Chronic arsenic poisoning

Author: Vanessa Ngan, staff writer

Chronic arsenic poisoning is due to repeated or continuous exposure to arsenic compounds, which leads to an accumulation of arsenic in the body. The 3 main sources of exposure are occupational exposure, natural contaminant of drinking water (from some deep water wells), and ancient Chinese medicinal remedies containing arsenic.

Occupational exposure is mainly from the smelting industry, in which arsenic is a by-product of ores containing lead, gold, zinc, copper, cobalt and nickel. It is also used in glass manufacturing and the microelectronics industry (where gallium arsenide is use to produce some semiconductor computer chips).

Absorption and distribution

There are several forms of arsenic. Pentavalent arsenic is well absorbed through the gut but less toxic than the trivalent form which is more lipid soluble and absorbed through the skin. The most toxic form is arsine gas, which is inhaled.

Arsenic compounds are well absorbed within 24 hours and redistributed to the liver, lungs, intestinal wall and spleen, where they bind to the sulfhydryl groups of tissue proteins. Arsenic also replaces phosphorus in the bone where it may remain for years. Hence, the effects of chronic poisoning can still be seen years after exposure has stopped.

Signs and symptoms of chronic arsenic poisoning

Signs and symptoms of chronic arsenic poisoning may not occur until 2 to 8 weeks after exposure.

Typical findings include:

Affected organFeatures
Skin
  • Excessive darkening of skin (hyperpigmentation) in areas that are not exposed to sunlight
  • Excessive formation of scaly skin on the palms and soles (arsenical keratosis)
  • Exfoliative dermatitis
  • Arsenic-induced skin cancers (especially Bowen disease)
Nails
  • Transverse white bands of arsenic deposits across the bed of the fingernails (Mee's lines)
Hair
  • Arsenic deposits in hair
Nervous system
  • Sensory changes, numbness and tingling in a “stocking-glove” distribution (sensory peripheral neuropathy)
  • Headache, drowsiness, confusion
  • Distal weakness of small muscles e.g. hands and feet
Blood and urine
  • Haemolytic anaemia (moderate)
  • leukopenia (low white cell count)
  • Proteinuria (protein in urine)
Other
  • Inflammation of respiratory mucosa
  • Peripheral vascular insufficiency
  • Increased risk of cancer of lung, liver, bladder, kidney and colon

Treatment of chronic arsenic poisoning

There is no specific treatment for chronic arsenic poisoning. Once it has been identified further exposure should be avoided. Recovery from the signs and symptoms may take weeks to months from when exposure is stopped. In particular, effects on the nervous system may take months to resolve and in some cases a complete recovery is never achieved.

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