Case Studies - Arsenic Species in Urine

The toxicity and biological activity of arsenic is dependant on its chemical form and oxidation state, as well as the amount present. Inorganic species of arsenic are more toxic than organic forms, and trivalent inorganic arsenic is more toxic than pentavalent inorganic arsenic. Low toxic, organic forms such as arsenobetaine are found in dietary sources, especially seafood. The more toxic forms of inorganic arsenic-containing compounds are widely used in industry; for example, in the manufacture of glass, in the semi-conductor industry and in wood preservatives. Occupational exposure in such industries may lead to skin disorders, and over a period of exposure to sub-acute gastrointestinal and nervous system disturbances. The World Health Organisation classifies arsenic as a human carcinogen and arsenic compounds have maximum exposure limits.

Arsenic is mostly excreted in urine and this is used for biological monitoring of occupational exposure. However, to assess more fully levels of exposure and potential risks, the different species of arsenic along with the dietary contribution should be considered.

HSL has developed a new method for urinary arsenic measurement that allows the separation of five individual species: trivalent inorganic arsenic; pentavalent inorganic arsenic; the metabolites of arsenic, dimethylarsinic acid and methylarsonic acid; and arsenobetaine. The method uses liquid chromatography to separate the species and detects them with an inductively coupled plasma emission mass spectrometer.

Recent work at HSL has been used to establish levels of individual arsenic species in urine samples from workers in the timber treatment and semiconductor industries, and from a control group of people not occupationally exposed. The effect of seafood on the arsenic levels in urine was also investigated. In this case volunteers collected a urine sample having eaten no seafood for three days and then a second sample 24 hours after eating seafood.

The results showed a four-fold increase in urinary arsenobetaine 24 hours after eating seafood. Increased levels of dimethylarsenic acid were also found. No toxic inorganic arsenic species were seen in the samples from the control group.

Concentrations of dietary-related arsenic species in samples from workers were similar to the control group who had not eaten seafood. Toxic inorganic arsenic species were found in small amounts in samples from the semiconductor workers, and in more significant amounts in the timber treatment workers. For timber treatment workers, 80% of the arsenic was occupationally related and only 20% was from dietary sources.

This new method of analysis gives more information about the type of exposure to arsenic, and will help to improve risk assessments for arsenic in and out of the workplace.

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