Scottish Trace Element and Micronutrient Reference Laboratory

Scotland's specialised laboratory for trace elements and vitamins in health and disease

Arsenic (As)

Trace Elements

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Arsenic is mainly measured to assess occupational exposure: eg. workers manufacturing semiconductors in the microelectronics industry; agricultural workers using a variety of arsenical herbicides and pesticides; workers exposed to wood preservatives containing copper, chromium, and arsenic.

Exposure can be monitored by measuring urinary excretion of arsenic, which is present as arsenite (AsIII), arsenate (AsV), their metabolites methylarsonic acid and dimethylarsinic acid and the more stable forms, arsenobetaine and arsenocholine. The latter two forms are non-toxic and are present in the normal diet especially in fish. This can lead to confusing results if total arsenic is measured. For this reason in our analytical procedure we use a preparatory step which removes these forms.

Until recently, this was thought sufficient to separate occupational exposure from dietary sources. However, recent evidence indicates that another category of arsenic species, arsenosugars, which are present in some shellfish (e.g. oysters, mussels, clams) and in seaweed extract, break down in the body to give monomethylarsonic acid and dimethylarsinic acid. Thus no method that measures inorganic arsenic and its metabolites would be able to distinguish between occupational exposure and a diet containing substantial amounts of shellfish. We have seen this ourselves in results on an occupational health nurse in a semiconductor plant who was not exposed to arsenic and thought to be a suitable control for the workers' exposure. Her urine arsenic was high and was related to a high intake of shellfish.

Hair arsenic provides a more integrated measure of arsenic exposure, although this is also subject to external accumulation of arsenic from the working environment.

In some parts of the world (Bangladesh, Thailand, China) arsenic is found in levels up to 500 µg/L (WHO recommended limit = 0.05 µg/L) in drinking water taken from wells. This has resulted in a large increase in cancer rates (especially skin cancer) and peripheral vascular disease causing gangrene.

Sample Requirements and Reference Values

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