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Assays / Trace
Metals/ Arsenic
Arsenic is an ubiquitous element, and although
it is apparently essential for certain animal species, its significance
in man lies in the acute and chronic toxicity that results from
overexposure. Fish and crustaceans contain particularly high amounts
of non-toxic forms of organic arsenic in their tissues, and in the
human body the element is concentrated largely in hair and nails.
The element is present in the ores used in the smelting of copper,
lead and zinc, and the resulting production of arsenic trioxide
is a potential health hazard. In both inorganic and organic forms
the element is widely used as an insecticide, herbicide, feed additive
and wood preservative. More recently, the semiconductor industry
has become a major user of arsenic compounds.
Toxicity
Although there are substantial
differences in the toxicities of different arsenic compounds, acute
exposure usually causes abdominal pain, weakness, trembling, increased
salivation, jaundice, diarrhoea and vomiting. Long term exposure
to smaller amounts causes similar symptoms in a milder form which,
of course, resemble those of many chronic diseases. This similarity
has made the element popular for many centuries as a deliberate
poison. Concern regarding the exposure of industrial workers to
arsenic compounds has increased following the realisation that arsenic
may be carcinogenic.
Traditional Asian remedies may contain
substantial amounts of arsenic, and cases of toxicity from their
use have been reported both from India and the UK.
Recent descriptions of siuations with
whole populations suffering from arsenic toxicity in areas of Bangladesh
and China are associated with drinking water with high natural levels
of arsenic, made available by new wells
The element probably exerts its toxic
effects by its ability to bind to sulphydryl groups in tissue proteins,
although cellular metabolism may also be disrupted by arsenate analogues
of phosphate compounds. The well known antidote to arsenic poisoning,
British Anti Lewisite (BAL; Dimercaprol) is effective by virtue
by its ability to bind arsenic through its sulphydryl groups.
Laboratory Indices of Exposure
Arsenic is excreted in the urine
and measurement of the urinary arsenic output is the determination
of choice. Concentrations both in blood and urine will increase
after the consumption of sea food. Separation of the arsenic species
in urine is necessary to distinguish between the toxic and non-toxic
forms. Alternatively known sources of non-toxic arsenic should be
excluded from the diet some five days before making an assessment.
References:
Kew J, Morris C, Aihe A, Fyshe
R, Jones S, Brooke D. Arsenic and mercury intoxication due to Indian
ethnic remedies. BMJ 1993; 306: 506-7
Vahter M. What are the chemical forms
of arsenic in urine and what can they tell us about exposure. Clin
Chem 1994; 40: 679-680
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