Gp Gori

The validity of urinary metabolites as indicators of low exposures to toluene.

SummaryExposure 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 < 0.05) on Day 1, r = 0.90 (P < 0.001) on Day 2, and r = 0.87 (P < 0.001) on Day 3. Orthocresol 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 < 0.001) on Day 2, and r = 0.65 (P < 0.05) on Day 3. Using all available data (41 observations), a very significant correlation (P < 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 < 0.001). The authors conclude that hippuric acid is a valid test for evaluating even low exposures to toluene.

Site of action of metals on the aminolevulinic acid dehydratase of human erythrocytes.

The site of action of four metals (copper, lead, nickel and zinc) on the aminolevulinic acid dehydratase of human erythrocytes was studied. Data obtained after denaturation of allosteric sites with heat treatment and after simultaneous incubation with two metals suggest the following conclusions: copper acts on the catalytic site, whereas lead, nickel and zinc act on the allosteric sites; zinc and nickel act on the same allosteric (metallic) site; zinc and lead only partially act on the same metallic site; nickel and lead act on different allosteric sites.

Postulated mode of action of lead on aminolevulinic acid dehydratase in chronic exposure.

SummaryThe authors studied in vitro the variations of erythrocyte ALA D activity in subjects exposed and not exposed to lead risk before and after three tests: heat treatment at 60° C for five minutes, addition of GSH (1 × 10−2 mol/1) and of zinc (1.5 × 10−4 mol/1). A study of the ratios before and after treatments showed that GSH and zinc were better than heating in identifying false positives, and that zinc was preferable, owing to lesser dispersion of results around the mean. The ratio of ALA D activity before and after treatment is more closely correlated with PbB levels than ALA D activity without treatment. The addition of GSH restored the enzyme activity of the exposed subjects to values equal to those obtained with heating; this did not happen in the nonexposed subjects. It is postulated that, in lead exposure, the metal acts only on the thiol groups, which may then be reactivated by an optimal concentration of GSH.