diphenyl ethers (PBDEs) and NBFRs were also
52
noted. Principal component analysis of NBFR concentrations revealed specific
53
pollution sources for different NBFRs coming from urban, BFR-related industrial, and
54
e-waste sites. For the first time, this study demonstrates a “point source fractionation
55
effect” for NBFRs and PBDEs. The concentrations of all NBFRs and PBDEs were
56
negatively and significantly correlated with the distance from BFR-related industrial
57
and e-waste regions. Positive and significant correlation between population density
58
and NBFR concentrations in soils was identified. Our study revealed that the primary
59
sources effects were stronger than the secondary sources effects in controlling the
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levels and distribution of NBFRs and PBDEs in soils in these five Asian countries.
61 62 63
KEYWORDS: Novel Brominated Flame Retardants, PBDEs, Surface Soil, primary sources, Asia.
ng/g
dw
in
the
vicinity
of
a
BFR-manufactory
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in
China.
In
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■ INTRODUCTION
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Brominated flame retardants (BFRs) are a diverse group of chemicals added to
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commercial products to reduce their flammability. More than 75 different compounds
67
have been produced and used as BFRs, with considerable attention paid to
68
polybrominated
69
bioaccumulation, potential toxicity and ubiquitous presence in the environment,
70
commercial pentabromodiphenyl ether (penta-BDE) and octabromodiphenyl ether
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(octa-BDE) mixtures have been listed as persistent organic pollutants (POPs) and are
72
regulated
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decabromodiphenyl ether (deca-BDE) has also been regulated in electrical and
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electronic appliances in Europe4 and partially regulated in the United States since
75
2013.5 To fulfill flammability standards of many consumer products, the market
76
demand for the alternative flame retardants is on the rise. For example, two novel
77
brominated flame retardants (NBFRs), i.e. decabromodiphenylethane (DBDPE) and
78
1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE or TBE), have been reported as
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replacements for commercial deca-BDE and octa-BDE mixtures, respectively.6-8
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Other known NBFRs include 2-ethylhexyl-2,3,4,5-tetrabromo-benzoate (EHTBB or
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TBB) and bis(2-ethylhexyl)-tetrabromophthalate (BEHTBP or TBPH). These two
82
compounds have been found in the commercial mixture called Firemaster 550, which
83
has been used as a replacement for pentaBDE.9
84
EHTBB
diphenyl
from
and
usage
ethers
under
BEHTBP
(PBDEs).1,
the
2
Stockholm
elicit
Due
to
their
Convention.3
endocrine
persistence,
Commercial
disruption
and
85
2,3,7,8-tetrachlorodibenzo-p-dioxin-like effects,10 and are shown to potentially affect
86
the reproductive axis of Japanese medaka.11 Environmental persistence of BEHTBP
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was also reported in sediments.12 Biomagnification of DBDPE and BTBPE in the
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food web was reported,13 and these two compounds also have the potential for in vitro
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and in ovo effects in chicken embryos.14
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The octanol-air partition coefficients (logKOA) for 19 target NBFRs at 25 oC (EPI
91
Suite, version 4.1) range from 8.01 to 19.2 [Table SI-1, Supporting Information (SI)],
92
implying that soils are important reservoirs of these NBFRs, and therefore can affect
93
cycling of NBFRs in environment.15 The degradation half-lives of these NBFRs in
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soil range from 1800 to 8600 h (Table SI-1, SI), suggesting that they persist in soils.
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Previous studies have focused on legacy POPs in soils.16-18 It is important to
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understand the pollution status of emerging NBFRs in soil to establish baseline levels
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and to evaluate future trends.
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These NBFRs have only recently started to receive strong attention. Although
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limited information is available on the production and consumption of NBFRs, their
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increasing environmental occurrence since the phase-out of PBDEs have been
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reported in recent studies.19-25 For example, increasing atmospheric levels of several
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NBFRs in the North American Great Lakes23, 24 and Northeast China25 have been
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documented. The concentrations of DBDPE in the atmosphere of Northern China
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were higher than those of its replacement (deca-BDE).26 DBDPE was one of the
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dominant compounds in soil samples collected from BFR-related industrial areas in
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China.27-29 Elevated concentrations of several NBFRs were observed in the marine
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atmosphere from Asia to the Arctic and from Asia to Antarctica.30, 31
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Asia has approximately 60% of the human population globally.32 The booming
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industrial and agricultural activities in several Asian countries have resulted in
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discharges of a considerable amount of hazardous chemicals including NBFRs into
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environment.32 In Asia, China in particular, other activities including e-waste
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recycling and BFR-related industrial activities,27,
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pollution by BFRs in these regions. NBFRs have been reported in air,8, 25, 30, 31, 34, 35
28, 33
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water,36 sludge,37 soil,21, 38, 39 house dust,40-43 and biota32, 44 from some Asian countries.
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However, there is still insufficient information available regarding these NBFRs in
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soils from Asian countries, such as Japan, South Korea, Vietnam, and India.
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Asian Soil and Air Monitoring Program (Asia-SAMP) is designed to study
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occurrence, sources effects and spatiotemporal variations of legacy and current-use
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organic chemicals, including NBFRs, in both surface soils and air in some Asian
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countries.45, 46 This study presents the first comprehensive survey of 19 NBFRs (Table
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SI-1) in soil samples collected from areas with no known point source
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(urban/rural/background sites, U/R/B sites), as well as from areas with known point
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source (vicinity of BFR-related industrial/e-waste sites, F/E sites) across five Asian
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countries, which are China, India, Japan, South Korea, and Vietnam. The objectives of
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the present study were to investigate the occurrence, spatial distributions and potential
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source profiles for NBFRs, the relationship between the primary and secondary
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sources of these chemicals in soils, and between the pollution levels of these
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chemicals and human activities in these five Asian countries.
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■ MATERIALS AND METHODS
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Soil Sample Collection. Surface soil samples (depth: 0−20 cm) were collected at
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195 sites across the five Asian countries during September and November, 2012. The
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locations of sampling sites are depicted in Figure SI-1, SI. Details of the number of
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samples collected from each country are shown in Table SI-2. In brief, 195 sampling
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sites include 82 urban (U), 80 rural (R) and 10 background (B) sites in all five
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countries, 13 e-waste sites (E) (10 in China, 2 in South Korea, and 1 in Vietnam), and
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10 sites in the downwind of a BFR-factory (F) in China with the distance ranged from
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0.4 to 3.5 km. The soil samples were taken from U/R/B sites that were away from
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BFR-related industrial and e-waste activities. Soil samples were also collected from 6
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highly contaminated regions (E/F sites). Five subsamples (0−20 cm) were collected
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and pooled to form one well mixed sample. Then the samples were sealed in
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precleaned aluminum containers. All soil samples were analyzed at IJRC-PTS
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laboratory in Harbin Institute of Technology, Harbin, China and kept frozen at -20 oC
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before analyzed.
144
Analytical procedure. The soil sample collection and extraction procedures have
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been presented previously,45, 47 and can be found in the SI. Soil samples were spiked
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with surrogate standards prior to a 24-h Soxhlet extraction in a mixture of acetone and
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hexane (1:1, V:V). The extracts were purified in multilayer silica chromatographic
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column. Target compounds were analyzed on an Agilent 6890 GC /5975 MS operated
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in electron capture negative ion mode.
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QA/QC. Instrument performance was monitored by analyzing calibration standards
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after every 10 samples. Accuracy was achieved by examining percent recoveries of
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NBFRs from matrix spiked samples for each batch of samples. Average spike
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recoveries were in the range of 76-92%. Average recoveries for surrogate standards
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(13C10-syn-DP,
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ranged from 81% ± 9% to 95 ± 11% (Table SI-3). Procedural blank samples were
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analyzed in each batch of samples. The values of NBFRs in procedural blanks were
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lower than 5% of those found in the real samples. The reported results were not blank
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or recovery corrected. The method detection limits (MDLs) for NBFRs were
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calculated from the average blank value plus 3 times its standard deviation. One-half
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of the MDLs were assigned for the compounds with values below MDLs for statistical
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analysis for highly skewed data48. The MDLs of NBFRs in soils were in the range of
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0.001 to 0.070 ng/g dry weight (dw) (Table SI-1). Principal component analysis (PCA)
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was applied to evaluate the clustering patterns for NBFRs that have a detection
13
C10-anti-DP,
13
C12-BDE-209 and CB-155) during sample processing
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frequency above 50%. The correlation analysis and PCA were performed using SPSS
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software V22.0 (IBM SPSS Inc., Chicago, USA). The spatial distribution maps were
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digitized by MapInfo Professional 11 (MapInfo Corporation, North Greenbush, NY,
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USA).
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■ RESULTS AND DISCUSSION
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Levels and Distribution. Data regarding the concentrations of NBFRs in soils
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collected from U/R/B and E/F sites of each country are presented in Table 1 and Table
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2, respectively. High variation in total NBFRs concentrations (∑19NBFRs) was
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observed in soil samples, with the geometric mean (GM) values ranged from 0.50
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ng/g dw in U/R/B sites in Vietnam to 540 ng/g dw in F sites in China. Figure 1 and
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Figure SI-2 to SI-8 illustrate the spatial distributions of NBFRs in soil from the five
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countries. For the U/R/B sites, Japan has the highest concentrations of ∑19NBFRs in
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soil, with GM concentrations of 9.3, followed by South Korea, China, India and
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Vietnam, with the GM values of 5.5, 2.9, 0.63 and 0.50 ng/g dw, respectively.
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Interestingly, similar trends of PBDEs among these five countries were found in our
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previous study on PBDEs,45 showing that the GM levels of ∑23PBDEs obtained for
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Japan, China, South Korea, India and Vietnam were 34, 16, 5.3, 0.70 and 0.61 ng/g dw,
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respectively. Total PBDE concentrations in soils collected from Shanghai, China
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(mean: 33 ng/g dw),49 Hung Yen, Vietnam (mean: 2.2 ng/g dw),50 Kocaeli, Turkey
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(mean: 26 ng/g dw)51 and Iraqe-Kuwaite-Saudi transect (mean: 17 ng/g dw)52 are
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comparable to those found for NBFRs. For the E/F sites, ∑19NBFRs GM
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concentrations in E sites in South Korea (8.6 ng/g dw) and Vietnam (21 ng/g dw)
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were higher than those of U/R/B sites in the two countries, but lower than that of E
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sites in China. High concentrations of ∑19NBFRs in the vicinity of the F site and E
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sites in China were detected, with the GM concentrations of 540 and 330 ng/g dw, 8
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respectively, approximately 1-4 orders of magnitude higher than those of U/R/B sites.
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The high concentrations of NBFRs have previously been reported in soils of E sites53
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and F sites in China.27, 28
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DBDPE. Total NBFRs was dominated by DBDPE in most soil samples, with the
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relative abundance ranging from 52.5 ± 20.2% in Vietnam to 71.8 ± 22.9% in India
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for U/R/B sites (Figure SI-9). The NBFRs profile showed higher contributions of
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DBDPE in E/F sites, with the values of 78.2 ± 10.7%, 97.4 ± 2.3%, 93.7% and 99.5 ±
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0.5% for E sites in China, South Korea, and Vietnam, and F sites in China,
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respectively. The highest GM concentration of DBDPE was in F sites in China (540
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ng/g dw), followed by E sites in China (250 ng/g dw). For the U/R/B sites, DBDPE
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GM concentration followed the order of: Japan (5.0 ng/g dw) > South Korea (2.4 ng/g
200
dw) > China (1.5 ng/g dw) > India (0.43 ng/g dw) > Vietnam (0.24 ng/g dw).
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Comparatively, DBDPE was detected with the concentrations ranging from 12 to 340
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(GM: 66) ng/g dw in agricultural soils in a BFR-related industrial region in
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Shouguang City, China,28 from 560-750 (median: 650) ng/g dw in e-waste
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contaminated soils in China,54 from not detected (ND) to 1600 (median: 0.53) ng/g dw
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in U/R/B soils from Northern China,55 from 17.6 to 35.8 in the farmland soils in
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southern China,38 from 0.005 to 1.3 (GM: 0.22) ng/g dw in Chinese background
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soils.21 DBDPE was detected in 100% samples with the concentration range of
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0.2-160 (GM: 2.7) ng/g OM (organic matter) in soil samples from Stockholm,
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Sweden.56
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BEHTBP. The second dominant NBFRs varied among samples and locations
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(Figure SI-9). BEHTBP was generally the second abundant compound in U/R/B sites
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of China, India and Vietnam with the percentage values of 17.5 ± 16.8%, 7.6 ± 5.5%
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and 19.9 ± 21.7% of total NBFRs, respectively. The highest GM concentration of
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BEHTBP was detected in China (0.26 ng/g dw), followed by Japan (0.24 ng/g dw),
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South Korea (0.13 ng/g dw), Vietnam (0.051 ng/g dw) and India (0.035 ng/g dw).
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With respect to those concentrations in the background sites in China, Japan and
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South Korea with the values of ND-0.31, 0.05-1.9 and ND-1.4 ng/g dw, respectively,
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similar values of BEHTBP were detected in Chinese forest soils (0.006-0.53 ng/g
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dw).21 However, these values in soils were much lower than the concentrations of
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BEHTBP in indoor dust samples from Vancouver Canada57 and China40 with the
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median values of 99 ng/g and 29 ng/g, respectively. In contrast to DBDPE, the spatial
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distribution of BEHTBP showed lower concentrations at the F sites but higher values
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at the E sites, suggesting that BEHTBP was not produced in the factory from where
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samples were collected, but it is widely used in electronic products that were
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dismantled in the e-waste region. BEHTBP is the major component of Firemaster 550
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(15%), Firemaster BZ-54 (30%) and DP-45(100%).25, 58 The first two commercial
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products have been produced by the Great Lakes Chemical Company in the USA.59
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EHTBB. Together with BEHTBP, EHTBB is another component of Firemaster 550
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(35%) and Firemaster BZ-54 (70%). As shown in Figure SI-3, the spatial distribution
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of EHTBB concentrations decreased in the order of China, Japan, South Korea,
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Vietnam and India, with the GM values of 0.025, 0.013, 0.004, 0.003, 0.003 ng/g dw,
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respectively, which were lower than BEHTBP. Lower levels of EHTBB (ND - 0.21
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pg/m3) than BEHTBP (ND - 2.8 pg/m3) were also detected in Marine atmosphere.30
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BTBPE. Spatial distribution of BTBPE demonstrated several hot-spots in urban
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cities in South Korea and Japan, and in E sites in China (Figure 1). Similar to
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BEHTBP, BTBPE was detected at relative low concentrations in F sites in China. The
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GM concentration of BTBEP was the highest in South Korea (0.36 ng/g dw),
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followed by Japan (0.11 ng/g dw), China (0.061 ng/g dw), Vietnam (0.020 ng/g dw),
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and India (0.006 ng/g dw) (Table 1). In comparison, concentrations of BTBPE in the
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e-waste soils and paddy soils were 17-22 and 0.16-0.23 ng/g dw, respevtively.54 The
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mean BTBPE concentration in background sites in China was 0.10 ng/g dw, and the
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reported concentrations in forest soils21 and farmland soils38 were 0.049 and 0.05 ng/g
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dw, respectively. As shown in Figure SI-9, BTBPE was the second abundant NBFRs
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in South Korea (16.2 ± 22.4%), suggesting the extensive usage of BTBPE in this
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country. The higher concentrations of BTBPE were also detected in birds60 and
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mussels44 from South Korea in comparison to those from other Asian countries.
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HBBZ. The spatial distribution of hexabromobenzene (HBBZ) indicated several hot
248
spots in China (Figure 1). However, HBBZ was widespread in Japan with the GM
249
concentration of 0.14 ng/g dw, which was 3 orders of magnitude higher than that of
250
other countries with the values ranging from 0.001 in Vietnam to 0.003 ng/g dw in
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China. The high concentration of HBBZ observed in Japan indicates the extensive
252
usage of this compound in Japan. In fact, HBBZ has been marketed as FR-B by the
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Nippon Chemicals Co. (Tokyo, Japan) and was widely used in Japan with the
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production volumes of 350 tons in 2001.2 The reported HBBZ concentration in
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Chinese forest soils was ND-0.34 (mean: 0.046) ng/g dw,21 and that in Stockholm,
256
Sweden, was ND-6.1 ng/g OM.56 HBBZ was the third dominant NBFRs in Japan with
257
the relative abundance of 7.3 ± 21.2% of the total NBFR concentrations.
258
DPTE. Spatial distribution of 2,3-dibromopropyl 2,4,6-tribromophenyl ether
259
(DPTE) showed high levels in Northern China and Japan (Figure SI-4). This is
260
interesting because the production of DPTE had ceased in the mid-1980s.61 The
261
estimated half-lives for DPTE are 63.6, 8640 and 4320 h in air, soil and water,
262
respectively (EPI Suite v4.1), indicating its persistence in the environment. The higher
263
concentration of DPTE in Northern China may be due to the long-range transport and
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cold condensation.62 However, further evidence is needed to confirm this hypothesis,
265
because DPTE may be reproduced after the phase out of the two commercial PBDEs.
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PBBA. The GM concentrations of pentabromobenzyl acrylate (PBBA) in the five
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countries were 0.089 ng/g dw for Japan, 0.009 ng/g dw for India, 0.024 ng/g dw for
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South Korea, 0.009 ng/g dw for Vietnam, and 0.007 ng/g dw for China. While PBBA
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was detected in 22% of air samples from the Great Lakes,63 the data for PBBA in soil
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are scarce. Studies on environmental occurrence and past/current use of
271
pentabromobenzyl acrylate (PBBA) are limited. PBBA is currently marketed by Dead
272
Sea Bromine as FR-1025.64
273
PBT. In this study, the GM concentrations of pentabromotoluene (PBT) ranged
274
from 0.001 in Vietnam to 0.028 ng/g dw in Japan. PBT has been listed as a moderate
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production volume chemical (1000-5000 tons/year) by the World Health Organization,
276
with a production volume of 600 tons/year in China.2 While PBT was widely detected
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in air,8, 63, 65 the concentration of PBT in soils was low with the value of ND-0.018
278
ng/g OM in Stockholm, Sweden.56
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PBEB. In comparison to the other NBFRs analyzed here, the spatial distribution of
280
pentabromoethylbenzene (PBEB) showed considerably lower variability with the GM
281
concentrations ranging from 0.001 to 0.002 ng/g dw, suggesting its lower usage.
282
Others. While the detection frequency for NBFRs discussed above is greater than
283
50%, the detection rates of the others were generally in the range of 10% to 43%.
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Among the other chemicals measured, 1,2,3,4,5-pentabromobenzene (PBBZ) was the
285
most detected with GM concentrations ranging from 0.001 (Vietnam) ng/g dw to
286
0.012 (Japan) ng/g dw. The spatial distribution also showed higher levels of PBBZ in
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Japan, South Korea and China.
288
Evidences for Simultaneous Application among BFRs. Correlations among the
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concentrations of NBFR compounds were all positive and statistically significant (p
E > U > R > B sites, except for HBBZ, EHTBB, BEHTBP and BTBPE,
386
which showed higher levels in E sites than F site [Figure 2(1)]. On the other hands,
387
the compositional profiles of NBFRs showed depletion of DBDPE and enrichment of
388
other lower molecular weight NBFRs in R/B sites than those of U/E/F sites [Figure
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2(2)]. While DBDPE is less volatile/more bound to particles, other lower mass
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NBFRs are more prone to long-range atmospheric transport from local source regions
391
(U/E/F sites) to B/R sites. This trend can also be observed for PBDEs (Figure 2),45
392
suggesting that the distribution and transportation of NBFRs and PBDEs are
393
dominated by primary sources, resulting in deposition of higher molecular weight
394
NBFRs to soils closer to the source center while the lower molecular weight NBFRs
395
can deposit to soils farther away from the source center. Both E and F sites can be
396
treated as point sources, thus we refer this as the “point source fractionation” for
397
NBFRs and PBDEs, similarly to the “urban fractionation” for PCBs.67, 67
398
A so called “longitudinal fractionation” phenomenon was identified for PCBs68 and
399
PBDEs45 in Chinese soil, which was also observed for NBFRs in this study with
400
decreasing levels of all NBFRs in soil, and decreasing fractions of DBDPE and
401
increasing proportions of other NBFRs with decreasing longitudes from east to west
402
(Figure SI-12). This phenomenon is unique for China caused by the higher population
403
density located on the east coast of China, indicating that population is a good
404
surrogates of emissions for PCBs, PBDEs, and NBFRs.
405
We need to point out that all the urban fractionation, longitudinal fractionation, and
406
point source fractionation patterns can be refer to the “primary fractionation”
407
pattern,16 which is a common distribution pattern found world-wide for many SVOCs.
408
This distribution pattern will gradually become the “secondary fractionation” pattern
409
many years after the stop use of these SVOCs. Under the “secondary fractionation, the
410
transport of chemicals is mainly driven not by primary emissions, but by temperature,
411
soil organic carbon (SOC) content, and ultimately the surface-air partition coefficients
412
(KSA) for the various environmental compartments or climate zones.16
413
Point Sources Effects. As 10 soil samples from e-waste sites and 10 samples from
17
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414
sites in the vicinity of a BFR-factory along with many soil samples from U/R/B sites
415
were collected and analyzed in China, the influence of point sources, i.e. the
416
BFR-related industrial and e-waste dismantling sites, on NBFR distribution could be
417
evaluated for this country. The PBDE concentrations as a function of distance from a
418
source can be described as a simple dilution model developed by McDonald and
419
Hites.69 After taking natural logarithmic form of the model, we obtained the following
420
relationship to be applied for NBFR,
ln ( Cd ) = ln a0 + a1 ln ( d )
(1)
421
where Cd is the NBFR concentration (ng/g dw) in soils at a distance of d (in km) from
422
the source center, a1 is the slope, and lna0 is the intercept.
423
There is actually a linear relationship between natural logarithm concentration of
424
NBFRs in soils and distance from the source center. As shown in Figure 3, the
425
concentrations of all NBFRs were negatively and significantly correlated with the
426
distance from E/F sites. The negative slope (a1) ranged from -1.25 for BEHTBP to
427
-0.52 for PBEB (with p < 0.05), suggesting that the levels of NBFRs in soils
428
significantly decreased with an increasing distance from the source centers. The
429
higher absolute value of slope for DBDPE than the others suggested the more rapidly
430
decreased in DBDPE concentrations with increasing distance from source center.
431
These trends can also be identified for PBDEs (Figure SI-13).
432
However, these slope values (-0.52 to -1.25 with p < 0.05) obtained in this study
433
were much greater than those by using radial dilution model (expected coefficients
434
equal to -2) for toxophene69 and Gaussian diffusion model (expected coefficients
435
equal to -1.5) for dechlorane plus and other flame retardants70 in tree bark, suggesting
436
that NBFR concentrations were not changing as rapidly as expected. We speculated
437
that the existence of unknown sources such as megacity can elevate the levels of
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NBFRs at the some surrounding sites, thus reducing the effects from the known point
439
sources.
440
Area Sources Effects. While the location of point sources is obviously an
441
important factor influencing the emission of NBFR from local environment, this
442
factor alone cannot fully predict the NBFR concentrations in soils. Accordingly, the
443
natural logarithm of NBFR concentrations were further regressed against the natural
444
logarithm of population density (PD, a surrogate for area sources of NBFR). The
445
correlations for all NBFRs were statistically significant for the five-country samples
446
(Figure SI-14), however, the correlations were not as strong as those obtained for the
447
each-country samples. The correlation coefficients for each country were significant
448
and positive in most cases, with population density explained 7.5% to 79.2% (r2, with
449
p < 0.05) of the variances in soil concentrations of NBFRs. Correlations were
450
significant for all cases for China and less significant for other countries due to the
451
smaller number of samples from these countries.
452
A greater slope of the regression indicates greater changes of soil NBFRs
453
concentrations as a function of PD. As shown in Table SI-7, the regression slopes of
454
DBDPE in the samples from Japan, China, India, South Korea, and Vietnam were
455
1.14, 0.86, 0.68, 0.25, and 0.14, respectively. These slopes indicated that an increase
456
in population density by a factor of 10 would result in an increase in DBDPE levels
457
by the factors of 13.8, 7.2, 4.8, 1.8, and 1.4 for the corresponding countries. The
458
stronger influence of population density on the levels of DBDPE further suggests that
459
DBDPE is now a widely-used flame retardant by Asian populations. Similarly, the
460
stronger influence of population density on the levels of HBBZ in Japan and of
461
BTBPE in South Korea was noticed.
462
Primary and Secondary Sources Effects. Ambient temperature and soil organic
19
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463
carbon (SOC) can be another two important factors in controlling the cycling of
464
NBFRs between atmosphere and surface soil and water, forming a “secondary
465
distribution pattern”.16 Starting with these known parameters, the natural logarithm of
466
NBFR concentrations were regressed for Chinese samples using a multiple linear
467
regression model including PD, distance from point sources (d1, d2, and d3), SOC, and
468
ambient temperature T:
ln ( C ) = b0 + b1 ln ( PD ) + b2 ln ( d1 ) + b3 ln ( d 2 ) + b4 ln ( d3 ) + b5 SOC + b6T
(2)
469
where b0 is intercept, and b1, b2, b3, b4, b5 and b6 are fitting coefficients describing the
470
change of NBFR concentration (C) as a function of population density (PD, in
471
person/km2), distance from F site (d1, in km), distance from E site 1 (d2, in km),
472
distance from E site 2 (d3, in km), SOC (in %) and annual average temperature of the
473
sampling site (T, in K).
474
In order to remove the insignificant parameters in Equation (2), the model was run
475
in the stepwise mode. The final results of the stepwise regression model for all
476
NBFRs are shown in Table SI-8. The indicators for secondary sources effect, SOC and
477
T, were usually not significant parameters in controlling soil NBFR concentrations at
478
any sites from China, indicating the distribution pattern for all NBFRs in China is
479
primary in nature. Thus, these 2 parameters were removed from Equation (2).
480
However, some exemptions existed. As determined from the significance of
481
coefficient b5 in equation (2), we found that SOC is a significant factor in controlling
482
the levels of DPTE, EHTBB, BTBPE, BEHTBP, TriBDE, TetraBDE, PentaBDE and
483
HexaBDE in soils in China (Table SI-8). Among these BFRs, the four PBDE
484
homologues are the major components of commercial penta-BDE and octa-BDE that
485
had been banned from use for more than ten years, DPTE had been banned from
486
production in the mid-1980s,61 and the effects of foreign sources could be greater than
20
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those of domestic sources for EHTBB, BTBPE and BEHTBP, as mentioned by the
488
PCA results. For DPTE, the effect of SOC was even greater than other five parameters,
489
as indicated by the absolute value of standardized coefficients [labeled as CST in Table
490
SI-8(3)]. We speculated that the domestic sources for these BFRs were not as strong
491
as other BFRs in China, and thus the secondary sources, the accumulated BFRs in
492
SOC, started to play important role in distributing these compounds in Chinese soil,
493
indicating the primary distribution pattern was changing to the secondary distribution
494
pattern in Chinese soil for these chemicals.
495
The fitted parameters (PD, d1, d2, and d3, indicators for primary sources effect) in
496
equation (2) were almost always significant, indicating that primary sources were
497
playing an important role. The BFRs with the highest standardized coefficients of
498
ln(d1) were PBT, PBEB, PBBA, DBDPE, TriBDE and DecaBDE (Table SI-8),
499
indicating the strong domestic sources of these compounds. The greater changes in the
500
concentrations of HBBZ, EHTBB, BTBPE, BEHTBP, TetraBDE, PentaBDE,
501
HexaBDE, OctaBDE and NonaBDE as a function of the distance from E sites (d2 and
502
d3) were noticed, suggesting that d2 and d3 were the most significant variables having
503
greater effects on soil concentrations of these BFRs. In conclusion, the primary
504
sources effects were stronger than secondary sources effects in controlling the levels
505
and distribution of NBFRs and PBDEs in soils, but the secondary factors became
506
more important for a few compounds of NBFRs and PBDEs which usage were
507
stopped many years ago.
508
■ ASSOCIATED CONTENT
509
Supporting Information
510
Additional tables and additional figures. This material is available free of charge via
511
the Internet at http://pubs.acs.org. 21
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512
■ AUTHOR INFORMATION
513
Corresponding Author
514
* Tel. +8645186289130; Fax: +8645186289130. *E-mail:
[email protected] 515
Notes
516
The authors declare no competing financial interest.
517
■ ACKNOWLEDGEMENTS
518
The authors thank IJRC-PTS colleagues in Japan, South Korea, India, Vietnam and
519
China for their contributions to this research. This work was supported by the National
520
Natural Science Foundation of China (21277038), the State Key Laboratory of Urban
521
Water Resource and Environment, Harbin Institute of Technology (HCK201533), and
522
the HIT Environment and Ecology Innovation Special Funds (HSCJ201608).
523
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sediments, soils and plants from an informal e-waste dismantling site, South
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(54) Zhang, Y.; Luo, X. J.; Mo, L.; Wu, J. P.; Mai, B. X.; Peng, Y. H., Bioaccumulation
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and translocation of polyhalogenated compounds in rice (Oryza sativa L.) planted
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in paddy soil collected from an electronic waste recycling site, South China.
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exposure risks of decabromodiphenylethane in soils of North China. Environ. Sci.
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and HBCDDs in Indoor and Outdoor Media in Stockholm, Sweden. Environ. Sci.
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current-use flame retardants in house dust from Vancouver, Canada. Environ.
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(58) Ma, Y. N.; Venier, M.; Hites, R. A., 2-Ethylhexyl Tetrabromobenzoate and
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Flame-Retardant Mixtures, Firemaster (R) 550 and Firemaster (R) Bz-54. Environ.
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volatility organochlorine compounds in polar regions. Ambio 1993, 10-18. (63) Venier, M.; Ma, Y. N.; Hites, R. A., Bromobenzene Flame Retardants in the Great Lakes Atmosphere. Environ. Sci. Technol. 2012, 46, (16), 8653-8660. (64) Weil, E. D.; Levchik, S., Current practice and recent commercial developments in flame retardancy of polyamides. J. Fire Sci. 2004, 22, (3), 251-264.
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Pollutants in the Atmosphere of North China: Levels, Distribution, and Sources.
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Table 1. Description of geometric mean (GM), mean and standard deviation (SD) concentrations (ng/g dw) of NBFRs in soil samples collected in U/R/B sites in five Asian countries. Compound
Japan, n = 14 South Korea, n = 20 China, n = 101 India, n = 24 GM Mean SD GM MEAN SD GM MEAN SD GM MEAN PBT 0.028 0.077 0.16 0.002 0.004 0.011 0.010 0.027 0.059 0.003 0.004 PBEB 0.001 0.003 0.005 0.001 0.002 0.002 0.002 0.008 0.016 0.001 0.002 DPTE 0.40 1.4 1.7 0.19 2.1 5.9 0.010 0.26 1.0 0.004 0.041 HBBZ 0.14 6.3 20 0.002 0.004 0.006 0.003 0.053 0.32 0.001 0.002 PBBA 0.089 0.18 0.15 0.024 0.061 0.064 0.007 0.027 0.077 0.009 0.080 EHTBB 0.013 0.054 0.12 0.004 0.012 0.021 0.025 0.13 0.22 0.003 0.004 BTBPE 0.11 0.23 0.36 0.36 5.2 16 0.061 0.20 0.57 0.006 0.031 BEHTBP 0.24 0.59 0.87 0.13 0.55 0.96 0.26 1.0 2.0 0.035 0.091 DBDPE 5.0 24 42 2.4 4.3 5.2 1.5 10 28 0.43 2.6 ∑10others 0.10 0.38 0.84 0.18 0.63 0.88 0.031 0.094 0.27 0.015 0.016 ∑19NBFRs 9.3 33 50 5.5 13 19 2.9 12 29 0.63 2.9 ∑10others: sum of ATE, α-TBECH, β-TBECH, p-TBX, BATE, α-TBCO, β-TBCO, PBBZ, TBCT and OBIND.
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SD 0.002 0.001 0.12 0.004 0.28 0.003 0.085 0.13 4.8 0.009 5.1
Vietnam, n = 13 GM MEAN 0.001 0.002 0.001 0.007 0.009 0.032 0.001 0.002 0.009 0.055 0.003 0.009 0.02 0.036 0.051 0.15 0.24 0.36 0.016 0.018 0.50 0.68
SD 0.003 0.021 0.051 0.001 0.14 0.021 0.036 0.20 0.38 0.011 0.56
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Table 2. Summary of minimum (Min), maximum (Max), geometric mean (GM), mean and standard deviation (SD) concentrations (in ng/g dw) of NBFRs in soil samples collected in E sites and F sites in China, Vietnam and South Korea. Compound
E, China (n = 10) Min
Max
GM
F, China (n = 10) Mean
E, Vietnam (n = 1)
E, South Korea (n = 2) Min
SD
Min
Max
GM
Mean
SD
Mean
Max
GM
Mean
SD
PBT
0.025
0.83
0.081
0.18
0.27
0.037
4.9
0.44
1.2
1.6
0.006
0.002
0.003
0.003
0.003
0.001
PBEB
ND
2.0
0.034
0.25
0.62
0.028
3.1
0.26
0.85
1.2
0.006
ND
ND
ND
ND
ND
DPTE
0.54
4.5
1.1
1.4
1.2
0.13
8.6
0.61
1.5
2.6
0.10
0.020
0.057
0.034
0.038
0.026
HBBZ
0.051
11
0.75
3.0
4.0
0.013
1.8
0.18
0.53
0.62
0.044
ND
ND
ND
ND
ND
PBBA
0.003
1.4
0.10
0.49
0.56
0.003
5.2
0.011
0.86
1.8
0.16
0.016
0.019
0.017
0.017
0.002
EHTBB
0.002
86
0.40
10
27
0.002
0.69
0.003
0.07
0.22
0.018
ND
ND
ND
ND
ND
BTBPE
0.39
23
2.8
6.4
8.3
0.001
5.2
0.046
1.2
1.9
0.67
0.014
0.22
0.056
0.12
0.15
BEHTBP
5.2
770
53
170
249
ND
ND
ND
ND
ND
0.23
0.019
0.020
0.020
0.020
0.001
DBDPE
18
2000
250
610
715
64
9000
540
1500
2700
20
2.1
33
8.4
17
22
Others
0.083
6.8
0.67
1.6
2.1
0.013
2.8
0.23
0.71
0.99
0.10
0.014
0.015
0.014
0.014
0.001
2.2
33
8.5
18
22
NBFRs 26 2500 330 800 926 64 9000 540 1500 2700 21 ND: not detected. Others: sum of ATE, α-TBECH, β-TBECH, p-TBX, BATE, α-TBCO, β-TBCO, PBBZ, TBCT and OBIND.
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1 45_N
(A)
35_N 25_N Ocean
15_N
ng/g dw >50 (B) 20 10 5 1 0.5 0.1 nd
(C)
(D)
2 3
Figure 1. Spatial distribution for DBDPE, BEHTBP, BTBPE and HBBZ in soil from
4
five Asian countries.
5 6
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Proportion (%) Concentration (ng/g dw)
7
105 104 103 102 101 100 10-1 10-2 102
(1)
F sites E sites
B sites
U sites R sites
(2)
101 100 10-1 10-2
8
P Z A B T B E E E E E rs E E E E E E PB PBE DPT HBB PBB HTB TBP HTB BDP Othe riBD raBD taBD aBD taBD taBD aBD aBD B BE D T Tet Pen Hex ep Oc Non Dec E H
9
Figure 2. Concentrations (1) and compositional profiles (2) for NBFRs and PBDEs in
10
soils collected from the five Asian countries.
11
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HBBZ DBDPE BEHT BP BT BPE EHT BB PBBA
ln(C, in ng/g dw)
DPT E
PBEB
PBT
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0
-0.86**
-0.90**
-0.77*
-0.84**
-0.79*
-0.81*
-0.87*
-0.91**
-4 0 -4 0
-0.82**
-5 0
-0.66*
-5 0
-0.85*
-4 -0.93**
3 -3 3
-0.80**
-0.98**
-0.92**
-0.83*
-0.96**
-0.91**
-0.93**
-3 7 0 8
-0.90**
0 0 2 4
ln(d1)
0 2 4
ln(d2)
0 2 4
ln(d3)
12 13
Figure 3. Correlation analysis between the natural logarithm concentrations of NBFR (ng/g dw)
14
and the natural logarithm distance (0-150 km) from F site [ln(d1)], E site 1 [ln(d2)], and E site 2
15
[ln(d3)]. Note: The correlation coefficients (r) (the numbers in blue color) were also given with *
16
and ** indicating the correlation significances at the 0.05 and 0.01 level (2-tailed), respectively.
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