Evaluation of urinary metabolites as biomarkers for occupational p-chloronitrobenzene exposure: a pilot study

We explored the feasibility of using urinary metabolites of p-chloronitrobenzene (p-CNB) as exposure biomarkers of occupational p-CNB exposure. Forty-two workers exposed to p-CNB during their jobs at a chemical enterprise in Shaoxing, Zhejiang Province, China were included in the exposure group, while administrative personnel who do not come into contact with p-CNB at work were included in the control group. Each worker in the exposure group was equipped with a personal air sampler to collect airborne p-CNB samples, and urine samples were collected at the conclusion of each shift. After sample collection, the airborne p-CNB concentrations and urinary metabolite concentrations were detected by gas chromatography-tandem mass spectrometry and ultra-performance liquid chromatography - quadrupole - orbitrap high resolution mass spectrometry, respectively. The urinary metabolite concentrations were corrected by the content of urinary creatinine. Subsequently, the correlations between the urinary metabolite concentrations and the p-CNB time-weighted average (TWA) concentrations were assessed using correlation analysis. All p-CNB TWA concentrations measured in this study were below the occupational exposure limit in the Chinese national standards. In the exposure group, N-acetyl-S-(4-nitrophenyl)-L-cysteine (NANPC), 2-chloro-5-nitrophenol (2C5NP), p-chloroacetanilide (p-CAA), p-chlorooxanilic acid (p-COA), 2-amino-5-chlorophenol (2A5CP), and p-chloroaniline (p-CA) were detected at varying levels. The percentages of NANPC, 2C5NP, p - CAA, p - COA, 2A5CP, and p - CA were 64.1%, 5.1%, 0.3%, 15.1%, 5.1%, and 10.3%, respectively. We found extremely significant positive relationships ( p  < 0.01) between the urinary metabolite concentrations (p-CA, 2C5NP, 2A5CP, NANPC, and p-COA) and the p-CNB TWA concentrations, with respective correlation coefficients of 0.827, 0.673, 0.790, 0.714, and 0.741. Thus, these five metabolites may be used as exposure biomarkers of occupational p-CNB exposure. Moreover, among these metabolites, NANPC was identified as the most suitable exposure biomarker because it had the highest correlation coefficient and the highest content in urine.