Mercury Release to Aquatic Environments from Anthropogenic

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Mercury Release to Aquatic Environments from Anthropogenic Sources in China from 2001 to 2012 Maodian Liu, Wei Zhang, Xuejun Wang, Long Chen, Huanhuan Wang, Yao Luo, Haoran Zhang, Huizhong Shen, Yindong Tong, Langbo Ou, Han Xie, Xuejie Ye, and Chunyan Deng Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b01386 • Publication Date (Web): 05 Jul 2016 Downloaded from http://pubs.acs.org on July 9, 2016

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Environmental Science & Technology

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Mercury Release to Aquatic Environments from Anthropogenic Sources in China

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from 2001 to 2012

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Maodian Liu,† Wei Zhang,*,‡ Xuejun Wang,*,† Long Chen,† Huanhuan Wang,† Yao

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Luo,† Haoran Zhang,† Huizhong Shen,† Yindong Tong,§ Langbo Ou,† Han Xie,†

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Xuejie Ye† and Chunyan Deng†

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†

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Environmental Sciences, Peking University, Beijing 100871, China

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‡

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100872, China

Ministry of Education Laboratory of Earth Surface Processes, College of Urban and

School of Environment and Natural Resources, Renmin University of China, Beijing

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§

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300072, China

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Corresponding authors:

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Wei Zhang. School of Environment and Natural Resources, Renmin University of

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China, Beijing, 100872, China. Tel: +86-10-62514030. E-mail: [email protected]

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Xuejun Wang. Ministry of Education Laboratory of Earth Surface Processes, College

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of Urban and Environmental Sciences, Peking University, Beijing, 100871, China.

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Tel: +86-10-62759190. E-mail: [email protected]

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Word count for text:

4475

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Word count for 6 figures:

6×300=1800

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Total Word count:

6275

School of Environmental Science and Engineering, Tianjin University, Tianjin

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ACS Paragon Plus Environment


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ABSTRACT: Based on an analysis of measured data and distribution factors, we

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developed the China Aquatic Mercury Release (CAMR) model, which we used to

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calculate an inventory of mercury (Hg) that was released to aquatic environments

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from primary anthropogenic sources in China. We estimated a total release of 98 tons

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of Hg in 2012, including coal-fired power plants (17%), nonferrous metal smelting

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(33%), coal mining and washing (25%), domestic sewage (17%), and other sectors

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(8.3%). The total primary anthropogenic Hg released to aquatic environments in

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China decreased at an annual average rate of 1.7% between 2001 and 2012, even

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though GDP grew at an annual average rate of 10% during this period. In addition to

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the Hg that was released to aquatic environments in China’s provinces, we estimated

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the Hg release amounts and intensities (in g/km2·yr) for China’s 58 secondary river

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basins. The highest aquatic Hg release intensities in China were associated with

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industrial wastewater on the North China Plain and domestic sewage in eastern China

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and southern China. We found that the overall uncertainty of our inventory ranges

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from -22% to 32%. We suggest that the inventory provided by this study can help

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establish a more accurate map of regional and global Hg cycling; it also has

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implications for water quality management in China.

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38 39

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Abstract art

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INTRODUCTION

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Mercury (Hg) can be released from both anthropogenic and natural sources1

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Anthropogenic mercury can alter the natural global Hg cycle, and because mercury is

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transported through the atmosphere and oceans, it can cause worldwide

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contamination.2-4 Most previous studies that examined Hg inventories have focused

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on atmospheric anthropogenic emissions,5 which amount to 2000-3200 tons/yr

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globally.6, 7 Hg release to aquatic environments is also important because this Hg can

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be converted into a bioavailable and more toxic form (MeHg), which increases the

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accumulation and biomagnification of Hg in aquatic food webs.5, 8 However, little

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research has examined Hg release to aquatic environments, including both

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anthropogenic and natural sources.5 AMAP/UNEP first produced a preliminary

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inventory of Hg releases from anthropogenic sources to aquatic environments; this

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was estimated to be 1100 tons globally in 2013.5 Mason et al.3 found that the current

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annual global Hg discharge from rivers to oceans was 5 times higher than during

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preindustrial times, reaching 1000 to 5500 tons/yr.4,

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recognized riverine Hg discharge to oceans as an important pathway for global Hg

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cycling,9-11 but detailed information on Hg sources and discharge to aquatic

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environments is not yet available. Therefore, a detailed estimate of Hg released from

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primary anthropogenic sources to the aquatic environment is important for

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understanding global Hg cycling.

9, 10

Other researchers have

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Previous studies have indicated that China is the largest contributor of atmospheric

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mercury in the world.5, 12 Streets et al.13 developed the first complete anthropogenic 4


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Hg emission inventory for China, estimating its atmospheric Hg emissions from

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anthropogenic sources to be 536 tons in 1999. Similarly, Pacyna et al.12 found that

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atmospheric Hg emissions from primary anthropogenic sources in China were 605

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tons in 2000 and 825 tons in 2005. However, to our knowledge, no inventory of

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aquatic Hg release from primary anthropogenic sources in China exists. The

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AMAP/UNEP inventory indicated that Hg release to aquatic environments from

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primary anthropogenic sources in East and Southeast Asia reached 520 tons/yr (49%

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of the total global release) and that atmospheric Hg emissions from anthropogenic

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sources in this region were 780 tons/yr (40% of the total global emissions).5 Another

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study7 reported that the ratio of commercial liquid Hg (from the intentional use of Hg

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in products and processes) released to water and air was approximately 1:2 in 2010.

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Therefore, primary anthropogenic Hg released to aquatic environments could be an

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important pathway of Hg release in China.

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Non-ferrous metal production, vinyl chloride monomer production, artisanal and

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small-scale gold mining (ASGM), and oil refining were the major sectors considered

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in the AMAP/UNEP inventory.5 Unlike atmospheric Hg emissions, there are few

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records of Hg release to aquatic environments from anthropogenic sources. The

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AMAP/UNEP inventory ignored several important sectors that largely release Hg to

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aquatic environments rather than air.5,

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estimates did not consider the coal washing industry, but this industry releases

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significant amounts of Hg to water.15 This is especially true in China, which is the

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largest coal producer in the world, accounting for 45% of the world’s production in

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For example, their aquatic Hg emission

5



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2011.16 Domestic sewage discharge from treatment plants can also be an important

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source of primary anthropogenic Hg to aquatic environments;17-19 again, this sector

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was not considered in the AMAP/UNEP inventory.5

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The purpose of this study was to develop the first complete inventory of Hg release

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to aquatic environments from primary anthropogenic sources in China, including the

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temporal distribution from 2001 to 2012 and the spatial distribution. In this inventory,

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primary anthropogenic Hg release was divided into industrial wastewater and

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domestic sewage, and we included all major sectors that discharge Hg in wastewater.

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Hg release to water was further divided into particulate and dissolved phases. The

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uncertainty associated with different sectors was calculated. The inventory produced

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in this study will help establish a more accurate map of regional and global Hg

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cycling and improve water quality management in China in the future.

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METHODS

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Model Description. The model developed in this study to estimate the primary

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anthropogenic aquatic Hg released in China is called the China Aquatic Mercury

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Release (CAMR) model. Parameterization of the uncertainty function was

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accomplished with Monte Carlo simulations, following the method of Zhang et al.20

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Aquatic Hg released from various sectors was divided into two groups (Table S1,

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Supporting Information). The first group (Group 1) was chosen based on measured

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Hg concentration data and the volume of wastewater released from various sectors.5, 9

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The volume of wastewater discharge for each sector in Group 1 was end-of-pipe

6


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discharge data, which we collected from the China Environmental Statistics

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Yearbook.21 Details regarding the concentration data are shown in Table S2 of the

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Supporting Information. In contrast to the method of estimating emission factors for

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atmospheric Hg emissions, aquatic Hg release from various sectors is estimated based

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on the volume of wastewater discharge multiplied by the Hg concentration. The Hg

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concentration data used in this study are end-of-pipe data following the recycling and

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treatment of wastewater. For those sectors that lack measured Hg concentrations

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(Group 2), we used a second estimation method. For Group 2, Hg release was

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estimated using the method developed by AMAP/UNEP,5 in which UNEP Toolkit

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distribution factors (the ratio of Hg released to air, water or soil from a given source)

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were used to estimate the Hg release to aquatic environments based on the air

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emission methods developed in previous studies.7 The CAMR model was established

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based on the probabilistic distribution and includes these two groups as follows:

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where

is the probabilistic distribution of the aquatic Hg released;

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the probabilistic distribution of the Hg concentration in industrial wastewater and

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domestic sewage (Tables S2 and S3, Supporting Information);

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industrial wastewater or domestic sewage discharged (Table S4, Supporting

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Information);

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of Hg emissions from a given industrial sector (Table S2, Supporting Information),

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based on the inventory of Zhang et al.20;

is the unit conversion factor;

is

is the volume of

is the probabilistic distribution

and

are the distribution factors of

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Hg released to water and air, respectively, for a given industrial sector (Table S5,

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Supporting Information);

is the province;

is the release sector of Group 1; and

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is the release sector of Group 2. The ratio of dissolved to particulate aquatic Hg

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released from anthropogenic sources was determined based on observational data

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from previous studies; it was set to be 1:4.22-25

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This inventory includes 20 aquatic Hg release sectors, which are categorized as

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industrial wastewater discharge or domestic sewage discharge. The industrial

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wastewater sectors include the energy industry, nonferrous metal smelting, iron and

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steel production, intentional use, and other low-release industries (Table S1,

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Supporting Information). We estimated the aquatic Hg released from the coal washing

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industry (part of the energy industry) based on the method used for Group 1. Given

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the lack of previous research and distribution factors for the aquatic Hg released from

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coal washing,5 the Hg concentration of wastewater from coal washing was estimated

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based on the Hg removal efficiency of coal washing and the coal washing rate, as

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follows:13, 26 (2)

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where

is the probabilistic distribution of the Hg concentration in coal washing

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wastewater;

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determined in previous study;20

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the China Energy Statistical Yearbook;27

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washing;

is the probabilistic distribution of the Hg content of raw coal, is the activity level of raw coal production from is the Hg removal efficiency of coal

is the coal washing rate in China;

is the unit conversion factor;

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is the water consumption volume of coal washing from the China Environmental

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Statistics Report;28 and

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ranged from 10% to 80%,29-33 and most estimates were between 25% and 60%. Based

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on previous research,13 30% was selected as the average and 25% to 60% as the range

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of Hg removal efficiency in this study. The coal washing rate in China was 16.6% in

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2002 and 50.9% in 2010.26, 34 Because the wastewater from coal washing is always

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directly discharged,35 treatment rates were not considered. The reuse rate of

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wastewater from the coal washing industry was considered based on the volumes of

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water consumption and wastewater discharge for the industry.

is the province. The Hg removal efficiency of coal washing

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We developed a new method of estimating the aquatic Hg release from domestic

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sewage discharge. This sector has rarely been considered in previous inventories.5

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Based on the development level of different regions, domestic sewage discharge was

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divided into treated versus non-treated discharge. The treatment rates of domestic

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sewage in different regions from 2001 to 2012 are shown in the Supporting

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Information (Tables S6 and S7) and come from the China Environmental Statistics

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Yearbook.21 For domestic sewage, the Hg removal efficiencies of sewage treatment

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plants were estimated based on the measured Hg data for different regions (Table S3,

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Supporting Information). Therefore, the Hg concentration of domestic sewage

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discharge is calculated as follows: (3)

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where

is the probabilistic distribution of the Hg concentration in domestic

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sewage;

is the probabilistic distribution of the Hg concentration in domestic

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sewage discharged after treatment (Table S3, Supporting Information);

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probabilistic distribution of the Hg concentration in domestic sewage discharged

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before treatment (Table S3, Supporting Information);

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domestic sewage; and

is the

is the treatment rate of

is the province.

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Basic River Basin Unit. To understand the contributions of Hg sources at the river

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basin level and to assist in river basin water quality management, the aquatic Hg

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release from anthropogenic sources in China was recalculated at the scale of

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individual river basins.36, 37 Mainland China was divided into 58 basins (Figure S1,

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Supporting Information) based on the Industry Standard of China; this number

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includes all of the secondary rivers in China.38 The geographic information layers for

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China’s administrative regions and river basin system were obtained from the

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National Geomatics Center of China (http://sms.webmap.cn/). The map of China’s

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river basins was created using ArcGIS 10.3 software.

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Mass Flow of Aquatic Hg. The mass flow of aquatic Hg to the ocean from primary

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anthropogenic sources in China was calculated. To accomplish this, we simplified the

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processes of Hg re-release from Hg-contaminated places, including erosion of

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Hg-contaminated land surfaces, river bank erosion, and resuspension of legacy

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anthropogenic Hg sources.5 This was necessary because, compared to atmospheric Hg

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emissions, the Hg released to aquatic environments has multiple sources and transport

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routes, making it more complex and difficult to quantify.5 Water resource data were

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obtained from the China Water Resources Bulletin39 and the China Environmental 10


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Statistics Yearbook.21 The China Water Resources Bulletin shows that, in 2012, 65%

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of China’s surface water resources flowed into seas adjacent to China through rivers,

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19% flowed to neighboring countries through rivers, 13% was stored in lakes and

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reservoirs, and 3.8% flowed into boundary rivers.

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To determine the contribution from aquatic Hg released from primary anthropogenic

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sources in China, we estimated the Hg discharged from rivers into seas adjacent to

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China in 2012. The total riverine Hg discharge into the seas was obtained from our

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previous study,40 and the estimation method is similar to that of Sunderland and

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Mason,4 who estimated the Hg discharge into oceans from rivers in the particulate

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phase (Hg(P)) and the dissolved phase (Hg(D)).

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of the Hg(P) discharged from a river is deposited on the river mouth and continental

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shelf, and only 28% reaches the open ocean.4,

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contribution of anthropogenic sources, we also calculated the natural sources of

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riverine Hg discharge. We estimated the Hg contributions from natural sources in

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rivers based on published discharge-Hg concentration relationships for Arctic rivers as

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previous studies,9, 44 due to the lack of observational data on the background of Hg

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concentrations in rivers. Rivers in the Arctic region are rarely affected by human

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activity, therefore, they should reflect natural sources. The contributions of legacy

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anthropogenic sources were obtained by subtracting the anthropogenic sources and

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natural sources from total riverine Hg discharge into Chinese adjacent seas.

According to previous studies, 72%

42, 43

To estimate the relative

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Uncertainty Analysis. A Monte Carlo simulation (10,000 runs) was used to

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characterize the uncertainty of the inventory. The uncertainty originated from the 11



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probabilistic distributions of Hg concentrations in Group 1, Hg emissions in Group 2,

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discharge volumes, and other parameters. The probabilistic distributions of Hg

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concentrations in Group 1 were assumed to follow a log-normal distribution based on

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measured data of previous studies.20,

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emissions found in previous studies were used; these had skewed distributions (e.g.,

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log-normal and Weibull distributions).20 For the discharge volumes and activity levels,

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uniform distributions with a fixed coefficient of deviation (5%) were assumed5, 48

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because the data were derived from official statistics.28,

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presented by the UNEP were used to estimate the Hg release from wastewater in

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Group 2,5 because Hg releases to aquatic environments from anthropogenic point

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sources are very poorly documented. We note that using these distribution factors

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might also involve the uncertainties associated with atmospheric emission estimates

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and increase the estimation uncertainties in the inventories of AMAP/UNEP and this

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study.5 Mean values and P20-80 confidence intervals of the statistical distribution of

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aquatic Hg release were calculated to quantify the aquatic Hg release and characterize

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the uncertainty.29

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RESULTS AND DISCUSSION

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In Group 2, the uncertainties of Hg

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Distribution factors

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Aquatic Hg Release from Primary Anthropogenic Sources and Trends. Figure

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1 summarizes the total aquatic Hg released by sectors associated with industrial

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wastewater and domestic sewage in China. The total aquatic Hg released from

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anthropogenic sources in China was 98 tons in 2012, with 78 tons of Hg(P) and 20

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tons of Hg(D). From 2001 to 2012, the maximum Hg release was 123 tons in 2001 12


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and the minimum was 87 tons in 2010. The total aquatic Hg release decreased

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discontinuously during this period but increased from 2002 to 2003 and from 2010 to

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2011. We note that the primary anthropogenic Hg emissions to the atmosphere

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increased over this time period;20 this is not inconsistent with the decrease in aquatic

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Hg releases that was observed in this study because the Chinese government has

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regulated wastewater discharge more stringently in recent years.21 Although air

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pollution control measures have reduced atmospheric Hg emissions in China, primary

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anthropogenic Hg emissions to the atmosphere still grew by an average of 4.2% per

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year from 2000 to 2010.20

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Because Hg releases to aquatic environments from primary anthropogenic sources

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are poorly documented,5 the total national aquatic Hg release was compared with the

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aquatic Hg release inventory developed by AMAP/UNEP and atmospheric Hg

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emissions estimated by previous studies.5, 12, 13, 20 In this study, we found that the ratio

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of anthropogenic Hg released to water and air in China is approximately 1:5,12, 13, 20

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which is lower than the global ratio of 1:2 estimated by previous studies.5,

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suggest that this result is inconsistent because (1) the specific industrial structure in

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China gives rise to greater atmospheric Hg emissions, including significant

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contributions from coal-fired power generation and nonferrous metal smelting;13, 20

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and (2) the aquatic Hg release intensities of various sectors in China estimated in this

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study differ from the estimates made by AMAP/UNEP. AMAP/UNEP estimated that

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the aquatic Hg released from artisanal and small-scale gold mining (ASGM)

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accounted for 83% of the total global aquatic Hg release and 87% of the release in 13


7

We


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East and Southeast Asia. However, following the implementation of strict regulations

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in China, ASGM has decreased sharply in recent years to only 1−3% of the total gold

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output in 2010.20, 50 As a primary pathway in the AMAP/UNEP inventory, aquatic Hg

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released from ASGM in China was only 2.7 tons in 2012 (2.8% of the total Hg

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released), which represents a decrease from 10 tons in 2001 (8.1%) at an average rate

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of 11% per year.

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Figure 1. Release of mercury to the aquatic environment from various sectors in China from 2001 to 2012. 15



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From 2001 to 2011, there was a variable amount of aquatic Hg released from other

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important sources, such as coal-fired power plants, nonferrous metal smelting, mining

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and washing of coal, and domestic sewage (Figure 2 (A)). As the leading source of

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anthropogenic Hg emissions in China (releasing 68 to 110 tons/yr),13, 20, 29 the release

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from coal-fired power plants decreased discontinuously. Due to the gradual decrease

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in wastewater discharged from coal-fired power plants,28 aquatic Hg release from this

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sector accounted for 31% of the overall release in 2001 and 17% in 2012, with an

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annual average decrease of 5.9%. Because these data were unavailable or incomplete,

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AMAP/UNEP did not consider the aquatic Hg release from coal-fired power plants.5

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However, there is now abundant measured data for aquatic Hg release from this sector

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in China.45 Aquatic Hg release from domestic sewage represents another sector that

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might have been ignored in the past; this also showed a gradual decrease (Figure 2

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(B)), accounting for 22% of the overall release in 2001 and 17% in 2012, with an

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annual average decrease of 3.0%. Because of the increase in the number of sewage

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treatment plants and the improved treatment rates in China (19% in 2001 and 83% in

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2012),28 the aquatic Hg release from treated domestic sewage increased gradually.

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The aquatic Hg released from nonferrous metal smelting (including Hg, Al, Zn, Pb,

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Cu, large-scale gold mining, and ASGM) also decreased gradually after 2003 at an

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average rate of 0.6%. In 2012, the aquatic Hg released from nonferrous metal

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smelting accounted for 33% of the total Hg release. Previous studies estimated that

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Hg emissions to the atmosphere were 90 to 240 tons/yr from nonferrous metal

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smelting in China,13, 20 and in this study, the release to aquatic environments was 16


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estimated to be 33.4 tons in 2012. Zn smelting was the largest nonferrous smelting

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source of aquatic Hg release; this was estimated to be 12.3 tons in 2012 (accounting

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for 13% of the total aquatic Hg release from anthropogenic sources in China), and it

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decreased at an average rate of 2.5% over the study period. The Hg releases from Pb

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smelting and Cu smelting were 6.9 tons (7.0%) and 0.7 tons (0.6%) in 2012, with

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average growth rates of 5.5% and -0.65%, respectively.

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Aquatic Hg release from coal mining and washing increased rapidly and accounted

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for 1.9% of the total release in 2001 and 25% in 2012, with an annual average growth

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rate of 25%. Aquatic Hg release from coal mining and washing is now the second

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largest anthropogenic source in China. This can be attributed to the increase in coal

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production18 and the wastewater discharged from this sector to the environment.29, 36

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If there is lack of strict governmental supervision and wastewater treatment and reuse

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rates are not improved, aquatic Hg release from coal mining and washing could soon

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become the largest anthropogenic source of aquatic Hg in China.

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Figure 2. Variations in aquatic mercury release from the four major sectors in China from 2001 to 2012 from (A) coal-fired power plants, domestic sewage,

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nonferrous metal smelting, and coal mining and washing; (B) aquatic Hg release from treated versus untreated discharge from domestic sewage.

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In addition to the four major aquatic Hg release sectors mentioned above, the

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manufacture of wearable textiles and apparel and the intentional use of Hg (including

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vinyl chloride monomer production, reagent production, thermometer production,

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fluorescent lamp production, and battery production) contributed 4.2% (4.1 tons) and

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3.3% (3.2 tons), respectively, to the overall release in 2012. Aquatic Hg released from

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the intentional use of Hg decreased at an annual average rate of 14% due to the

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decreased use of Hg in China.20 However, aquatic Hg release from the manufacture of

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wearable textiles and apparel increased at an annual average rate of 20% due to the

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growth in wastewater discharge from this sector. Other small sources of aquatic Hg

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release, including oil refining, iron and steel production, the printing industry, and

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waste resource utilization, together accounted for 1.0 tons (1.0%) of Hg in 2012, and

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had an annual average growth rate of 6.1% from 2001 to 2012.

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Spatial Distribution of Aquatic Hg Release from Primary Anthropogenic

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Sources in China. Figure 3 shows the distribution of aquatic Hg released from

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various primary anthropogenic sources by province in China in 2012. The five

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provinces with the highest aquatic Hg releases were Henan (8.8 tons in 2012 and

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8.6% of the national total), Shandong (8.2 tons, 8.0%), Hunan (7.3 tons, 7.2%),

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Shanxi (6.5 tons, 6.4%), and Hebei (5.5 tons, 5.4%). These values are similar to

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previously reported provincial distributions of atmospheric Hg emissions.20 The high

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aquatic Hg release from Henan could be attributed to abundant Pb smelting

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(accounting for 29% of the total aquatic Hg released in the province) and coal mining

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and washing (14%). Shandong’s numbers are likely due to coal mining and washing 19



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(accounting for 28%) and large-scale gold mining (21%). Zn smelting was the

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primary Hg release source in Hunan (40%). In Shanxi and Hebei, coal mining and

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washing contributed 73% and 67%, respectively.

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We found that the major sources of aquatic Hg release varied by province (Figure

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3). In Guangdong, domestic sewage (45%) was the major source of aquatic Hg

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because Guangdong has the largest population and is one of the most developed

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provinces in China (Figure S3). Hg mining (29%) was the major source in Guizhou.

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The lowest aquatic Hg release occurred in Tibet (0.07% of the national total release),

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where domestic sewage (79%) was the major source of Hg.

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Figure 3. Provincial distribution of mercury release to the aquatic environment in China in 2012.

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Figure 4 (A) and (C) show the distributions of aquatic Hg released from industrial

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wastewater and domestic sewage into 58 Chinese secondary river basins in 2012.

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There are significant differences in the aquatic Hg release from industrial wastewater

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and domestic sewage among the basins. The Yellow River basin (ID: 18) in northern

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China showed the largest Hg release from industrial wastewater, with a total of 9.0

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tons, and Dongting Lake basin (ID: 31) in central China showed the largest release

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from domestic sewage, with a total of 1.1 tons. In contrast, the Senggecangbu River

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basin (ID: 50), located on the western Tibetan Plateau, released the smallest amount

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of Hg from both industrial wastewater and domestic sewage, with 0.9 × 10-3 ton/yr

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and 3.1 × 10-3 ton/yr, respectively.

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Figure 4 (B) and (D) show the aquatic Hg release density (g/km2·yr) of industrial

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wastewater and domestic sewage in 58 Chinese secondary basins in 2012. On the

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whole, among all Chinese basins, the highest aquatic Hg release density of industrial

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wastewater occurred on the North China Plain (IDs: 12, 13, 14, 15, 16, 19, 21, 22, 23,

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24, and 34; Figure 4 (B)). Because aquatic Hg release from coal-fired power plants is

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associated with economic level and population density, the release density in eastern

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China (IDs: 16, 21, 23, 34, 35, and 36) was higher than in other regions (Figure S4

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(F)). Aquatic Hg release from coal mining and washing and nonferrous metal smelting

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is associated with the distribution of coal and non-ferrous metal resources. Therefore,

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the highest release density from coal mining and washing occurred on the North

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China Plain (IDs: 11, 12, 13, 14, 15, 16, 19, 21, and 23; Figure S4 (D)) and the

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highest release densities from nonferrous metal smelting occurred in central China 22


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360

and the North China Plain (IDs: 16, 21, 22, 23, 30, and 31; Figure S4 (H)).

361

In general, aquatic Hg release from domestic sewage is affected by economic level

362

and population density. Thus, the aquatic Hg release densities of domestic sewage

363

were highest in eastern China (IDs: 23, 24, 34, 35, and 36) and southern China (IDs:

364

39, 41, 42, 43, and 45), the two most populous regions in China (Figure 4 (D)).

365

Mainland China can be separated into two parts (east and west) by the famous “Hu

366

Huanyong line” (Figure 4 (D)); this division highlights the impact of population

367

density on the distribution of aquatic Hg release. Aquatic Hg release from domestic

368

sewage in the eastern part of China is an order of magnitude higher than in the

369

western part. Similar results have been reported for other pollutants, such as

370

antibiotics, steroids, black carbon, and personal care products.36, 37, 51, 52

23



371 372

Figure 4. Distribution of mercury release to aquatic environments from industrial wastewater

373

(A and B) and domestic sewage (C and D) in Chinese secondary river basins in 2012. (A) and

374

(C) show the total release in units of ton/yr; (B) and (D) show the release densities in units of

375

g/m2·yr. The black line in (D) is the “Hu Huanyong line” through China. Basin Ids are shown

376

in Table S1 in the Supporting Information.

377

Mass Flow of Aquatic Mercury to Rivers and the Ocean from Anthropogenic

378

Sources and Environmental Implications. Figure 5 shows the mass flow of aquatic

379

Hg from primary anthropogenic sources in China in 2012. In our previous study, we

380

estimated that the amount of Hg discharged from rivers into seas adjacent to China

381

was 157 tons in 2012.40 Of this total, 16% (27 tons) came from industrial wastewater 24


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382

and domestic sewage, which are direct anthropogenic sources. An additional 23% (36

383

tons) came from natural sources (such as leaching, runoff and erosion processes from

384

land), a total which is consistent with the results of previous studies that estimated a

385

natural Hg release of 20% to 46% globally.3-5, 53 Finally, 61% (94 tons) came from

386

legacy anthropogenic sources, including (1) erosion of Hg-contaminated land surfaces;

387

(2) resuspension of Hg-contaminated river bed sediments; and (3) land and water

388

management practices.5 Therefore, anthropogenic sources contributed up to 77% of

389

the riverine Hg discharge, which is similar to previously published values.3 Hg(D)

390

discharge from Chinese rivers into ocean margins accounted for 45% of the total Hg

391

discharge;40 this would result in more Hg transported to the open ocean.4 Because of

392

the limited information that is currently available, more studies involving extensive

393

sampling and monitoring are needed.

394

With its large population and rapid industrialization, China releases abundant Hg

395

from anthropogenic sources into the aquatic environment. Although aquatic Hg

396

releases from primary anthropogenic sources in China decreased from 2001 to 2012,

397

there was still a release of 98 tons in 2012. Aquatic Hg releases from anthropogenic

398

sources threatens not only local environments but also global marine ecosystems.

399

Therefore, it is essential to reduce the discharge of industrial wastewater in the future

400

by increasing the recycling rate and enhancing the use of environmentally-friendly

401

technologies in production and wastewater treatment processes.

25



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402

403

404 405

Figure 5. Mass flow of aquatic mercury release from anthropogenic sources to seas adjacent to China in 2012. (A) Mass flow of aquatic primary

406

anthropogenic Hg; (B) Contributions of anthropogenic and natural sources to the riverine Hg discharge into the seas. Note: Hg deposition in the river channels

407

was estimated based on the distribution of Hg in the dissolved versus particulate phases near the river mouth areas in our previous study.40 In that study, we

26


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408

found a 45%:55% ratio of Hg in the dissolved versus particulate phases in riverine Hg discharge into the seas, while previous studies have found a ratio of 1:4

409

in wastewater (see the Method section). We assumed that all the Hg(D) released from anthropogenic sources reached the adjacent seas, which were 12 tons

410

calculated using the ratio of 1:4. The ratio of Hg(P) released from anthropogenic sources and reached the adjacent seas was calculated by (1/4) × (55%/45%),

411

which was 31% (15 tons). Therefore, we assumed that 69% (33 tons) of Hg(P) released from anthropogenic sources deposited in river channels before

412

reaching the river mouths. 4.7 tons Hg (4.8% of wastewater) were discharged into the seas directly and 93 tons were released into aquatic environment of

413

mainland China, according to the China Marine Statistical Yearbook.54 The contribution of Hg remobilization in rivers is involved in estimates of the

414

contributions of legacy anthropogenic Hg release and natural Hg release.

27



415

Uncertainties Associated with the Inventory. We estimated the uncertainties

416

associated with the aquatic Hg released from anthropogenic activities in China and in

417

each sector based on the probabilistic distribution of Hg concentrations and emission

418

factors (Figure 6). The overall uncertainty ranged from -22% to 32% (P20-80). The

419

smallest uncertainties were associated with coal-fired power plants (-35%, 52%) and

420

domestic sewage (-42%, 77%), while the largest uncertainty was associated with

421

ASGM (-80%, 400%). This can be attributed to the large uncertainty in production

422

data from this sector in China. In addition, when the statistical distribution of a

423

parameter in this sector was unknown, we assumed a uniform distribution. The

424

uncertainties associated with coal mining and washing (-58%, 260%) were second

425

only to ASGM; these uncertainties largely mainly from the probabilistic distribution

426

of Hg concentrations in the raw materials from each province.20

427 428

Figure 6. Uncertainties (%) associated with the inventory by sector. 28


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429

ASSOCIATED CONTENT

430

Supporting Information

431

The Supplemental Information includes the Hg concentrations of wastewater in Group

432

1, distribution factor in Group 2, activity levels of each sector, treatment rates of

433

domestic sewage in China, Hg concentrations collected at river mouths, and detailed

434

descriptions of some of the data used to estimate Hg release from anthropogenic

435

sources in China. The trend of detailed anthropogenic Hg release to the aquatic

436

environment in China from 2001 to 2012, provincial distribution of aquatic Hg release

437

from domestic sewage in China, Hg discharge from major Chinese rivers into seas

438

adjacent to China are also provided in the supporting information.

439

ACKONWLEDGEMENTS

440

This work was funded by National Natural Science Foundation of China (41571484,

441

41130535 and 41471403). The authors would like to thank the editor and reviewers

442

for their insight comments and suggestions on the manuscript.

443

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