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349
KEYWORDS
ISSN: 0974 - 0376
NSave Nature to Survive
: Special issue, Vol. III:
www.theecoscan.inAN INTERNATIONAL QUARTERLY JOURNAL OF ENVIRONMENTAL SCIENCES
Prof. P. C. Mishra Felicitation Volume
Paper presented in
National Seminar on Ecology, Environment &Development
25 - 27 January, 2013
organised by
Deptt. of Environmental Sciences,
Sambalpur University, Sambalpur
Guest Editors: S. K. Sahu, S. K. Pattanayak and M. R. Mahananda
Ajit K. Misra et al.
Residual mercury
Mercury pollution
Chlor-alkali industry
Physico-chemical parameters
Estuary
River and plants
349 - 366; 2013
MERCURY POLLUTION IN AND AROUND A CHLOR-ALKALI
INDUSTRY: A REVIEW
350
AJIT K. MISRA1*, ALAKA SAHU2, SURYASMITA KANWAR, DEORAJ SARMA3 AND A. K. PANIGRAHI
Environmental Science Division, Department of Botany, Berhampur University,
Berhampur-760 007, Odisha. INDIA1T. T. College, Puroshattampur, Ganjam, Odisha
2R. N. College, Dura, Berhampur. Odisha3TSR and TBK College, Gajuwaka, Visakhapatnam, Andhra Pradesh
E-mail: [email protected]
INTRODUCTION
Indian industrial sector is ranked as the tenth biggest in the world in gross industrial
output. Pollution problems arising from the industries, at least in India, are partly
because of their location about 80% of her industries are concentrated in 10 or
12 big cities forming isolate pockets. Dispersal location of industries may have
helped to reduce the amount of a pollutant at a specific location. But realistically
“dilution is not the solution” as far as pollution problems are concerned (Panigrahi
and Sahu, 2012). The rapid growth of industries has resulted in the production
and use of substances some of which create health hazards. A significant amount
of these compounds (wastes) are released into the environment, affecting the
flora and fauna. Waste is defined as any gaseous, solid or liquid material that is
discarded because it has no further apparent use for the industrial manufacturer.
These wastes are pollutants cannot be eliminated but must be disposed of and
contained within the global environment. Industrial waste is in the form of gases,
solids, liquid effluents and slurries containing a range of organic and inorganic
chemicals. Industrial processes are continually changing, as new and modified
technologies are developed. Consequently products, plant and premises may
become obsolete and worn out, so causing waste disposal and dereliction
problems. In general term, solid waste can be defined as waste not transported by
water that has been rejected for further use. The chief aspect of land pollution is
basically caused by solid and semi-solid waste disposal methods, the presence of
hazardous chemicals in the environment and the despoilation and degradation
of the land surface. Hazardous wastes are those, which could be harmful to the
human health, other organisms and the environment. Many inorganic elements
as Mercury (Hg), Lead (Pb), Cadmium (Cd), and Arsenic (As) are biological poisons
at concentrations in the parts per billion (ppb) range. Once the chemicals find
their way into the environment, a major portion reaches the soil and sediment,
which in turn serve as sink. Leaching of waste chemicals discharged from the
chlor-alkali industry pose ground water contamination problems (Panigrahi and
Sahu, 2012). Plants absorb these toxic leached chemicals along with water and
other nutrients and accumulate in different tissues. These plants store chemicals
in their body and these chemicals pass through the food chain from one trophic
level to the other higher trophic level. These toxic chemicals are poorly excreted,
hence retained as residual chemicals in the body. A significant build up of the
toxic chemicals in different organs / tissues of the organisms are achieved through
the process of bioconcentration and biological magnification (Panigrahi and Sahu,
2012). Metals differ from other toxic substances in that they are neither created
nor destroyed by humans. Nevertheless, utilization by humans influences the
potential for health effects in at least two major ways. First, by environmental
transport that is by anthropogenic contributions to air, water, soil and food and
NSave Nature to Survive QUARTERLY
The study indicated that Ganjam Rushikulya
estuary and the surrounding area of Jayashree
Chemicals Pvt. Limited, a caustic soda plant
released huge amount of mercury into the
environment. Evaporated mercury from the
Mercury cell house contaminated the
surrounding biota leading to elevated mercury
levels beyond prescribed limit is the major
concern at present. The discharged mercury
in the effluent of the industry contaminated
the Rushikulya River and estuary lead to
elevated mercury level in aquatic plants and
animals. The sediment from the treatment tank
and effluent channel contained a significant
amount of mercury which was dumped in
nearby places raised the residual mercury
concentration in all types of plants (producers)
and in animals (consumers). The mercury
pollution in and around the industry a
significant problem up to 2006 was grim and
grave. But due to change in technology in the
industry, the mercury concentration declined
significantly in the effluent channel. The
decline in mercury level in water, sediment
and effluent channel, solid waste dumping site,
available plants and animals at present when
compared to earlier reports is a positive sign
for the area. But our concern rests on the
future, as all mercury discharged from the
industry ultimately entered in to Bay of Bengal
by rain run off water, by leaching from the
solid waste dumping sites, by leaching from
the effluent stocking pond near the river basin.
ABSTRACT
*Corresponding author
351
MERCURY POLLUTION AROUND CHLOR - ALKALI INDUSTRY
second, by altering the speciation or biochemical form of the
element. Human industrial activity may greatly shorten the
residence time of metals in ore, form new compounds and
greatly enhance worldwide distribution. It is estimated that
mercury or its compounds are used in at least 80 industries
and in more than 3000 different ways.
Chlor-alkali industry (one of the large source of mercury
discharge):
One of the major users of metallic mercury is the chlor-alkali
industry, in which chlorine and caustic soda (NaOH) are
simultaneously produced by the electrolysis of brine solutions
using a flowing cathode of metallic mercury. The sodium ion
(Na+) which amalgamates with mercury at the cathode is
converted to NaOH in presence of water and the released
mercury is recycled into the cell. The schematic reaction for
the Chlor-alkali process is (Bouveng, 1968) as follows:
NaCl (soln.) → Electrolysis → Cl2(anode)↑+NaHg
x (Cathode)
NaHgx →
H
2O → NaOH + Hg + ½ H
2↑
If chlorine and hydrogen are given off together, an explosive
mixture can result. So, to prevent this, mercury-sodium
amalgam is pumped into a second reaction vessel, where,
water is introduced and hydrogen and sodium hydroxide are
formed. Due to the demand of pure caustic soda (i.e. having
fewer chlorine ions) the chlor-alkali industries switched from
the use of diaphragm cell to mercury cell process. Because of
mercury’s unusual property to form an amalgam with the
reduced sodium metal derived from salt brine, the mercury
cell process results in a very pure grade of caustic soda (NaOH).
Mercury is lost in different routes, (I) solid wastes or sludges -
brine purification sludge; (ii) water; (iii) product hydrogen,
caustic; (iv) handling loss, (v) unknown losses including loss
of Hg of vapour in cell room and (vi) washing of mercury
cathode as washings. Brine mud generation is around 30kg/
tonne caustic soda in India which is more than double the
international average, indicating higher impurities in the salt.
Further, the mercury content in brine mud ranges from 2.5 to
30 mg. g-1. The quantity of Hg lost in water is fairly low but
much higher than acceptable limits for direct disposal. Thus,
among the different routes by which Hg is lost nearly 65% of
the total loss ends up in brine mud or sludge. Losses occur
due to the volatility of mercury, its presence in suspension
and solution in brine, in caustic soda, spillage during operation
and maintenance of the cells and with solid wastes from brine
purification and NaOH filtration. The caustic soda produced
by this method will contain varying amounts of mercury at
the trace level, depending on the degree of purification. There
is also a risk of secondary contamination in the environment
through the fallout of mercury around the industry as a result
of losses to the atmosphere, through the ventilation of air and
the hydrogen gas produced. The products of the industry
such as sodium hydroxide also give rise to secondary
contamination depending on their further uses.
The most significant source of mercury availability in the
environment is mostly due to the chlor-alkali industries
(Bouveng, 1968; Hortung and Dinman, 1974; Skei, 1978;
and Sahu et al., 1987; Panigrahi and Sahu, 2012). In 1969,
15-19 metric tonnes of mercury were discharged into the air
from Swedish chlor-alkali factory. Loss of mercury from the
mercury cell processes has been estimated in the order of
0.172kg for each ton. of chlorine so produced. A typical
modern 30 m2 mercury cell of a chlor-alkali industry can
contain up to 12,000 lb of Hg which is circulated in a closed
system and reused indefinitely. However, due to circumstances
of its operation, there is a loss of 150-250g of Hg per 1000kg
chlorine produced (Mitra, 1986). Mercury emissions from
chlor-alkali plants were assumed to consist mostly of Hg vapour
as elemental (metallic) mercury (Hgº) and bivalent Hg (Hg II as
HgCl2). About 65% of total chlorine production in the U. S. A.
makes use of the mercury cells process instead of diaphragm
process. Mercury cells account for over 80% of chlorine /
caustic soda production in Japan and the European countries.
In India at the beginning of 1984 the total installed capacity for
caustic soda was 9, 09, 900 tonnes per annum of which 88%
came from mercury cells and the rest from diaphragm cells. In
1983, the total quantity of caustic soda made from mercury
cells was 5, 14, 700 tonnes (64.2% of capacity). It is estimated
that the rate of mercury consumption is 394 gm per tonne of
caustic against the targeted value of 350 g Hg per tonne it is
90g Hg per tonne in industrialized countries. Pollution of
surrounding biota through the discharges of effluents and solids
wastes from chlor-alkali industries have been amply
demonstrated (Shaw et al., 1986a, b; 1989a, b; 1990). Wallin
(1976) reported that samples of the carpet forming moss
Hypnum cupressiforme from sites around six Swedish chlor-
alkali plants all contained higher mercury levels. It was highest
close to the industry and decreased with the increasing distance
from each industry. Reports of mercury dispersion and
contamination in Yatsushiro Sea (Kudo and Miyahara, 1983)
and Lake Superior region (Glass et al., 1986) are available.
Suckcharoen (1978 and 1980) reported residual mercury in
the vegetation around a caustic soda plant in Thailand. Shaw
et al. (1985, 1986a, 1988a, b and 1989a, b) reported the
residual mercury accumulation in different biotic systems
available in and around a chlor-alkali industry. Shaw et al.
(1988a, b) reported the changes in aquatic primary productivity
of the estuary contaminated with the effluent of the chlor-alkali
industry. The monitoring and assessment of mercury pollution
in the vicinity of a chlor-alkali plant has been done by Panda
et al. (1989).
Research work done on Chlor-alkali wastes
There is no doubt that chlor-alkali industries are seriously
polluting the surrounding environments. But comparatively
very few reports are available on the toxicity and toxicological
effects of chlor-alkali industrial wastes on different biotic
systems. Mishra and Misra (1984) studied the changes in
morphological behaviour of rice seedlings grown in solid waste
extract of a chlor-alkali industry. Using the same solid waste,
Mishra et al. (1985 a, b) investigated the chances of reclamation
with Blue-green algae in paddy field but no significant results
were obtained regarding decontamination of polluted
environments. Nanda et al. (1986) demonstrated the toxic
effects of the solid waste extract of a chlor-alkali industry on
the changes in pigment concentration of a crop plant,
Phaseolus aureus, Roxb. Mishra (1986) investigated the
changes in growth and morphological variables of a crop plant
exposed to saturated waste extract. Sahu et al. (1987, 1988,
1990), Shaw et al. (1988, 1989 a, b) and Sahu and Panigrahi
352
(2000) studied the toxicity of the effluent and solid waste of a
chlor-alkali industry containing mercury on different blue-
green algae and reported the toxicity of mercury at higher
concentrations and also indicated that at sub-lethal
concentrations of mercury, stimulation in growth of BGA was
noticed. Panda et al. (1989) studied the bioconcentration,
bioavailability and geno-toxicity of mercury from the solid
waste of a chlor-alkali industry. Berndt and Bavin (2012) studied
the methyl mercury and dissolved organic carbon relationships
impacted by elevated sulfate from mining. Wiener et al. (2012)
studied the risks of mercury in yellow perch a species important
in trophic transfer of methyl mercury in the Laurentian Great
Lakes region.
Industry under study (M/S Jayashree Chemicals Pvt. Ltd.,
Ganjam):
The chlor-alkali industry M/S Jayashree Chemicals Pvt. Ltd., is
situated at Ganjam, on the Bank of Rushikulya estuary about
1.5 km. Away from the sea, Bay of Bengal, on the East and 30
km. North of Berhampur city (Fig. 1 and 2) on the south-eastern
side of India at 84º53’E L and 19º16’N L. The industry was
established in 1962 and started manufacturing caustic soda,
liquid chlorine and hydrochloric acid by using a sheet of
elemental mercury as a mobile cathode for the electrolysis of
brine water (saturated sodium chloride solution) since August
1967.
In the process of manufacture of chemicals the factory
discharges the effluent containing mercury and chlorine, into
the estuary and deposits solid waste (brine mud, enriched
with mercury) on the adjacent land areas. Mercury is thus,
discharged into the environment through effluent and solid
waste routes, contaminating the adjacent aquatic and terrestrial
ecosystems, respectively. This addition of mercury is the
primary contamination. The secondary contamination occurs
through the chimney into the atmosphere and its fall out by
the process of precipitation. All these discharges collectively
seem to cause a major environmental threat to crop production
and also to fisherman engaged in fishing both in the river and
also in the estuary. So this industrial pollution affecting the
human health, agriculture and economy of the locality became
he cause of public resentment which led to the filing of a
petition on July 25, 1977 at the Rajya Sabha (the upper house
of the Parliament) by the residents of Ganjam town and
neighboring villages with an appeal for protection of human
life and environment from the industrial pollution.
Consequently, a Parliamentary Committee was formed which
after an investigation released a 20 point remedial
recommendation and felt the need of a more in-depth scientific
study of the pollution problem.
Mercury - an environmental pollutant
Mercury pollution of the environment has created some serious
hazards for mankind. As mercury has been used since ancient
times, mercury poisoning also has a long history. The most
significant incidents of the toxicity of this metal from the
scientific and epidemiological points of view have been those
in Japan in Minamata (1953-60) and Niigata (1965); these
were caused by industrial release of mercury and its
compounds into Minamata Bay and the Agano River
respectively (Fujuki, 1973; Tsubaki and Irukayama, 1977).
Again during 1971-72, the largest outbreak of methyl mercury
poisoning ever recorded occurred in Iraq as a result of
consumption of home bread prepared from wheat seed treated
with methyl mercury fungicide. Alkyl-mercury fungicide used
for seed dressings are important original sources of mercury
in terrestrial food chains (WHO, 1976). Even today the dreadful
repercussion of 1956 Minamata disease is still prevalent
among the population.
Movement of mercury in the environment
Because of its high volatility, mercury becomes dispersed over
a very large fraction of the atmosphere. It is dispersed as vapour
or as particles associated with dust, smoke, volcanic gases,
and the natural degassing of soils. Any mercury deposited
back into the soil may be revolatilised in aerobic terrestrial
environments. The high volatility of the metallic phase and of
Figures 1 and 2: Photograph showing the position of Jayashree Chemicals Pvt. limited at Ganjam, Odisha, Rushikulya estuary, Bay of Bengal
in India and a portion magnified showing the study sites at Ganjam)
AJIT K. MISRA et al.,
353
inorganic (mainly mercuric chloride) and organic compounds(mainly monomethyl or dimethyl mercury) leads to wideranging transport of mercury in air. Annually more than 8000tones of mercury are mined and processed for use in industry.Mercury is released into the atmosphere when fossil fuels areburnt and ores are roasted. Besides chemical and otherindustrial activities, agricultural and mining contribute majoramounts of mercury to the ecosystem, including land (soil),water and air, via bacterial action, a portion of this would beconverted to methyl mercury and some would be concentratedin fish. Fish eaters then accumulate mercury in their bodies.The amount of mercury in air varies with height but is often 10to 20 times greater at ground level than at 120m.The mercuryreleased can either stay close to the source for long periods orbe dispersed world wide within several weeks.
The sea water, air and also the hair of the people, of thenorthern hemisphere are found to contain greater amounts ofmercury than those in the southern hemisphere. This isbecause of the greater industrialization in the north via globalcycling mercury finally accumulates in the sea. The sea servesas the ultimate sink for mercury. However, small amounts of
mercury may be released from sea and aquatic systems by
bio-methylation and volatilization into the air and finally
become fixed in aquatic sediments. It was indicated that the
presence of a water table above mercury deposits does not
greatly reduce the rate of mercury loss by vaporization. This
suggested that land surface is the principal source of mercury
in the atmosphere. Little information is available as to the
extent of the reactions of gaseous mercury with earth materials.
Noble metals such as platinum, gold and silver readily form
amalgams with mercury. Organic matter and clays absorb
gaseous mercury and therefore the atmospheric mercury level
is continually being decreased by reaction with air borne
particulate matter and land surfaces. Some of the mercury
bound up in wet soil can be revolatilised as the soil dries,
while some may be trapped by humus material. A considerable
amount of Hg released into the atmosphere from soil and
mineralized land areas and by volcanic activity. The rate of
vaporization of mercury and its compounds follows the
patterns:
Hg > Hg2Cl
2 > HgCl
2 > HgS > Hgº
Role of biota in movement of mercury
Microbes play an important role in the movement of mercury
in nature, especially in the soil, sediments and aqueous
environments. The main result of microbial action on mercury
seems to be its volatilization, whether it involves reduction of
the mercuric ion or methyl or phenyl mercury compounds to
volatile Hgº, or whether it involves conversion of the mercuric
ion to dimethyl mercury or of the phenyl mercuric ion to
diphenyl mercury. The mercuric ion (Hg2+) may be methylated
by bacteria and fungi to give methyl mercury [(CH3) Hg+],
which is water soluble. Some bacteria may further methylate
methyl mercury and convert it to dimethyl mercury, which is
volatile and escapes into the air.
Upon weathering, mercuric sulphide (cinnabar, HgS) is
converted to mercuric sulphate and becomes disseminated in
soil and water. Bacteria, fungi, and humic acid reduce Hg2+
and cause a wider range of distribution. Methyl mercury, as
well as phenylmercury, may again be enzymatically reduced
to volatile Hgo by bacteria. This causes detoxification of soil.
Phenyl-mercury, which is usually anthropogenic in origin,
may be reduced by soil bacteria and converted to diphenyl
mercury. Biogenic H2S may convert the mercuric ion to HgS,
again under anaerobic conditions. The mercury bio-cycle is
as in the Fig. 5.
Following the application of mercury fungicides, the metal is
transferred to fruits, tubers or seeds in plants. Foliar
applications of phenyl mercuric acetate to rice resulted in the
3a 3b
Figure 3: 3a. Map of Ganjam area showing the chlor-alkali industry,
Jayashree Chemicals; 3b. Effluent stocking pond near the Rushikulya
Rive
Figure 4: Photo showing the industry (pin point), effluent channel
(triangle), three study sites in the river and one study site at the
estuary
Ph2Hg PhHg+ Hgº
Hg2+HgS
biogenic H2S
weathering
fungi
Bacteria MeHg+ MeHgBacteria H2S
chemical reaction
UV-lightBacteria
Bacteria
Figure 5: Mercury Transformation by microbes and chemical or
physical agents
MERCURY POLLUTION AROUND CHLOR - ALKALI INDUSTRY
354
transfer of mercury to the grain. Terrestrial animals accumulate
mercury mainly from their food. Birds accumulate mercury
mainly by eating seeds and grain treated with mercurial
fungicides etc. Mercury is transformed into methyl mercury,
mainly by micro-organisms, and eventually becomes
concentrated in large fish. A very limited conversion of mercury
components to methyl mercury occurs in hens. A methyl
mercury-fed hen laid eggs containing only methyl mercury.
Mercury tends to accumulate in the growing feathers, claws
and beaks of birds and all of the bodily content of mercury is
eventually deposited in feathers and other keratinous
structures.
Study Site and Sample collection at M/S. Jayashree Chemicals
Pvt. Limited at Ganjam, Odisha
Eco- toxicological effects of mercury
Toxicity is the inherent property of a chemical molecule to
produce injury on reaching a susceptible site on or in an
organism. The toxicity of a pollutant to living organisms (plants
and animals) can be evaluated by exposing a small group of
them under controlled laboratory conditions. Dose is the single
most important factor that determines the degree of injury
produced by a toxicant. Some of the possible mechanisms
through which toxic agents can impair important biochemical
processes and physiological functions in living organisms are
cell membranes, enzymes, lipid metabolism, protein
biosynthesis, microsomal enzyme systems, regulatory
processes and growth, carbohydrate metabolism and
respiration etc. (Bruin, 1976).
Eco-toxicity is the effect of toxic substances on ecosystems
which can be through a number of different ways. But in
simplest form two basic types of effect are possible. (1) Acute
lethal toxicity, over a short time period due to discharge of a
toxic substance, or treatment of an area with a toxic material
on a single occasion. (2) Chronic sub-lethal effects can occur
in an area due to exposure to sub-lethal concentrations over a
longer time period on a continuous or intermittent basis.
Assessment of the ecological impacts of toxicants are derived
from spot observations of the fields receiving different wastes,
sewage, industrial discharges or sludges containing sufficient
toxicant content to which toxicity can be assigned. Grain seeds
dressed with mercury based agrochemicals accumulate
mercury via translocation. Hens fed with crop seeds, pretreated
with mercurial compounds could concentrate the metal in
their livers and eggs. Mercury is concentrated up through the
food chain due to biological magnification amounts only slightly
above those ordinarily found in sediments, could be potentially
dangerous. The inorganic form of mercury is toxic, but it is
much more toxic in its organic form (Olson and Panigrahi,
1991). Rai et al. (1981) showed reduction in the chlorophyllcontent of Chlorella vulgaris exposed to HgCl
2. Hg increased
the length of the lag phase, during the growth of the green alga
Scenedesmus quadricauda and blue-green algae (Sahu, 1987;
Shaw, 1987). Organomercurials retard the growth and viability
of several species of marine algae more effectively than
inorganic mercury. The chronic toxicity of HgCl2, MMC
(Methylmercuric chloride) and PMA have been studied on
Daphnia magna. Panda et al. (1989) have assessed the
distribution, bio-availability, bio-concentration and
genotoxicity of mercury from some waste and sediment
deposits of a chlor-alkali plant by Allium Micronucleus (MNC)
assay. The growth, biochemical composition, Hill activity and
pigment content in different algal forms is quite prominent on
the presence of mercury (Rath et al., 1983, 1985; Mishra et
al., 1985; Shaw et al., 1989, a).Toxicity of various salts of
mercury is related to cationic mercury per se whereas solubility,
biotransformation and tissue distribution are influenced by
valency state and anionic component. Metallic or elemental
mercury volatilizes to mercury vapour at ambient air
temperature and most human exposure is by inhalation.
Bioassays for toxicity testing
A bioassay is conducted to find out the toxicity of a substance.
The laboratory bioassay technique is generally favoured
because experimental conditions can be controlled and the
response of test organisms observed or monitored to a greater
degree. Response of test organisms can be of 3 types.
(1) an acute effect; (2) a sub-acute effect and (3) a chronic
effect.
In practice, most bioassay results are expressed in terms of
acute lethal toxicity which measures certain sub-lethal
responses in test organisms over a specified period of time.
For sub-lethal measurements the results may be expressed as
the “Median effect concentration” in which 50% of the test
organisms display the response being measured. Toxicity tests
such as acute lethality tests, chronic toxicity tests for
reproduction effects and tests on bioconcentration /
bioaccumulation are useful for assessing chemical hazards to
aquatic life. So, bioassays using aquatic organisms have a
long history of use in estimating the toxicity of industrial wastes
In many bioassays, microorganisms are used because of their
rapid growth rates, easy to handle, faster production of results
and ubiquitous distribution in aquatic and terrestrial
environments. Of all aquatic life, algae offer the best possible
tool as biological indicator because (1) One can study a largenumber of individuals and species without disturbing thenatural communities; (2) Individuals are small and can easilybe collected and transported; (3) Microbial species usuallyrepresents the major productive biomass in aquatic systemsand are having extremely important characteristics. The releaseof hazardous wastes into the aquatic ecosystems produces avariety of complex responses, apart from lethality, to specificorganisms (Christman et al., 1973). Hidden injury such asinhibition of photosynthesis or alteration in oxygenconsumption most significantly affect the role that a primaryproducer plays in the phytoplankton - zooplankton - copepod- minnow - sunfish - bass, pyramid (Ammann and Terry, 1985).When the sub-lethal concentration condition exists, suddenelimination of organisms may not occur, but as growth and
reproduction of a species are affected over a period of time
the final result could well be the same. Growth and
photosynthesis are intimately related, each being a function
of the utilization of light and nutrients. Recent studies have
shown that blue-green algae alter their pigment concentrations
as a function of changes in light (Jones and Myers, 1965),
temperature and CO2 concentration (Eley, 1971). So pigment
concentration should not be considered as a reliable indicator
of cell numbers for these organisms.
Inhibition of photosynthesis and respiration in plant cells by
AJIT K. MISRA et al.,
355
solution of mercury and zinc salts has been reported (Overnell,
1975; Filippis and Pallaghy, 1976 and Rath et al., 1985).
Photosynthetic rate is a valuable indicator of energy expanded
to meet the demands of an environmental alteration.
Assessment of the photosynthetic rate of exposed algae offers
the best and most rapid method of evaluating the impact of
any toxicant or industrial wastes introduced in an aquatic
system, affecting primary producers. The effects of industrial
wastes on photosynthesis rate of algae have hardly been
reviewed. Shaw et al. (1988, 1990, 1991a, b) reported the
effect of chlor-alkali industry effluent on the oxygen evolution
rate of the blue-green algae, W. prolifica, Janet. But the present
work was designed to investigate the effect of the effluent of
the industry on the photosynthetic rate of the BGA. The
assimilation of xenobiotic chemicals within organisms at sub-
lethal or lethal levels may induce a sequence of biological
effects, ranging from molecular interference with biochemical
mechanisms to interactions with cellular organelles (e.g. DNA
and RNA molecules), through pathological changes at the
cellular, tissue and organ levels. Finally, these result in an
integrated functional or behavioral response, experienced at
the whole organism level, which may be reversible or
irreversible. So the change in biochemical profile may be
considered as an index of pollution status in the pollution
assessment. It is already an established fact that disturbances
in growth and growth substances are always related with
metabolic changes inside the plant (Levitt, 1972; Poljakoff-
Mayber and Gale, 1975). Several biochemical changes
precede any change in growth because growth is the
culmination of many biochemical processes; andphysiological and biochemical effects are the underlying causeof measurable whole organism effects. Effect of the toxicantson growth may be studied by examining the macromoleculesinvolved in growth, such as dna, rna, protein, free amino acids
(a precursor of protein) as well as glycogen which is a reserve
food in case of bga, like animals. Heavy metals specifically
mercurials have long been recognized as agents which poison
and interact with proteins in general and enzymes in particular
(Fox et al., 1975). In living cells, there are so many proteins,
polypeptides and substances belonging to other classes of
biochemical which do contain-SH groups that mercury and
mercurials would seem to affect more structures, enzymes
and co-factors than they leave unaffected. Therefore, when a
mercurial compound acts on a living cell, it is usually an
exceedingly difficult task to establish the quantitative
relationship between the primary site of action and an observed
toxic effect. Methyl-mercury is known to cause chromosomal
damage and induces hepatic protein synthesis in rats. Reactions
of proteins with mercurials were reviewed by Webb (1966).
De et al. (1985) reported that the highest dose of mercury in
the form of HgCl2 (20.0 mg/L) in Pistia stratiotes promoted
plant senescence by decreasing chlorophyll content, protein,
rna, dry wt., catalase and protease activities and by increasing
free amino acid content. Heavy metals and other chemical
agents affect the DNA, RNA and protein content of cell and
cause DNA damage, in vivo. Singh and Singh (1984) reported
decrease in the levels of DNA, RNA and protein in a blue-
green alga exposed to sodium metabisulphite. Filippis and
Pallaghy (1976) reported increase in the levels of DNA, RNA
and protein in Chlorella treated with HgCl2. DNA and RNA
synthesis in intact cells were inhibited by MeHg. But during
the study of nucleic acid synthesis in vitro in isolated nuclei, it
was found that MeHg specifically stimulated RNA synthesis
by RNA polymerase II but inhibited RNA synthesis catalyzed
by polymerase I and III, as well as DNA synthesis.
The alteration in the enzyme activity can serve as a sensitive
index of pollution, as the xenobiotic agents affect several
systems. The abnormal enzymatic disorders always result in
abnormal biochemical change. In general toxic chemicals,
attack the active sites of enzymes, inhibiting essential enzyme
function. Heavy metal ions, in particular, Hg2+, Pb2+ and Cd2+
act as effective enzyme inhibitors. They have affinity for
sulphur containing ligands (-SH). The mercurials occupy a
special niche in the subject of enzyme inhibition. They are
useful for demonstrating the presence of SH groups in enzyme
reactions, but lack specificity towards particular enzymes or
classes of enzymes. Since so many enzymes contain reactive
-SH groups at or near the active center, the mercurials would
seem to inhibit more enzymes than they leave unaffected.
When mercurial acts on living cells, one cannot state which
enzymes are affected most readily (Webb, 1966). Within cells,
mercury may bind to a variety of enzyme systems, including
those of microsomes and mitochondria producing non-
specific cell injury or cell death. Complexes between Hg2+
and certain purines and pyrimidines, especially thymine, are
quite stable. It is widely believed that active transport processes
in biological membranes are driven by the energy, stores in
ATP and released by the activity of ATPase. It has been
reported that a significant depression of Na+, K+ -ATPase is
associated with excessive absorption of mercury (Panigrahi
and Misra, 1978a, b; 1980; Sahu et al., 1987, 88, 90). Mercuric
ions and their organic derivatives serve as probes in
investigations of membrane transport, when they are used to
block carrier sites. ATP can be used as a measure of living
phytoplankton carbon in the aquatic system. De et al. (1985)
reported that the highest dose of Hg (20.0 mg/L) in the form of
HgCl2 promoted plant senescence by decreasing chlorophyll
content, protein, RNA, dry wt., catalase and protease activities.
Microbial ecosystems can drastically alter the fate of metals in
the lithosphere or hydrosphere. Bacteria and fungi can alter
the valency state of the metal via methylation, chelation,
complexation, absorption, oxidation and reduction. Thus,
microorganisms affect the bioavailability and dispersion of
metals in both aquatic and soil ecosystems; ultimately
influencing the movement of the metals into and up the food
chain. The existence and significance of atmospheric transport
and dispersion of Hg as well as its deposition to the ecosystem
has been documented over many years. In comparison to the
concepts of aerial transport and deposition of Hg, the notion
of re-emission of this contaminant from environmental surfaces,
such as water, soil and vegetation is of more recent origin. The
first information gathered on microbial alteration of mercurial
compounds was based on observations of decreased biocidal
properties of Hg containing fungicides in both aquatic and
soil environments. Mercuric ion is volatilized from the soil or
the sediment and these volatile forms enter the atmosphere or
the water column. When uptake of a toxic substance occurs,
microorganisms are frequently able to perform detoxification,
thereby yielding a product that can be more toxic to higher
MERCURY POLLUTION AROUND CHLOR - ALKALI INDUSTRY
356
AJIT K. MISRA et al.,
organisms. It is true for the bacteria production of methyl
mercury, which may be regarded as a means of resistance
against mercurials by conversion to an organic form and
subsequent secretion. It thus appears that microorganisms do
not require mercury, but rather deal with it when present in
their food supply. The ability to transform mercury compounds
is not restricted to a small group of microorganisms; aerobic
and anaerobic bacteria, as well as fungi, but on the basis of
numerous laboratory experiments (supported by a rather
limited number of in situ field measurements strong evidence
exists for volatilization of Hg from a large variety of vascular
plants, leguminous seeds, non-vascular plants such as lichens
and mosses, algae, phytoplankton, the oceanic surface, at least
in biologically productive, up-welling equatorial locations,
various types of mercuriferous and non-mercuriferous soils
(Lindberg et al., 1979) and Hg-containing solid waste deposits.
Objective of the review
The present review was designed to discuss the impact and
fate of mercury in the effluent discharged from the chlor-alkali
industry. The present review focuses on the mercury pollution
problem at Ganjam and Rushikulya estuary of Bay of Bengal.
Aquatic and terrestrial contamination
The effluent which when released from the factory finds its
way into the Rushikulya river estuary, was found to contain
very high amount of mercury (Table 1). Out of twelve analyses
carried out in twelve months, only once, in the month of
March, a lower concentration of mercury (0.0268 mg 1-1) was
observed. Though the concentration in March was low, the
value was in itself much higher than the permissible limit of
0.01 mg 1-1. Maximum concentration of mercury, as recorded
in the month of January, was to the tune of 1.5487 mg 1-1.
Concentration of mercury in the effluent was found to be much
Plants around the industry Sample size Mean Mercury level,
mg.g-1 dry weight
1986 2010 1986 2010
Cynodon dactylon 11 15 14.83±2.12 22.6±4.5
Cyperus rotundus 17 16 25.17±2.61 28.3±4.9
Eragrostis ciliata 17 22 15.77±3.11 18.1±3.2
Ipomoea digitata 14 18 7.9±0.85 14.2±5.4
Lippia nodiflora 15 18 40.17±3.25 42.6±6.5
Pandanus odoratissimus 17 14 3.57±0.66 11.6±2.8
Plants around the solid waste deposits
Plants Sample size Mean Mercury level
1986 2010 1986 2010
Jatropha gossypifolia 12 19 19.7±3.91 24.6±8.2
Justicia simplex 15 22 13.83±2.87 17.93.4
Calotropis procera 12 18 9.73±1.42 14.32.6
Acalypha indica 14 16 5.33±1.01 7.8±1.8
Amaranthus spinosus 18 15 4.08±0.85 4.9±0.8
Mimosa pudica 17 14 4.00±0.91 5.6±1.2
Croton sparsiflorus 25 18 2.17±0.22 4.9±0.7
Amaranthus viridis 14 12 2.13±0.31 5.2±1.1
Azadirachta indica 17 11 1.87±0.28 4.9±0.8
Argemone mexicana 20 16 1.32±0.19 5.4±0.7
Boerhaavia repens 18 21 1.23±0.09 3.6±0.9
Plants from the nearby populated localities
Amaranthus spinosus 18 14 2.12±0.14 3.45±0.8
Solanum melongena 8 12 1.58±0.22 2.66±0.5
Hibiscus sabdariffa 17 14 1.13±0.14 2.55±0.4
Luffa cylindrica 10 15 0.90±0.31 1.84±0.3
Zizyphus jujuba 13 18 0.82±0.26 1.92±0.4
Vigna sinensis 11 17 0.82±0.18 0.96±0.3
Azadirachta indica 16 16 0.76±0.19 0.82±0.2
Ocimum basillicum 9 12 0.74±0.17 0.81±0.3
Justicia simplex 11 14 0.71±0.11 0.63±0.2
Phaseolus vulgaris 15 9 0.58±0.21 0.44±0.1
Dolichos lablab 8 11 0.58±0.32 1.23±0.5
Phaseolus mungo 12 9 0.58±0.19 1.86±0.4
Acalypha indica 8 6 0.58±0.12 0.66±0.2
Euphorbia prostrata 10 12 0.56±0.09 0.540.4
Psidium guayava 14 13 0.54±0.02 2.911.4
Momordica charantia 15 20 0.54±0.11 1.540.8
Cucurbita maxima 15 20 0.42±0.06 1.310.7
Oryza sativa 12 25 0.42±0.04 2.120.8
Croton sparsiflorus 12 14 0.38±0.01 0.850.2
Table 2: Residual mercury level (mg kg -1 dry wt) in different plant
species collected from the contaminated area within 1 km radius of
the factory. Data are mean of samples±standard deviation
fluctuating having a mean value of 0.4474 ± 0.0426 mg 1-1 in
1986. In 1996, the value depleted to 0.3894±0.0258 mg.L-1,
where 12.96% decrease was recorded. Out of the four stations
selected for studying mercury dynamics in the estuary, station
II, which is the junction point was found to be having the
highest amount of mercury in comparison to other stations.
The range was 0.0176 mg 1-1 in the month of March to 0.4838
mg 1-1 in the month of February with a mean value of 0.1690
± 0.1536 mg 1-1 (Table 1). Mercury levels at this station were
found to be dependent on the levels of mercury in the effluent
to some extent except in the month of January in 1986. In
1996, the mean mercury level increased by 1.42% and
0.1714±0.0844 mg of Hg. L-1 was recorded (Table 1). Levels
of mercury at other stations were lower in comparison to station
II. Out of the three stations, station IV was found to contain the
lowest amounts of mercury (Table 1). Levels of mercury at
station I and III were nearly identical with a tendency of little
Stations Mean ± S.D. (1986) Mean ± S.D. (1996) % change
Water (mg of Hg. L-1)
I 0.0374 ± 0.0359 0.0321 ± 0.0217 -14.17
II 0.1690 ± 0.1536 0.1714 ± 0.0844 ±01.42
III 0.0346 ± 0.0315 0.0380 ± 0.0118 ±09.80
IV 0.0273 ± 0.0269 0.0133 ± 0.0035 -51.28
E 0.4474 ± 0.0426 0.3894 ± 0.0258 -12.96
Sediments (mg of Hg. Kg-1 dry weight )
I 0.98±0.81 1.16±0.64 +18.37
II 369.25±169.19 288.44±65.88 -21.89
III 0.96±0.68 2.26±0.35 +135.42
IV 0.78±0.60 1.05±0.28 +34.62
E 929.39±405.23 658.32±64.58 -29.17
Water (mg of Hg. L-1 )
I 0.0321±0.0217 0.0211±0.0112 -34.26
II 0.1714±0.0844 0.0952±0.0234 -44.45
III 0.0380±0.0118 0.0214±0.0119 -43.68
IV 0.0133±0.0035 0.0096±0.0024 -27.81
E 0.3894±0.0258 0.1128±0.0542 -71.03
Sediments (mg of Hg. Kg-1 dry weight )
I 1.16±0.64 0.74±0.32 -36.21
II 288.44±65.88 132.85±18.36 -53.94
III 2.26±0.35 1.08±0.24 -52.21
IV 1.05±0.28 1.35±0.34 +28.57
E 658.32±64.58 486.54±38.19 -26.09
Table 1: Mercury concentration in water and sediment at different
stations in 1986, 1996 and 2006 and percent change of mercury
when compared to 1986 and1996 value
357
When compared to 1996 mercury levels, in 2006, at Station-
I- 34.26% decrease; in station-II-44.45% decrease, in station-
III-43.68% decrease, in station-IV- 27.81% decrease and in
the effluent channel, Station-E, 71.03% decrease in mercury
level was recorded. The significant decrease in mercury
concentration in all the 5 sites was probably due to the change
of technology from Electrolytic cell process to Diaphragm
process by the industry. Sediment analysis showed the
presence of a remarkable quantity of mercury (Table 1).
Maximum amount of mercury was found in the sediment from
the effluent channel. The levels of mercury fluctuated much,
the maximum being 2053.3 mg kg-1 dry wt in the month of
July and the minimum 456.67 mg kg-1 dry wt in the month of
Season Solid waste deposit area Station Direction I Direction II Direction III Means for each station
along different direction
Pre- monsoon 87.08± 6.93 a 19.58±1.24 12.28±1.58 11.76±0.89 14.54
b 2.48± 0.14 2.78±0.26 1.28±0.04 2.18
c 0.58± 0.18 0.48±0.04 0.39±0.04 0.48
Monsoon 77.06±1.58 a 12.67± 0.26 6.67±0.36 7.76±0.38 9.03
b 2.28± 0.06 1.98±0.04 0.98±0.15 1.75
c 0.54± 0.04 0.55±0.07 0.41±0.03 0.50
Post-monsoon 90.12±5.78 a 15.81± 0.96 8.28±0.26 10.78±0.39 11.62
b 2.68± 0.04 2.18±0.06 1.01±0.08 1.96
c 0.56± 0.04 0.63±0.13 0.31±0.03 0.50
Table 3: Residual mercury level in the Cynodon dactylon samples (mg kg-1 dry wt) collected along different directions and in different seasons
from the area within 2 km radius of the factory (Shaw et al., 1986 a, b and Sahu, 1987)
Name of the Plant Soil Root Stem Leaf Fruit
Croton sparsiflorus 1 610.00±17.32 4.61± 0.11 5.00± 0.25 24.03± 0.35 3.15± 0.16
2 576.67±11.55 3.52± 0.06 4.6± 0.26 18.03± 0.23 2.16± 0.08
3 660.00±14.25 7.4± 0.45 10.43± 0.23 27.9± 0.2 3.52± 0.03
4 613.33±11.55 2.48± 0.06 3.42± 0.13 15.43± 0.12 1.14± 0.06
5 2.13± 0.25 1.55± 0.15 2.93± 0.14 2.32± 0.14 0.39± 0.07
Jatropha gossypifolia 1 82.67±5.77 10.07±0.25 16.33± 0.29 18.25± 0.26
2 12.17±1.33 0.97± 0.03 1.38± 0.06 2.32± 0.14
3 503.33±25.17 8.85± 0.14 12.37±0.29 14.38± 0.41
4 9.02± 0.52 1.78± 0.13 1.28± 0.21 2.88± 0.06
Ipomoea digitata 1 288.67±5.77 4.6± 0.26 2.12± 0.20 7.07± 0.14
2 202.00±5.00 15.07± 0.51 4.62± 0.20 19.87± 0.91
3 210.28± 3.80 13.18± 0.41 3.18± 0.18 17.06± 0.7
Argemone mexicana 1 5.2± 0.17 3.92±0.13 3.82± 0.41 4.27± 0.23 3.82 ± 0.4
2 3.87± 0.12 3.02± 0.14 3.02± 0.14 3.44± 0.13 2.77± 0.14
3 4.60± 0.11 3.42± 0.10 3.25± 0.22 4.15± 0.19 3.05± 0.14
Calotropis procera 1 893.33±11.55 15.07± 0.50 10.7± 0.36 38.83±1.44
2 130.00± 5.2 3.33± 0.06 2.43± 0.14 14.73±0.25
3 210.00± 8.45 7.67± 0.41 3.84± 0.09 23.24± 0.89
Table 5: Levels of mercury in the soil and root, stem, leaf and fruit of the plants at different sites (Conc. of Hg in mg kg-1 dry wt.). Data
presented, Means of five samples±standard deviation. (Shaw et al., 1986 a, b and Sahu, 1987)
higher levels at station I than at station III, except in the month
of April when the value was less than at station III. No particular
trend of increase or decrease in the levels of mercury was
noted at any of the station. However, all the three stations
showed their minimum and maximum levels in the monsoon
and pre-monsoon seasons, respectively. The levels of mercury
during monsoon season at these stations were much less and
very similar to each other. The trend of decrease or increase in
the levels of mercury was also similar. When compared to
1986 mercury levels, in 1996, at Station-I, 14.17% decrease;
in station-II,1.42% increase in station-III,9.8% increase in
station-IV, 51.28% decrease and in the effluent channel,
Station-E, 12.96% decrease in mercury level was recorded.
Table 4: Mercury level in the soil samples (mg kg-1 dry wt) collected along different directions and in different seasons from the area within
2km radius of the factory. (Data presented, Mean of five samples ±standard deviation. Station- a, b and c are stations at ½ km, 1km and 2km
distance from the industry respectively.) (Shaw et al., 1986 a, b and Sahu, 1987)
Season Solid waste deposit area station Direction - I Direction -II Direction -III Means for each station
along different direction
Pre- monsoon 610.98 ± 30.98 a 70.28±5.98 48.99±3.96 45.28 ±2.98 54.85± 13.49
b 5.92±1.02 4.98±0.98 4.91 ± 0.86 5.27±0.56
c 0.78±0.10.04 0.68±0.13 0.58 ±0.09 0.71±0.15
Monsoon 599.96 ± 12.89 a 25.98±3.88 10.90±1.09 9.96 ± 0.98 15.61±8.99
b 2.20±0.04 0.98 ±0.04 1.02 ±0.09 1.40 ±0.69
c 0.62±0.04 0.56 ±0.04 0.46 ± 0.02 0.55 ±0.08
Post-monsoon 640.28 ± 33.09 a 60.86±6.10 38.68 ±4.21 44.78 ±3.28 48.11 ± 11.46
b 6.98±0.96 5.21 ±1.02 3.98 ±0.88 5.39 ±1.51
c 0.71±0.08 0.71 ±0.09 0.62 ±0.04 0.68 ±0.05
MERCURY POLLUTION AROUND CHLOR - ALKALI INDUSTRY
358
Table 6: Levels of mercury in the soil and root, stem, leaf and fruit of
the plants (fresh wt. basis) at different sites (Conc. of Hg in mg kg-1
dry wt.). Data presented, Means of five samples ± standard
deviation. (Shaw et al., 1986 a, b and Sahu, 1987)
Name of the Plant Conc. of mercury in mg / kg fresh wt.
(For soil, it is kg dry wt.)
Soil Root Stem Leaf Fruit
Croton sparsiflorus 1 610.00 2.62 3.05 6.63 1.04
2 576.67 1.98 2.80 4.98 0.71
3 660.00 4.17 6.36 7.7 1.15
4 613.33 1.40 2.08 4.26 0.39
5 2.13 0.87 1.79 0.64 0.13
Jatropha gossypifolia 1 82.67 2.17 3.33 3.98 -
2 12.17 0.21 0.28 0.51 -
3 503.33 1.91 2.52 3.13 -
4 9.20 0.38 0.26 0.63 -
Ipomoea digitata 1 288.67 1.77 0.72 2.28 -
2 202.00 5.79 1.56 6.42 -
3 212.28 5.07 1.22 5.51 -
Argemone mexicana 1 5.20 0.94 0.75 1.24 1.04
2 3.87 0.74 0.60 1.01 0.76
3 4.60 0.87 0.64 1.20 0.83
Calotropis procera 1 893.33 4.93 1.95 4.95 -
2 130.00 1.09 0.44 1.88 -
3 210.00 2.51 0.70 2.96 -
Root Stem Leaf Fruit
Croton sparsiflorus
Soil 0.649NS 0.514NS 0.900 0.754NS
(p ∠ 0.050)
Root - 0.967 0.895 0.929
(p∠0.010) (p∠0.050) (p∠0.010)
Stem - - 0.771NS 0.806NS
Leaf - - - 0.960
(p∠0.010)
Jatropha gossypifolia
Soil 0.606NS 0.521NS 0.533NS -
Root - 0.992 0.995 -
(p∠0.001) (p∠0.001)
Stem - - 0.999 -
(p∠0.001)
Ipomoea digitata
Soil -0.998 -0.875NS -0.995 -
(p∠0.010) (p∠0.010)
Root - 0.904NS 0.999 -
(p∠0.001)
Stem - - 0.921NS -
Root Stem Leaf Fruit
Argemone mexicana
Soil 0.993 0.956 0.947NS 0.949NS
(p∠0.010) (p∠0.050)
Root - 0.984 0.901NS 0.980
(p∠0.050) (p∠0.050)
Stem - - 0.811NS 1.000
(p∠0.001)
Leaf - - - 0.790NS
Calotropis procera
Soil 0.961 0.998 0.966 -
(p∠0.050) (p∠0.010) (p∠0.050)
Root - 0.977 1.000 -
(p∠0.050) (p∠0.001)
Stem - - 0.981 -
(p∠0.050)
Table 7: Matrices showing correlation coefficients (r) between mercury
concentration in soil and different plant tissues (dry wt. Basis). P =
Level of significance, NS= Not significant. (Shaw et al., 1986 a, b
and Sahu, 1987)January. The mean mercury value was 929.39 ± 405.23 (Table
1). Out of the four stations of the estuary, station II was the site
of maximum mercury contamination similar to that of water
(Table 1). Here also the concentration of mercury fluctuated
much. Mean value was 369.25 mg kg-1 dry wt (Table 1). No
particular trend of increase or decrease was marked. However,
lower concentrations of mercury were observed in the
monsoon and the post monsoon seasons, i.e., from June to
December. No relationship could be noticed between the
concentration of mercury in sediment of this site and that of
the effluent channel. Unlike water samples, levels of mercury
were slightly higher at station I than at station III. When
compared to 1986 mercury levels, in 1996 in station-I,18.37%
increase; in station-II, 21.89% decrease; in station-III,135.42%
increase; in station-IV,34.62% increase and in the effluent
channel, station-E, 29.17% decrease in mercury concentration
was recorded. Within 10 years time (1986-1996), significant
increase in mercury level was recorded in station- II and III
and sediment mercury level in station-I, III and IV (Table 1).
When compared to 1996 mercury levels, in 2006 in station-I-
36.21% decrease; in station-II- 53.94% decrease; in station-
III-52.21% decrease; in station-IV-28.57% increase and in the
effluent channel, station-E- 26.09% decrease in mercury
concentration was recorded. The significant decrease in the
sediment mercury concentration was mostly due to periodic
removal of sediments from the effluent channel and dumping
them in the Rushikulya river estuary and due to the change in
technology by the industry, where mercury was no more used.
The decrease in mercury concentration in the effluent channel
was due to periodic removal of sediments from the channel
and dumping the wastes in a nearby site. No particular trend
of increase or decrease in the mercury concentration was
noticed at any station during the entire period. However, the
levels of mercury were lower in the monsoon and the post
monsoon season at all the three stations. While studying the
total mercury distribution in the Rushikulya River and estuarine
bed and estuary, the highest level (1043.33 mg kg-1 dry wt) of
mercury was marked in the sediment from the effluent channel.
This was followed by the sediment zone, the lowest samples
from the junction zone. The lowest concentration of mercury
at upstream was 0.03 mg kg-1 dry wt in 1986, 0.02 mg kg-1 dry
wt in 1996 and 0.01 mg kg-1 dry wt in 2006, whereas at down
stream, at a similar distance from the junction concentration
was 0.28 mg kg-1 dry wt in 1996 and 0.12 mg kg-1 dry wt in
2006. The observations in 2006 were significantly less than
1996 and 1986 values. The depletion in mercury level was
probably due to recycling technology adopted by the industry
by way of effluent treatment by chemical and biological
methods and by change in technology. Concentrations of
mercury in the samples collected from the middle region of
the estuary were always higher in comparison to the samples
collected from the bank regions at the same distance from the
junction.
The plant species collected from the contaminated area during
1986 and 2010 were analyzed for residual mercury
accumulation. Table 2 shows the comparative account of
residual mercury retention/ accumulation. The data revealed
AJIT K. MISRA et al.,
359
Table 8: Matrices showing correlation coefficients (r) between mercury
concentration in soil and different plant tissues (fresh wt. Basis) P =
Level of significance, NS= Not significant. (Shaw et al., 1986 a, b
and Sahu, 1987)
Root Stem Leaf Fruit
Croton sparsiflorus
Soil 0.652NS 0.513NS 0.900 0.756NS
(p∠0.050)
Root - 0.965 0.897 0.928
(p∠0.010) (p∠0.050) (p∠0.010)
Stem - - 0.770NS 0.801NS
Leaf - - - 0.960
(p∠0.010)
Jatropha gossypifolia
Soil 0.607NS 0.520NS 0.531NS -
Root - 0.992 0.995 -
(p∠0.001) (p∠0.001)
Stem - - 0.999 -
(p∠0.001)
Ipomoea digitata
Soil -0.998 -0.954 -0.975 -
(p∠0.010) (p∠0.050) (p∠0.050)
Root - 0.970 0.999 -
(p∠0.050) (p∠0.001)
Stem - - 0.979 -
(p∠0.050)
Argemone mexicana
Soil 0.991 0.949NS 0.954 0.944NS
(p∠0.01) (p∠0.050)
Root - 0.899 0.986 0.891NS
(p∠0.050)
Stem - - 0.812NS 1.00
(p∠0.001)
Leaf - - - 0.801NS
Calotropis procera
Soil 0.961 0.998 0.967 -
(p∠0.050) (p∠0.010) (p∠0.050)
Root - 0.977 1.000 -
(p∠0.050) (p∠0.001)
Stem - - 0.982 -
(p∠0.050)
Name of the Plant Conc. of Hg in mg kg-1 dry wt., 1987
Croton sparsiflorus 0.012
Jatropha gossypifolia 0.014
Ipomoea digitata 0.011
Argemone mexicana 0.004
Calotropis procera 0.004
Table 9: Natural background levels of mercury in some plant species
under study
Data presented are the mean of three samples
Name of the species Sample size Concentration of mercury in mg kg-1 wet wt
Blood Liver Muscle Brain
Domestic Goat (Capra hircus) 7 9.15 4.16 34.25± 11.35 2.86± 0.96 2.81 ± 0.44
Red sheep (Ovis orientalis) 7 8.24 ± 3.26 26.14 ± 8.52 2.91±0.86 3.11 ± 0.91
Table 10: Residual mercury level in some animal samples collected from the contaminated area. (Shaw et al., 1986 a, b and Sahu, 1987)
Table 11: Analysis of variance for total mercury content of the water at different stations along the Rushikulya River estuary (Shaw et al., 1986
a, b and Sahu, 1987)
Source of variation degree of Freedom Mean Squares F ratio LSD at p ≤p ≤ 0.001 0.010 0.050
Stations 3 0.06 6.00 0.010 - 0.11 0.08
Months 11 0.01 1.00 NS - - -
Residual 33 0.01 - - - - -
Total 47 - - - - - -
significant amount of mercury in their body. It was observed
that the plants collected from the solid waste dumping site
and in and around the effluent channel showed highest amount
of mercury accumulation. The values of 2010 were much
higher than 1986 values. This increase indicated that with
time, growth and age of the plant, residual mercury significantly
increased pointing at biomagnification of mercury in the plant
system (Table 2). It was alarming to note that significant amount
residual mercury was available in plants grazed by herbivores.
The herbivores accumulated significant amount of mercury
in their body which ultimately comes from the grazed plants
available in the contaminated sites. Insignificant amount of
residual mercury was recorded in the plants collected from
the nearby populated localities of the industry. The amount
may be insignificant but the very presence of mercury in those
plants is interesting and draws the attention of ecologists.
Cynodon dactylon was collected from three different directions
from the industry (I, II, III) and from ½ (a), 1(b), 2(c) km distance
from the factory. Station-a showed the highest concentration
of residual mercury, when compared to station-b and c. Station-
c situated at a distance of 2km showed the lowest amount of
residual mercury in Cynodon dactylon. The values clearly
indicated that the industry is the origin of mercury and with
increase in distance the amount of residual mercury decreases
significantly (Table 3). The availability of mercury in direction-
I, II and III (a, b, c) was probably due to the mercury volatilized
in the Cell house of the industry carried by wind and dispersed
in all the three directions. The residual mercury availability in
Cynodon dactylon was also strongly seasonal (Table 3). This
particular grass was of interest only because the grass was
available in all the stations and in all the directions.
Data presented, Mean of five samples ± standard deviation. a,
b and c are stations at ½ km, 1 km and 2 km respectively.
The table also indicated the fluctuation of residual mercury
concentration in the solid waste in different monsoon periods
(Table 3). The values presented in Table 3 were significant, as
this grass is generally grazed by all the grazers. Table 4 showed
the mercury level in the soil samples (mg kg-1 dry wt) collected
along different directions and in different seasons from the
area within 2km radius of the factory. The Table 4 indicated
the mercury concentration in the solid waste deposit in different
monsoon periods. This table was important as the select grass
was collected from these sites, where solid waste was
deposited. The residual accumulation of mercury in different
plants was only due to the mercury absorbed from the solid
MERCURY POLLUTION AROUND CHLOR - ALKALI INDUSTRY
360
waste deposit area. As the soil is rich in mercury concentration,
we may practically expect high mercury values in plants
growing in these sites.
All the plants collected showed the presence of an
objectionable amount of mercury in their tissues (Table 2).
Maximum amount of mercury was found in the plants
collected from the areas of solid waste deposits. A significant
amount of mercury, 19.07 mg kg-1 dry wt. was found in Jatropha
gossypifolia. A minimum tissue concentration of 1.23 mg kg-1
dry wt. was found in Boerhaavia repens. Plants collected from
the nearby populated localities showed decreasing
concentrations of mercury. The levels of mercury ranged from
2.12 mg kg-1 dry wt. as in Amaranthus spinosus to 0.38 mg kg-
1 dry wt. as in Croton sparsiflorus. Some economically
important plants used as daily food, such as L. cylindrica,
Dolichos lablab, Oryza sativa etc. also showed a remarkable
accumulation of mercury in their tissues.
Geographical distribution of mercury
Tables 3 and 4 represent the levels of mercury in Cynodon
and soil samples collected in and around the factory.
Concentrations of mercury in both the soil and the Cynodon
samples were remarkably high. Samples of the soil collected
from the area of solid waste deposit showed mercury
concentration as high as 640.28 mg kg-1 dry wt, where as the
Cynodon samples showed a maximum value of 90.12 mg kg-
1 dry wt. Concentrations of mercury in both the cases declined,
rather abruptly, with increase in distance from the factory.
Deposition of mercury was higher in direction I then the other
directions. Levels of mercury declined in the monsoon season,
particularly the stations located closer to the industry were
affected. Decline in the mercury levels at Station ‘c’ was not
pronounced during the monsoon season, rather Cynodon
samples showed higher accumulation during the monsoon
and post-monsoon seasons.
Absorption and tissue distribution
Results obtained in this study are presented in Tables 5 - 8.
Table 5 represents the residual Hg levels in mg kg-1 dry wt,
whereas Table 6 represents the values in fresh wt. Tables 7
and 8 represent the correlation coefficient values for the soil
vs root, stem and leaf mercury concentrations and for the inter
tissue mercury concentrations, separately for each plant species
analysed on the basis of dry wt and fresh wt., respectively. No
definite relationship between the concentration of mercury in
the soil and the amount of mercury in different tissues of the
plant was marked. Even negative correlation between soil and
different tissues were observed in case of Ipomoea digitata
(Table 7 and 8). However, in some cases highly significant
correlation values were obtained as in C. procera. The values
were r = 0.961 (p ∠ 0.050) for soil vs root, r = 0.998 (p ∠
0.010) for soil vs stem and r = 0.966 (p ∠ 0.50) for all vs leaf
(Table 2.6). Correlation values were also similar for fresh weight
conversion except for soil vs leaf where it was r = 0.967
(Table 8).
Concentration of mercury in the root tissue of Croton was
found to be 1.55 mg kg-1 dry wt (0.67 mg kg-1 fresh wt) when
the soil mercury concentration was 2.13 mg kg-1, however, in
the same species the root tissue mercury concentration of
only 7.4 mg kg-1, dry wt (4.17 mg kg-1 fresh wt) was noted even
though the mercury level in the soil was many times more
(660 mg kg-1 dry wt). Besides, in some cases a negative trend
was marked, i.e. when the soil mercury concentration was
more, concentration of mercury in root and other tissues were
less or vice-versa as in Jatropha and Ipomoea. In Jatropha
when the soil mercury concentration was 9.2 and 12.17 mg
kg-1 dry wt, the root tissue mercury concentration were 1.78
and 0.97 mg kg-1 dry wt. (0.38 and 0.21 mg kg-1 fresh wt),
respectively. Similarly, when the soil mercury concentrations
were 82.67 and 503.33 mg kg-1 dry wt, the root tissue mercury
concentration recorded were 10.07 and 8.85 mg kg-1 dry wt.
Ipomoea showed highly significant negative correlation value
(r = -0.998) on dry wt. as well as on fresh wt. basis. In Argemone
correlation between the soil mercury concentrations and
concentrations of mercury in different tissues were highly
significant. Though concentrations of mercury in the soil were
very low the absorption and accumulation were very high,
comparatively. This is evident from the fact that when the soilmercury concentration were 5.2, 4.6 and 3.87 mg kg -1 drywt., the root mercury concentrations were 3.92, 3.42 and3.02 mg kg-1 dry wt (or 0.94, 0.87 and 0.74 mg kg-1 fresh wt),respectively. In general, relationship between the concentrationof mercury in soil and its accumulation in plant tissue appearto be much fluctuating. Relationship between the mercuryconcentrations of root and stem as well of other tissues, suchas leaf and fruit, were high significant. In Calotropis therelationship was remarkably significant (r =1.000, p∠ 0.001).One thing of importance to note is that the concentrations ofmercury in the root were always less in comparison to leaf,but when compared to stem the concentration were less inCroton and Jatropha whereas more in Ipomoea, Argemoneand Calotropis. Relationship between stem and leaf as well asbetween stem and fruit with respect to mercury concentrationswere found to be appreciably high with significant correlationvalue (p∠ 0.050) in majority of the cases. No correlation existedfor stem vs. leaf mercury concentration in Croton and inArgemone. From the results it can be said that stem tends toaccumulate less mercury than leaf. However, the amount ofmercury was always higher in stem than in fruit. Theaccumulation of mercury in leaf was much more significant
than in other tissues. A highly significant correlation was noted
between leaf and fruit in Croton (p∠ 0.010) with respect to
AJIT K. MISRA et al.,
Table 12: Analysis of variance for total mercury content of the sediment at different stations along the Rushikulya river estuary (Shaw et al.,
1986 a, b and Sahu, 1987)
p = Level of significance; LSD = Least significant difference; NS= Not significant
Source of variation Degree of Freedom Mean Squares F ratio p< LSD at p<
0.001 0.010 0.050
Stations 3 99133.33 10.85 0.001 138.55 105.38 78.84
Months 11 9136.36 1.00 NS - - -
Residual 33 9139.39 - - - - -
Total 47 - - - - - -
361
accumulation of mercury, both on fresh and dry wt. basis,
however, similar result was not marked in Argemone. The
level of accumulation in fruit was appreciable in comparison
to root and stem accumulation.
The effluent which when released from the factory finds its
way into the Rushikulya river estuary, was found to contain
very high amount of mercury (Table 11). Out of twelve analyses
carried out in twelve months, only once, in the month of
March, a lower concentration of mercury (0.0268 mg 1-1) was
observed. Though the concentration in march was low, the
value was in itself much higher than the permissible limit of
0.01 mg 1-1. maximum concentration of mercury, as recorded
in the month of January, was to the tune of 1.5487 mg 1-1.
Concentration of mercury in the effluent was found to be much
fluctuating having a mean value of 0.4474 ± 0.4466 mg 1-1.
Out of the four stations selected for studying mercury dynamics
in the estuary, station II, which is the junction point was found
to be having the highest amount of mercury in comparison to
other stations. The range was 0.0176 mg 1-1 in the month of
March to 0.4838 mg 1-1 in the month of February with a mean
value of 0.1690 ± 0.1536 mg 1-1. Mercury levels at this station
were found to be dependent on the levels of mercury in the
effluent to some extent except in the month of January. Levels
of mercury at other stations were lower in comparison to station
II. Out of the three stations, station IV was found to contain the
lowest amounts of mercury. Levels of mercury at station I and
III were nearly identical with a tendency of little higher levels at
station I than at station III, except in the month of April when
the value was less than at station III. No particular trend of
increase or decrease in the levels of mercury was noted at any
of the station. However, all the three stations showed their
minimum and maximum levels in the monsoon and pre-
monsoon seasons, respectively. The levels of mercury during
monsoon season at these stations were much less and very
similar to each other. The trend of decrease or increase in the
levels of mercury was also similar. Sediment analysis showed
the presence of a remarkable quantity of mercury. Maximum
amount of mercury was found in the sediment from the effluent
channel. The levels of mercury fluctuated much, the maximum
being 2053.3 mg kg-1 dry wt in the month of July and the
minimum 456.67 mg kg-1 dry wt in the month of January. The
mean mercury value was 929.39 ± 405.23 (Table 8).
Out of the four stations of the estuary, station II was the site of
maximum mercury contamination similar to that of water. Here
also the concentration of mercury fluctuated much. Maximum
value was recorded in February (665.00 mg kg-1 dry wt) and
minimum value in July (44.33 mg kg-1 dry wt). Mean value was
181.69 mg kg-1 dry wt (Table 11). No particular trend of increase
or decrease was marked. However, lower concentrations of
mercury were observed in the monsoon and the post monsoon
seasons, i.e., from June to December. No relationship could
be noticed between the concentration of mercury in sediment
of this site and that of the effluent channel. Unlike water
samples, levels of mercury were slightly higher at station III
than at station I with exception of May and October.
Concentrations at station IV were found to be the lowest when
compared to the other stations except in September and
November. No particular trend of increase or decrease in the
mercury concentration was noticed at any station. However
the levels of mercury were lower in the monsoon and the post
monsoon season at all the three stations. Analysis of variance
revealed no significant difference in the mercury levels in water
(Table 12) and sediment (Table 13) between different seasons.
However, different stations did differ from each other with
respect to the mercury levels. From correlation analysis (Table
11) it appears that significant correlation existed between the
concentration of mercury in water and sediment at station I, III
and IV, but not at station II and E. However, at all the stations
many examples were marked relating to increase in
concentration of mercury in water with concomitant decrease
of the same in the sediment.
All the plants collected from the industrial area and from nearby
field/ locality showed the pressure of an objectionable amount
of mercury in their tissues. Maximum amount of mercury was
recorded in plants, collected from the solid waste deposit areas.
Alarming level of mercury was found in plant s used for human
consumption. The plants collected within 1km radius showed
higher level of mercury. Cyperus rotendus showed 27.9 ± 6.8
mg of Hg kg-1 dry weight. Whereas, Cynodon dactylon showed
22.8 ± 3.6 mg of Hg kg-1 dry weight. Lippia nodiflora showed
24.2 ± 9.5 mg of Hg kg-1 dry weight. Pandanus odaratissimus
showed 18.5 ± 1.6 mg of Hg kg-1 dry weight, which has
ecological significance. Ipomea digitata showed the least
amount of residual mercury accumulation among the plants
collected from 1km radius area of the industry. The plants
collected from solid waste deposit area, showed higher
accumulation of mercury. Jatropha gossypifolia accumulated
23.8 ± 9.2 mg of Hg kg-1 dry weight and Justicia simplex showed
19.2 ± 4.4 mg of Hg kg-1 dry weight. Colotropis procera showed
15.6 ± 1.8 mg of Hg kg-1 dry weight. Ageratum conyzoids
showed 9.6 ± 3.1 mg of Hg accumulated in kg-1 dry weight of
the sample. Croton and Desmodium showed the least amount
of mercury accumulation. Amaranthus viridis showed 5.9 ±2.2mg of Hg kg-1 dry weight, where as Azadirachta indica
showed 5.6 ± 0.9 mg of Hg kg-1 dry weight of the sample.
Table C showed the residual mercury accumulation in plants
collected from the populated localities of the Ganjam areaand also the cultivated plants available in the contaminatedareas. Amaranthus spinosus showed 4.12 ± 1.08 mg of HgKg-1 dry weight. Solanum melongena showed 3.04 ± 0.8 mgof Hg kg-1 dry weight and Zizyphus jujuba showed 2.14 ± 0.7mg of Hg kg-1 dry weight. Ocimum basillcum showed 1.14 ±0.5 mg of Hg kg-1 dry weight. Among cultivated plants,Phaseolus vulgaris showed 0.54 ± 0.3mg of Hg Kg-1 dry weight,Phaseolus mungo showed 0.86 ± 0.7 mg of Hg kg-1 dry weight.Psiduim guayava accumulated 2.88 ± 0.9 mg of Hg kg-1 dryweight. Oryza sativa interestingly showed 2.11 ± 0.7 mg ofHg kg-1 dry weight, which is highly significant, as rice is regularlyneeded as food by the local people. Cucurbita showed 1.36 ±0.5 mg of Hg kg-1 dry weight, Hibiscus esculentus showed0.88 ± 0.4mg of Hg kg-1 dry weight. Momordica charantiashowed 1.32 ± 0.8mg of Hg kg-1 dry weight. The values
presented for domesticated plants may look very small but
these values were highly significant, when we consider it long
run effect and future bio-magnification of mercury in the food
chain. Table showed the natural background level of mercury
in the plants collected from the area. Croton showed 0.014 ±0.003 mg of Hg Kg-1 dry weight. Jatropha showed 0.029 ±0.006 mg of Hg Kg-1 dry weight. Ipomoea digitata showed
MERCURY POLLUTION AROUND CHLOR - ALKALI INDUSTRY
362
0.011 ± 0.002 mg of Hg kg-1 dry weight Argemone showed
0.008 ± 0.001 mg of Hg kg-1 dry weight. Calotropis procera
showed 0.012 ± 0.003 mg of background Hg kg-1 dry weight
of the sample (Table 3).
The samples collected from the solid waste deposit area
indicated significantly high level of mercury contamination.
During pre monsoon period the solid waste contained 585.60
± 38.34 mg of Hg kg-1 dry weight which is very high. During
monsoon period, the mercury level declined to 498.65 ± 18.50
mg of Hg Kg-1 dry weight and in post monsoon period, the
mercury level was 476.12 ± 29.65 mg of Hg kg-1 dry weight. In
station ‘a’ the mercury level in the soil decreased with the
increase in distance from station ‘a’ to station ‘c’ at all the three
seasons and all the three directions. Significantly low level of
mercury was recorded in station ‘c’ in direction I, direction II
and direction III (Table 4). Table clearly indicated that station
‘a’ in all the three direction, showed higher amount of mercury.
Hence, zone ‘a’ i.e. 1/2 km radius from the factory is the hot
zone, where significant amount of soil mercury is available.
The geographical distribution indicated that the mercury is
available within 2kms radius from the factory. Beyond 2kms
distance, mercury was not recorded in all the three directions.
Hence, the available mercury’s source is the chlor-alkali industry
situated at Ganjam area (Table 4). Results of the investigations
represent the gross primary productivity values at station I, II,
III and IV. Station II was noted as the least productive zone, the
minimum and maximum GPP values being 0 and 0.075 g Cm-
2d-1. The most productive zone was station IV, the values ofGPP ranged from 0.853 to 1.331 g Cm-2d-1. The productivityvalues were more or less constant with a slight increase in thepre-monsoon period, probably due to increase inconcentration of the nutrients (Sahu, 1987; Shaw, 1987).Unfortunately no standard GPP values are available from anyregion of the world for comparison. Presence of mercury inthe environment has received considerable attention. Studiesby Jensen and Jernelov, (1969a, b) Jernelov and Wallin (1973),Wallin (1976), Panigrahi and Mishra (1978a and b, 1980),Powell (1983) and Huckabee et al., (1983) pertaining toresidual mercury level in water bodies, soil vegetation aroundchlor-alkali industries and mercury mines, and aquatic andterrestrial animals from the contaminated system stress uponthe importance of the problem of environmental mercurypollution. Reports were also available pertaining to thegeographical distribution (Wallin, 1976; Huckabee et al.,1983) of mercury and the intensity of mercury pollution.
Plants collected from the area showed heavy accumulation ofmercury in their tissue (Table 2) the residual levels recordedwere much more than the natural background levels thatranged from 0.04 to 0.08 mg kg-l dry weight. Soil analysis fromthe area also revealed heavy contamination. These resultssuggest an unnaturally high deposition of mercury in thevicinity of the industry. Decrease in the level of mercury in
both plant and soil with increase in distance from the industry
is indicative of the fact that the industry was the source of
mercury. In a similar work Wallin (1976) and Lodenius and
Tulisalo (1984) reported a gradual reduction of mercury
contamination in mosses with increase in distance from the
factory confirming the source of mercury to be a caustic
chlorine industry. The accumulation in moss bags and the
concentration in mosses and lichens were significantly higher
near the chlor-alkali plant than at a distance of 20-100 km or
in the background are (Lodenius and Tulisalo, 1984).
Difference in the levels of mercury in the tissues of the different
plants species may be assigned to difference in availability of
mercury to them as well as their capacity of absorption,
accumulation and retention inside their tissue system.
Geographical distribution of mercury was more pronounced
in direction I as revealed from its level in Cynodon and the soil
samples, probably due to the prevalent south east wind.
Decrease in the levels of mercury in the monsoon season may
be attributed to the leaching and washing away of the
deposited mercury due to heavy rain. Retention of mercury in
the soil during the monsoon season was in some way related
with its concentration in the pre monsoon season i.e. greater
the concentration, higher was the retention. This indicated
that the mercury particles, to a minimum value depending
upon the original soil concentration, were bound tightly to
the soil particles to be washed away by the rain. Vascular
plants accumulation mercury by three routes of uptakes
through the root from the soil, through the stomata from the
atmosphere and by the retention of particular mercury with
atmospheric uptake predominating in the above ground parts
of herbaceous plant (Lindberg et al., 1979). At the mercury
concentrations prevailing in soils, plants retain mercury almost
exclusively within the root, where it seems to be relatively
tightly bound to acid groups of cell walls, only at exceptionally
high soil mercury contents, there occurred significant
translocation to shoot. Lindberg et al. (1979) reports the
accumulation of more mercury in leaves in comparison to
other tissues of the plants. More mercury concentration in thestem than in the root in Jatropha species and Croton furthersupports the idea. In other plants greater amounts mercurywere observed in the root. The analysis carried out byHuckabee et al. (1983) with Quercus species three samplesfrom Almaden mines areas showed a higher amount of mercuryin the stem than in the leaf. Further same author added thathad there been aerial absorption of mercury, the levels ofmercury in leaves, at least in plants of the same species wouldhave been similar. Moreover, highly significant correlationobserved between the root and the leaf mercury concentrationin all cases, contradicts the possibility of aerial absorption.Higher levels of mercury in the leaves may be attributed to thefact that mercury absorbed from the soil might be gettingtransferred immediately to the leaves. Leaf tissues of the plantssystem may be compared with liver of an animal system withrespect to mercury accumulation where the concentration ofmercury has been found to be the highest in most of the cases(Shaw et al., 1985, 1986a, b; 1988, 1991a, b; Smith andArmstrong, 1975) in comparison to other tissues, primarilybecause both the centers of active metabolic activities. Duringtransportation of the mercury from root to leaf, the stem tissuemight be accumulating mercury resulting in a higher level
than the root, as found in some cases. However, this appears
to be mostly a species dependent phenomenon. The existence
of poor correlations between the concentration of mercury in
soil and different tissues may be explained by the fact that the
soil mercury concentration might not be acting as a limiting
factor. This is evident from the result of Argemone species
where the soil mercury concentration acted as a limiting factor
and the correlation values for the soil vs. Different tissue
AJIT K. MISRA et al.,
363
mercury concentrations were highly significant. Presence of
highly elevated levels of mercury in the plant tissue under this
observation goes against the view of Lorenz (1979) that in
terrestrial ecosystem mercury generally does not enter the food
chain in significant quantities and thus does not play a
significant role because of its chelation by soil organic matter
and its binding to functional groups of cells walls in plants
root. Higher concentration of mercury in leaves than in other
tissues of the plants, as well as in grasses, draw the attention of
ecologists because grazers mostly depend on grasses and
leaves of the plants. Thus, the grazers of the area (Cows, sheep,
goats) must be accumulating a considerable amount of
mercury in their tissues via food chain since they are totally
dependent on the live flora of the area.
Plant systems unlike animals system tend quickly and visibly
to reflect changes in their environment (Naegeta, 1974). This
is because plants lack the complex internally balanced
homeostatic mechanisms that regulate body function and
adaptation that are found in animals. Because of this
homeostasis animal systems tend to ameliorate the adverse
effects of environment. Thus, animals tend to withstand, adjust
and ameliorate the contamination in their external environment
in such a way that only major changes in their environment
become externally detectable. Plants, on the other hand,
respond noticeably to minor, as well as major changes in their
environment. However, the response of a plant to a pollutant
in its environment is an integrated responsibly many other
environmental components. The plant system has a limited
number or finite number of responses to the environment in
which they live. In may ways their responses are generalized
in that they do not have broad varieties of specific behaviorable
responses which animal system have, as a consequence, the
responses of a plant to air pollution is very similar in form.
During samples collections no visible abnormalities in the
plants structure were marked except that the growth was
stunted which might be due to water scarcity. Leaves ofAesculus hipocastanum L. and Quercus petres L from airpolluted areas showed a higher water loss than normal leaves.Trivedi and Dubey (1978) reported even a higher amount ofmercury (15mg) in the effluent of a caustic chlorine industry atBirlagram Nada (M.P) High amount of mercury has beenreported in water receiving industrial discharges contaminatedwith mercury (Zingde et al., 1980; Zindge and Desai, 1981).At the point of discharge in Tyhane creek, the mercuryconcentrations varied from 79 to 320 mg-l (Zingde and Desai,1981). Level of contamination of the Chambai River, whichreceived effluent from Gwalior rayon and caustic chlorineindustries at Birlagram Nagade (M.P), was such that it wasfound to be unfit for fish growth up to 35km downstream(Trivedi and Dubey 1978). Presence of mercury at upstreammay be attribution to the tidal effects of the sea, the water levelswells and carries the contaminated water towards upstream.
Thus during high tide the level of mercury at the upstream
may be higher than at the downstream. Similarly, during low
tide the contaminated water may be carried to a greater distance
towards downstream and thus a higher concentration at site
IV may be resulted. A particular trend of increase or decrease
in the levels of mercury at different stations can’s be expected
since the contamination was related to the effluent discharge
which was periodic but not a continuous one and highly
variable with respect to mercury concentration. Dove et al.
(2011) who analyzed water sampled from the Great Lakes and
connecting channels during 2003-2009 found that mean
concentrations of total mercury in unfiltered waters were less
than 1.0ng/L at most sampling sites within the five great lakes.
Berndt and Bavin (2012) quantified total mercury, methyl
mercury, dissolved organic carbon and sulfate in stream water
from St. Louis River and tributaries draining sub basins in
northeastern Minnesota. Zhang et al. (2012) studied the
seasonal variation in mercury and food web biomagnifications
in Lake Ontario, Canada and reported that highest mercury
concentration in 6 invertebrate species and 8 fish species in
spring and lowest in the summer for most biota.
Concentration of mercury in sediment is rather more important
in indicating the pollution status of the system than water. This
is because the sediment rapidly binds mercury and also the
sedimentations decrease its availability to aquatic system. As
expected, maximum amount of mercury was found in the
sediment of the effluent channel followed by the sediment
from the junction zone. Contamination of sediment with
mercury has been reported in lake, river and coastal water
(Clifton and Vivian, 1973). The levels of mercury were usually
lower than 10 mg kg-l. Sediment of Minamata bay in Japan in
1963 showed a mercury level varying from 28 to 73 mg kg-l
.dry weight (Fujuki, 1973). Mercury discharged in an aquatic
system is generally lost to sediments (Clifton and Vivian, 1973).
Mercury may be deposited in sediment by precipitation or by
death of contaminated aquatic organisms which finally settle
down at the bottom as human. Arise in the oxygen content
and pH of water in estuarine zone promotes the formation of
metal hydroxides which constitute significant ‘sink’ of heavy
metal by the effect of co precipitation (Lee et al., 1973). When
mercury in first deposited in sediment, it is rapidly and strongly
complexed to various component of the sediment. Mercury is
not strongly bound to Sulfur containing organic and inorganicparticles. Such type of binding is up to 62% (Walters andWolery, 1974). To a lesser extent mercury is also boundstrongly to clays, minerals sediments containing iron andmanganese oxides, and to find sands. Only a small portion ofmercury in sediment is released into the pore water. In thisindustrial water, mercury appears to be associated primarilywith organic acid as fulvates and humates with little or none ofthe mercury in unbounded form. With or without agitation,the rate of release of mercury from sediment is slow and fromsulfur containing sediments is hardly measurable. Mercury insediments can return to water bodies by two processes. Bystirring of bottom sediments, which resulted in the suspensionof the absorbed mercury particles of its compounds in thebottom. However, suspension is only temporary. Moreimportant process of release of mercury from the sediment isthe methylation by microorganism. This is the key reactionleading to mercury contamination of aquatic organisms.Methylation proceeds only at the top layer of the sediment.
Burrowing animals however, expose mercury present in
deeper layers to the methylation processes (Jernelov, 1970
and 1974). Significant correlation between the concentration
of mercury in sediment and water samples at station I, III and
IV in the present study and nearly similar trend of increased or
decrease of mercury levels in water and sediment samples atthose station suggest that the release of mercury from the
MERCURY POLLUTION AROUND CHLOR - ALKALI INDUSTRY
364
sediment into the water was dependent upon theconcentrations of mercury in the sediment and that the bedsediment of the estuary was not completely saturated withmercury. Reasons for the absence of significant correlation atstation II and E may be large fluctuation in the levels of mercuryin the effluent. The industry was forced to change thetechnology as the old technology was discharging hugeamounts of mercury in to the environment through untreateddischarge of effluents. Our publications, inference inconferences and seminars, public agitation regarding mercurypollution both aquatic and terrestrial, probably forced theauthorities at Jayashree Chemicals to change the technologyfrom Mercury cell electrolytic process to membrane systemwhere no mercury is required. At present due to change intechnology in caustic soda production, the intensity of mercurypollution decreased significantly. Now, the data of recentinvestigation indicated that the effluent channel is almost freefrom mercury but the sediments do contain mercury. Theolder plants and perennial plants showed presence of mercurybut the annual plants and fresh plants did not show significantpresence of mercury.
Transport or mercury, released due to the agitation ormethylation or from the site where the mercury is beingdischarged to the other sites may be transport of the alreadysuspended mercury particles in wave action or force of thewater flow in the river to lower site. Higher tidal action inestuary is responsible for the upstream contamination. Mercuryassociated with the bottom sediment acts as a reservoir ofmercury for long after the primary source is removed and mayinfluence the water quality and aquatic life. High amount of
mercury was detected in the bed sediments event after 45
days of the closure of the chlor-alkali factory (Jernelov, 1974).
Return of the immobilised heavy metals in the bottom
sediments of rivers lakes and sea into the water bodies
constitutes a potential hazard to the water quality and the
aquatic life. Polluted sediments are widely accepted as the
primary source of fish contamination in most aquatic systems.
However, there is no unanimously accepted view on the
pathway of Hg from sediment to fish. A pathway of Hg from
sediment to fish via suspended particulate matters and
zooplankton was suggested by Nishimura and Kumagai (1983).
Levels of mercury in the sediments at the mouth region of the
estuary do not seem to present an immediate threat since a
level less than 1mg Kg–l. dry weight has been considered safe
by the Japanese government (Kudo and Miyahara, 1983).However, if discharge of mercury from the factory continuedat this pace then a tragedy similar to Minamata Bay incidencemay not be avoided in near future. After repeated requests,reminders, publications, agitations etc, at present, the industryhas changed the technology from Mercury cell process toMembrane system for producing Caustic soda, where mercuryis no more used. This is a big relief for the area and for us butwe are definitely worried about the fate of the total mercurywhich was released earlier along with effluent in to theenvironment i.e. Rushikulya River, Rushikulya estuary andBay of Bengal.
ACKNOWLEDGEMENT
The authors wish to thank authorities of Berhampur University
for the laboratory and library facilities provided for the work.
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