Mercury pollution due to coal mining and thermal power plants in India- A Review

Ayushi Gupta, Rajani Srivastava*, Monalisa MohapatraInstitute of Environment and Sustainable Development (IESD), Banaras Hindu University,

Varanasi-221005

* Corresponding Author Email id–rajani.srivastava25@gmail.com

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Abstract

The present paper reviews information from the existing literature about mercury (Hg), a

dynamic polluter with potentiality to cause adverse impacts on human and ecosystem. It is as a

global polluter and land and ocean play a vital role in redistribution of Hg in all ecosystems. The

cumulative release of Hg has increased with industrialization that cause human health and

environmental risk in more intense way. 70% of Hg entering in the biogeochemical cycle are due

to anthropogenic emissions. There are various forms but the most prominent is methyl mercury.

UNEP 2018 report states that mercury can never be removed from environment as it may resides

up to decades in the form of methylmercury in soil and up to two years in atmosphere as

inorganic elemental mercury. The world has already seen the consequences of Hg pollution

caused by Minamata disease poisoning. In the last decade the Indian population has been

exposed to approximately 56.86 ton of Hg as per the UNEP calculation protocol. Although this

factor is not as accurate in Indian scenario but it brings the attention of the agencies, researchers

and law makers to incorporate better treatment design for the same. So, this review focuses on

that assessment of global sources of Hg, chemical and physical behaviour of mercury in the

atmosphere, pathways of mercury in the context of human health as well as economic ideas for

reducing all these.

Keywords: Mercury pollution, global sources, pathways, emission scenarios human health, policy-making, treatment Technology

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1. Introduction

Heavy metal toxicity is a major concern among the scientific community. Metals with a density

of more than 5 are considered heavy metal. Mercury (Hg) with a density of 14 is a major

concern. Atmospheric behaviour and contamination of mercury lead to a global impact on the

environment as well as on human beings. It is a strongly dispersed element, having a complex

biogeochemical cycle and capacity of biomagnification in the food chain. Mercury (Hg derived

from Greek word hydrargyrum; hydr-water and argyros- silver) is a silvery fluid having a unique

electronic configuration and chemical properties. It is slightly soluble in water and its solubility

increases by 1.3 per 10-degree increase in temperature (Gaffney and Marley, 2019). Naturally

Hg present in two forms, one as dimeric cation, mercury (I) (Hg2+, mercurous ion) and another in

form of mercury (II) (Hg+ mercuric ion). Mercury (II) (Hg+) can bind strongly with natural humic

materials present in an aquatic environment and more harmful to humans (Gaffney et al., 1996).

Exposure to environmental contaminants comes through various routes, including natural

sources (e.g., groundwater, metal ores, and metal leaching from the soil), industrial processes,

commercial products, and contaminated dietary supplements and food (e.g., fish). Elevated

mercury exposure in human being causes various neurological and cardiovascular diseases and,

in some cases, it even causes reproductive and immune system diseases also (Sundseth et al.

2017). The largest emission source of Hg is fuel combustion, mainly coming from coal (power

plants). In the coal production sector, India is the third-largest in the world. This coal mainly

contains mercury in the form of inorganic compounds- sulphides (cinnabar, HgS), chlorides and

sulphates depend on its types and origin. Atmospheric average resident year of mercury is 0.8 to

2 years. Due to anthropogenic emission, there have been about 70% of the rise in mercury levels

during the last hundred years (Gaffney and Marley 2014).

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Local users are the major concern under environment contamination by toxic substances like Hg,

as it cannot be possible to avoid the exposure. Large growing pollution tends towards mass

production and accumulation of Hg in soil and the aquatic region directly or indirectly.

Therefore, it is high time to obtain knowledge about mercury contamination, their route of

inhalation in human beings and its cycle in nature. It is also important to understand established

policies and its limitation and identify strategies to overcome problems related to mercury.

Bhattacharya et al. (2009) in India studied the Chlor-alkali industry from 2000 to 2004 and

reported that the replacement of the mercury through the membrane method reduced emissions

in the related industry from 123 tons to 6.2 ton (from 2000 to 2004). The concentration of toxic

metal in the environment is already more than limit, as reported by WHO (2008) and USEPA

(US Environmental Protection Agency). To protect humans and the environment from

anthropogenic emissions and the release of Hg- UNEP Minamata Convention has been signed in

the year 2014 by more than 120 nations. In this paper, our focus is on reviewing the existing

global and local studies on mercury to better understand sources, pathways and deposition of Hg

and its potential health hazards. This review also suggests some suitable strategies for the

prevention or minimization of Hg pollution.

1.1 How Mercury reaches to the human being

Mercury emission in the environment from various sources (atmosphere, lithosphere, biosphere,

and hydrosphere) causes the risk to human health and wildlife globally. Hg releases from natural

sources (like geothermal activity, mercury-containing rocks and volcanism) in small quantity

whereas, bulk quantity is released from anthropogenic sources. According to one estimate,

natural sources release Hg about 76-300 Mg/yr, whereas, 2000 Mg/yr released by anthropogenic

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sources (Street et al. 2019). Understanding the emission sources, transport and deposition

patterns of mercury in the atmosphere is critical for assessing the presence and future risk for

human health and for identifying effective policy options at local, regional, and global scales.

Mercury is directly mobilized by a human through various activities causing environmental and

human perturbations. Different sources of mercury, transport, deposition and pathway are shown

in Figure 1. As we know the majority of mercury emission is from anthropogenic sources and the

most significant source is the industrial plant. It releases Hg directly into air and water and if Hg

contaminated water used for irrigation, it gets deposited in the soil. Fishes take Hg directly from

contaminated water whereas, in other animals, it enters through the process of ingestion and

inhalation. By the process of inhalation, deposition and diffusion it also enters into the animal

body from air. Through all sources, like air (via inhalation), water (via ingestion), soil (via plants

and animals) and food (example, fish), Hg get deposited in human and cause diseases (Figure 1).

1.2 Types of Sources

Mercury is a naturally occurring trace element extracted with many other economically valuable

minerals and coal. Mercury is economically extracted from cinnabar. There are four types of

mercury emissions.

1.2.1 Primary natural sources

Mercury released from natural weathering from the rocks. Volcanoes release mercury in an

episodic manner. The geothermal activity also transports the underground mercury to air. The

pathways of these are quite well understood by some recent researcher's models. According to

these model’s mercury emission due to primary natural sources are contributing 1/2 or 1/3rd to

the total emission in the atmosphere (Branch 2008).

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1.2.2 Primary anthropogenic sources

The main sources for this kind of pollution are coal burning, mining for various metal ores,

production of Cement. In all these activities the mercuric emission is as a kind of byproduct. The

mercury is present in trace amounts in coal but the proportion of coal burned is higher hence coal

burning contributes the most to mercury emission (Sunderseth and Pacyna 2017).

1.2.3 Secondary Anthropogenic sources

When mercury is produced for human use it becomes a potential secondary source. Mercury is

used in many products example batteries, paints, electrical and electronic devices, blood pressure

gauges, switches, thermometers, fluorescent and energy-saving lamps, dental amalgam,

fungicides, pesticides, medicines and cosmetics. A major contributor to mercury release is from

the steel industry and Artisanal/small scale gold mining which are often dispersed and

unregulated. Another major secondary anthropogenic source is the Chlor-alkali industry, where it

uses mercury cell technology.

1.2.4 Re-mobilization and Re-emission

Re- mobilization is the process is when mercury that had been taken out of atmospheric

circulation is re-released. For example, mercury deposited in soil sediments may get re-

mobilized to the aquatic area due to heavy rains. Re-emission occurs when the reactive form gets

converted to elemental mercury, which can be again converted to gaseous form. Re-mobilization

and Re-emission can be either natural or anthropogenic. Estimating these processes is quite

difficult (Sunderseth and Pacyna 2017).

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1.3 Depicting Emissions by sector

According to AMAP/UNEP 2018, Updated Global and Oceanic Mercury Budgets for the United

Nations Global Mercury Assessment 2018 (Outridge, Mason et al. 2018) which is the updated

version of Technical Background Report known as `The global atmospheric mercury assessment,

sources, emission and transport` (Pacyna et al. 2010) describes eight major sources of Mercury

Pollution. These sources are artisanal and small scale gold mining, combustion of coal, non-

ferrous metal and cement industry, through the disposal of mercury-added products, stationery

and ferrous metal production and from other sources (Figure 2). This mercury emitted in the air

which is deposited back in the dry gaseous form and can travel miles of miles with country

boundaries and return to earth in the form of rainfall. It can be carried by rain and snowmelt

runoff to the state’s surface waters and will contaminant the water resources. The anthropogenic

emission leads to add up pools of mercury globally which repeatedly circulate and re-emit into

the atmosphere and still have a chronic effect which was released earlier. According to Global

Mercury Assessment (2018) by UNEP, mercury can never be removed from the environment as

may reside up to decades in the form of methylmercury in soil and up to two years in the

atmosphere as inorganic elemental mercury.

2. Mercury forms

2.1 Inorganic Mercury

2.1.1 Metallic (Hg0) Mercury

About 80% of metallic mercury vapor which is dangerous when it gets inhaled by a human while

7- 10% is ingested directly as metallic mercury and 1% is absorbed by the skin (Bernhoft 2012),

mercuric mercury when it enters in the bloodstream and through placenta it lodges in the fetal

brain rapidly oxides cause a blood-brain barrier. When it enters the body it creates disfunction in

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some organs such as in the brain, thyroid (Bjorkman & Lundekvam et al. 2007), muscles, adrenal

glands, liver, salivary glands, reproductive organs of human (Berlin & Zalups 2007), kidneys

(Guzzi & Grandi et al. 2006), skin, pancreas (Berlin & Zalups 2007), lungs (Hahn & Kloiber et

al. 1989), etc.

2.1.2 Mercurous (Hg2 ++) Mercury

Mercury salt forms poorly soluble in water in the form of Hg2Cl2 (calomel) and is absorbed by

the intestine where some of its portions undergo oxidation which is the best suitable form of its

absorption (Goodman 1996), calomel is associated with pink disease or acrodynia.

2.1.3. Mercuric (Hg++) Mercury

It gets deposited in the liver, accumulates in the placenta (Takemoto et al.1977), accumulates in

some parts of the testes, epithelial tissue and brain. It causes corrosive effects to the intestine

(Kostial & Kello et al. 1978) after chronic exposure to this mercuric chloride (HgCl2). Previously

it was used as preservatives and used in the photographic film which causes skin cancer because

it penetrates the skin (Goodman 1996), and gets suspended in plasma (Clarkson & Gatzy et al.

1961). Mercuric mercury excreted through urine, sweat, breast milk, and stool (Rahola &

Hattula et al.1971).

2.2 Organic Mercury Compounds

The most common way to the exposure of organic methyl mercury is naturally via fish (Berlin &

Zalups 2007). The evaporation efficiency of methyl mercury is similar to metallic mercury

vapor, it is absorbed by the skin and intestinal absorption is due to intake of fish. After four days

of exposure, it will also get deposited in the human body and blood. (Kershaw & Dhahir et al.

1980). The excretory half-life of methyl mercury in the human body is about 70 days as 90% or

more is excreted in the form of stool and urine. More than 20% get excreted through breast milk

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if applicable (Berlin & Zalups 2007). Table 1 summarizes the different forms of inorganic and

organic mercury.

Massive coal production enhances the mercury emission and increases the level of mercury more

than 10 ppm in groundwater and ponds. The government of India is reviewing the standards of

0.1mg/m3 set up by the Occupational Safety and Health Administration, USA for its

implementation in our country. Concentration limit of mercury only up to 0.001 ppm in drinking

water and 0.05 mg/kg in soil set by Bureau of Indian Standards (BIS) and the World Health

Organization (WHO). India permits 0.50 ppm concentration in fish. While the limit set by EPA

is 0.10 mg/kg/day, which is one fifth to that of WHO. The WHO guideline for mercury intake by

fish is 0.47 mg/kg/day ( UNEP 2008).

3. Impacts of Mercury on Environment and Human Health

The impact of mercury can be seen in terms of air pollution, water pollution, soil pollution and

human health.

3.1 Air Pollution: At room temperature metallic mercury, is a liquid it evaporates into the air,

where it can be inhaled. If it released into an enclosed space in a small amount, it can raise

concentrations of mercury in the air to a toxic level which is harmful to health. As long as people

breathe the contaminated air, the greater the risk to their health. It’s very difficult to wash or

remove out metallic mercury and its vapors from clothes, furniture, carpet, and other porous

items.

Mercury sources in the air are available in household products, including thermostats, glass

thermometers and switches in large appliances. Barometers which use to measure the air pressure

have small openings, which create a pathway for the gradual release of mercury. A small

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amount of mercury vapor is present in fluorescent bulbs whether accidental or intentional spills

of metallic mercury in a home also cause exposure to mercury at home and it can settle down

there on a different form of household items which is difficult to remove (Von Muehlendahl

1990).

3.2 Water Pollution:  Mercury contamination is a major concern for water. Liquid mercury

called quicksilver. The river in India mainly receives effluent from various industries, untreated

sewage, agricultural effluent runoff, domestic sewage along with bleach, acid. Intake of infected

fish from these rivers directly causes human health effects. Mercury rapidly moves in the

ecosystem food web whereas, atmospheric form deposit direct in the aquatic ecosystem.

3.3 Impacts on human health: Mercury adversely affected human health. It affects our nervous

system, endocrine, digestive and reproductive systems.

Nervous System: Methylmercury and metallic mercury vapors are more harmful than other

forms. The nervous system is very sensitive to all forms of mercury, if methylmercury reaches

the brain it dis-function the nervous system. Higher exposure to all forms of mercury can

permanently damage the brain, kidneys, and developing fetus (Azimi & Moghaddam 2013).

Strength reduction in arms and legs has been reported due to high exposure.

Several deadly effects of mercury on the nervous system are seen in terms of protein inhibition,

damaged or disrupted neurotransmitters, dysfunction of mitochondria, a damaged framework of

neurons structure, destruction of the structural framework of neurons, blindness and cerebral

palsy.

Digestive and Renal Systems: Various digestive disturbances can be cause due mercury

absorption through epithelial cell as it reduce the production of the digestive trypsin,

chymotrypsin, and pepsin, xanthine oxidase (Vojdani & Pangborn et al. 2003). There is various

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problem by mercury exposure like abdominal pain, indigestion, inflammatory bowel disease,

ulcers and bloody diarrhea, increase the amount of undigested food products in the bloodstream

which cause immune-mediate mediate ( Summers & Wireman et al. 1993).  

Endocrine System: Some low exposure level of mercury affect the endocrine system in people

by disruption of the pituitary, thyroid, adrenal glands and pancreas and animals (Rice & Walker

Jr et al. 2014). Some of the hormones got effected like insulin, estrogen, testosterone, and

adrenaline. The ability to reduce hormone-receptor binding is due to mercury that might impair

endocrine function through its (Iavicoli & Fontana et al.2009). Rather than kidney thyroid and

pituitary retain more inorganic mercury. A study found levels of mercury in the pituitary gland

ranged from 6.3 to 77, another study concluded mean levels to be 28 ppb, levels found to be

neurotoxic and cytotoxic (Nylander & Wwiner 1991). Depression and suicidal thoughts among

teenagers and other vulnerable groups is by low levels of pituitary dysfunction.

Reproductive System:  Mercury exposure were associated with infertility in both men and

women (Dickman & Leung et al. 1980), this was studied in Hong Kong demonstrated among

few groups of men and women. Mercury can have adverse effects on spermatogenesis in males

(Cychosz & Guillet et al.2107) epididymal sperm count, and testicular weight. In female effects

of estrogen and progesterone levels leading to ovarian dysfunction, painful or irregular

menstruation, premature menopause, and tipped uterus (Li & Chen et al 2006). Mercury has

been shown to inhibit the release of FSH and LH from the anterior pituitary which in turn can do

menstrual disorders including abnormal bleeding, short, long, irregular cycles, and painful

periods (Davis & Price et al. 2001) it reduces the growth of children who infected from this.

Fetal toxicity: Spontaneous abortions, stillbirth, small head and low birth weights, miscarriages

are associated with mercury and feto toxicity .(Yoshida 20002, Aaseth & Hilt et al. 2018). MeHg

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blood levels were moderately related in decreased pregnancy rates (Burbacher & Monnett et al.

1984). The brain of the fetus is where MeHg easily enters through the placenta and after that

babies may be born with a variety of birth defects (Finkelman & Tian 2018).

4. Average distribution and reach of Mercury

The classification of trace elements is carried from the US National Research Council (NRC) for

coal. This was based on trace-element`s geochemistry found in coal resource known as Chemical

of Potential concern (COPCs) related to environmental quality and health’. This report classified

these trace elements based on the level of concern based on known adverse health effects or

because of their abundances in coal. This report classified Mercury as a major concern due its

high volatility and other properties.

One of the most prominent source of Mercury pollution is due to coal consumption in thermal

power plant as mentioned in section 1.3. Hence accounting the levels of mercury to which Indian

population is exposed to, becomes crucial.

In India the coal used in thermal power plants are from one or the other coal fields. Hence,

burning these coals in thermal power plants would release these heavy metals to air, water and

land in contact with the biosphere. The mercury released from the power sector for the last 18

years has been calculated using the following equations.

Mercury in feed = (Amount of coal fed to power plants in a year) X (Hg concentration in coal)

….(1)

Amount of coal fed to power plants in a year (ton/year) and average Hg concentration in

coal(g/ton)) average from table 2.

Emissions factor = (Input factor) X (output distribution factor to air) ….(2)

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where, Input factor = Mercury Input Factor of coal (Hg concentration in coal(g/ton)) taken as

average from (table 2) and Output distribution factor to air = 0.9 as per UNEP Tool kit for plants

having General ESP (Inter 2011).

Estimated Mercury Release (ton/year) = (Activity rate) x (Emissions factor) ….(3)

Activity rate is Amount of coal fed to power plants in a year (ton/year) and emission factor was

taken from eq (1). The results for the period 2001 to 2018 are depicted in Fig. 3.

A study conducted by (Das, Choudhury et al. 2015) accounted direct emissions measurement

carried out in one boiler unit at three pulverized coal power plants along with the unit generation

capacities of the boiler units are 210MW, 250MW and 500MW in table 3.

As mercury content in coals show significant variation, there is a high degree of uncertainty in

this estimate since the bulk of the emissions are estimated using emission factors obtained with

limited number of coal samples. It needs to be mentioned that use of the default value of 0.9 is

likely to give a higher estimate of the emissions. Implicit in the default value 0.9 is the

assumption that the volatile mercury is entirely carried in the flue gas and depending on the

efficiency of the existing air pollution control system a fraction of the mercury is retained and

more than 90% is released in the air. This default value considers only 10% retention of mercury

in the solid combustion products. Although these assumptions vary from place to place hence

needs to be corrected but the definite values are not certain.

5. Mercury Pollution in India

Sonbhadra District of Uttar Pradesh from where 15 drinking water samples were analyzed, of

theses 3 samples (20%) contained mercury ranging from 0.003– 0.026 ppm of mercury. Sample

number W01 which was collected from hand pump at Dibulganj contained 0.026 ppm of

mercury which is 26 times higher than the desirable limit of mercury in drinking water (0.001

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ppm). Similarly sample numbers W02 (dug well at Annpara) and W06 (hand pump at Chilika

Daad) contained 0.008 and 0.003 ppm of mercury respectively which is 8 and 3 times higher

than the desirable limit of mercury in drinking water. (Sahu & Saxena et al.2012).

Aditya Birla Chemicals (India) Ltd. (ABCL) which produces the chlor alkali products release the

effluent in Dongiya nallah Mercury level in water near chlor alkali industry has been reported as

high as 0.176 ± 0.0003 ppm in water (Sahu & Saxena et al.2012)..

Methyl mercury in fish sample collected from Ganges River at West Bengal. This study may

provide a baseline of mercury contamination from water samples on 19 species of fish from

ganga river West Bengal, it was investigated on muscle of fishes which is approximately 50-84%

of Hg was organic mercury tended to accumulate high levels of Hg. It was found that presence of

total mercury (Hg) and organic mercury levels in the muscle of 19 common fresh water fish

species is higher than level. The expected results give a shocking result that’s the total mercury

level found in this study was surprisingly very high and toxically unacceptable which may not

cause any toxic effect. A strong positive correlation between mercury levels in fish length (age)

and muscle with food habit and was found. Wallago attu species possessed the highest amount of

organic mercury in their muscle tissues which was estimated as was 0.93 ± 0.61 μg Hg/g of wet

weight. Whereas in small-sized fishes Cirrhinus mrigala, Tilapia mossambicus, Eutropiichthys

murius, Puntius sarana, Mystus vittatus. It was below the detection limit. The MeHg level found

in some species of this study indicates that it can trigger early nervous system dysfunction,

unfavorable impact on human health who will consume this.

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6. Treatment technologies to remove Mercury

Ninety-five percent of mercury occurring in the air is Hg0 (total gaseous mercury), and its

residence time in the air is estimated at 6 to 18 months. The residence times of its Hg2+ (gaseous

oxidized mercury) and that in Hgp (total particulate mercury) are estimated at hours and days

(Gworek, et al. 2017). These forms have a shorter atmospheric lifetime and will deposit to land

or water bodies within roughly 100 to 1,000 kilometres of their source. The ocean currents are

the reason for long range mercury transport

(https://www.env-health.org/IMG/pdf/mercury_chapter2.pdf). Hence further we will dicuss the

technologies available to reduce mercury from water.

7. Removal of Mercury by Chemical Precipitation

7.1 Bolkem Process

When mercury is reacted with the sulfuric acid (H2SO4) forms Mercury (II) sulfate (HgSO4) by

capturing the mercury. The first step involves at temperature lower than 50°C where 80% H2SO4

acid get concentrated. Second step of the process is carried out in a conventional tower operating

with 93% H2SO4. Mercurous sulfate resulted out from the reaction of mercury with the acid

which is shown below:

H 2 SO4+Hg → Hg2 SO 4 (4)

This is a very affordable and simple method using which we can easily carry out removal of

mercury(Shafeeq, Muhammad et al. 2012).

7.2 Sulfide Precipitation

The sulfur reacts with the Hg to form crystalline mercury sulfide (HgS). This technique works

with less concentrated acid of less than 85% H2SO4. Higher acid concentrations could result in

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the oxidation of sulfur to form sulfur dioxide (SO2).

H2SO4 + Na2S2O3 → S + Na2SO4 + H2O + SO2 (5)

The product acid also contains sodium sulfate that is not desirable in the product acid. Sodium

thiosulfate (Na2S2O3) dosage in above reaction must be controlled otherwise it produces mercury

sulfide (HgS) which is not easy to filter. By the use of this method, the mercury concentration

could be decreased from 15 ppm to 0.5 ppm in an hour at neutral pH. Hydrogen sulfide could be

one of the important sources of sulfide for the precipitation of mercury along with other metals.

This technique is preferred when the sodium sulfate is not desirable in the end product. The

process efficiency starts to decreases as pH goes above 9. In the chlor alkali plant, this process

could be a better option with the efficiency of 95 to 99% (Shafeeq & Muhammad et al.2012).

7.3 Toho Process

This process comprises of adding potassium iodide and mercury is then precipitated as mercuric

iodide as shown below:

Hg + I2 → HgI2 (6)

2KI + 3H2SO4 →I2 + 2KHSO4 + SO2 + 2H2O (7)

Cuprous iodide is added along with the potassium iodide to form a more stable precipitate of

Cu2HgI4. The separation of precipitated mercury is done by filtration (Lee & Park 2003, Seo et

al.2004, Mullett & Tardio et al.2007).

7.4 Removal of Mercury by using some flocculants

Flocculants are chemicals that cause flocculation of smaller particles suspended in liquids to

aggregate and form a bigger floc. Flocculants are widely applied for waste water treatment

processes for the purpose of improving the sedimentation or filterability of small particles.

Flocculants could be employed in swimming pool or waste water treatment to help in the

removal of mercury metal that would be the cause of water turbidity. A number of cations

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chemicals forms complexes at appropriate pH, and temperature react with water to produce

insoluble hydroxides. These hydroxides on precipitation form long chains and trap the small

particles in the form of larger floc (Shafeeq & Muhammad et al.2012).

Heavy metal flocculent known as mercaptoacetyl polyethyleneimine (MAPEI) which is a novel

example of water-soluble macromolecule which is synthesized by reacting polyethyleneimine

(PEI) with thioglycolic acid (TGA). The removal ratio of mercury ions (Hg2+) using MAPEI is

above 95% which is considered as highest percentage. Many studies the results suggests that,

the removal rate increases with the increase in pH or molecular weight of PEI, alkali metal and

alkaline-earth metal ions and chloride ions (Cl-) and nitrate (NO3-) ions which are responsible for

the removal of Hg2+ while sulfate (SO42-) will suppresses the process. The wastewater which

containing both turbidity and mercury ions in the process of treating, both have a synergic

removal effect with each other (Xu & Chang et al.2009).

7.5 Removal of Mercury Blue PRO reactive filtration process

By using multiple removal steps, the Blue PRO reactive filtration process could lower down the

particulate as well as dissolved species of mercury. Blue PRO is a wastewater tertiary treatment

process and it is capable of overcoming diffusion limitations within a continuous backwash filter

for filtering of particulates simultaneously removing mercury to ultra-low levels Hydrous ferric

oxide (HFO) adsorptive media is used which is regenerated inside the filter. Rather than other

tertiary wastewater treatment processes for mercury removal Blue PRO is cost effective

compared to lower levels. operating costs as checked it attributes to lower capital and compared

to membrane, reverse osmosis, granular activated carbon and coagulation systems (Shafeeq &

Muhammed et al.2012). The fig 4 shows the design of a typical reactor.

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7.6 Removal of Mercury Using Bio Films

A complex structure of microorganisms contributes to formation of bio film that grows on a solid

substrate is attributed to the fixation of microorganisms to a surface. Initially, they adhere to the

surface through weak van der waals forces. In case of not being separated immediately from the

surface, they could adhere to the surface permanently using cell adhesion molecules. These

membranes are highly efficient in removing the high molecular metallic species like mercury in

the waste water from chlor alkali plant. The most important thing about these bio films is that

these are environment friendly operation with ease of regeneration with latest techniques. For

efficient removal of mercury, the growth of these bio films is on a large scale. These bio films

provide millions of sites for mercury adsorption and could be a leading process in the near

future. Japan is using this technique on a medium scale in the chlor alkali plants (Shafeeq &

Muhammed et al.2012).

A bacterial strain Pseudomonas putida Spi3 was isolated from river sediments which is mercury

resistant is able to reduce ionic mercury to metallic mercury which was used to remediate in

laboratory columns wastewater bioreactors were continuously filled with sterile synthetic model

wastewater or nonsterile, neutralized, aerated chloralkaline wastewater which was mercury

containing produced during electrolytic production of chlorine. From several chloralkaline plants

in Europe factory effluents were analyzed, and these effluents contained mercury between 1.6

and 7.6 mg/liter was found with high chloride concentrations (up to 25 g/liter) and had pH values

range from either acidic (pH 2.4) or alkaline (pH 13.0). Levels of mercury retention efficiency

between 90 and 98% were obtained when wastewater samples from three different chloralkaline

plants in Europe were used. Thus, for removal is a potential biological treatment for

chloralkaline electrolysis wastewater is microbial mercury (Von & Canstein Li et al. 1999).

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7.7 Removal of Mercury by Reverse Osmosis

Reverse Osmosis (RO) system consists of granular activated carbon pre-filters, a RO membrane,

a storage tank, and a faucet for the delivery of the low concentration liquid stream. Commonly

used RO membranes are Thin Film Composite (TFC) and Cellulose Triacetate (CTA). TFC

membranes are relatively more efficient compared to CTA membrane. Both have a very high

rejection rate for mercury types as well as its different contaminants. These are also cheap and

cost about 5 cents per gallon of pure water (Shafeeq & Muhammed et al.2012). Many

investigations have assessed the viability of using cross-flow reverse osmosis filtration (RO) to

concentrate the mercury in a smaller aqueous stream. A study done by (Mullett & Mohamed

2009) including number of series of flat-sheet membrane tests were conducted at pH 2 and 7

using a feed solution with a concentration of 30 mg/L Hg. The data produced was used to model

filtration plant design determined at different pH scenario. 

7.8 Ion Exchange Treatment

Ion exchange process has been widely used process for waste water treatment. This technique is

used for mercury removal from aqueous solutions. For cationic mercury resins containing the

iminodiacetic group will exchange for selectively over calcium and magnesium, but copper and

cobalt are also readily exchanged with it (Laboratory 1997). Anion exchange resins used to treat

the mercury in the form of anionic complexes like (HgCl3). Duolite GT-73 (cationic resin

contains the thiol (-SH) group) is selective for its three oxidation states of mercury (Ritter &

Bibler et al.1992). A packed column Ion exchange processes is usually employed. Usually for

complete ion exchange cycle is operated in four steps i.e., service, backwash, regeneration, and

rinse (Laboratory 1997).

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This technique is more applicable in cases in which extremely low effluent mercury

concentration is expected. However, this typically technique cannot be used for waters with high

total dissolved solid content. When chloride content in wastewater is high (chlor-alkali plant)

removal of inorganic mercury has been typically carried out using anion resins in the ion

exchange technology since mercury presents in the negatively charged complex mercury

chloride form in the high concentration of chloride (Sorg 1979).If the anion content of

wastewater is low than cation exchange of mercury may be effective (Sorg 1979, Laboratory

1997). For effective ion exchange treatment of mercury present in industrial wastewater, certain

cation exchange resins such as Amberlite IR-120 and Dowex-50W-X8 are reported to be used

(Patterson 1975). A full-scale ion exchange process at a defense processes facility has

consistently removed mercury via ion exchange from 0.2 to 70 mg/L down to levels of 1 to

5µg/L, following 0.2 µm prefiltration

(Ritter & Bibler et al.1992).

7.9 Adsorption on adsorbents

Adsorption, another widely used process for mercury removal from waste water with the

potential to achieve high efficiencies of mercury removal and/or low effluent mercury levels

(Laboratory 1997).

Adsorption on Modified Natural Polymers

In removal of mercury from waste water using porous cellulose carrier modified with the

polyethyleneimine. By using polyethyleneimine (PEI) into porous cellulose carrier as adsorbent

for heavy metal is synthesized. Preliminary analysis of the adsorbent revealed extensive

crosslinking of PEI with modified matrix is the main reason for adsorption. Batch adsorption

20

study shows the ability of cell-PEI to selectively trap mercury even at specific acidic regions. An

adsorption capacity and Hg ligand stability constant of approximately 288.0 mg/g was found.

The diffusivity of Hg in the carrier was found to be approximately 7.30 x 1014m2/sec. Extensive

Crosslinking of PEI chains that restricts ligands mobility is the most crucial factor contributing to

these observed properties. The capacity of the adsorbent to other types of metals is decreased as

a consequence of reduced ligand mobility. Although this property is advantageous in other

applications such as recovery of specific precious metals, for general waste water treatment, high

selectivity becomes a limitation especially in dealing with wastes of different compositions

(Navarro & Sumi et al.1996).

Mercury ions can also be adsorbed by different adsorption mechanisms present in diverse

functional groups on which natural and crosslinked (glutaraldehyde and epichlorohydrin)

chitosan matrices induce. X-ray photoelectron spectroscopy (XPS) revealed that Mercury binds

to glutaraldehyde-crosslinked chitosan, differently from the other kinds of matrices. XPS

analysis confirmed that chitosan crosslinking with glutaraldehyde and epichlorohydrin occurs

preferentially on amino and hydroxyl groups leading to final structures with different functional

groups. Hg (II) ions presents higher adsorption capacity in this kind of matrix. Mercury ions

would bind well onto natural and crosslinked chitosan, with different mechanism in

glutaraldehyde-crosslinked chitosan, which would involve more chemical groups to metal ions

justifying the higher adsorption capacity found for this specific type of matrix (Vieira & Oliveira

et al.2011).

7.10 Adsorption on modified agriculture and biological wastes

The predominant adsorption process utilizes activated carbon, but the carbon used are the

modified agriculture product (Walterick Jr & Smith 2017). Now days for replacement for

21

current costly methods of removing heavy metals from water and wastewater with the help of

agricultural products and by-products (Kumar 2006). Some of the agricultural materials can be

effectively used as a low-cost sorbent which includes processed vegetable or mineral materials

such as bicarbonate-treated peanut hull carbon (BPHC), modified Hardwicikia binata bark

(MHBB) etc (Walterick Jr & Smith 2017). Modification of agricultural by-product could

enhance their natural capacity and add value to the by-product. In this review, an extensive list of

adsorbent literature has been compiled to provide a summary of available information on a wide

range of low-cost agricultural product and by-product sorbent and their modification for

removing heavy metals from water and wastewater in table 4. An inherent example of absorptive

treatment, when the adsorbent displays isothermal or quasi-thermal behavior, thus increasing

treatment efficiency with incremental adsorbent dosage. Common variables include wastewater

pH and pollution speciation (Walterick Jr & Smith 2017).

As an adsorbent for the adsorption of lead and mercury from aqueous water the use of rice husk

ash, an agricultural waste is studied. Studies are carried on the basis of ionic strength, particle

size, and ph. For the adsorption of lead and mercury ions rice husk ash is found to be a suitable

adsorbent for it. Its adsorption capability and adsorption rate are considerably higher for mercury

ions. The more mercury ions absorbed on rice husk ash when the rice husk ash finer particles

used, the higher the pH of the solution and the lower the concentration of the supporting

electrolyte, potassium nitrate solution is used. Equilibrium data obtained have been found to fit

both the Langmuir and Freundlich adsorption isotherms (Feng & Lin et al 2004).

8. Comparisons between treatments available for mercury reduction

The main techniques, which have been utilized to reduce the heavy metal ion content of

effluents, include lime precipitation, ion exchange, adsorption into activated carbon (Dean &

22

Bosqui et al.1972), membrane processing, and electrolytic methods (Brauckmann 1990). These

methods have been found to be limited, since they often involve high capital and operational

costs and may be associated with the generation of secondary waste which itself presents as

treatment problems, such as the large quantity of sludge generated by precipitation processes. On

the other hand, ion exchange, reverse osmosis and adsorption are more attractive processes

because the metals values can be recovered along with their removal from the effluents.

Reverse osmosis and ion exchange do not seem to be economically feasible because of their

relatively high investment and operational cost. Adsorption has advantages over the other

methods because of simple design with a sludge free environment and can work even low

investment in term of both initial cost and land required (Viraraghavan & Dronamraju et al.

1993). Activated carbon has been recognized as a highly effective adsorbent for the removal of

heavy metal-ion from the concentrated and dilute metal bearing effluents (Netzer & Hughes

1984, Redd & Arunachalam et al. 19994). But the process has not been used by small and

medium scale industries for the treatment for their metal bearing effluents, because of its high

manufacturing cost. However, efforts are being put into to develop new adsorbent and improving

the existing adsorbents to have an alternative to activated carbon. These materials range from

industrial products such rubber tyres (Knocke & Hemphill 1981), industrial wastes and some

natural material including agricultural product and by-product (Kumar 2006). This could really

help in improving treatment of effluents with mercury and other heavy metals economically.

9. Successful cases reducing mercury pollution

9.1 Western Lake Superior Sanitary District (Duluth, Minnesota)

23

The Western Lake Superior Sanitary District (WLSSD) was created by the Minnesota

Legislature in 1971 to deal with pollution in the lower St. Louis River. Today, the WLSSD is the

largest point source discharger on the U.S. side of Lake Superior. Its primary mission is to

protect the environment.

WLSSD began to address mercury issues following reports of high levels of mercury in fish in

the St. Louis River in 1989. Initial efforts focused on internal practices, such as scrubber water

management, and evolved into a broader examination of mercury contributions from the

community at large. Under its current National Pollutant Discharge Elimination System

(NPDES) permit, the WLSSD must meet an effluent mercury limit of 0.03 parts per billion

(ppb). New regulations adopted under the Great Lakes Water Quality Initiative (GLI) was even

more stringent water quality criteria for mercury. After evaluating the costs involved to meet the

proposed limits with end-of-pipe technology, WLSSD concluded that pollution prevention is

preferable

With support from the Great Lakes Protection Fund, WLSSD conducted a two-year Mercury

Zero Discharge Project from 1995-1997 to examine the sources of mercury to its wastewater

treatment plant and to determine how to reduce or eliminate those sources. This project included

cooperative initiatives with industries known to be discharging mercury, programs aimed at

specific uses of mercury, a monitoring program to identify additional sources and a public

awareness campaign. In addition to these external programs, WLSSD also examined its own

facilities and practices. WLSSD influent saw a reduction in mercury concentrations as a result of

this project and continues to see reductions as a result of ongoing work in mercury pollution

prevention in fig 5. Mercury concentration in WLSSD’s influent in 2001 averaged .09 ppb (parts

per billion) (Pickard 2003).

24

9.2 MWRA / MASCO -Hospital Mercury Work Group

In the fall of 1994, the Massachusetts Water Resources Authority (MWRA) formed a Mercury

Products Work Group. The Work Group’s mission is to examine and develop strategies to reduce

the amount of mercury being discharged into the wastewater stream. Hospital participation in

this process was coordinated through the Medical Academic and Scientific Community

Organisation (MASCO) and involved the active participation of 28 hospitals in the greater

Boston area.

On October 4, 1996, NWF, along with MHA, the U.S. Environmental Protection Agency (EPA)

and several supporting organizations, sponsored an educational workshop, ‘Mercury Pollution

Prevention: Healthcare Providers Protecting People and the Great Lakes’, for the healthcare

community and interested citizens. This conference was planned in recognition of the nationwide

interest on mercury and, specifically, on the role of the healthcare industry as a source of

mercury pollution. Many leaders in the industry have become aware of the need for change in the

standard practices of most hospitals when it comes to mercury use and are interested in learning

and doing more to reduce their impact on the environment. The positive response from

healthcare providers at the conference resulted in the development of this guide, which captures

the fundamentals of the various mercury reduction programs presented at the conference.

By the end of 1997, the Hospital Mercury Work Group has reduced the average concentration of

mercury in hospital wastewater from 22.7 ppb to less than 13 ppb. In addition, based on the

analysis of the hospitals participating in the Hospital Mercury Work Group, MWRA concludes

that it has reduced the amount of mercury entering its system by more than 70% involving

various the participating hospitals.

10. Conclusion

25

Mercury is toxic as according to the level of exposure, we cannot deny the use of mercury in

some of common consumer products like automotive parts, batteries, cosmetics, dental

amalgams, barometer, thermometers but there is a permit to use, as its not only harm the

environment but also effecting human being in the form of number of diseases which will remain

long lasting many decades. All forms of mercury are toxic to humans because its effects organs

depend on duration, exposure, chemical composition and the way they enter the body. Mercury

has different forms of mercury deposit in different tissue compartments, which has different

toxic profiles Community education is needed for a reduction in use of products within limit.

Mercury are dangerous because they tend to bioaccumulate in different form using different

media to travel from one boundary to other. Long-term exposure of all form of mercury may

result in chronic prolonged degeneration in terms of physical, muscular, and neurological nature.

In past years many cases and areas affected by mercury pollution have been reported in India.

With few exceptions all the other cases occurred due to coal mining and thermal power plants.

Mercury limits and standards need to be reestablished and reviewed to control mercury pollution

at the source level keeping in mind with the irreversible neurotoxic effects it causes. Treatment

technologies need to be implemented by the thermal power plants and coal washeries. Drinking

Water authority need to install specific and economic treatment measures in affected and prone

areas. The research and development need to be done more on the treatment technologies

keeping in mind the climatic conditions and local availability of raw materials in affected areas.

If low-cost adsorbents perform well in removing heavy metals at low cost, they can be adopted

and widely used in industries not only to minimize cost inefficiency, but also improve

profitability. Using flue gas cleaning waste incinerators should be equipped with this. In

addition, if the alternative adsorbents mentioned previously are found highly efficient for heavy

26

metal removal, not only the industries, but the living organisms and the surrounding environment

will be also benefited from the decrease or elimination of potential toxicity due to Mercury.

27

Table 1 Different forms of inorganic and organic mercury (Quotient)

SI No. Inorganic Organic

1 Mercuric Chloride Ethyl mercury

2 Mercuric Iodide Methyl mercury

3 Mercuric oxide Merbromin

4 Mercuric sulphide Merthiolate

5 Mercuric Chloride Phenyl mercuric salts

28

Table 2 Average mercury content in coal samples of India (Choudhury et al.2015)

Sl No. Coal Source (Air Dried Basis) Hg g/ton

1. CCL (Central Coalfields Ltd) 0.22

2. BCCL (Bharat Cooking Coal Ltd) 0.08

3. MCL (Mahanadi Coalfields Ltd) 0.20

4. NCL (Northern coalfields Ltd) 0.06

5. WCL (Western Coalfields Ltd) 0.12

6. ECL (Eastern Coalfields Ltd) 0.08

7. SECL (Southeastern Coalfields Ltd) 0.10

8. SCCL (Singareni Collieries Company) 0.12

29

Table 3 Mercury concentrations in Flue gas and combustion products (Choudhury et al.2015)

Power plantUnit Capacity(MW)

LOI* of Fly ash (Wt. %)

Solid ProductsMercury concentration (dry

basis)

Flue gas (µg/Nm3)

Speciation

Fraction of Hg emitted(average)Fly

ash (g/t)

BottomAsh (g/t)

MillRejects(g/t)

SPM(g/t)

Hg2+

%Hg0

%

500 0.64 0.097 0.006 - 0.066 14.84 30.8 60.1 0.81210 0.85 0.158 0.011 1.373 0.057 11.50 11.3 88.1 0.61250 2.05 0.242 0.017 0.143 0.105 4.24 41.6 58.1 0.27(*LOI = loss of ignition)

30

Table 4: Hg2+ adsorption capacity (mg/g) by different agricultural products and by-products

S. N. Material Adsorption capacity of Hg2+ (mg/g)

References

1- Douglas fir bark 100 (Masri & Reutar et al.1974)

2- Black oak bark 400 (Teles de Vasconcelos & Gonzalez et al 1994)

3- Redwood bark 250 (Masri & Reutar et al.1974)

4- Sulfuric acid lignin 150 (Masri & Reutar et al.1974)5- Xanthate saw dust 30.1, 40.1 (& Carnahanet al.1979)

6- Rastunsuo dust 16.2 (Tummavuori & Aho 1980)7- Dry redwood leaves 175 (Masri & Reutar et al.1974)8- Dyed bamboo pulp 15.6 (Shukla & Skhardande 1992) 9- Undyed bamboo pulp 9.2 (Shukla & Skhardande 1992) 10- Dyed jute 13.7 (Shukla & Skhardande 1992) 11- Dyed sawdust 18.0 (Shukla & Skhardande 1992) 12- Modified wool 632 (Shukla & Skhardande 1992) 13- Undyed sawdust 8.5 (Shukla & Skhardande 1992) 14- Rice husk ash 66.66 (Kumar & Bandyopadhyay 2006) 15- Modified hardwickia

binate bark21 (Deshicar & Bokade et al. 1990)

16- Bark 400 (Randall & JM et al. 1974)17- Xanthane 1.149 (Shukla & Skhardande 1992)18- CEPI cotton 1000 Roberts & Rowland et al.1973) 19- Palm Shell Powder 20 (Kushwaha & Sodye et al.2008) 20- Activated carbon from

mango kernal7.13 (Somayajula & Aziz et al.2013)

21- Activated carbon from Rosamarinus Officinalis Leaves

19.76 (Erhayem 7 Tohami et al.2015)

22- Peel Biomass of Pachira Aquatica Aubl

- (Santana & Dos Santos et al.2016)

23- Coal fly ash 0.44 (Attari & Bukhari et al. 2017)24- Roasted Date Palm 282 (Al-Ghouti & Da’ana et al.2019) 25- Activated carbon 120 (Al-Ghouti & Da’ana et al.2019)

26- Sulphur Modified Roasted Date Pits

280 (Al-Ghouti & Da’ana et al.2019)

27- Silane Modified Roasted Date Pits

90 (Al-Ghouti & Da’ana et al.2019)

31

Figure 1: Mercury pathways: Sources, transport, deposition and reaching to humans being

32

Figure 2: Diverse sources of Mercury pollution (Mason et al. 2018)

33

artisanal and small-scale gold mining

stationary combustion of coal

non-ferrous metal production

cement production

disposal of mercury added product waste

stationary combustion of other fuels including biomass

ferrous-metal production

other sources

0% 5% 10% 15% 20% 25% 30% 35% 40%

38%

21%

15%

11%

7%

3%

2%

2%

Mercury Sources

Figure 3: Mercury in coal feed and estimated emissions from the power plant (Coal usa source- https://www.ceicdata.com/en/indicator/india/coal-consumption)

34

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 20180

10

20

30

40

50

60

70

80 Mercury in feed Mercury in Emission

Year

Mer

cury

(ton

)

Figure-4 Layout of a typical Blue Pro system (Muhammad et al. 2012)

1-Influent; 2- Central Feed Chamber; 3-Radial Arms; 4- Spherical Silica Media; 5- Filtrate; 6- Fixed Effluent Weir; 7-Wash box; 8- Reject Stream; 9-Airlift; 10-Adjustable Reject Weir; 11- Tortuous Path

Fig 5 Mercury concentration in WLSSD influent (https://archive,epa.gov)

35

Jan-93 Jul-93 Jan-94 Jul-94 Jan-95 Jul-95 Jan-96 Jul-96-8.32667268468867E-17

0.0999999999999999

0.2

0.3

0.4

0.5

0.6

ppb

References

Aaseth, J., et al. 2018. Mercury exposure and health impacts in dental personnel. Environmental research 164: 65-69.

Aboud, O. 2010. Impact of pollution with lead, mercury and cadmium on the immune response of Oreochromis niloticus. NY Sci. J 3: 9-16.

Al-Ghouti, M. A., et al. 2019. Adsorptive removal of mercury from water by adsorbents derived from date pits. 9(1): 1-15.

Attari, M., et al. 2017. A low-cost adsorbent from coal fly ash for mercury removal from industrial wastewater. 5(1): 391-399.

Azimi, S. and M. S. Moghaddam 2013. Effect of mercury pollution on the urban environment and human health. Environment and Ecology Research 1(1): 12-20.

Berlin, M. and R. Zalups 2007. Mercury/Handbook on the Toxicology of Metals, GF Nordberg, BA Fowler, M. Nordberg, LT Friberg (Eds.)–New York: Elsevier.

Bernhoft 2012. "Mercury toxicity and treatment: a review of the literature." . Journal of Public Health.

Bjorkman, L., et al. 2007. Mercury in human brain, blood, muscle and toenails in relation to exposure: an autopsy study. Environmental health 6(1): 30.

Branch, U. C. 2008. The Global Atmospheric Mercury Assessment: Sources. Emissions and Transport, Geneva: UNEP-Chemicals.

Brauckmann, B. J. B. o. h. m. 1990. Industrial solutions amenable to biosorption. 52-63.Burbacher, T. M., et al. 1984. Methylmercury exposure and reproductive dysfunction in the

nonhuman primate. Toxicology and applied pharmacology 75(1): 18-24.Clarkson, T., et al. 1961. Studies on the equilibration of mercury vapor with blood, Office of

Technical Services, Department of Commerce.Cychosz, K. A., et al. 2017. Recent advances in the textural characterization of hierarchically

structured nanoporous materials. Chemical Society Reviews 46(2): 389-414.Das, T. B., et al. 2015. Mercury emissions from coal fired power plants of India-case study.

International Journal of Energy, Sustainability and Environmental Engineering Vol 2(1): 21-24.

Das, T. B., et al. 2015. Mercury emissions from coal fired power plants of India-case study. 2(1): 21-24.

36

Davis, B., et al. 2001. Mercury vapor and female reproductive toxicity. Toxicological Sciences 59(2): 291-296.

Dean, J. G., et al. 1972. Removing heavy metals from waste water. 6(6): 518-522.Deshicar, A., et al. 1990. Modified Hardwickia binata bark for adsorption of mercury (II) from

water. 24(8): 1011-1016.Dickman, M. D., et al. 1998. Hong Kong male subfertility links to mercury in human hair and

fish. Science of the Total Environment 214(1-3): 165-174.Erhayem, M., et al. 2015. Isotherm, kinetic and thermodynamic studies for the sorption of

mercury (II) onto activated carbon from Rosmarinus officinalis leaves. 6(01): 1.Feng, Q., et al. 2004. Adsorption of lead and mercury by rice husk ash. 278(1): 1-8.Fillings, M. I. D. A. A comprehensive review of the toxic effects of mercury in dental amalgam

fillings on the Environment and Human Health.Finkelman, R. B. and L. Tian 2018. The health impacts of coal use in China. International

Geology Review 60(5-6): 579-589.Flynn, C. M., et al. 1979. Adsorption of heavy metal ions by xanthated sawdust, Department of

the Interior, Bureau of Mines.Goodman, L. S. 1996. Goodman and Gilman's the pharmacological basis of therapeutics,

McGraw-Hill New York.Guzzi, G., et al. 2006. Dental amalgam and mercury levels in autopsy tissues: food for thought.

The American journal of forensic medicine and pathology 27(1): 42-45.Gworek, B., et al. (2017). Air contamination by mercury, emissions and transformations—a

review. Water, air and soil pollution 228(4): 123.Hahn, L. J., et al. 1989. Dental" silver" tooth fillings: a source of mercury exposure revealed by

whole-body image scan and tissue analysis. The FASEB Journal 3(14): 2641-2646.Hylander, L. D. and M. J. S. o. t. T. E. Meili 2003. 500 years of mercury production: global

annual inventory by region until 2000 and associated emissions. 304(1-3): 13-27.Iavicoli, I., et al. 2009. The effects of metals as endocrine disruptors. Journal of Toxicology and

Environmental Health, Part B 12(3): 206-223.INTER, I. 2011. Toolkit for Identification and Quantification of Mercury Releases.IS10500, B. 2012. Indian standard drinking water–specification (second revision). Bureau of

Indian Standards (BIS), New Delhi.Kershaw, T. G., et al. 1980. The relationship between blood levels and dose of methylmercury in

man. Archives of Environmental Health: An International Journal 35(1): 28-36.Knocke, W. and L. J. W. r. Hemphill 1981. Mercury (II) sorption by waste rubber. 15(2): 275-

282.Kostial, K., et al. 1978. Influence of age on metal metabolism and toxicity. Environmental Health

Perspectives 25: 81-86.Kumar, U. and M. J. B. t. Bandyopadhyay 2006. Sorption of cadmium from aqueous solution

using pretreated rice husk. 97(1): 104-109.Kumar, U. J. S. R. E. 2006. Agricultural products and by-products as a low cost adsorbent for

heavy metal removal from water and wastewater: A review. 1(2): 33-37.

37

Kushwaha, S., et al. 2008. Equilibrium, kinetics and thermodynamic studies for adsorption of Hg (II) on palm shell powder. Proceedings of World Academy of Science, Engineering and Technology.

Laboratory, N. R. M. R. 1997. Capsule Report: Aqueous Mercury Treatment, US Environmental Protection Agency.

Lee, S.-H. and Y.-O. J. F. P. T. Park 2003. Gas-phase mercury removal by carbon-based sorbents. 84(1-3): 197-206.

Lee, S. J., et al. 2004. Removal of gas-phase elemental mercury by iodine-and chlorine-impregnated activated carbons. 38(29): 4887-4893.

Li, Y., et al. 2006. Elimination efficiency of different reagents for the memory effect of mercury using ICP-MS. Journal of Analytical Atomic Spectrometry 21(1): 94-96.

Masri, M. S., et al. 1974. Binding of metal cations by natural substances. 18(3): 675-681.Mukherjee, A. B., et al. 2009. Mercury emissions from industrial sources in India and its effects

in the environment. Mercury fate and transport in the global atmosphere, Springer: 81-112.Mullett, M. and L. J. E. O. F. A. W. u. t. t. C.-S. Mohamed, Burswood Entertainment Complex

2009. Removal of mercury from solution using reverse osmosis filtration. 2207.Mullett, M., et al. 2007. Removal of mercury from an alumina refinery aqueous stream. 144(1-2):

274-282.Nagpal, N., et al. 2017. A review of mercury exposure and health of dental personnel. Safety and

health at work 8(1): 1-10.Navarro, R. R., et al. 1996. Mercury removal from wastewater using porous cellulose carrier

modified with polyethyleneimine. 30(10): 2488-2494.Netzer, A. and D. J. W. R. Hughes 1984. Adsorption of copper, lead and cobalt by activated

carbon. 18(8): 927-933.Nylander, M. and J. Weiner 1991. Mercury and selenium concentrations and their interrelations in

organs from dental staff and the general population. Occupational and Environmental Medicine 48(11): 729-734.

Outridge, P. M., et al. 2018. Updated global and oceanic mercury budgets for the United Nations Global Mercury Assessment 2018. 52(20): 11466-11477.

Pacyna, E. G., et al. 2010. Global emission of mercury to the atmosphere from anthropogenic sources in 2005 and projections to 2020. Atmospheric Environment 44(20): 2487-2499.

Patterson, J. J. A. A. S. P., Ann Arbor, MI 1975. Treatment technology for phenols in wastewater treatment technology.

Pickard, B. C. J. F. F. E. J. 2003. Mercury minimization measures to meet total maximum daily load requirements. 14(1): 109-121.

Quotient, L. I. Heavy-Metal Toxicity—With Emphasis on Mercury. Integrative Medicine 6(2).Rahola, T., et al. 1971. The Elimination of 203 Hg-methylmercury in man. Scandinavian Journal

of Clinical and Laboratory Investigation 27(supplement 116): 77.Randall, J., et al. 1974. Use of bark to remove heavy metal ions from waste solutions.Reed, B. E., et al. 1994. Removal of lead and cadmium from aqueous waste streams using

granular activated carbon (GAC) columns. 13(1): 60-64.Rice, K. M., et al. 2014. Environmental mercury and its toxic effects. Journal of preventive

medicine and public health 47(2): 74.

38

Ritter, J. A., et al. 1992. Removal of mercury from waste water: large-scale performance of an ion exchange process. 25(3): 165-172.

Roberts, E. J., et al. 1973. Removal of mercury from aqueous solutions by nitrogen-containing chemically modified cotton. 7(6): 552-555.

Sahu, R., et al. 2012. Mercury Pollution in Sonbhadra District of Uttar Pradesh and its Health Impacts. Centre for science and environment 41.

Santana, A. J., et al. 2016. Removal of mercury (II) ions in aqueous solution using the peel biomass of Pachira aquatica Aubl: kinetics and adsorption equilibrium studies. 188(5): 293.

Shafeeq, A., et al. 2012. Mercury removal techniques for industrial waste water. 6: 12-26.Shukla, S. and V. J. J. o. a. p. s. Sakhardande 1991. Metal ion removal by dyed cellulosic

materials. 42(3): 829-835.Shukla, S. and V. J. J. o. A. P. S. Skhardande 1992. Column studies on metal ion removal by dyed

cellulosic materials. 44(5): 903-910.Sokol, J. 2020. New mercury compound spotted in mass poisoning, American Association for the

Advancement of Science.Somayajula, A., et al. 2013. Adsorption of mercury (II) ion from aqueous solution using low‐cost

activated carbon prepared from mango kernel. 8(1): 1-10.Sorg, T. J. J. J. A. W. W. A. 1979. Treatment technology to meet the interim primary drinking

water regulations for organics: Part 4. 71(8): 454-466.Summers, A., et al. 1993. Mercury released from dental" silver" fillings provokes an increase in

mercury-and antibiotic-resistant bacteria in oral and intestinal floras of primates. Antimicrobial agents and chemotherapy 37(4): 825-834.

Sundseth, K., et al. 2017. Global sources and pathways of mercury in the context of human health. International journal of environmental research and public health 14(1): 105.

Suzuki, T., et al. 1977. Mercury in human amniotic fluid. Scandinavian journal of work, environment & health: 32-35.

Teles de Vasconcelos, L. and C. J. E. W. P. C. Gonzalez Beca 1994. Adsorption equilibria between pine bark and several ions in aqueous solution, 2. Pb (II). 4: 41-41.

Tsubaki, T. and K. Irukayama 1977. Minamata disease. Methylmercury poisoning in Minamata and Niigata, Japan, North-Holland Publishing Company, PO Box 211, Amsterdam, The Netherlands.

Tummavuori, J. and M. J. S. Aho 1980. On the ion-exchange properties of peat. Part II: On the adsorption of alkali, earth alkali, aluminium (III), chromium (III), iron (III), silver, mercury (II) and ammonium ions to the peat. 31(4): 79-83.

UNEP, W. 2008. Guidance for identifying populations at risk from mercury exposure. Geneva: United Nations Environment Programme (UNEP), Division of Technology, Industry and Economics (DTIE), World Health Organization (WHO), Department of Food Safety, Zoonoses and Foodborne Diseases, Cluster on Health Security and Environment.

Vieira, R. S., et al. 2011. Copper, mercury and chromium adsorption on natural and crosslinked chitosan films: an XPS investigation of mechanism. 374(1-3): 108-114.

Viraraghavan, T., et al. 1993. Removal of copper, nickel and zinc from wastewater by adsorption using feat. 28(6): 1261-1276.

39

Vojdani, A., et al. 2003. Infections, toxic chemicals and dietary peptides binding to lymphocyte receptors and tissue enzymes are major instigators of autoimmunity in autism. International Journal of Immunopathology and Pharmacology 16(3): 189-199.

Von Canstein, H., et al. 1999. Removal of mercury from chloralkali electrolysis wastewater by a mercury-resistant Pseudomonas putidaStrain. 65(12): 5279-5284.

Von Muehlendahl, K. 1990. Intoxication from mercury spilled on carpets. Lancet 336(8730): 1578-1578.

Walterick Jr, G. and L. Smith 2017. optimizing mercury removal processes for industrial wastewaters.

Xu, M., et al. 2009. Study on the treatment of wastewater containing mercury by macromolecular heavy metal flocculant mercaptoacetyl polyethyleneimine. 2009 3rd International Conference on Bioinformatics and Biomedical Engineering, IEEE.

Yoshida, M. 2002. Placental to fetal transfer of mercury and fetotoxicity. The Tohoku journal of experimental medicine 196(2): 79-88.

Web Sources1. https://archive.epa.gov/greatlakes/p2/web/pdf/blueprint.pdf2 http://www.newmoa.org/prevention/topichub/22/mercury_pollution_prevention_in _healthcare_nwf.htm3. http://www.mfe.govt.nzbe4. https://www.ceicdata.com/en/indicator/india/coal-consumption5. http://www.mercuryconvention.org6. https://www.env-health.org/IMG/pdf/mercury_chapter2.pdf 

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