Benzene is naturally occurring in for example crude oil and petrol as well as cigarette smoke. It is a colorless, flammable liquid that evaporates quickly when exposed to air. The main exposure route is by inhaling air contaminated with benzene, although benzene can also be absorbed through dermal contact with benzene containing liquids. Benzene is a well-documented carcinogen. It has been established that long-term exposure to elevated levels of benzene can cause leukemia.

S-phenylmercapturic acid (S-PMA) is one of the most widely used biomarkers of benzene exposure. Since there are no other substances, exogenous or endogenous, known to be metabolized to S-PMA except benzene, the excretion of this metabolite can only be attributed to benzene exposure. The American Conference of Governmental Industrial Hygienists (ACGIH) recommends a biological exposure index (BEI®) of 25 µg/g creatinine in the end-shift urine of workers when assessing occupational exposure to benzene [1].

[1] ACGIH, Threshold Limit Values and Biological Exposure Indices, ACGIH, Cincinnati, OH, 2009.