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IntroductionAtomic mass 75. A metalloid that primarily exists with an oxidation state of +3 or +5. Arsenic forms stable covalent inorganic and organic compounds. The toxicity of arsenic and its compounds varies widely. Tri-valent compounds are most toxic, while marine organo-arsenicals are essentially non-toxic. Arsenic is used widely in industry as an insecticide, in glass manufacture, semiconductors and timber preservation. The smelting of gold, copper and lead ores cause arsenic to become volatile leading to an air pollution hazard. ExposureExposure to the industrial processes indicated above presents an occupational hazard. Arsenic can be concentrated in the natural environment leading to localised water and soil hazards. Use of arsenicals in the cotton and wood preserving industries and semi-conductor manufacturing increases the risks of inadvertent exposure to these products.AbsorptionArsenic absorption from the gastrointestinal tract is related to compound water solubility. Marine organo-arsenicals are readily absorbed and excreted over a period of days. Significant absorption of arsenic aerosols and fumes occurs directly from the lungs.DistributionMore than 90% of an injected dose of arsenic is cleared from the blood within a few hours. Circulating arsenic is able to cross the placenta. Target organs include skin, hair, nails, kidney and liver.ExcretionInorganic arsenicals are rapidly methylated and excreted to the urine. Methylated arsenicals are less toxic and more readily excreted relative to inorganic arsenicals.PathologyAcute arsenic poisoning can produce severe gastrointestinal irritation. If the dose is large enough (100 to 200 mg) peripheral circulatory failure is then seen. Neuropathy may follow non-lethal acute exposures. Arsine gas (generated through the action of acids on arsenides) produces devastating intravascular haemolysis.Chronic arsenic poisoning can produce symptoms such as weakness, lassitude, hair loss, weight loss, dementia and anaemia. Pigmentation and hyperkeratosis are dermatological signs. Mees lines in all nails in the same position, and brown pigmentation around eyelids, nipples, axillae, groin, temple and back characterise the pigmentation changes. Hyperkeratoses are surmounted by small corns (2 to 5 mm) and are found on the palms and soles. Peripheral vascular lesions have been described during exposure to contaminated drinking water. Peripheral neuropathy is a frequent finding in chronic exposure. Skin cancers have been found to be associated with prolonged exposure to arsenicals. MonitoringBlood determinations are of little value in assessing arsenic exposure because of the rapid clearance from this compartment. Urine determinations provide a reliable estimate of recent exposure. Interpretation of the urine total arsenic result provided by most laboratories may be difficult in the presence of a history of seafood consumption. PaLMS Trace Elements Service routinely determines seafood-derived arsenicals where urine total arsenic exceeds the reference range quoted, to assist in the interpretation of results. The concentration of arsenic in hair and nails has been reported to be increased in cases of exposure. The interpretation of results from these samples is always difficult due to the possibility of environmental contamination.TreatmentArsine poisoning is managed by support including exchange transfusion and hemodialysis, chelation therapy is not indicated. Support therapy and chelation (dimercaprol or penicillamine) is indicated for acute arsenic poisoning. Chronic arsenic poisoning is managed by removal of the source of exposure and support therapy as required. Chelation is of marginal use.AnalysisGraphite furnace and hydride generation atomic absorption spectrometry have been used to determine arsenic. PaLMS Trace Elements Service uses inductively coupled plasma mass spectrometry to determine total arsenic in various matrices. Partial speciation of arsenic compounds is carried out using selective complexation, extraction and graphite furnace atomic absorption spectrometry. The service is conducting research to develop a hybrid technique to fully speciate arsenic compounds in various samples. |