Common sources of arsenic are its sulphide ores such as Arsenopyrite (FeAsS), Mispickel (FeS As), Realgar (AsS), Cobaltite (CoAsS) etc.
The element is produced as a by-product from metal mines in Australia, Canada and Brazil. Smelting of lead, copper, gold and iron ores yields volatile oxides of arsenic which gets deposited in flues from where they are collected and refined. Leading producers of arsenic are Sweden, Mexico, France, South West Africa (Namibia) and some Russian states.
Arsenic is ubiquitous in distribution. In lime-stones and siliceous deposits its concentration ranges between 0.5 to 2.0 ppm while in volcanic rocks as much as 20 ppm of arsenic could be found. The highest concentration of arsenic almost 10,000 ppm has been recorded from Waitapu Valley in New Zealand and from Buns in Switzerland. Natural processes such as weathering and degradation of rocks annually release about 80,000 tons of arsenic into the environment. Global emission of this metal due to human activity has been estimated to be about 240,000 tons per year.
The total daily intake of arsenic from all sources in India by humans ranges between 0.20-0.35 mg per day. Cases of arsenic induced dermatitis, jaundice and damaged liver have been reported from West Bengal where people were forced to drink underground water with high arsenic levels.
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Trivalent compounds of arsenic are known to be the main toxic forms of this metal. Absorption of trivalent arsenic through lungs depends upon the particle size, but its absorption from intestinal track is almost complete nearly 95%. It tends to accumulate in nails and hairs. Excretion of absorbed arsenic is predominantly through sweat and urine.
A number of proteins and enzymes containing sulph-hydril groups have been found to be altered by exposure to arsenic. Mitochondrial enzyme system are particularly affected which disturbs tissue respiration. Ingestion of large doses of arsenic is followed, after a brief period, by a feeling of constriction at the throat, difficulty in swallowing and severe pain in stomach. This is followed by vomiting and diarrhoea. Weak pulse and breathing is usually the symptom preceding respiro- cardiac arrest in acute cases.
Chronic arsenic poisoning is characterised by a general feeling of weakness, nausea, loss of appetite, often vomiting and diarrhoea. Copious secretions of mucus in respiratory track, hoarseness, bronchitis and liver dysfunction or jaundice follow. Nerves of limbs are affected and loss of sensation in hands and feet occurs. Peripheral neuritis which results in loss of muscle power leads to difficulty in walking and carrying out coordinated movements.
There may be local effects on skin causing inflammatory, eczema like changes characterised by blackening and mottling of skin. Though oral administration of arsenic in experimental animals has failed to provide any conclusive evidence, carcinogenic properties of arsenic as a sequel to prolonged exposures to low doses have been well documented (Tseng, 1977).
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Small concentrations of arsenic are known to stimulate plant growth; larger concentrations present in irrigation water may cause reduction in overall yield of crop plants.