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Health
Hazards of Heavy Metals
By: U.N. Rai
and Amit Pal
For the
first time in his entire cultural history, man is facing one of the most
horrible ecological crisis- the problem of pollution of environment especially
with toxic metals, which sometime in the past was pure, virgin, undisturbed,
uncontaminated and basically quite hospitable for him. Today, the cry of
"Pollution" is heard from all the nooks and corners of the globe and it has
become a major threat to the very existence of mankind on the planet earth.
Heavy metal pollution affects flora, fauna and other abiotic components of the
ecosystem. Metal leads to various metabolic alterations and undesirable
changes, which in many cases may cause severe injury and health hazards. There
are several factors like human population explosion, unplanned urbanization,
deforestation, profit oriented society and technological advancement etc.,
whose cumulative effect is responsible for the origin of pollution crisis on
the earth. The ecological crisis of environmental pollution has been blamed on
different things and one of the major things is the pollution due to metals in
the environment.
Toxic metal
pollution can be a much more serious and insidious problem, as these are
intrinsic components of the environment. At high concentrations, all the metals
are toxic to animals and plants both. Metals are omnipresent in the environment
occurring in varying concentrations in parent rock, soil, water, air and all
biological matter. Moreover, metals are also released into environment from a
wide spectrum of anthropogenic sources such as smelting of metallic ores,
industrial fabrication and commercial application of metals, agro-chemicals
pesticides as well as burning of fossil fuels. These metals are redistributed
in the biosphere and dispersed in the air, soil, water and consequently in
human beings through food chain bio-magnification causing chronic ailments.
Metals are
significant to human because some of them are most important trace elements as
a co-factor in various metabolic enzymes and constituents of cells. Zinc,
copper and iron form important component of cell and co-factor in several
metalloenzymes, while organically chelated chromium (Cr3+) compound
act as a co-factor in insulin hormone response controlling carbohydrate
metabolism in human. Some non-essential metals are present in all tissue and
organs of man like under normal conditions more than 90% of lead (Pb) is
retained in the skeleton. Human can tolerate 100-200 times its total body
content of Cr without harmful effects. However, increased concentration of
these metals can affect mineral and enzyme status of human beings. The metals
irreversibly bind to active sites of enzymes, thereby destroying normal
metabolism producing high-level toxicity. Human can be affected directly by
air, water and soil metal pollutants as well as indirectly through contaminated
food supplies. In recent past, a large number of silent epidemics have been
reported due to metal contamination, which is escalating day by day.
In 1947 an
unusual and painful disease of rheumatic nature was recorded in the case of 44
patients from a village on the banks of jintsu River, Toyama prefecture, Japan.
During subsequent years it became known as 'itai-itai' disease (meaning
'ouch-ouch') in accordance with the patients shrieks resulting from painful
skeletal deformities. The incubation period for chronic cadmium intoxication
varies considerably usually between 5-10 years but in some cases upto 30
years. During the first phase of poisoning, a yellow discolouration of teeth,
"cadmium ring" is formed, the sense of smell is lost, and mouth becomes dry,
subsequently the number of red blood cells is diminished which results in
impairment of bone marrow. The most characteristic feature of diseases is
lumbar pains and leg myalgia. These conditions continuing for several years
until the patient becomes bed ridden and clinical conditions progress rapidly.
Urinary excretion of albuminous substances result from the severe kidney
damage. Cadmium induced disturbances in calcium metabolism accompanied by
softening of bones; fractures and skeletal deformations take place with a
marked decrease in body height up to 30 cm.
The
importance of arsenic as a health hazard, which is also known as 'slow killer'
is now well recognised. The most obvious signs are the blisters on the palms of
the hands and soles of the feet, which can eventually turn gangrenous and
cancerous. Meanwhile, the poison also attacks internal organs, notably the
lungs and kidneys, which can result in a battery of illnesses including
cancers. Arsenic (As) poisoning has been reported from several places. A major
outbreak of arsenic poisoning occurred in young children in the summer of 1955
in Japan. The intoxication stemmed from the consumption of dry milk powder to
which arsenic contaminated sodium phosphate had been added as a stabilizer. The
sodium phosphate was a waste product generated during production of aluminum
from bauxite. Altogether 12000 cases were reported and 130 of them more fatal.
The poisoning has been due to persistent changes in central nervous system
including mental disturbances and changes in electroencephalograms.
Epidemiological studies on children, living in the vicinity of a coal power
plant in Czechoslovakia where coal that was used contained about 1000-1500 g
arsenic per tonne, showed respiratory symptoms and hearing loss. Long term
ingestion of arsenic contaminated drinking water produced gastrointestinal,
skin, liver and nerve tissue injuries. In Taiwan, wide spread occurrence of
black foot disease resulted from high levels of As in ground water. The maximum
arsenic value amounted to 2.5 ppm. Chronic As poisoning appears to be regional
but certainly not limited to Taiwan. For example in Mexican village, Toreon,
60% of the inhabitants showed varying degrees of chronic intoxication from
drinking water which contained 4-6 ppm As. Similar cases of As poisoning have
been reported from West Bengal (India) and Bangladesh in recent years. In the
1970s, international agencies headed by the UNICEF began pumping millions of
dollars of aid money into Bangladesh for tube-wells to provide "clean" drinking
water. According to the World Health Organization, the direct result has been
the biggest outbreak of mass poisoning in the history. Upto half the country's
tube-wells, now estimated to number 10 million, are poisoned. Tens, perhaps
hundreds of thousands will die. Indeed the WHO released a report in September
estimating that between 35 and 77 million Bangladeshis may be drinking water
containing more than the safety limit of 10 parts per billion of arsenic.
According to the report's author, Allan Smith of the University of California,
Berkeley, the scale of the disaster is "beyond Bhopal; beyond Chernobyl."
So far as we
know there is no medicine available for chronic arsenic toxicity. The only
treatment is safe water, nutritious food and time. This can clear up the skin
blotches on people in the early stages of poisoning. But once gangrene and
cancer have taken hold they may be beyond hope.
Mercury (Hg)
is considered to be highly toxic metal for living organisms. Even at very low
concentration, Hg and its compounds present potential hazards due to enrichment
in food chain. Poisoning by methyl mercury compounds presents a bizarre
neurological picture as observed in large-scale outbreaks in Japan, China, Iraq
and various parts of the world. The profound capacity of soft acid (acceptor)
CH3Hg+ to bind soft ligands explains the high toxicity of
methyl mercury compounds than Hg. The outbreaks of a hitherto unknown and
mysterious, non-injections neurologic illness amongst inhabitants especially
fishermen and their families who mainly subsist on seafood - living around
Minamata bay in South Western Kyushu, Japan. The patients who had consumed fish
and shellfish from that region progressively suffered from a weakening of
muscles, loss of vision, impairment of cerebral functions and eventual
paralysis, which in numerous cases resulted in coma and death. This disease was
known as Minamata disease and after extensive investigations it was
revealed in 1959 that the deaths were caused by the consumption of the fish and
other foodstuffs contaminated with methyl mercury.
In 1960
fatal incidents of lung cancer were reported from the Kiryama factory of
Nippon-Denki concern on the Islands of Hokkaido; Medical warnings were issued
that inhalation of dust containing Cr in high oxidation states (IV) and (VI)
was associated with malignant growth in the respiratory tract and painless
perforation in nasal septum among trivalent and hexavalent states being the
most stable and common in terrestrial environments. Hexavalent chromium is the
form considered to be the greatest threat because of its high solubility, its
ability to penetrate cell membranes and its strong oxidizing ability. Hence, Cr
(+6) is more toxic than Cr (+3) because of its high rate of absorption on
living surface. Cr (+6) exists only as oxy-species such as Cr03, Cr04,
and Cr207 and is strong oxidizing agent. An incidence of
catastrophic heavy metal poisoning was reported from highly toxic Cr(VI)
contained in untreated slimes and factory wastes. The largest chromium consumer
in Japan, the Nippon chemical industries has deposited approximately 530,000
tonnes of uninduced slimes and wastes containing hexavalent chromium around
Tokyo and in the neighbouring Chiba prefacture. Due to its hardening properties
the material has found extensive use for construction purposes. Complete
housing blocks have been erected in Tokyo, on spoil heaps containing highly
toxic Cr(VI) compounds. However, authorities paid no heed to this problem and
it is a 'tragic irony' that the factory workers themselves regarded perforated
nose as a status symbol, displaying 'sincerity' and loyalty towards a
particular employment. Few official figures of this catastrophe: 30 dead, over
200 incurables which only appear to herald the beginning of a
corporeal, scandalous
disaster.
Lead is the
number one environmental poison amongst the toxic heavy metals all over the
world, causing serious health hazards to humans, especially to young children.
In a developing country like India, lead poisoning remains a serious problem.
The full impact of lead poisoning on the health of children and adults is
becoming clearer to most countries, and many governments have begun to take
action. Significant health and economic benefits have been realized by those
countries which have developed lead prevention programs.
The ancients
regarded lead as the father of all metals, but the deity they associated with
the substance was Saturn, the ghoulish titan who devoured his own young. The
very word "saturnine," in its most specific meaning, applies to an individual
whose temperament has become uniformly gloomy, cynical, and taciturn as the
results of lead intoxication.
Lead was a
key component in face powders, rouges, and mascaras; the pigment in many paints
("crazy as a painter" was an ancient catch phrase rooted in the demented
behavior of lead-poisoned painters); a nifty spermicide for informal birth
control; the ideal "cold" metal for use in the manufacture of chastity belts; a
sweet and sour condiment popular for seasoning and adulterating food; a wine
preservative perfect for stopping fermentation or disguising inferior vintages;
the malleable and inexpensive ingredient in pewter cups, plates, pitchers, pots
and pans, and other household artifacts; the basic component of lead coins; and
a partial ingredient in debased bronze or brass coins as well as counterfeit
silver and gold coins.
The Romans
were aware that lead could cause serious health problems, even madness and
death. However, they were so fond of its diverse uses that they minimized the
hazards it posed. Romans of yesteryear, like Americans of today, equated
limited exposure to lead with limited risk. What they did not realize was that
their everyday low-level exposure to the metal rendered them vulnerable to
chronic lead poisoning, even while it spared them the full horrors of acute
lead poisoning.
Although
human body contains sufficiently large amounts of lead, moderately increased Pb
concentrations become toxic from health point of view. The large affinity of Pb+2
for thiol (-SH) and phosphate containing legands inhibits the biosynthesis of
heme and thereby affects the membrane permeability of kidney, liver and brain
cells. These result in either reduced functioning or a complete breakdown of
these tissues since Pb is a cumulative poison. A British military unit
stationed in Hong Kong, was overtaken by acute lead poisoning and suffered from
severe vomiting intestinal cramps and circulatory disorder. The source was
traced to lead chromate, which had been used to improve the colouration in
curry powder. Analysis revealed a lead content of 1.08%. Since this spice is
effective in many countries it should be subject to government control.
Ecosystems
supporting clusters of sporadic Transmissible Spongiform Encephalopathy (TSE)
are characterized by common properties of high-manganese (Mn)/low-copper (Cu),
zinc, selenium mineral status, and high altitude/snow-covered/pre-Cambrian
mountain terrain where above-average intensities of ultra violet/ozone oxidants
are prevalent. For instance, TSE outbreaks have erupted for the first time in
Germany, Spain and Italy, while continuing to increase in European countries
already affected such as France, Ireland and Portugal despite bans on meat and
bone meal inclusions into their cattle feed rations being implemented back in
1990. TSE outbreaks are currently escalating across many regions of N. Europe,
presenting a potentially serious pubic health crisis. Could the UK's increased
loading of a cocktail of environmental oxidants that penetrated the central
nervous system of the UK bovine (ultra violet microwaves/ozone/ systemic
Cu-chelating insecticides) account for a more virulent Mn4+ mediated
acceleration of the TSE degenerative process in Mn-contaminated/genetically
predisposed individuals, manifesting as the widespread emergence of new-variant
bovine BSE, variant Creutzfeldt-Jacob disease in younger mammals? Preventive
measures and pharmacological therapies for controlling TSEs can only be
effectively implemented once the original cause of this insidious disease has
been thoroughly comprehended.
The extent
of the growing crisis in contamination of the environment and food chain by
endocrine disrupting chemicals is reflected by the growing list of health
advisories regarding eating fish and wildlife which would serve as a warning
that similar bioaccumulation and effects are occurring in people as in fish and
wildlife. For 1999 the US EPA list of warnings that are in effect regarding
toxic levels in fish or wildlife included over 52,000 U.S. lakes, 20% of total
significant lakes, all Great Lakes, and approx. 7% of all U.S. river miles. The
number of health warnings rose again for mercury. In addition to the health
advisories regarding the danger in eating fish and wildlife, there are
widespread findings of hormonal and reproductive disorders/failures in wildlife
caused by the toxic exposures, and this is also true in most urban and
industrial coastal waters. There were approx. 50,000 warnings regarding mercury
in water bodies in at least 42 states. Large quantities of endocrine system
disrupting chemicals that have adverse effects on the hormonal and reproductive
systems of animals and humans have been released into the environment since
second world war and are accumulating in the food chain, animals, and humans.
These chemicals have been found to act as estrogens, anti-estrogens, androgens,
anti-androgens, or to interfere with thyroid hormone, cortisol, insulin, or
growth regulators. Evidence that they are having widespread catastrophic
effects on wildlife and domestic animals, and serious widespread effects on
humans are now also being seen. A recent report by the National Research
Council found that 50% of all pregnancies in the U.S. are now resulting in
prenatal or postnatal mortality, significant birth defects, neurological
conditions, or chronically unhealthy babies. Approximately, 250,000 U.S.
children are born each year with birth defects diagnosed at or shortly after
birth.
The toxic
metals mercury, lead, and cadmium have also been found to have reproductive and
endocrine system disrupting effects.
Aluminum has
been found to cause Alzheimer's disease in human beings reported from several
parts of the world. Exposure to relatively low levels of these chemicals have
been documented to have had catastrophic effects on populations of Beluga
whales, alligators, turtles, mink, otters, bald eagles, osprey, cormorants,
terns, herring gulls, migratory birds, chickens, lake trout, chinook and coho
salmon, etc. throughout the U.S. and Canada. Animals and human foetal
development is dependent on hormonal levels at various phases of development
and the endocrine, reproductive, neurological, and immune systems are all being
affected, often seriously or catastrophically. These chemicals are being found
to have estrogenic effects and/or antiandrogenic effects on the
hormonal/endocrine system.
Dr. U. N.
Rai is a Scientist and Dr. Amit Pal is a Research Associate at National
Botanical Research Institute, Lucknow-226001, India. |
