Evaluation of synergistic factors on BTEX urinary biomarkers in motorcycle riders exposed to heavy traffic in a megacity.

Fuel combustion is a major source of volatile organic compounds such as benzene, a known human carcinogen. Benzene is metabolized into intermediate biomarkers that can be used to assess the extent of exposure. This study aimed to investigate the association between urinary concentrations of creatinine (Cr), muconic acid (MA), trans, trans-muconic acid (tt-MA), and hippuric acid (HA) with demographic, lifestyle, and occupational factors among motorcyclists exposed to heavy traffic in the Shiraz metropolis, both before and after shift work. Data on demographic characteristics, lifestyle habits, and working conditions were collected through structured interviews and questionnaires. Urinary biomarkers were extracted using a solid-phase extraction method and analyzed by HPLC with a strong basic anion-exchange cartridge (60 mg/3 mL). The results confirmed a significant increase in biomarker concentrations, particularly HA, after the work shift. Notably, HA levels exceeded the recommended limit in 13.79% of pre-shift samples and 68.97% of post-shift samples. A significant odds ratio (OR) for elevated HA was observed in relation to smoking (OR: 6.37), proximity to traffic, and having a second job. Additionally, riders over the age of 40 were more likely than younger individuals to exceed acceptable tt-MA levels after their shift. Before the work shift, tt-MA levels were partially associated with lifestyle factors such as higher BMI (OR = 2.89; 2.69–19.28), smoking (OR = 1.87; 0.1–11.5), and engagement in a second job. These findings provide evidence of a synergistic effect between demographic and lifestyle factors, increasing the health risks faced by workers during shift-based occupations.