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Minamata:
a lesson not learnt |
During the
1960s and 70s, the Minamata Bay mercury pollution disaster received global media
attention, opening the world’s eyes to the negative health effects of methyl-mercury.
Between 1932 and 1968, the Japanese Chisso Corporation discharged about 27 tonnes of
methyl-mercury with its wastewater into the Bay. The pollution caused severe damage to the
central nervous system of the people who ate large quantities of contaminated fish and
shellfish from the Bay. In addition, congenital Minamata disease occurred as many infants
were born with a condition resembling cerebral palsy caused by methyl-mercury poisoning of
the foetus during pregnancy. The disease, which was officially recognised on 1 May 1956,
caused many people to lose their lives or suffer from physical deformities.
After the cause of the disease was
finally confirmed, a number of measures were implemented, ranging from regulation of the
factory effluent, voluntary restrictions on harvesting of fish and shellfish from the Bay,
installation of dividing nets to enclose the mouth of the Bay and prevent the spread of
contaminated fish, and dredging of mercury-containing sediments. It was only in October
1997 that the dividing nets that had closed off the Bay for 23 years were removed. After
several studies confirming that mercury levels in fish were below regulatory levels and
had remained so, for three years, Minamata Bay was reopened as a general fishing zone.
Till 1992, 2,252 people were diagnosed with "Minamata Disease", with 1,043
deaths reported. |
Fish contamination
The coastal areas of India are significantly polluted with
mercury and a high level of it is being detected in Indian fish, both saline and
freshwater. Consuming mercury-methyl contaminated fish can be fatal. The Minamata Disaster
in Japan in 1950’s, which affected more than 3,000 people, was caused by consuming
mercury-methyl contaminated fish (see Box:Minamata: a
lesson not learnt ). To prevent such a tragedy from happening in
India, people who eat fish need to be made aware of mercury contamination and its
consequences.
Soil and sediments contamination
The level of mercury in soil is an indicator of its potential to contaminate rainwater and
groundwater. It also gives an indication of its potential to contaminate crops and
vegetables grown in that soil. Soil contamination could be caused either by direct dumping
or land-filling of mercury-contaminated wastes or due to the presence of mercury in the
atmosphere. The level of mercury in waterbody sediments represents the history of
contamination in that waterbody. The Minamata Bay had to be dredged of toxic
mercury-contaminated sediments in order to restore the water quality.
From the map, it is clear that mercury hotspots are distributed
uniformly throughout the country. Due to the extremely mobile nature of mercury, it is
likely that there could be more hotspots. This needs to be investigated by further testing
of point sources such as smokestacks, ambient air, surface and groundwater, contaminated
soil, dumping grounds and landfills, and random soil samples from other locations.
Mercury exposure |
| Guidelines and standards for
chronic mercury exposure |
| Exposure |
Guideline or Standard |
Agency |
| Air (elemental) |
0.2
mg/m3
0.3 mg/m3 |
Agency for Toxic
Substances and Disease Registry (ATSDR), USA |
| Air (inorganic) |
1
mg/m3 |
WHO |
| Drinking water |
1
mg/L
(total mercury)2 mg/L EPA
(inorganic mercury) |
WHO |
| Food (methyl mercury) |
0.1
mg/kg/day0.3 mg/kg/day |
EPA
ATSDR
1.0 mg/g FDA |
| Chronic oral intake (inorganic) |
0.3
mg/kg/day |
EPA |
| Source: :-Donald
T. Wigle 2003, Child Health and the Environment, Oxford University Press, USA, pp 100-135. |
Where does the mercury go?
Once released by various sources the metal persists in the
environment in various forms, It pollutes air, water, sediments of various water-bodies
and even soil. It also enters into the various life forms through the foodchain. The form
of mercury released varies, depending on source type and other factors. The majority of
air emissions are in the form of gaseous elemental mercury, which is transported globally
even to regions far from the emission source. Elemental mercury in the atmosphere can
breakdown into ionic mercury, providing a significant pathway for its deposition in soil,
sediments and various water sources.
Once deposited, it can change (primarily by microbial metabolism) to
methyl-mercury. This methyl-mercury has the capacity to collect in organisms
(bioaccumulate) and to concentrate up in the food chains (biomagnify), especially in the
marine foodchain (fish and marine mammals). Methyl-mercury is therefore the form of
greatest concern. Nearly all of the mercury found in fish is methyl-mercury. The other
emissions are in the form of gaseous inorganic ionic mercury forms (such as mercuric
chloride) and other forms of mercury remain bound to the emitted particles. All these
forms have a shorter atmospheric lifetime and gradually deposit in land or waterbodies
within roughly 100 to 1,000 kilometres of their source. Even while in air mercury vapour
can also enter human and animal bodies during inhalation or absorption through skin. This
form of exposure to mercury affects the kidneys, nervous, digestive and respiratory system
(see Box: Mercury is toxic to the human body). Various agencies have prescribed
limits for exposure to mercury on a day-to-day basis (see Table: Mercury exposure).
Mercury
is toxic to the human body
Short-term exposure to high
concentrations of mercury vapour leads to acute mercury poisoning. At higher levels, it
can damage vital organs such as kidneys and lungs and the nervous, digestive and
respiratory systems. An exposure of 1 to 44 mg/m3 of mercury for four to eight hours can
cause chest pain, cough, coughing up blood, impaired lung function and inflammation of the
lungs. Inflammation of the oral cavity is one of the manifestations of acute mercury
exposure. Effects to the digestive system are in the form of abdominal pain, nausea,
vomiting and diarrhoea
Mercury is a potent neurotoxin. Even
at extremely low levels of exposure, it can permanently damage the human central nervous
system. Typical symptoms of mercury poisoning include loss of sensation in the fingers and
toes, tremors, blurred vision, poor muscular coordination and disintegration of brain
cells.
Allergic reactions on the skin are
reported in people with occupational exposure to mercury liquid or vapour. The symptoms of
methyl mercury poisoning are varied and can mimic other illnesses. In relatively mild
cases, the condition is barely distinguishable from other ailments such as headache,
chronic fatigue and generalised inability to distinguish taste and smell. Many of the
symptoms take a number of weeks, or even months, to appear. The symptoms include tingling
and numbness of extremities, depression, emotional instability, memory reduction,
irritability, defects in hearing, vision and speech, difficulty in writing, delays in
motor and language development, inability to walk properly and tremors. In extreme cases,
state of madness, loss of consciousness or death occurs.
Chronic exposure also results in
fertility impairment and adverse pregnancy outcomes. Foetuses are at a high risk from
methyl-mercury poisoning. Methyl-mercury can cross the placental barrier and cause foetal
brain damage without any symptoms in the expectant mother. Newborn babies may experience
mental and physical disabilities as well as delayed development of motor and verbal
skills. High level of prenatal methyl-mercury exposure causes mental retardation,
seizures and other neurological disturbances. Low level of exposure causes visual memory
deficits, abnormal behaviour and reduced growth at puberty. This has been demonstrated in
non-human primates. Children get susceptible to skin changes on exposure to organic
mercury. This includes rash followed by skin peeling on the palms, soles, itching and
joint pain.
Methyl-mercury can pass through the
placenta and blood brain barriers. It then enters the tissues where it gets converted to
divalent mercury. This form of mercury generates free radicals that attack proteins and
DNA in the body. Cord blood concentration of the metal is 20-30 per cent higher than that
of maternal blood indicating foetal exposure during gestation.
|
| Source: Anon
2005, Lurking Menace, Toxic Link, New Delhi, pp 19-21. |
Elemental mercurY: Intentional use of mercury has to be stopped as soon as
possible. There are economically viable non-mercury containing substitutes for almost all
current applications where mercury is used.
Mercury compoundS: The Minamata disaster in Japan was caused by a
mercury compound called mercuric chloride, which was released with the effluent from a
company producing fertilisers, petrochemicals and plastics. In India, unusually high
levels of mercury have been detected in groundwater not only near chlor-alkali units
(where elemental mercury is used) but also near industries manufacturing or using dyes,
paints, pigments, chemicals (such as H-acid, sulphonic acid and vinyl sulphone),
pesticides and herbicides, pharmaceuticals and plastics. It is obvious that these
industries still use mercury compounds even though most developed countries have stopped
using them (see Table: Alternatives are available).
Alternatives are available |
| Guidelines and standards for
chronic mercury exposure |
| Product or application
chlor-alkali industry |
Membrane technology |
Higher investment costs for
conversion but lower operational, waste treatment and disposal costs |
| Mercury used in dental amalgam |
Gold,
silver, ceramic, porcelain, polymers, composites, glass ionomers amalgam fillings |
While some are less
expensive and easy to apply, others are more expensive and difficult to apply |
| Mercury based batteries |
Virtually
mercury-free batteries are available |
Cost of mercury-free
batteries may be higher or about the same but their usage is preferable to costly cleaning
of mercury contaminated wastes |
| Laboratory use |
It
is possible to restrict mercury use in school or university laboratories to a few
controllable uses |
The
alternatives are generally no more expensive |
| Thermometers |
Other
liquids, gas, electric and electronic sensors |
More
expensive but one electronic thermometer may replace several broken mercury ones |
| Pressure measuring and control
equipment |
In
pressure gauges, switches and transmitters, mercury can be substituted using flexible
membrane, piezoelectric crystals and fibre-optic pressure sensors In barometers and
manometers, mercury can be replaced by other liquids or gases |
Electrical
and electronic instruments are slightly more expensive but alternatives based on gas,
other liquids or mechanical spring show no significant price difference |
| Tilt switch Electronic switch
Reed switch Proximity sensor/switch |
In
pressure gauges, switches and transmitters, mercury can be substituted using flexible
membrane, piezoelectric crystals and fibre-optic pressure sensors In barometers and
manometers, mercury can be replaced by other liquids or gases |
Electrical
and electronic instruments are slightly more expensive but alternatives based on gas,
other liquids or mechanical spring show no significant price difference |
Tilt switch
Electronic switch
Reed switch
Proximity sensor/switch |
Mechanical
or micro switch
Solid state and optical switch conductor
Inductive, capacitive, photo-electric sensor, ultrasonic |
No
significant price differences |
Artisanal gold extraction
Pesticides and biocides |
Non-mercury
electrolytic process, Minataur process pesticides and biocides or use easily degradable
substances |
Not
more expensive
Cost is roughly comparable and environmental benefits are considerable |
| Source: :-Global
Mercury Assessment, UNEP Chemicals, December 5, 2002 |
The government should immediately ban or
restrict, through certain fiscal disincentives like high taxes and import duties, the
usage of elemental mercury and mercury compounds and provide incentives (lower or zero
taxes or import duties) for those using mercury alternatives. In cases of uncontrolled
disposal of mercury-containing products or wastes, possible reductions in releases from
such practices might be achieved by making these practices illegal and by enhancing access
to hazardous waste disposal facilities. Clearly, the central government has to come up
with proper legislations to monitor and control release of mercury impurities from all
processes that involve the use of this metal.
Experts on Mercury
R C Shrivastava
member UNEP Working Group & co-chairperson Mercury Drafting Group
Tel : 0522-278947
J S Chopra
editor-in-chief World Neurology.
professor, Emeritus, Post Graduate Institute of Medical Education & Research,
Chandigarh.
Tel : 0172-661532,665532.
E-mail: jagjitsc@sify.com |
Source: R Kamolika &
Chandrabhushan 2003, Mercury Menace, special supplement in Down to Earth, Green Rating
Project, Centre for Science and Environment, New Delhi.
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