Comprehensive urinary metabolite profiles of workers exposed to aniline, 2,4-dimethylaniline, and 2-methylaniline

Biological exposure monitoring is particularly useful for understanding skin absorption of hazardous substances; however, existing measurement methods for aromatic amines show room for improvement, as they focus only on unchanged compounds. This study aimed to determine urinary concentrations of the unchanged compounds and metabolites of 3 aromatic amines (aniline, 2,4-dimethylaniline [m-xylidine], and 2-methylaniline [o-toluidine]) following enzymatic hydrolysis pretreatment, to calculate their proportions, and to assess markers for occupational biological exposure monitoring.

Urine samples were collected at the end of work shifts on consecutive days from 11 workers at a plant handling aromatic amines. Samples were enzymatically hydrolyzed using glucuronidase and sulfatase. The urinary concentrations of 25 substances were determined using liquid chromatography-tandem mass spectrometry.

After exposure to the 3 aromatic amines, the major urinary excretion types were benzene ring-hydroxylated compounds, ring-hydroxylated and N-acetylated compounds, and side-chain methyl group oxides. The presence of unchanged and N-acetylated compounds was minor. Metabolism and urinary excretion were relatively different between the workers in our study and reported values from animal studies.

Excluding metabolites with low specificity, the sum of unchanged compounds and primary metabolites in urine could be a useful marker for biological exposure monitoring. Regarding aniline exposure, the relevant markers are the sum of aniline, N-acetyl-4-hydroxyaniline, and 2-hydroxyaniline. For 2,4-dimethylaniline exposure, the markers are the sum of 2,4-dimethylaniline, N-acetyl-4-carboxy-2-methylaniline, and 6-hydroxy-2,4-dimethylaniline. For 2-methylaniline exposure, the markers are the sum of 2-methylaniline, N-acetyl-4-hydroxy-2-methylaniline, 4-hydroxy-2-methylaniline, and 6-hydroxy-2-methylaniline. Urine sampling is recommended at the end of work shifts on consecutive working days.