variations were small. The background concentrations
of hipp`u`rc acid normally found in urine are
high, however, and there are large inter-individual
variations. Szadkowski et al have shown that a meal
of food containing benzoic acid caused a threefold
and in particular cases a 10-fold increase of hippuric
acid excretion.29 The normal concentration of hippuric
acid in the morning urine is 1-2 g/l and after a
meal with low intake of benzoic acid 0-75 g/l. Soft
drinks may increase the concentration of hippuric
acid in urine as much as exposure to 200 mg/m3
toluene.2730 Consequently hippuric acid in urine is
questionable as a biological index of exposure to
toluene.