Urinary Trans, Trans -Muconic Acid is Not a Reliable Biomarker for Low-level Environmental and Occupational Benzene Exposures

Abstract

BackgroundBenzene is a known occupational and environmental pollutant. Its urinary metabolite trans, trans-muconic acid (tt-MA) has been introduced by some environmental and occupational health regulatory associations as a biological index for the assessment of benzene exposure; however, recently, doubts have been raised about the specificity of tt-MA for low-level benzene exposures. In the present study, we investigated the association between urinary levels of tt-MA and inhalational exposure to benzene in different exposure groups.MethodsBenzene exposure was assessed by personal air sampling. Collected benzene on charcoal tube was extracted by carbon disulfide and determined by a gas chromatograph (gas chromatography with a flame ionization detector). Urinary tt-MA was extracted by a strong anion-exchange column and determined with high-performance liquid chromatography–UV.ResultsUrinary levels of tt-MA in intensive benzene exposure groups (chemical workers and police officers) were significantly higher than other groups (urban and rural residents), but its levels in the last two groups with significant different exposure levels (mean = 0.081 ppm and 0.019 ppm, respectively) showed no significant difference (mean = 388 μg/g creatinine and 282 μg/g, respectively; p < 0.05). Before work shift, urine samples of workers and police officers showed a high amount of tt-MA and its levels in rural residents’ samples were not zero.ConclusionOur results suggest that tt-MA may not be a reliable biomarker for monitoring low-level (below 0.5 ppm) benzene exposures.

Factors Affecting Urinary tt-Muconic Acid Detection among Benzene Exposed Workers at Gasoline Stations

“…We found that over 25% of workers excreted tt-MA that exceeded the recommended 500 µg/g Cr. Some previous studies have shown that tt-MA levels in different groups of workers who might be exposed to benzene (e.g., refinery workers [23], turnaround maintenance workers [24], traffic policeman [25,26,27] and gasoline station workers [28]) did not exceed 500 µg/g Cr. In one case study conducted in Thailand, it was found that significant differences in tt-MA levels only existed between workers occupationally exposed to benzene and the general population [29].…”

Exposure to volatile organic compounds and airway inflammation

“…About 2% of the total benzene taken up by humans is excreted via urine as tt-MA, and its excretion half-life is < 6 h [ 33 ]. Although urinary tt-MA has been recommended as a biomarker to assess occupational exposure to benzene, Jalai et al showed that tt-MA cannot be used as a reliable biomarker for exposure to low dose benzene [ 34 ].…”

Environmental Assessment and Evaluation of Oxidative Stress and Genotoxicity Biomarkers Related to Chronic Occupational Exposure to Benzene

“…The levels of tt MA encountered in the urine samples of the workers from Group I and Group II were below the baseline levels reported in the literature, which vary from <0.01 to 0.66 mg g −1 Cr [61,62]. Recent studies have investigated the association between urine tt MA concentrations and occupational/environmental exposure to benzene, suggesting that tt MA is not sensitive enough as a biomarker for monitoring exposure to benzene at concentrations below 0.1 ppm, which is the situation of the study population here [60,63,64]. Melikian et al [65] did an extensive study of the specificity and sensitivity of the biomarkers of benzene, tt MA and S -PMA, at low exposure levels and found that the variation in the percentage of benzene transformed into S -PMA and tt MA diminished as the concentration of benzene itself diminished, especially the conversion of benzene into tt MA.…”