Benzene Urine Testing
Solvents & VOCs · Solvents & VOCs overview
Benzene is a Group 1 IARC carcinogen with a UK WEL of 1 ppm 8-hour TWA. Urinary S-phenylmercapturic acid (S-PMA) is the specific biomarker of choice; t,t-muconic acid (t,t-MA) is used as a supporting non-specific marker.
Why benzene needs specific biomonitoring
At low workplace concentrations urinary phenol (the historical biomarker) is dominated by dietary and environmental background and is no longer recommended. S-PMA, a glutathione conjugate of benzene oxide, is detectable at ppb-level exposures and is specific to benzene metabolism. It is the preferred biomarker for petrochemical, refinery, coke-oven and laboratory exposures.
Method and reference values
S-PMA is quantified by LC-MS/MS in end-of-shift urine. ACGIH BEI is 25 µg/g creatinine. t,t-MA can be measured as a supporting marker (ACGIH BEI 500 µg/g creatinine) but is confounded by dietary sorbic acid (a common food preservative).
Programme considerations
Smoking is a substantial confounder for both biomarkers; smoking status is recorded against each sample. Cohorts mixing smokers and non-smokers should be analysed in stratified form. The ALARP principle applies — any group geometric mean above 50% of the BEI is treated as a control review trigger.
Frequently asked questions
Why measure S-PMA instead of urinary phenol?
S-PMA is specific to benzene metabolism and detectable below 1 ppm exposure. Urinary phenol is dominated by background at workplace concentrations and gives false reassurance.
Does smoking affect benzene biomonitoring?
Yes. Tobacco smoke is a significant source of benzene exposure; smokers typically have S-PMA levels several times those of non-smokers. Smoking status must be recorded against each sample.
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