Excretion of hippuric acid and m- or p-methylhippuric acid in the urine of persons exposed to vapours of toluene and m- or p-xylene in an exposure chamber and in workshops, with specific reference to repeated exposures.

382-385. Four male volunteers were exposed to 200 p.p.m. of toluene for five one-hour periods separated by one-hour intervals. The excretion curve of hippuric acid showed multi-peaks, and almost concided with a theoretical curve previously described. The fraction of the toluene absorbed which was accounted for as hippuric acid was only slightly lower than after a single exposure. In a paint spraying shop exposure was measured both from the concentrations of toluene in the air by a Kitagawa detector and from the exceretion of urinary hippuric acid. The results were in general agreement, with a correlation coefficient of 0·67. Urinary hippuric acid and methylhippuric acid were determined on urines from two workers in a shipbuilding yard who used paint thinned with toluene and xylene. The concentrations of the acids varied from day to day depending on the kind and the duration of work. From the concentrations found the mean concentrations to which the workers were exposed were calculated as a fraction of the maximum allowable concentration (M.A.C.). One worker was, on this evidence, exposed to more than the combined M.A.C. on three days out of six.