flames can be achieved using different mixtures of gases, depending on the desired temperature and
burning velocity. Some elements can only be converted to atoms at high temperatures. Even at high
temperatures, if excess oxygen
is present, some metals form oxides that do not redissociate into atoms.
The GFAA and flame AAS measurement principle is the same. The difference between these two
techniques is the way the sample is introduced into the instrument. In GFAA analysis, an electrothermal
graphite furnace is used instead. The sample is heated stepwise (up to 3000єC) to dry. The advantage of
the graphite furnace is that the detection limit is about two orders of magnitude better than that of
AAS. The analysis of different species of a given element is important because different oxidation
states
of the same element may present different toxicities and, consequently, different risks. Therefore,
sequential extraction procedures for the separation and further analysis of a species havebeen
developed for several metals.
Results
SOUCES OF HEAVY METAL - Environmental pollution from hazardous metals and minerals can arise
from naturalas well as anthropogenic sources. Natural sources are: seepage from rocks into water,
volcanic activity, forest fires etc. Pollution also arises from partitioning of polluting elements (which are
concentrated in clay minerals with high absorption capacities), between sedimentary rocks and their
precursor sediments and water. With rapid industrialization and consumerist life style, sources of
environmental pollution have increased. The pollution occurs both at the level of industrial production
as well as end use of the products and run-off. These toxic elements enter the human body mostly
through food and water and to a lesser extent through inhalation of polluted air, use of
cosmetics, drugs, poor quality herbal formulations‘ (herbo-mineral preparations) and `Unani’
formulations, and even items like toys which have paints containing lead.
Sources of heavy metals - Chromium (Cr)-Mining, industrial coolants, chromium salts
manufacturing, leather tanning
• Lead (Pb) lead acid batteries, paints, E-waste, Smelting operations, coal- based thermal power
plants, ceramics,
bangle
industry
• Mercury (Hg) Chlor-alkali plants, thermal power plants, fluorescent lamps, hospital waste
(damaged thermometers, barometers, sphygmomanometers), electrical appliances etc.
• Arsenic (As) Geogenic/natural processes, smelting operations, thermal power plants, fuel
• Copper (Cu) Mining, electroplating, smelting operations
• Vanadium (Va) Spent catalyst, sulphuric acid plant
• Nickel (Ni) Smelting operations, thermal power plants, battery industry
Cadmium (Cd) Zinc smelting, waste batteries, e-waste, paint sludge, incinerations & fuel combustion
• Molybdenum (Mo) Spent catalyst
• Zinc (Zn) Smelting, electroplating
One group of factors that may be detrimental to all organisms within urban ecosystems is metal
contaminants, such as lead, zinc, copper, cadmium, mercury, nickel, and iron, that get deposited in soil.
Metal contaminants are introduced into food webs at the bottom of the food chain and reach
earthworms and other invertebrates that live in the soil. When consumed by organisms such as birds
and snakes, the contaminants and their potential toxic effects accumulate within sensitive organs and
tissues.
HUMAN EXPOSURE THROUGH FOOD, AIR AND WATER
Heavy metal pollution of surface and underground water sources results in considerable soil
pollution and pollution increases when mined ores are dumped on the ground surface for manual
dressing. Surface dumping exposes the metals to air and rain thereby generating much AMD. When
agricultural soils are polluted, these metals are taken up by lants and consequently accumulate in their
tissues. Animals that graze on such contaminated plants and drink from polluted waters, as well as
marine lives that breed in heavy metal polluted waters also ccumulate such metals in their tissues, and
milk, if lactating.
In summary, all living organisms within a given ecosystem are variously contaminated
along their cycles of food chain.
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Discussions
HEAVY METAL POISONING AND BIOTOXICITY
- The biotoxic effects of heavy metals refer to the harmful
effects of heavy metals to the body when consumed above the biorecommended limits. Although
individual metals exhibit specific signs of their toxicity, the following have been reported as general signs
associated with cadmium, lead, arsenic, mercury, zinc, copper and aluminium poisoning: gastrointestinal
(GI) disorders, diarrhea stomatitis, tremor, hemoglobinuria causing a rust–red colour to stool,ataxia,
paralysis, vomiting and convulsion, depression, and pneumonia when volatile vapours and fumes are
inhaled. The nature of effects could be toxic (acute, chronic or sub-chronic), neurotoxic, carcinogenic,
mutagenic or teratogenic. Cadmium is toxic at extremely low levels.
In humans, long term exposure
results in renal dysfunction, characterized by tubular proteinuria. High exposure can lead to obstructive
lung disease, cadmium pneumonitis, resulting from inhaled dusts and fumes. It is characterized by chest
pain, cough with foamy and bloody sputum, and death of the lining of the lung tissues because of
excessive accumulation of watery fluids. Cadmium is also associated with bone defects, viz;
osteomalacia, osteoporosis and spontaneous fractures, increased blood
pressure and myocardic
dysfunctions. Lead is the most significant toxin of the heavy metals, and the inorganic forms are
absorbed through ingestion by food and water, and inhalation (Ferner, 2001). A notably serious effect of
lead toxicity is its teratogenic effect. Lead poisoning also causes inhibition of the synthesis of
haemoglobin; dysfunctions in the kidneys, joints by food and water, and inhalation. A notably serious
effect of lead toxicity is its teratogenic effect. Lead poisoning also causes inhibition of the synthesis of
haemoglobin; dysfunctions in the kidneys, joints
and reproductive systems, cardiovascular system and
acute and chronic damage to the central nervous system Zinc has been reported to cause the same signs
of illness as does lead, and can easily be mistakenly diagnosed as lead poisoning. Zinc is considered to be
relatively non-toxic, especially if taken orally. However, excess amount can cause system dysfunctions
that result in impairment of growth and reproduction. The clinical signs of zinc toxicosis have been
reported as vomiting, diarrhea, bloody urine, icterus (yellow mucus membrane) .liver failure, kidney
failure and anemia. Mercury is toxic and has no known function in human biochemistry and physiology.
Inorganic forms of mercury cause spontaneous abortion, congenital malformation and GI disorders (like
corrosive esophagitis and hematochezia).
Poisoning by its organic forms, which include monomethyl and
dimenthylmecury presents with erethism (an abnormal irritation or sensitivity of an organ or body).
Acknowledgement
The toxic elements enter the body mainly through water, food and air. Cosmetics, dental products,
some drugs, particularly Ayurvaid and Unani drugs also contribute. More research is needed to assess
the extent to which these products affect human health. Public awareness should be created. There
should be monitoring and control over the concentration of heavy metals in cosmetics. Heavy metals
are important in many respects to man, especially in the manufacturing of certain important products of
human use, such as accumulators (Pb), mercury-arch lamps and thermometers (Hg), utensils (Al) and a
wide range of other products. But the biotoxic effects, when unduly exposed to them could be
potentially life threatening hence, cannot be neglected. While these metals are in
many ways
indispensable, good precaution and adequate occupational hygiene should be taken in handling them.
Although heavy metal poisoning could be clinically diagn - osed and medically treated, the best option is
to prevent heavy metal pollution and the subsequent human poisoning.
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Annual report 2005–2006, pp 62–64
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Goel P.K. Water pollution causes effects and control, new age international publisher.
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