Experimental human exposure to toluene

Summary

The relationship between the individual toluene uptake and the urinary hippuric acid excretion was studied under experimental conditions. Six healthy male subjects were exposed to various concentrations in inspired air (50, 100, 125, 150, and 200 ppm) at rest or under different levels of physical effort.

The hippuric acid excretion near the end of the exposure appeared under all circumstances directly proportional to the time-weighted uptake rate of toluene. The correlation between respiratory uptake rate and the rate of metabolite excretion near the end of the exposure period proved not to be systematically influenced by personal factors such as body weight, amount of body fat, urine flow rate and urinary pH. The relatively pronounced differences in background excretion of hippuric acid and, perhaps, distribution phenomena of toluene between different tissues under heavy workload conditions, can partly explain the greater variability in metabolite excretions as compared to the individual uptake rates.

The correlation between the individual uptake rate of toluene and the hippuric acid excretion proved substantially better when using the end exposure excretion rate as exposure parameter as compared with the end exposure hippuric acid concentration, even after correcting the latter for urine density.

Reasonable biological limit values complying to an acceptable time-weighted toluene dose were found to be 3000–3500 mg/l and 2.0–2.5 mg/min, resp. for average hippuric acid concentrations and excretion rates in spot samples during the second half of a complete work shift.