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Impacts of Atmospheric Mercury Deposition on Human Multimedia Exposure: Projection from Observation in the Pearl River Delta Region, South China Minjuan HUANG, Sixin Deng, Hanying Dong, Wei Dai, Jiongming Pang, and Xuemei Wang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b00514 • Publication Date (Web): 31 Aug 2016 Downloaded from http://pubs.acs.org on September 6, 2016
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Impacts of Atmospheric Mercury Deposition on Human Multimedia Exposure: Projection from Observations in the Pearl River Delta Region, South China Minjuan Huang 2, Sixin Deng
2,3
, Hanying Dong
2,3
, Wei Dai
2,3
, Jiongming Pang2,
Xuemei Wang 1 *
1. School of Atmospheric Science, Sun Yat-sen University, Guangzhou, 510275, PR China
2. School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou, 510275, PR China
3. Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, PR China
*Corresponding author e-mail:
[email protected] 1
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Abstract: A preliminary projection was performed to determine human multimedia exposure
2
to mercury (Hg) based on deposition flux observations and to identify the impacts of
3
atmospheric Hg deposition in Pearl River Delta (PRD) region, South China. The Monte-Carlo
4
technique was used to propagate the variability throughout the projection. The regional
5
specific probability density functions (PDFs) of the studied parameters were regressed from
6
the provincial/national published data, except when the data were deficient. The atmospheric
7
Hg deposition flux ranged from 112.60 to 321.19 µg/m2/year and did not significantly
8
contribute to Hg accumulation in the regional topsoil, freshwater bodies and most food items
9
except fish. The consumption of fish and milk/dairy products was the major contributor to the
10
total exposure for adults (>18 years)/6- to 12- year children and 0- to 6- year children
11
respectively. The projected concentrations and exposure levels were the results combining
12
MeHg and inorganic Hg (Hg2+). Under the 30-year projection, the probability of risks caused
13
by Hg deposition (combining Hg2+ and MeHg) was the highest for 0- to 6- year children,
14
followed by 6- to 12- year children and adults. The ground effects driven by precipitation had
15
a significantly greater effect relative to the mass transport effects in this region.
16 17
Keywords: atmospheric deposition, mercury, flux monitoring, multimedia, human exposure,
18
Monte-Carlo technique
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INTRODUCTION
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Mercury (Hg) is a potent neurotoxin of significant ecological and public health concern,
21
and it occurs in the atmosphere as vaporous elemental mercury (Hg0), vaporous divalent
22
mercury (Hg2+) and particulate mercury (HgP). Hg0 emissions generally enter the global cycle
23
because of its long residence times in the atmosphere (0.5-1.5 years). The relatively shorter
24
atmospheric lifetimes of Hg2+ (hours to days) and HgP (hours to weeks) indicate that they are
25
deposited close to their emission points 1. Deposition represents a unique pathway for the
26
vertical transportation of atmospheric Hg to the ground; subsequently, the settled Hg
27
accumulate in surface soils and water bodies, where they are methylated and magnified
28
within organisms; finally, atmospheric Hg bio-transfers to the human body through two ways:
29
(1) food chain and (2) contact with contaminated soil and water 2.
30
China is one of the largest Hg emitters in the world and accounts for approximately 30%
31
of the anthropogenic global Hg emissions (1960 tons) based on inventories recorded in 2010 3,
32
4
33
emission contributors in China; the Hg emissions primarily occur within the Pearl River
34
Delta (PRD) region 5. The PRD region is one of the largest metropolitan regions in China and
35
has experienced dramatically rapid development and urbanization in recent decades. Based
36
on the 2008 emission inventory, the anthropogenic Hg emissions in the PRD region are
37
estimated as 17,244 kg 6. Numerous studies have found that Hg emitters (such as metal
38
smelting and chlor-alkali industries) contribute to Hg contamination of the topsoil, surface
39
water and crops in their surrounding environments
40
level in the regional surface water, river sediment and estuarine sediment are indicated
. Guangdong (GD) Province is located in South China and is ranked as one of top 10 Hg
7-9
. In the PRD region, the elevated Hg
3
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predominantly attributed to industrial and urban sources 10-13.Therefore, Guangdong Province
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and the PRD region in particular might be suffering from unidentified environmental impacts
43
and human health risks related to the significant regional anthropogenic Hg emissions.
44
Previous studies that evaluated multimedia exposure to emitted pollutants have
45
generally been conducted using a series of deterministic models, including emission models,
46
dispersion and deposition models, environmental media accumulation models and human
47
exposure models
48
Hg emitted from a municipal solid waste (MSW) gasification plant, compared with inhalation,
49
soil ingestion and dermal adsorption from soil 15. However, it did not consider the deposition
50
resulting water Hg load and bio-magnification in fish, although fish consumption has been
51
widely considered as an important exposure source of Hg for human 17. Morisset et al. (2013)
52
also attempted to achieve a comprehensive risk assessment of Hg for French infants and
53
toddlers by evaluation of multimedia exposure
54
sources (e.g., deposition, waste water eluent and sludge discharge) for Hg accumulation in
55
the environmental media. The current study performs a preliminary evaluation of the human
56
multimedia exposure to Hg caused by atmospheric deposition in the PRD region using
57
simplified versions of the empirical models developed by the U.S. Environmental Protection
58
Agency (USEPA) 19. Briefly, observational Hg deposition fluxes are incorporated rather than
59
simulated results from emission models, dispersion and deposition models. To differentiate
60
among the impacts of atmospheric deposition and other surface contamination sources (e.g.,
61
waste water effluent and sludge discharge), the Hg levels in the topsoil, water bodies and
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food items were projected in the present study solely based on regional atmospheric
14-16
. Vegetable diet was reported as a major exposure pathway (>80%) of
18
. However, it could not distinguish the
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deposition fluxes. According to the empirical models established by the USEPA
,
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atmospheric depositions influence the ground environment through vertical mass transport
65
and ground effects driven by precipitation. In this study, the impacts of these factors on
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human exposure were identified and discussed according to the background soil levels and
67
urbanization process using a preservative exposure scenario, which assumes that (a) the study
68
population (adults >18 years and children between 0-12 years) were native; (b) all of the local
69
residentially consumed food items (grains, vegetables, fruits, meats, eggs, milk/dairy
70
products, freshwater fish) and drinking water were grown, produced and supplied within the
71
study area; and (c) all of the residents' water recreation activities occurred in an outdoor
72
natural freshwater body (e.g., rivers and lakes). The human Hg exposure pathways related to
73
atmospheric deposition included accidental ingestion of and dermal contact with soil and
74
surface water during recreation, drinking water consumption, and dietary intake.
75
In summary, the present study aims to (1) project the accumulation of Hg in
76
environmental media through observations of depositional flux, (2) evaluate the aggregate
77
multimedia human exposure and provide a comprehensive human health risk assessment
78
related to deposition for the native residents in the PRD region, and (3) identify the impacts
79
of deposition on human exposure and the roles played by precipitation and vertical mass
80
transport.
81 82
MATERIALS AND METHODS
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Monitoring Atmospheric Hg Deposition Fluxes
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Mercury emissions in the PRD region are located primarily in the central area (e.g., 5
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Guangzhou, Foshan and Dongguan) rather than in the east or west (SI Figure S1). In the
86
present study, the Guangzhou urban site (representing an area with abundant Hg emissions)
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and the Dinghushan Natural Reserve site (representing an area with relatively low emissions)
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were selected as two representative monitoring sites.
89
A total of 415 deposition samples were collected at the Guangzhou urban site (115 wet
90
deposition and 63 dry deposition) and the Dinghushan Natural Reserve site (166 wet
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deposition and 71 dry deposition) continuously from Jan. 2010 to Dec. 2012 (SI Figure S1)
92
using automated wet-dry samplers (Tianhong Instrument Factory, China, ASP-2), a water
93
surface sampler. The sampler was equipped with a movable polyethylene cover that
94
alternately covered the dry or wet deposition sampling dish and was regulated by a rain
95
sensor
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deposition samples consisted of an aggregate collected over 15 days. The dish for dry
97
deposition sampling was filled with Milli-Q water to maintain a water depth of approximately
98
2.5 cm manually
99
with 10% HCl solution and Milli-Q water for 3 times respectively. The blank for the sampler
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was collected from the lastly rinsing Milli-Q water. The total Hg in both wet and dry
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deposition samples was preserved by the addition of aliquots of concentrated HNO3 and
102
AuCl3
103
spectrometry (AFS-820, Beijing Jitian Instruments Co., Ltd, China), with a detection limit of
104
0.002 µg/l. The QA/QC data are summarized in Supporting Information. All of the
105
experimental performance indices in this study fell into the range of quality control
106
acceptance criteria of EPA Method 163122. Information on precipitation time and amount of
20
. The wet deposition samples were collected after rain events, whereas the dry
21
20
. Prior to sampling each time, the water surface containers were rinsed
and determined using a double channel hydride generation atomic fluorescence
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rainfall
at
both
sites
during
sampling
were
provided
by
the
108
Dinghushan Forest Ecosystem Research Station, CAS and Sun Yat-sen University Resource
109
Platform of Atmosphere and Environmental Science. The annual recovery rates for the rain
110
collections ranged from 78.1% to 86.1%.
111
The deposition fluxes were calculated using Eqs. 1 and 2, where Dw and Dd represent the
112
wet and dry deposition fluxes (µg/m2) respectively, R is the annual rainfall (mm), T is the
113
annual period without rainfall (h), ri is the recorded rainfall specific to each wet deposition
114
sample (mm), tj is the sampling period for each dry deposition sample (h), Hj is the water
115
depth specific to each dry deposition sample (cm), Ci/Cj is the Hg concentration in the
116
wet/dry deposition samples (µg/l), n is the number of wet deposition samples, and m is the
117
number of dry deposition samples. =
∑ × 10 ∑
Equation 1
118
=
∑
× 10 ∑
Equation 2
119 120 121 122
Evaluation of Human Multimedia Exposure In this study, environmental media accumulation models established by the USEPA
19
123
were employed to project the Hg accumulation in the topsoil, surface freshwater bodies and
124
food items. These models are a set of box models that predict the steady-state mass of Hg
125
accumulated in the ground environment resulting from air emissions. The observational
126
results for the Hg deposition fluxes rather than the simulated results from a Hg emission 7
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model and dispersion and deposition model were employed to simplify the environmental
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media accumulation estimate. Detailed information on the associated equations is provided in
129
the Supporting Information (SI) (SI Eqs. S1-S7, SI Eqs. S13-S25, SI Tables S1 and S2, SI
130
Figure S2). In order to investigate the soil effects driven by precipitation, the “with soil
131
background” and “without” scenarios were respectively projected in the current study.
132
The human non-dietary ingestion and dermal adsorption of Hg via soil and surface water
133
during outdoor recreation were estimated according to the accumulation of Hg in
134
environmental media using SI Eqs. S8-S11 23, 24. Exposure via drinking water and food items
135
was estimated based on SI Eq. S12 23. The parameters in SI Eqs. S8-S12 are described in SI
136
Table S1. All of the processes related to plant, livestock/poultry and human exposure to Hg0
137
were not considered in the present study.
138
All of the parameters employed in the models and their references are summarized in SI
139
Table S2 and S3. To project the environmental impacts and human exposure as accurately as
140
possible, the probability density functions (PDFs) of the model parameters (related to the
141
meteorological/hydrological conditions, soil characteristics, land-use information, plant
142
growth information and exposure factors) were achieved by fitting the probability
143
distributions to the available regional data from the Web of China Met. Data Services
144
the Agriculture Statistical Yearbook of Guangdong
145
Resources 28, the China Soil Scientific Database 29, the Survey of National Land Use 30, the
146
Ministry of Agriculture of the PRC
147
Factors Handbook of Chinese Population
148
food consumption rates for 0- to 6-year children and certain hydrological and empirical data)
31
25, 26
,
27
, the Bulletin of Guangdong Water
, the China Statistical Yearbook
32
and the Exposure
33
. However, some regional deficient data (e.g.,
8
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The Monte-Carlo technique was applied to propagate and integrate the variability
151
throughout the environmental media accumulation models 19 and human exposure models 23,
152
24, 34
in the present study.
153 154
RESULTS AND DISCUSSION
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The projections of environmental accumulation and human exposure in the current study
156
considered the process of Hg methylation. As the MeHg % in total Hg contained in both
157
settled dust and rainfall are very low (1) caused by Hg2+ and MeHg respectively. .
477
23
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78. USEPA SCL Table http://www.epa.gov/risk/regional-screening-table; U.S. Environmental Protection Agency: 2015. 27
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Figure 1. Distribution (10000 trials, 5-95%, Line: Lognormal fit, column: forecast values of the TDI of Hg by adults (left panel) and children (right panel) in the 10-year projections.
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Figure 2. Contribution (%) of each type of intake to the variance of the (1) TDI by adults and children (0-12 year) (the upper two rows of charts) and (2) DDI by two different age groups of children (the bottom two rows of charts) in the 10-year projections (A: in “without soil background” scenario, B: in “with soil background” scenario)
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Figure 3. Probabilities of health risks (HQs>1) caused by Hg2+ and MeHg respectively.
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TOC/Abstract Graphic
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