Impacts of Atmospheric Mercury Deposition on Human Multimedia

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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]

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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

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a significantly greater effect relative to the mass transport effects in this region.

16 17

Keywords: atmospheric deposition, mercury, flux monitoring, multimedia, human exposure,

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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,

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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

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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.

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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

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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

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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

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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

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and human health risks related to the significant regional anthropogenic Hg emissions.

44

Previous studies that evaluated multimedia exposure to emitted pollutants have

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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)

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also attempted to achieve a comprehensive risk assessment of Hg for French infants and

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toddlers by evaluation of multimedia exposure

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sources (e.g., deposition, waste water eluent and sludge discharge) for Hg accumulation in

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the environmental media. The current study performs a preliminary evaluation of the human

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multimedia exposure to Hg caused by atmospheric deposition in the PRD region using

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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

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simulated results from emission models, dispersion and deposition models. To differentiate

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among the impacts of atmospheric deposition and other surface contamination sources (e.g.,

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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

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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

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urbanization process using a preservative exposure scenario, which assumes that (a) the study

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population (adults >18 years and children between 0-12 years) were native; (b) all of the local

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residentially consumed food items (grains, vegetables, fruits, meats, eggs, milk/dairy

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products, freshwater fish) and drinking water were grown, produced and supplied within the

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study area; and (c) all of the residents' water recreation activities occurred in an outdoor

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natural freshwater body (e.g., rivers and lakes). The human Hg exposure pathways related to

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atmospheric deposition included accidental ingestion of and dermal contact with soil and

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surface water during recreation, drinking water consumption, and dietary intake.

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In summary, the present study aims to (1) project the accumulation of Hg in

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environmental media through observations of depositional flux, (2) evaluate the aggregate

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multimedia human exposure and provide a comprehensive human health risk assessment

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related to deposition for the native residents in the PRD region, and (3) identify the impacts

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of deposition on human exposure and the roles played by precipitation and vertical mass

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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

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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.

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A total of 415 deposition samples were collected at the Guangzhou urban site (115 wet

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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)

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using automated wet-dry samplers (Tianhong Instrument Factory, China, ASP-2), a water

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surface sampler. The sampler was equipped with a movable polyethylene cover that

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alternately covered the dry or wet deposition sampling dish and was regulated by a rain

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sensor

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deposition samples consisted of an aggregate collected over 15 days. The dish for dry

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deposition sampling was filled with Milli-Q water to maintain a water depth of approximately

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2.5 cm manually

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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

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AuCl3

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spectrometry (AFS-820, Beijing Jitian Instruments Co., Ltd, China), with a detection limit of

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0.002 µg/l. The QA/QC data are summarized in Supporting Information. All of the

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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

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Dinghushan Forest Ecosystem Research Station, CAS and Sun Yat-sen University Resource

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Platform of Atmosphere and Environmental Science. The annual recovery rates for the rain

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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

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wet and dry deposition fluxes (µg/m2) respectively, R is the annual rainfall (mm), T is the

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annual period without rainfall (h), ri is the recorded rainfall specific to each wet deposition

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sample (mm), tj is the sampling period for each dry deposition sample (h), Hj is the water

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depth specific to each dry deposition sample (cm), Ci/Cj is the Hg concentration in the

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wet/dry deposition samples (µg/l), n is the number of wet deposition samples, and m is the

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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

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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

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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

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background” and “without” scenarios were respectively projected in the current study.

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The human non-dietary ingestion and dermal adsorption of Hg via soil and surface water

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during outdoor recreation were estimated according to the accumulation of Hg in

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environmental media using SI Eqs. S8-S11 23, 24. Exposure via drinking water and food items

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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.,

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were not included.

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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

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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

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478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521

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Regional and Global Scales. Springer: U.S., 2005. 62. Zhang, H.; Feng, X.; Larssen, T.; Qiu, G.; Vogt, R. D., In Inland China, Rice, Rather than Fish, Is the Major Pathway for Methylmercury Exposure. Environmental Health Perspectives 2010, 118, (9), 1183. 63. USEPA Integrated Risk Information System — Methylmercury (MeHg) (CASRN22967-92-6); National Center for Environmental Assessment, U.S. Environment Protection Agency: 2015. 64. USEPA Integrated Risk Information System — Mercuric chloride (HgCl2); CASRN 7487-94-7; National Center for Environmental Assessment, U.S. Environmental Protection Agency: 2015. 65. Shao, D.; Liang, P.; Kang, Y.; Wang, H.; Cheng, Z.; Wu, S.; Shi, J.; Lo, S. C. L.; Wang, W.; Wong, M. H., Mercury species of sediment and fish in freshwater fish ponds around the Pearl River Delta, PR China: Human health risk assessment. Chemosphere 2011, 83, (4), 443-448. 66. Asselt, M. B. A. V.; Rotmans, J., Uncertainty in Integrated Assessment Modelling. Climatic Change 2002, 54, (1-2), 75-105. 67. Walker, W. E.; Harremoës, P.; Rotmans, J.; Sluijs, J. P. v. d.; Asselt, M. B. A. v.; Janssen, P.; Krauss, M. P. K. v., Defining Uncertainty: A Conceptual Basis for Uncertainty Management in Model-Based Decision Support. Integrated Assessment 2003, volume 4, (1), 5-17. 68. Kumar, V.; Mari, M.; Schuhmacher, M.; Domingo, J. L., Partitioning total variance in risk assessment: Application to a municipal solid waste incinerator. Environmental Modelling & Software 2009, 24, (2), 247-261. 69. NTU Compilation of Exposure Factors; Colleague of Public Health, National Taiwan University: 2008. 70. USEPA, Exposure Factors Handbook. Office of Reeach and Development. National Center for Environmental Assessment. U.S. Environmental Protection Agency. Washingtong, DC 20460. 1997. 71. USEPA Exposure Factors Handbook: 2011 Eddition; National Center for Environmental Assessment, Office of Research and Development, U.S. Environmental Protection Agency: Washington, D.C., 2011. 72. Amos, H. M.; Jacob, D. J.; Streets, D. G.; Sunderland, E. M., Legacy impacts of all-time anthropogenic emissions on the global mercury cycle. Global Biogeochemical Cycles 2013, 27, (2), 410-421. 73. Chen, L.; Frauenfeld, O., Impacts of urbanization on future climate in China. Clim Dyn 2015, 1-13. 74. Wang, X.; Liao, J.; Zhang, J.; Shen, C.; Chen, W.; Xia, B.; Wang, T., A Numeric Study of Regional Climate Change Induced by Urban Expansion in the Pearl River Delta, China. Journal of Applied Meteorology & Climatology 2014, 53, (2), 346-362. 75. Chang, M.; Fan, S.; Fan, Q.; Chen, W.; Zhang, Y.; Wang, Y.; Wang, X., Impact of refined land surface properties on the simulation of a heavy convective rainfall process in the Pearl River Delta region, China. Asia-Pacific J Atmos Sci 2014, 50, (1), 645-655. 76. Schets, F. M.; Schijven, J. F.; de Roda Husman, A. M., Exposure assessment for swimmers in bathing waters and swimming pools. Water research 2011, 45, (7), 2392-2400. 77. EA Soil Guideline Values for mercury in soil; Environment Agency United Kingdom, 2009.

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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