The following points highlight the five metals that cause disorders in human. The metals are: 1. Mercury 2. Cadmium 3. Lead 4. Copper 5. Zinc.

Metal # 1. Mercury (Hg):

Interest in chemical speciation has actually originated in 1953 after the occurrence of the Minamata disaster in Japan. A factory producing acetaldehyde and vinyl-chloride began using mercuric oxide as a catalyst. The effluent containing mercury was discharged into the Minamata bay. This ultimately led to nervous disorders and death of human lives.

Mercury in aquatic environment is con­verted by microorganisms to the highly toxic methyl mercury compound [(CH3)2Hg], which is readily taken up by the tissues. This methyl mercury compound is the villain in all fatal incidents due to Hg. The high level of Hg found in water bodies and in fish tissues is due to the formation of soluble CH3Hg+ and volatile (CH3)2Hg.

The sources of Hg in aquatic systems are:

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1. Natural inputs from the weathering of Hg bearing rocks and ores.

2. Fallout of atmospheric gases from the volcanos.

3. Contamination of surface waters from the atmosphere due to combustion of fossil fuels.

4. Anthropogenic sources include min­ing, refining, lumber and paper pulp indus­tries, antifouling paints in the shipping industry, pesticides and seed dressings in agriculture, and the industries of thermo­meter, batteries, pharmaceuticals etc. The effects of these generally lead to the common Minamata disease.

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The effects are:

1. Speech disturbance and delirium.

2. Nervous disorder and difficulties in walking.

3. Kidney damage, numbness in limbs, muscles, lips.

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4. Blurred vision leading to blindness and emotional disturbances.

Metal # 2. Cadmium (Cd):

Cadmium (Cd2+) is believed to exert no toxic effect. The toxic effects of cadmium are associated with the metal’s affinity for organic ligands contain­ing sulphur, nitrogen or other electronegative functional groups. The sources of cadmium are fertilisers, mine drainage, sewage, dust and fume.

In 1955 a disease called itai-itai (ouch-ouch) was reported from the Jintsu basin of Japan near the city of Tcyama.

It was charac­terised by:

1. Back and joint pains;

2. Duck-like gait;

3. Kidney lessions;

4. Protein and sugar in urine and

5. Decalcification of bones lea­ding in some cases to multiple bone fractures.

Metal # 3. Lead (Pb):

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Lead compounds in water are Pb(CH3)4, Pb2(OH)2CO3 etc. The ionic alkyl Pb compounds are considered to be highly toxic to mammals. The sources of Pb in water are lead processing industries, lead coated plastic water pipes, lead used in insecticides, food, beverages, ointments etc..

Lead poisoning causes damage to liver and kidney, reduction in haemoglobin forma­tion, mental retardation and abnormalities in fertility and pregnancy. Chronic lead poison­ing may lead to gastrointestinal disorder, neuromuscular effects and CNS syndrome that may result into coma and death.

Metal # 4. Copper (Cu):

Copper in both sea water and fresh water is found to be strongly associated with organic matter. Copper com­pounds in sea water are Cu(OH)2, CuCO3, while Cu-humic acid complexes dominate in fresh water. Copper occurs in earth in free native state and in the form of its ores. Excessive large doses of copper com­pounds may lead to mucosal irritation, wide­spread capillary damage, hepatic and renal damage.

Metal # 5. Zinc (Zn):

Zinc is abundantly formed in earth’s crust. Water resources may be contaminated with Zn through air and industrial waste. Zn may be leached into water from galvanized pipes, brass and zinc containing fittings. Symptoms of zinc toxicity in humans include vomiting, dehydration, electrolyte imbalance, abdominal pain, nausea and lethargy. Acute renal failure caused by zinc chloride has been reported.

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