Abstract
Nine male volunteers were exposed to 2H,-
toluene (200 mg/m3 for two hours during a
workload of 50 W) via inspiratory air with the
aid of a breathing valve and mouthpiece.
Labelled toluene was used to differentiate between
hippuric acid originating from exposure
to toluene and hippuric acid normally excreted
in urine. The total uptake of toluene was 2-2
(standard deviation (SD) 0 2) mmol, or 50% of
the amount inhaled. Four hours after the end
of exposure 1-4 (SD 0 3) mmol or 65% of the
total uptake had been excreted in urine as 'Hhippuric
acid and 20 hours after the end of
exposure the cumulative excretion of 'H-hippuric
acid was 1-8 (SD 0-3) mmol, or 78% of the
total uptake. By contrast the cumulative excretion
of labelled plus unlabelled hippuric acid
exceeded the total uptake of toluene already
after four hours. The excretion rate of 'Hhippuric
acid was highest, about 5 pmol/min,
during exposure and the SD between the
subjects was low. The background concentrations
of unlabelled hippuric acid in urine were
high, however, and there were large differences
between subjects. These findings confirm
earlier indications that for low exposure, urinary
hippuric acid concentration cannot be used
for biological monitoring of exposure to
toluene.