Arsenic As

Signs and symptoms of acute arsenic poisoning are primarily gastrointestinal, whereas chronic exposure leads to muscle weakness, neurological effects, and renal damage. Arsenic is one of the few elements that undergoes biotransformation in vivo. The toxic forms of arsenic are the trivalent [As(III)] and pentavalent [As(V)] inorganic forms. Although the use of arsenic is not widespread in industrial processes, the inorganic toxicants can be found at significant levels in groundwater, in wood preservatives, and also in some insecticides. Upon absorption, these forms are metabolized in the liver to much less toxic forms (monomethylarsine and dimethylarsine) and excreted over the course of 1-3 weeks. More commonly seen are the relatively non-toxic organic forms such as arsenobetaine and arsenocholine. These organic species are found at substantial levels in many foods, especially shellfish and predatory fish, and are rapidly cleared (within 1-2 days) through the urine. The structures of the relatively common inorganic and organic forms of arsenic are given in Fig 3. The concentration of organic forms is included and is indistinguishable from the inorganic forms in laboratory results that do not separate inorganic and organic forms. This inclusion in the "total" arsenic concentration leads to significant confusion as to the clinical significance of an elevated total arsenic concentration. Thus, elevated arsenic results require speciation or fractionation to interpret.

Urine is the sample of choice for arsenic testing because it is sensitive to detection of toxic forms for up to 3 weeks following an exposure. The extremely brief halflife of inorganic arsenic in serum and whole blood (4-6 h) disfavors the use of these sample types except in very acute exposures or research settings. When a total arsenic concentration is determined, foods such as fish and seafood that are likely to contain the non-toxic organic arsenic should be avoided for at least 72 h prior to sample collection. Dietary restriction is not necessary if the analytical method discriminates between inorganic and organic forms. Chromatographic techniques such as high performance liquid chromatography can be readily employed in conjunction with ICP-MS to discriminate the concentrations of inorganic and organic forms of arsenic in biological samples. A liquid-liquid or other extraction method may also separate inorganic and organic forms prior to analysis by ICP-MS. Storage of urine samples for up to 2 months does not appear to affect the quality of speciation results (35).

For chronic exposure to arsenic, hair, and/or nails may be the specimens of choice. The high affinity of arsenic for keratin in the hair and nails enables these samples to be used to document historical arsenic exposure. In nails, visible evidence of arsenic exposure may be manifested by the appearance of white transverse striae (Mees' lines) after a few weeks. Formation of Mees' lines does not always occur, however, so the absence of such lines does not exclude exposure (5,36,37).

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