Exposure to toluene was studied in a group of 14 subjects working in a printing industry, who were exposed to this solvent only. Environmental monitoring was carried out using personal samplers for the whole workshift over three consecutive days. Toluene TWA concentrations ranged from 37 to 229 mg/m3. At the end of the workshift on each day of investigation, urine samples were collected for the determination of hippuric acid and ortho-cresol. Hippuric acid was also determined for urine before the workshift and on the Saturday and Monday mornings after the end of exposure; hippuric acid was also determined in 16 controls over the same five-day period. At the end of the workshift, hippuricuria levels in exposed workers always turned out to be statistically different from pre-workshift levels and those of the controls. The end-of-workshift hippuricuria levels of exposed workers were significantly correlated with the mean daily environmental concentration (TWA): in the three days of comparative study, we found r = 0.63 (P less than 0.05) on Day 1, r = 0.90 (P less than 0.001) on Day 2, and r = 0.87 (P less than 0.001) on Day 3. Ortho-cresol turned out to be correlated with daily exposure less significantly than hippuric acid: r = 0.49 (n.s.) on Day 1; r = 0.78 (P less than 0.001) on Day 2, and r = 0.65 (P less than 0.05) on Day 3. Using all available data (41 observations), a very significant correlation (P less than 0.001) was found between the TWA and both metabolites (r = 0.80 for hippuric acid; r = 0.68 for o-cresol). The values of the two metabolites in the end-of-workshift urine samples (41 observations) also turned out to be well correlated (r = 0.70; P less than 0.001). The authors conclude that hippuric acid is a valid test for evaluating even low exposures to toluene.

The distribution of 2,5-HD concentration was log-normal and the corresponding centiles at the 95% confidence interval were as follows: the 50th centile, 0.270 mg/l for men and 0.191 mg/l for women; the 75th centile, 0.352 and 0.330 mg/l, respectively, for men and women; and the 95th centile, 0.762 and 0.582 mg/l, respectively, for men and women. The reference value, calculated as the upper unilateral 95% tolerance interval at 95% of confidence, was 0.795 mg/l for men and 0.627 for women.

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Exposure to nitrous oxide in surgical theaters was evaluated for duration, numbers, and types of surgical procedures. The concentration of the gas in the air was 92-444 ppm. Before and after the surgical sessions, samples of urine and expired air were collected from surgical theater personnel for gas determination. Nitrous oxide concentrations in urine and in expired air showed a good correlation with gas concentration in the air (r = 0.760 and r = 0.921, respectively). Moreover, a good correlation (r = 0.823) between gas concentration in urine and that in expired air was also found. A biological threshold limit value (TLV) of 20.6 micrograms/liter for urine and of 29.6 ppm for expired air was calculated, based on the limit of 50 ppm in the air proposed by the American Conference of Governmental Industrial Hygienists (ACGIH). Other biological TLVs corresponding to higher proposed limits (200 and 500 ppm) were also calculated.