Benzene — biological monitoring

When to suspect: Petroleum refining, petrochemical, coke ovens, rubber, solvents, fuel handling, printing.

Urine S-phenylmercapturic acid (S-PMA) · t,t-muconic acid (t,t-MA) (µg/g creatinine)

Level	Interpretation
S-PMA < 1–2	Non-exposed background (S-PMA is benzene-specific)
S-PMA 25	ACGIH BEI — end of shift
t,t-MA 500	ACGIH BEI — end of shift

S-PMA is more specific; t,t-MA is confounded by dietary sorbic acid. Smoking raises both — record smoking status.

Biological exposure index

ACGIH BEI: S-PMA 25 µg/g creatinine; t,t-MA 500 µg/g creatinine — both end of shift. (Benzene TLV cut to 0.02 ppm in 2024; BEIs unchanged.)

Basis: ACGIH BEI (systematic-review + lab corroboration).

Sample collection & preparation

Clean plastic urine container → standard transport tube (organic metabolites; trace-metal-free not required).
END OF SHIFT; creatinine-corrected.
Avoid sorbic-acid food preservatives (raise t,t-MA); record smoking status. No fasting.

Statutory basis. Factories Act 1948 sets only AIR limits (Second Schedule TWA/STEL, s.41F) and mandates the hazardous-process exam (s.41C, ≤12-monthly); it gives NO blood/urine values. The ranges below are ACGIH BEI / OSHA / clinical benchmarks (India has not adopted biological limits into law).

Reference information for occupational-health professionals — not medical advice, and not a substitute for examination by a qualified physician.

All 27 agents — toxicology & biological monitoring

MedFactory — Occupational Health Centre software for Indian factories