Anthropogenic Mercury Flows in India and Impacts of Emission

Landfills may be secured and controlled, noncontrolled, ash ponds, or open dumps. In this work, burial grounds are also considered as landfills. Landf...
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Anthropogenic Mercury Flows in India and Impacts of Emission Controls Laura Burger Chakraborty,† Asif Qureshi,*,‡,§ Carl Vadenbo,† and Stefanie Hellweg† †

Institute of Environmental Engineering, ETH Zurich, Zurich CH-8093, Switzerland Department of Environmental Health, Harvard University, Boston, Massachusetts, 02215, United States

‡

S Supporting Information *

ABSTRACT: India is a major emitter of mercury, a pollutant of global importance. However, quantitative information on mercury flows in the country is lacking. Here, we quantify major transfer pathways for anthropogenic mercury, its emissions to the environment (air, water, soil), and storage in consumer products and anthropogenic sinks (e.g., landfills) in India in the period 2001− 2020, and evaluate the potential influence of six pollution control measures. Total mercury emissions in India were approximately 415 tonnes in 2001, 310 tonnes in 2010, and are projected to rise to 540 tonnes in 2020. In 2010, 76% of these emissions went to the atmosphere. The most important emission sources to atmosphere are coal power plants and zinc production. Pesticides were the most important source for emissions to soil in 2005 and dental amalgam in later years. Mercury stocks in products rose from 700 tonnes in 2001 to 1125 tonnes in 2010, and in landfills and ash-made structures (e.g., embankments) from 920 tonnes in 2001 to 1450 tonnes in 2010. These stocks are expected to rise further and may be regarded as stored toxicity, which may become a concern in the future. Total mercury emissions can be reduced by about 50% by combining pollution control measures that target different mercury emission sources. al.13 only estimated atmospheric mercury emissions from industrial processes and wastes for the years 2000 and 2004. While Pacyna et al.5 estimated atmospheric emissions in India in 2005 from processes and products, the emissions from products were calculated by aggregating all South Asian countries into one group and allocating the consumption of mercury-laden products, and the release of mercury, by correlating it to the purchasing power parity of the region. Emissions from individual products in India have not yet been quantified. Additionally, neither emissions to water nor soil in India have been quantified even though they may be relevant, as demonstrated in the case of the European Union.4 Further knowledge gaps exist on the build-up of mercury stocks in the Indian society. The fate and possible impacts, either at present or in the future, of mercury captured in landfills and fly ash are also unclear. In this work, we use a dynamic material flow analysis approach4,12,14 to estimate emissions of mercury from industrial and nonindustrial processes and consumer products to air, water, and soil, and its build-up in the Indian society in product stocks and anthropogenic sinks, in the period 2001−2020. We identify the main sources and critical flows of mercury, and evaluate pollution reduction measures that may reduce mercury

1. INTRODUCTION Mercury is a toxic pollutant of global significance. Emitted from natural and anthropogenic sources, it can travel large distances, bioaccumulate in food chains and cause harmful neurological and cardiovascular health effects.1,2 Human activities have caused a substantial increase in mercury mobilization compared to preindustrial times.3 Examples of such activities are combustion of fossil fuels and processing of mineral ores, in which mercury is present as an impurity, and mercury use in consumer products that may cause emissions, particularly at the product end-of-life stage.4 India is a major emitter of mercury to the atmosphere.5,6 The country’s rapidly growing economy has led to increased energy demand that is primarily met through coal combustion.7 Additionally, increase in income8 and consumer spending on health care, personal, household, and electronic goods9 may also increase the demand and consumption of mercurycontaining products. As such, a sustained economic growth of India may have important consequences in terms of mercury emissions to the environment and its possible health impacts within India and abroad.1,10 In the light of the newly agreed global Minamata convention on mercury,11 knowledge on mercury sources is crucial for planning mercury pollution control strategies. While mercury flows have been investigated in Europe4 and the United States12, although attempts have been made to estimate mercury emissions in India5,13 key information on mercury flows and emissions is still missing. For example, Mukherjee et © 2013 American Chemical Society

Received: Revised: Accepted: Published: 8105

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Table 1. Mercury Content in Ores and Productsa

emissions in India. We also identify priority research areas for improving the quantification of mercury flows in India.

2. MATERIALS AND METHODS 2.1. Material Flow Analysis. Material flow analysis (MFA) is based on the principle of the conservation of matter and enables the identification and quantification of sources of a substance into a study system, its temporal build-up within the system and its transfer to natural or anthropogenic sinks.14 The substance-bearing goods or materials undergo intermediate transformation, transport, or storage processes. The transfer of such process inputs to outputs is described using transfer coefficients. The MFA approach is useful for identifying the most important sources and sinks, for planning emission reductions and long-term storage or disposal.4,14 Dynamic MFA includes a time component and addresses the accumulation and depletion of stocks over time. 2.2. System Definition. The geographical system boundary for our work is the political border of India. Flows are quantified in tonnes per year in the time period 2001−2020. Only anthropogenically mobilized mercury was considered. Natural emissions or re-emissions of anthropogenic mercury were not considered. The most relevant mercury sources for the Indian context were identified based on an initial literature review. Three broadly defined source categories are considered, (i) industrial and nonindustrial processes in which mercury is used intentionally, (ii) processes utilizing fuels or ores that contain mercury as an impurity, and (iii) products that are in circulation in the society, which encompass personal, household, and health care goods (consumer goods) including amalgam tooth filling. 2.3. Mercury Mobilization from Sources. India is not a primary producer of mercury13 and its domestic demand is met through import. However, the allocation of imported mercury to individual industry sectors is unclear. Mercury quantities mobilized by different sources were thus quantified based on activity, manufacture and product import rates. Total imports of raw mercury were then back-calculated. Mined quantities of mercury-containing material were also back-calculated, assuming a negligible delay between mining and consumption after extraction.4 Possible losses during mining, transportation and product manufacture were not included. Mercury is intentionally utilized in chlor-alkali and vinyl chloride monomer (VCM) production, artisanal, and smallscale gold mining (ASGM), gold recovery from electronic waste and pesticides. The amount of mercury mobilized is calculated by multiplying the activity rate of the process with a rate of mercury loss, that is, the quantity of mercury lost per unit of activity. Mercury is released as an impurity byproduct from coal and lignite power plants, petroleum combustion, cement production, iron, steel, and nonferrous metal (zinc, copper, lead) production and other usages of coal (industries producing paper, cotton, jute, bricks, soft coke, colliery and fertilizers). The amount of mercury mobilized by each process was calculated by multiplying the activity rate of the process with the mercury concentration of the fuel or ore. Activity rates were obtained from national statistics15−23 or derived from industrial and technical reports (Supporting Information (SI) section S2.1.1). Missing activity rates between 2001 and 2010 and future projections to 2020 were estimated based on the observed growth rates and past trends. Mercury concentrations and rates of mercury loss were obtained from literature (Tables 1 and 2). A detailed description of data sources and the

mercury content; most likely value (lower range-upper range)

category

Processes. g-Hg (Tonne Processed Ore)−1 cement (limestone) 0.065 (0.03−0.1) cement (total) 0.13 (0.05−0.21) g-Hg (tonne cement)−1 coal 0.272 (0.11−0.376) iron and steel 0.04 (0.032−0.048)

metals−copper metals−lead metals−zinc petroleum Products. g-Hg (Piece amalgam batteries lamps−CFLs lamps−FTLs lamps−Hg vapor sphygmomanometer switches (vehicles and A/C) thermometer

references 58 estimated13,22,33,58,59 estimated13,36,37 estimated,5,33 these factors exclude the mercury mobilized in the coal, which is accounted for separately. 58 estimated5,58 estimated5,58 5,33

8 (1−15) 5 (2−100) 25 (10−120) 0.033 (0.001−0.065) Product)−1 0.8 (0.27−1.2) 0.014 (0.0035−0.025) 0.012 (0.003−0.021) 0.040 (0.015−0.064) 0.503 (0.005−1) 52.5 (20−85) 3 (0.1−6)

6,60 61,62 44,63 44,63 64 58,65 13,64

1 (0.3−3)

64,65

a

More information on values estimated in this work is provided in SI section S2.1.3. CFL = compact fluorescent lamps, FTL = fluorescent tube lights, A/C = air conditioner.

derivation of mercury quantities is provided in SI section S2.1.1. The following products were considered in this study: mercurycontaining lamps (compact fluorescent lamps, fluorescent tube lights, mercury vapor lamps), thermometers, sphygmomanometers, batteries, switches, and dental amalgam. The mercury mobilized in each product stream was quantified by multiplying the annual domestic manufacturing rate and net imports with the product mercury content. Product manufacturing rates were obtained or estimated from industrial and governmental reports (SI section S2.1.2). Product import and export data were obtained from national statistics.24 Products imported and produced in a given year were assumed to be sold in the same year. Missing manufacturing rates and projections were estimated using a similar procedure as for processes. Imports for unreported years were assumed to be the same as for the nearest preceding or succeeding year. A detailed description of data sources and the derivation of mercury quantities are provided in SI section S2.1.2. 2.4. Mercury Flow Distribution and Emissions. Following its mobilization, mercury may follow different distribution pathways before entering the environment. These distributions were obtained by means of literature derived transfer coefficients (SI section S2.2). While most of the mercury contained in fuels and ores is emitted directly, the remaining quantity is transferred to fly ashes and residues25,26 and kiln dust.27 The ashes and residues may be used as raw material in clinker kilns,27−29 or they may be used for agricultural purposes;29 moreover, ashes, residues, and kiln dust may be landfilled.28,29 The ashes may also be used for the construction of embankments, roads, dykes, and mine filling.29 Considering the substantial amount of fly ashes produced annually in India,29 the latter utilizations and the 8106

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Table 2. Mercury Rates of Lossa category

mercury rate of loss; most likely value (lower range-upper range)

references

artisanal and small-scale gold mining

N/A

chlor-alkali industry gold recovery from e-waste pesticide application

78.3 g-Hg (tonne chlorine)−1 (12.9−143.3) 3.5 g-Hg (g gold recovered)−1 (1.3−5) 0.68 g-Hg (g Methoxy Ethyl Mercury Chloride (MEMC) used)−1 47 g-Hg (tonne VCM capacity)−1 (1−61)

vinyl-chloride monomer (VCM) production a

mercury quantities directly derived from literature66,67 estimated68 estimated69−71 calculated from the chemical formula of MEMC estimated33,72−74

More information on values estimated in this work is provided in SI section S2.1.3.

resulting ash-made structures are here considered in a separate category and are referred to as ash structures. Mercurycontaining process wastewater may be treated in wastewater treatment plants or discharged directly to water bodies.30 Some mercury contained in products is emitted directly to the environment due to product breakage. After use, products are generally disposed as waste. This waste may be incinerated or landfilled.31,32 Dental amalgam in our analysis may fall from the tooth33 or be cremated or buried with the body after death; this is in contrast to other studies that consider an average mercury content in cremated bodies.5,12 Landfills may be secured and controlled, noncontrolled, ash ponds, or open dumps. In this work, burial grounds are also considered as landfills. Landfills and ash structures are termed “anthropogenic sinks” here, since they may delay or (at least partly) prevent emissions to the environment. An example of flow derivation is provided in SI section S1. 2.5. Stocks. Product stocks build up because of the delay between product sales and disposal. The total refuse of mercury-containing products for each postsale year is calculated using an obsolescence function,34 based on the average and standard deviation of the lifetime of each product (SI section S2.3.1). Buildup of mercury in product stocks is calculated via a mass balance of the products entering the use phase and the calculated products disposed at any given year. Initial stocks were estimated for the year 2001 (SI section S2.3.2). Although most of the mercury accumulates in landfills and ash structures, a fraction of it is released to the environment in the form of leachate or gaseous emissions. The yearly release of mercury that entered these compartments is calculated from the 100 year transfer coefficients that are assumed to be constant in this period35 (SI section S2.3.3). Stocks in landfills and ash structures for the year 2001 were estimated as described in SI section S2.3.4, since no documentation could be found. 2.6. Evaluation of Emission Reduction Measures. We calculated the potential impact of six pollution control measures based on the most likely estimate for mercury emissions in the year 2010. Some measures may be somewhat extreme, but serve to illustrate maximum reduction potentials. A. Mercury phase-out: All intentional mercury applications, in products and processes, are banned. In order to see the potential impact on the emissions in 2010, the mercury ban was assumed to take place from 2001 onward to account for the delay occurring between product usage and disposal. B. Selective sourcing of coal based on its mercury concentration: Mercury content of Indian coal has a high natural variability.13,36−38 Selective use of lowmercury coal can reduce total mercury emissions. The

calculation of emission reductions was based on a mercury concentration of 0.11 g mercury per tonne (gHg tonne−1)37 for the use of mercury-low coal in coal power plants; cement, iron, and steel industries, and other coal usages, instead of the concentration of 0.272 g-Hg tonne−136 used for the most likely estimate (Table 1). C. Coal beneficiation: Washing of coal may reduce mercury release during combustion.39 We estimated the impacts of collecting 21%39 of mercury used in coal power plants, in ashes and residues, by coal-washing before combustion. D. Widespread use of flue-gas desulfurization (FGD) technology: Most power plants in India currently only use electrostatic precipitators.40 However, FGD is likely to be more common in the future.7,40,41 A switch to FGD in power plants may enhance mercury recovery from stack gases.42 We estimated the impacts of achieving mercury removal efficiencies of 40% and 70%42 in coal power plants. E. Recovery of mercury from zinc smelters:43 We assumed that half of the Indian zinc is produced in large smelters (annual production capacity around 100 000 tonnes) that have installed the mercury recovery technology, with capture efficiency of 93%.43 F. Recycling of intentionally used mercury: Mercury can be recovered from discarded products. Although recycling of mercury from some products, for example, lamps, has been recommended by the Indian government,44 no information could be found on actual recycling practices for mercury products in India. Here we assessed the impacts from recovering all intentionally used mercury that is not emitted directly, that is, all the mercury that enters the waste stream. Measures A and B reduce the total amount of mobilized mercury directly, while Measures E and F will also lead to a reduction in demand of primary mercury by substitution with mercury recovered from products and processes. Measures C and D minimize emissions to air, water, and soil through emission control. 2.7. Uncertainties. In addition to estimating average/most likely estimates (MLEs) for mercury flows, we also calculate lower range estimates (LREs) and upper range estimates (UREs) of mercury emissions from all sources, by combining possible lower and higher values of activity/production rates, mercury contents of ores and products and rates of loss. This information is used to highlight the data uncertainty and identify priority research areas. A qualitative data uncertainty assessment was performed and is described in SI section S3.4. 8107

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3. RESULTS AND DISCUSSION 3.1. Mercury Sources and Emissions. Total anthropogenic emissions to air, water, and soil increased from 415 tonnes in 2001 to 693 tonnes in 2005 (Figure 1A). They

emissions to soil were dominated by the use of pesticides. However in 2010, emissions to soil are primarily caused by dental amalgam (about 60% of total emissions to soil) (Figure 1B). Losses in the dental office12,47 are not considered here, and hence the total emissions from amalgam might be underestimated. Emissions from secondary metal production are most likely negligible (SI section S3.5), in contrast to findings in the U.S.12 Our estimates for atmospheric emissions in 2005 are consistent with those from Pacyna et al.,5 but our figures for 2004 are somewhat lower than those from Mukherjee et al.13 One reason for the latter discrepancy is their higher assumed mercury concentration in coal of 0.376 g-Hg tonne−1,13 which corresponds to our upper range of possible values (Table 1). We also note that while Mukherjee et al.13 estimate an air emission decrease between 2000 and 2004 due to mercury phase-out in chlor-alkali industry, in our work, decreased emissions from chlor-alkali industry are counteracted by emission increases from other sources. Mukherjee et al.13 list waste incineration as a major source to air, whereas in our work waste incineration was less relevant. Again the discrepancy arises from different assumptions about concentrations of mercury in municipal solid waste. Mukherjee et al. assumed 1 gHg (tonne waste)−1, whereas we obtained 0.2 g-Hg (tonne municipal solid waste)−1 from our model (SI section S3.6). 3.2. Mercury Flow Distribution. Figure 2 shows the results of the MFA for the year 2010. The corresponding graphs for 2001 and 2020 are shown in SI section S3.1. Most of the mercury present in ores and fuels is released to the air during combustion or processing. Less than 20% is transferred to ashes, residues, and kiln dust, and is landfilled or utilized in ash structures. In processes using mercury intentionally, emissions to soil are mainly caused by pesticide use and to air by chlor-alkali industry. 80% of the mercury used in products is imported separately, whereas the rest is already embedded in imported products. The majority of the mercury contained in products is lost at the time of product breakage, for example in the case of lamps. Human cremation leads to mercury emissions to air due to the presence of amalgam in tooth fillings. 3.3. Stock Build-Up. Mercury in product stocks increased from 700 tonnes in 2001 to 1125 tonnes in 2010 and is projected to exceed 3500 tonnes in 2020 (SI section S3.2) mainly due to the increased number of sphygmomanometers. In 2010, the largest stocks were dental amalgam tooth fillings and sphygmomanometers (SI section S3.2). Annual mercury gross input into product stocks is also increasing, from 103 tonnes in 2001, to 167 tonnes in 2010 and 756 tonnes in 2020 (Figure 3A). We estimate that the quantity of mercury entering product stocks may exceed air mercury emissions by 2020. As such, a large proportion of mercury in India is being transmitted through the commodity consumption pathway. We anticipate that even if all intentional utilizations of mercury were totally banned in the future, a time-period of the order of decades may be required before the stocks are depleted substantially. Combined annual mercury input to landfills and ash structures increased with time, from 43 tonnes in 2001 to 72 tonnes in 2010, and are projected to rise to 145 tonnes in 2020 (Figure 3A). This is about one-fourth of total emissions to the environment in 2010. The cement industry mobilizes a considerable amount of mercury, which mostly ends up in landfills and ash structures due to a relatively high collection

Figure 1. Mercury emissions to the environment in India from 2001 to 2020. Years 2011−2020 are projections based on extrapolated growth rates. ASGM = artisanal scale gold mining. VCM = vinyl chloride monomer.

dropped to 257 tonnes in 2006, after which they increased again up to 309 tonnes in 2010. Modeled emissions rise to 541 tonnes in 2020. The emissions were predominantly to the soil before 2005 and to the air thereafter. The irregular pattern of the emissions and their magnitude up to 2005 is caused by the use of pesticides. While pesticide consumption data for years 2005−2009 come from governmental sources, consumption for earlier years was derived from the import of organo-chlorides (SI section S2.1.1), which is the reason for the highly variable pattern. The drop in pesticide use in 2005−2006 might be a delayed consequence of the fact that the use of methoxy ethyl mercury chloride, the only seemingly relevant mercurycontaining pesticide, was restricted in 2001 to application in seed treatment only.45 In 2010, the majority of air emissions were caused by processes (Figure 1B), which is consistent with previous estimates.5 Coal power plants were the biggest sources of atmospheric mercury emissions. Metal production, of which 95% is caused by zinc production, is also an important contributor, along with the category “other coal usages”. Contribution from the chlor-alkali industry was minor, and is likely to decrease even further due to the phase-out of mercury cells.46 Products contribute to about 10% of atmospheric mercury emissions. These are primarily caused by sphygmomanometers, lamps, and dental amalgam. Up to 2005, mercury 8108

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Figure 2. Mercury flows (tonnes) in the year 2010 according to the most likely estimate. Amounts inside the boxes, in usage, ash structures, and landfills, refer to the absolute stocks, and in brackets to the change in stock. Arrow colors refer to the mercury-containing materials. Orange: ores and fuels; Yellow: ashes, residues and kiln dust; White: raw mercury; Green: products; Blue: waste. Red arrows refer to emissions. Numbers with (*), ash structures and landfills, exhibit a high uncertainty.

efficiency27 (see transfer coefficients in SI section S2.2). Coal power plants contribute to landfill stocks through fly ashes. This fraction will probably mostly be transferred to the ash structures in the future when fly ashes are required to be completely reused.48,49 An important fraction of the mercury flowing to landfills originates from batteries. In contrast to thermometers or lamps, which lose a substantial amount of mercury at the time of breakage, batteries generally enter the waste stream with their full mercury load. Mercury may also be released from landfills and fly ashes.35 The 100 year release factors for Swiss landfills35 suggest that approximately 10% of mercury that is landfilled is released within the following 100 years. Assuming a constant release over time, the immediate release of mercury in the year of disposal in the landfill and ash structures is small. However, further research is crucial to estimate the actual ability of landfills and ash structures in India to store mercury. Differences may exist in the fate of mercury in Indian landfills compared to Swiss landfills. For example, in contrast to the reference landfills used by Doka,35 numerous landfills in India are uncontrolled.32 In the case of open dumping,32 mercurycontaining materials are likely to end up on grounds lacking protection from leaching. Open air burning on landfills, which was not considered here, was reported as common practice in India32 and might increase the release of mercury to air. Similarly, little is known about the fate of mercury in ash structures. Also, since mercury cannot be degraded, we note that landfills and ash structures may merely delay mercury emissions by “storing the toxicity”.50 3.4. Pollution Reduction Measures. Table 3 shows the impact of the selected pollution reduction measures on the environment and on anthropogenic sinks. Among the individual measures tested, the shift to mercury-low coal

(selective coal sourcing) achieves the greatest impact with a reduction of 29% and 38% of total and atmospheric emissions, respectively. The use of flue gas desulfurization (FGD) also reduces air emissions substantially; this, however, increases the transfer of mercury to anthropogenic sinks by more than 100% and, thus, slightly increases emissions to water and soil. With respect to water and soil emissions, phasing mercury out is the most efficient measure (49% and 66% reduction in water and soil emissions, respectively). The total environmental emissions are reduced by 23%; a higher reduction will be observed in later years as the quantity of mercury-laden products stocks decreases. Similarly to phase-out, recycling reduces mercury input to landfills, and therefore the related stored toxicity. It reduces the need for further mercury imports and may generate some monetary inflow. The mercury emissions possibly occurring from the recycling process itself, however, may reduce the positive impact of this measure. Mercury recovery from zinc smelters induces comparable emission reductions to FGD with 40% mercury removal efficiency, and also achieves an additional reduction in the total mercury mobilized. The impact may increase if smaller zinc smelters also install the recovery technology, and not only the large ones as considered here. We note that some measures may be somewhat drastic and that there are practical constraints associated with them. The shift to low-mercury coal reduces the total quantity of mobilized mercury. However, choosing coal deposits based on their mercury content may lead to further environmental and social impacts if new mines are opened.51−53 Therefore, this measure requires a comprehensive assessment to ensure that the environmental impacts are not merely shifted. Coal beneficiation has a small effect compared to other measures, and increases the stored toxicity in anthropogenic sinks. One 8109

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anthropogenic sinks is required to clarify the fraction of mercury that may subsequently leach in the near and in the long term. A mercury phase-out is only feasible or effective if environmentally and socially sound substitutes are used. For example, substitutions of fluorescent lamps by energy-intensive incandescent lamps may not be appropriate because they require more energy, and may increase demand for coal combustion.54 Moreover, a ban on mercury might be difficult to implement for informal activities such as ASGM. Even with the optimistic assumptions made here, no individual measure is able to achieve more than one-third reduction in total emissions. Selective coal sourcing and FGD both target coalderived mercury; combined, they reduce total mercury emissions by 39% only. In contrast, combining selective coal sourcing and mercury phase-out, which target different mercury sources respectively, achieves a total emission reduction of 53%. 3.5. Uncertainty Assessment and Knowledge Gaps. Lower (LREs) and upper range estimates (UREs) for total mercury emissions vary by a factor of 7 in 2010 to 15 in 2020 (Figure 4A-i). LREs and UREs for total mercury emissions are 108 and 819 tonnes in 2001, 98, and 665 tonnes in 2010, and 113 and 1739 tonnes in 2020. The absolute difference between URE and LRE has a maximum contribution from zinc production, of about 170 tonnes in 2010 (Figure 4A-ii). This is because of the large zinc production in India and the potentially high mercury concentration in Indian zinc ores. Emissions from coal power plants may also vary considerably because of the natural variability in mercury concentration in coal.13,36−38 A sensitivity analysis (SI section S3.3) shows that a 1% increase in the mercury concentration of coal adds 1.75 tonnes to the total mercury mobilized in 2010. In contrast, a 1% increase in the mercury concentration of zinc ores adds 0.37 tonnes of mercury, and in copper and lead ores it adds 0.01 tonnes to the total mercury mobilized. Amalgam in toothfillings also exhibits a large uncertainty due to the lack of available data. LREs and UREs for mercury flows to anthropogenic stocks also vary considerably (Figure 4B-i), with the maximum influence coming from batteries (Figure 4Bii). A qualitative data uncertainty assessment shows that data on processes using mercury intentionally, as well as data on products are more uncertain than data regarding processes

Figure 3. Mercury inputs to stocks in India from 2001 to 2020. Years 2011−2020 are projections based on extrapolated growth rates.

additional benefit of FGD is the removal of pollutants other than mercury; the impact of FGD is however strongly dependent on the removal efficiency of the system42 (Table 3). Captured mercury is then transferred to landfills and ash structures, and further analysis on the fate of mercury in

Table 3. Change in % (Tonnes) of Mercury Flows to the Environment (Air, Water, and Soil) and to Anthropogenic Sinks (Landfills and Ash Structures) Due to Different Pollution Control Measures with Respect to the Most Likely Estimate in 2010 without Measuresa total to anthropogenic sinks

total mercury mobilized

control measure

air

water

soil

land-fills

ash structures

total to environment

phase-out coal sourcing coal washing FGD 40% efficiency FGD 70% efficiency recoveryb recyclingb coal sourcing + phase-out coal sourcing + FGD 70% efficiency

−12 (−29) −38 (−89) −10 (−24) −16 (−38) −33 (−76) −13 (−31) −7 (−17) −51 (−119)

−49 (−16) 0 (0) 0 (0) 0 (0) 1 (0) 0 (0) −9 (−3) −49 (−16)

−66 (−27) 0 (0) 1 (0) 1 (0) 2 (1) 0 (0) −2 (−1) −66 (−27)

−36 (−21) −17 (−10) 26 (15) 40 (23) 81 (47) −4 (−2) −43 (−25) −53 (−31)

0 (0) −35 (−5) 62 (9) 96 (14) 195 (29) −10 (−1) 0 (0) −35 (−5)

−23 (−73) −29 (−90) −8 (−24) −12 (−37) −24 (−75) −10 (−31) −7 (−21) −53 (−162)

−29 (−21) −21 (−15) 33 (24) 51 (37) 104 (75) −5 (−4) −35 (−25) −49 (−36)

−25 (−94) −27 (−104) 0 (0) 0 (0) 0 (0) −9 (−35) −12 (−46) −52 (−198)

−51 (−120)

0 (0)

1 (0)

16 (9)

44 (7)

−39 (−120)

22 (16)

−27 (−104)

FGD = flue gas desulfurization. bFor recycling and recovery from zinc smelters, the change in total mobilized mercury quantity is calculated by assuming that the recovered mercury is reused in India itself.

a

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Figure 4. (A) Upper and lower range estimates of total annual mercury emissions to the environment (air, water, and soil). (B) Upper and lower range estimates of mercury inputs to anthropogenic sinks (landfills and ash structures).

help better quantify total mercury emissions to the environment. Finally, we note that most informal sector related activities, such as informal coal mining,55 were not addressed here. As such, our results should be interpreted as a “best guess” and should be complemented with further investigations before decision-making processes. In our work, the fate of mercury after its emissions to air, water and soil was not considered. Under a simplified assumption that all emitted divalent and particulate mercury emitted in India is deposited within India, and using the mercury speciation of different sources compiled by Streets et al.,56 half of atmospheric emissions may eventually deposit to land and water. Coupling of our emission analysis with mercury fate and transport models57 would help clarify the fate of mercury once emitted from processes and products, the role of re-emission of anthropogenic mercury, and would help better estimate the possible adverse health and environmental effects from mercury exposure in India. Our work addresses key knowledge gaps on anthropogenic mercury flows in India.13 This information may help inform regulatory actions on mercury.11 Among the different measures considered in this work, selective use of low-mercury coal and FGD appear to achieve the greatest reduction of atmospheric mercury emissions. However, FGD may increase mercury flows to anthropogenic sinks, with a risk of future emissions. Mercury

involving mercury-containing fuels and ores (SI section S3.4). The latter are mostly provided by the government, and literature provides a range of estimates for mercury content in ores and fuels. In contrast, industry data on intentional use of mercury in processes or products is difficult to obtain, and the assumptions required to estimate the data increase the uncertainty of the calculations. In summary, the uncertainties in emissions from processes are primarily influenced by the natural variability in fuel and metal ore mercury content, while those from products are largely influenced by scarcity of industrial data on activity rates. More information on these would better reflect total mercury emission estimates in India, as well as the relative importance of different sources. Moreover, our projections are based on extrapolated growth rates and hence represent a “business-as-usual” scenario. Market studies are required to better constrain these rates. Additionally, further information on transfer coefficients is required to constrain mercury flows since very little data specific to India could be found. More information is also required on the fate of mercury in landfills, for instance the fraction of Indian landfills that are secured or covered, and how much mercury can be emitted to air or percolated through bottom soil in landfills. Mining is an important source for mercury pollution in some countries.12 Information on emissions at mining and production sites in India would also 8111

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phase-out and recycling are effective in reducing emissions to water and soil. As such, the relevance of each pollution reduction measure depends on the targeted emission pathway. If a reduction in stored toxicity in landfills is desired along with reductions in emissions to the environment, measures to reduce the overall amount of mobilized mercury such as use of lowmercury coal, mercury phase-out and recycling should be preferred. A combination of measures targeting different mercury sources may be necessary to achieve an important overall emission reduction. In order to identify the most appropriate strategy, we suggest that a comprehensive cost-benefit analysis of individual measures should be conducted, as well as further research into mercury emissions from coal, zinc and dental amalgam, and into the fate of mercury in anthropogenic sinks.

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ASSOCIATED CONTENT

S Supporting Information *

Additional information as noted in the text. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Present Address §

A.Q.: IIT Hyderabad, Yeddumailaram AP 502205.

Notes

The authors declare no competing financial interest.

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REFERENCES

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