Biological Monitoring as a Preventive Occupational Healthcare Tool: Urinary Biomarkers of Benzene and Toluene Exposure Among Small-Scale Printing Workers in South Korea

Background/Objectives: Small-scale workplaces often have limited access to occupational health services, despite potential exposure to hazardous solvents. Biological monitoring can provide worker-level evidence of internal exposure when routine environmental monitoring is limited. This study evaluated urinary biomarkers of benzene and toluene exposure among workers in small-scale printing workplaces in South Korea and examined whether self-reported chemical handling corresponded with biomarker patterns. Methods: In this cross-sectional field biomonitoring study, 21 workers from eight printing companies provided end-of-shift urine samples. Creatinine-adjusted urinary concentrations of trans,trans-muconic acid (t,t-MA), S-phenylmercapturic acid (SPMA), phenol, and o-cresol were analyzed and compared with applicable biological reference values. Associations between reported chemical handling and elevated biomarker levels were estimated using Firth’s penalized logistic regression, and correlations among log-transformed biomarkers were explored. Results: Nine workers (42.9%) had urinary o-cresol concentrations at or above the American Conference of Governmental Industrial Hygienists (ACGIH) biological exposure index of 300 μg/g creatinine. Workers reporting benzol handling, a local term for petroleum-based cleaning products, had higher odds of elevated SPMA, although the estimate was imprecise and hypothesis-generating (age-adjusted OR 6.04, 95% CI 0.75–104.90, p = 0.093). The correlation between SPMA and t,t-MA was stronger among workers reporting benzol handling (r = 0.94) than among those reporting toluene handling (r = −0.01). Conclusions: These exploratory findings indicate that toluene-related internal exposure is a relevant occupational health concern in small-scale printing workplaces, while reported benzol handling may indicate possible low-level benzene-related exposure. Urinary biomonitoring may support exposure surveillance and preventive occupational healthcare in small enterprises when interpreted alongside workplace observations, product information, ventilation, protective equipment use, and worker education.