Trans,trans-muconic acid, a biological indicator to low levels of environmental benzene: Some aspects of its specificity

Background The specificity of trans, trans-muconic acid (MA) as a biomarker of exposure to low benzene levels and the role of sorbic acid (SA) as a co nfounding factor were evaluated. MA, a urinary ring-opened metabolite of be nzene, has been recently proposed for the biological monitoring of populati ons exposed to low levels of this chemical. The usual presence of MA in uri ne of non-occupationally exposed people is generally attributed to benzene world-wide contamination (mainly by smoking habits, urban pollution, and ma ybe by food contamination). However; the scientific literature reveals that the common food preservative and fungistatic agent SA is converted into MA though in trace amounts. Methods Urinary benzene and MA before and after administration of SA were m easured in smokers and non-smokers. Benzene dissolved in urine was analyzed injecting a headspace sample in a gas-chromatografic system. Urinary MA wa s measured by means of a HPLC apparatus. Results The mean background values of MA were about 60 mg/L (or 50 mg/g cre at.); after experimental admistration of SA (447 mg), the mean urinary MA c oncentration became more than 20 rimes higher The biotransformation rates o f SA into MA after ingestion of 447 mg of SA ranged from 0.05 to 0.51%. The ratio between unmetabolized benzene in the two groups of smokers and non-s mokers was significantly different from the ratio between MA in the same tw o groups. Discussion Other sources of MA excretion, different from benzene, influence the urinary concentration of the metabolite: only 25% of MA background val ues can be attributed to benzene. The urinary MA induced by 100 mg of inges ted MA is 77% of that expected after an 8-hour benzene exposure to 0.5 ppm (current threshold limit value according to ACGIH). In conclusion, MA is no t a sufficiently specific biomarker of low benzene exposure; a significant effect of SA ingestion is predictable. Am. J. Ind. Med. 35:511-518, 1999. ( C) 1999 Wiley-Liss, Inc.