Arsenic is found in copper, lead, cobalt and nickel ores. Smelting, of these ores releases arsenic
Glass, ceramics, paints and insecticides are the other industries contributing arsenic. Arsenicals are used in a number of products, which include insect, rodent and weed killers.
Free arsenic and all its compounds are strong poisons. Arsenic compounds, in general, are skin irritants leading to dermatitis. Inorganic arsenic is extremely toxic, both acute and chronic. Of these, As (III), or arsenite, compounds are the most toxic (e.g. insecticides containing arsenious oxide, calcium or lead arsenate). Most natural waters contain the more toxic inorganic forms of arsenic. Organic species of arsenic are found in aquatic organisms. Organoarsenites are less toxic. The potency depends also on the oxidation state. H3As03 is sixty times more toxic than H3As04. The quaternary arsenium compounds (arsenocholine) are essentially non-toxic.
The potential hazards of arsenic to humans and animals are due to inhalation, or ingestion, usually from drinking water containing high concentration of inorganic arsenic compounds. Exposure may be accidental or an occupational hazard. Inorganic arsenic compounds can be degraded to arsenic or organorsine (AsCH3,) by microorganisms.
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Arsenic causes mesothelioma, cancer of pulmonary lining, and damage to many organs, and in some respects its toxicity resembles that of lead and mercury. Arsenic is believed to exert its toxicity by combining with certain enzymes (inhibits SH groups in enzymes). In persons exposed to arsenic, the discernable effects are destruction of red blood cells and damage to kidneys. In the case of chronic exposure, pigmentation and scaling of skin are clearly detected. Nervous manifestations marked by paralysis and confusion may be noted at some stage. Sooner or later the characteristic streaks appear across the nails.
As (III) and As (V) inhibit pyruvate dehydro-genase. As (III) or arsenite compounds are more toxic. Because of the chemical similarities of arsenic to phosphorus, As (III) interferes with some biochemical reactions involving phospherylation (citric acid cycle) reactions (no ATP formed). The clinical manifestations of arsenic poisoning are myriad. It is difficult to diagnose early symptoms of arsenicosis because such nonspecific symptoms may also present in many other diseases. Its ingestion may result in internal malignancies, including cancer of kidneys, bladder, liver and other organs.