Self-collected urine sampling to study the kinetics of urinary toluene (and o-cresol) and define the best sampling time for biomonitoring

Purpose To study the excretion kinetics of urinary toluene, TOL-U, and o-cresol, o-C, following occupational exposure to toluene in order to define the best time for sample collection, to apply a non-invasive approach based on self-collected urine sampling. Methods Five rotogravure printing workers exposed to uncontrolled levels of toluene collected spot urine samples over three consecutive working days and the following day of rest. In each sample TOL-U and o-C were measured and kinetics of excretion evaluated. Results Toluene exposure ranged from 48.3 to 75.3 mg/ m3; TOL-U and o-C ranged from 1.4 to 34.6 lg/L and from 0.013 to 1.012 mg/L. A time course trend was obtained: TOL-U and o-C increased during the shift and peaked at the end of exposure and up to 2 h later, respectively; afterwards they rapidly decreased following apparent first order kinetics. Considering TOL-U, the elimination halflife for the first fast phase was 79 (±35 standard error) min, and for the second slow phase was 1,320 (±1,162) min. For o-C the elimination half-life for the first fast phase was 231 (±48) min. Considering a toluene uptake of 86%, TOL-U and o-C excreted in urine were about 0.0067 and 0.18% of the up taken. Conclusion Our results support the use of end shift TOLU as a short term biomarker of occupational exposure to toluene and show the feasibility of self-collected urine sampling to investigate the elimination kinetics of industrial toxics in humans.