Toluene: correlation between occupational exposure limits and biological exposure indices

Threshold limit values for chemical substances and biological exposure indices are the main tools used in occupational hygiene and occupational medicine to control worker exposure levels. The correlation between these limits and indicators is of fundamental importance. The setting of new toluene exposure limits has raised discussion about which indicator to use. This article aims to enrich this debate with scientific data. Through a literature review, we provide a broad analysis of the factors that led to the lowering of the occupational exposure limit. Although internationally, biological indicators for toluene were replaced more than a decade ago, Brazilian authorities only began to discuss changing them in 2020. Toluene is a concern due to critical effects observed in exposed individuals, especially miscarriage. Urinary οrtho-cresol was suggested as the main biomarker in 2007. Given the broad data analysis, there are no doubts about the utility of οrtho-cresol as a biological indicator for toluene; what is lacking now is implementation of a monitoring system to comply with the legislation.