F. Brugnone

Biomonitoring of occupational toluene exposure

SummaryToluene exposure was studied in 20 workers employed in painting and hand-finishing in an art furniture factory. Toluene was determined in the environmental air of places of work and in the alveolar air and blood of the workers. Hippuric acid and cresols were also tested in the workers urine. Blood and urine tests were carried out before the work shift on Monday and Friday morning and at the end of the work shift on Friday afternoon. The other tests were performed on Friday afternoon only. Alveolar toluene concentrations, which were significantly correlated with environmental toluene concentrations (r= 0.6230; P < 0.01), corresponded to 19.4% of the toluene concentration in the atmosphere. Blood toluene was also found in painters on Monday morning and was significantly correlated with the other parameters. On Friday afternoon it was three times higher than the environmental toluene concentration. Urinary o-Cresol was highly correlated with toluene in the atmosphere, in blood and with hippuric acid in urine. On the basis of the slope of the regression line the ratio between urinary o-Cresol and blood toluene concentration was 0.99. At the end of the work shift urinary hippuric acid concentration was highly correlated with o-Cresoluria and with toluene in blood and in the atmosphere.

Biomonitoring of industrial solvent exposures in workers' alveolar air

SummaryTen different solvents, viz., toluene, styrene, methylethyl ketone, acetone, dimethylformamide, cyclohexane, n-hexane, methylcyclopentane, 2-methylpentane, and 3-methylpentane were determined in environmental air and in the alveolar air of workers during the work shift.As regards all ten solvents studied, alveolar concentration (Ca) and the difference between environmental concentration (CO and alveolar concentration (Ci - Ca), were correlated with environmental concentration.According to the slopes of the regression lines, the ratio between alveolar and environmental concentration (Ca/Ci) and the alveolar retention ((Ci - Ca)/Ci) in the case of all ten solvents studied were complementary, i.e., their sum was equal to unity. The solvents with high solubility in blood, i.e., toluene, styrene, methylethyl ketone, acetone, and dimethylformamide showed a Ca/Ci ratio lower than 0.5 and the solvents with low solubility, i.e., cyclohexane, hexane, and their isomers showed a Ca/Ci ratio higher than 0.5. According to the findings which prove that the alveolar concentration of all solvents studied during the work shift is a function of variations in the environmental concentrations it seems reasonable to suggest the use of alveolar tests for monitoring environmental exposure to solvents during the work shift.

Experimental Neurotoxicity and Urinary Metabolites of the C5-C7 Aliphatic Hydrocarbons Used as Glue Solvents in Shoe Manufacture

Rats were intermittently exposed (9 to 10 h/d, 5 to 6 d/week) to controlled concentrations of single analytical grad solvents in ambient air. After periods ranging from 7 to 30 weeks the animals were perfused with glutaraldehyde and samples of nerves were processed for light microscopy of sections and of teased fibers. Animals treated with n-hexane at 5000 ppm (14 weeks) or 2500 ppm (30 weeks) developed the typical giant axonal degeneration already described in rats treated continuously with 400 to 600 ppm of the same solvent for 7 weeks or more. No such alterations were found in rats subjected to the following intermittent respiratory treatments: n-hexane 500 ppm (30 weeks) or 1500 ppm (14 weeks), cyclohexane 1500 or 2500 (30 weeks), n-pentane 3000 ppm (30 weeks), n-heptane 1500 ppm (30 weeks), 2-methylpentane 1500 ppm (14 weeks), and 3-methylpentane 1500 ppm (14 weeks). The following metabolites were found in the urine of rats according to treatment (in parenthesis): 2-methyl-2-pentanol (2-methylpentane); 3-methyl-2-pentanol and 3-methyl-3-pentanol (3-methylpentane), 2-hexanol, 3-hexanol, gamma-valerolactone, 2,5-dimethylfuran, and 2,5-hexanedione (n-hexane). 2-Hexanol was found to be the main urinary metabolite of n-hexane, while 2,5-hexanedione was present only in a lesser proportion. This feature of rat metabolism suggests that in this species 2,5-hexanedione reaches an effective level at its site of action during intermittent respiratory treatment with n-hexane with difficulty and explains the high concentrations necessary to cause polyneuropathy in rats subjected to this treatment.

Metabolic interaction between n-hexane and toluene in vivo and in vitro

SummaryMetabolic interference between n-hexane and toluene was studied both in vivo and in vitro. In in vivo experiments the urinary excretion of n-hexane and toluene metabolites was tested in rats treated with the two solvents separately or in combination. The same experimental program was repeated in rats pretreated with phenobarbital (PB). The urinary excretion of n-hexane metabolites in rats treated with the two solvents showed a significantly decreased excretion of all n-hexane metabolites in comparison with those treated with n-hexane alone. In rats pretreated with PB the excretion of n-hexane metabolites was significantly higher compared with that of unpretreated rats; the combined administration of the two solvents showed in this case, too, that n-hexane metabolite excretion was less than that found in rats treated with n-hexane alone. The biotransformation of toluene to o-cresol and hippuric acid studied in the urine of rats treated with or without n-hexane and pretreated or not with PB did not show any difference. The in vitro metabolic interference was studied by measuring the disappearance of solvents from rats incubated liver microsomes. The maximum velocity (Vmax) of n-hexane was 2.8 nmol/g/min when incubated alone, 1.9 and 0.9 nmol/g/min when incubated with 5 and 20 μM of toluene respectively. The Vmax of toluene was 14.9 nmol/g/min when incubated alone and 13.1 and 10.5 nmol/g/min when incubated with 10.4 and 20.9 μM of n-hexane respectively. The inhibition constant (Ki) of toluene on n-hexane biotransformation was 7.5 μM and that of n-hexane on toluene was 30 μM. The data show that a mutual non-competitive interference exists in vitro betweeen n-hexane and toluene. The interference of toluene on n-hexane biotransformation was detectable also in vivo experiments, while n-hexane did not modify the biotransformation of toluene.

Biological monitoring of occupational exposure to n-hexane by measurement of urinary 2,5-hexanedione.

SummaryOccupational exposure ton-hexane in shoe factory workers was monitored by measuring urinary 2,5-hexanedione, the major metabolite of this solvent and the probable cause of peripheral neuropathy in exposed workers. Solvent pollution was monitored in the work environments of 189 employees, of whom 123 (65%) worked in Alicante, Spain, and 66 (35%) in Veneto, Italy. 2,5-Hexanedione was measured in spot urine samples collected from workers at the end of the shift. Information on working conditions was obtained from a previous study. A significant linear correlation was found between mean environmental concentration ofn-hexane and urinary concentration of 2,5-hexanedione. The variability in the correlation may have been due to the variable use of protective clothing (gloves), and to variations in exposure during the working week. In numerous workers, percutaneous absorption ofn-hexane represented as much as 50% of the total absorbed dose. Urinary concentrations of 2,5-hexanedione tended to increase during the working week. Simultaneous exposure ton-hexane and toluene tended to reduce urinary excretion of 2,5-hexanedione, whereas exposure ton-hexane and methyl ethyl ketone tended to increase excretion of the metabolite.

Urinary excretion of n-hexane metabolites in rats and humans

SummaryThe urinary excretion of n-hexane metaboites was studied in rats which were either treated or not with phenobarbital before n-hexane treatment and in workers occupationally exposed to n-hexane.A new hexane metabolite, 3-hexanol, and 2-hexanol were found in rat urine, but not in workers urine. The amount of 2-hexanol excreted during 24 h after n-hexane administration, was equal to 1.2 – l.7 % of the dose. The ratio between 3-hexanol excreted and n-hexane injected was much less than 1 %. Phenobarbital affected 3-hexanol excretion but not 2-hexanol excretion.The lack of n-hexane metabolites in workers urine, which can be explained by the low ratio of metabolite excretion to the n-hexane absorbed, suggests that urine analysis is unsuitable for monitoring hexane exposure during work.

Measurement of the urinary metabolites of N-hexane, cyclohexane and their isomers by gas chromatography

SummaryA gas chromatographic method for analyzing the urinary metabolites of n-hexane (2-hexanol, 2,5-hexanedione, 2,5-dimethylfuran and γ-valerolactone), of 2-methylpentane (2-methyl-2-pentanol), of 3-methylpentane (3-methyl-2-pentanol), and of cyclohexane (cyclohexanol) was developed. Processing of urine and the gas chromatographic conditions are described. The recovery rate of all hexane metabolites, except 2,5-dimethylfuran, ranged between 92 and 100%. The variation coefficient of metabolites determination was between 1.5 and 5%, apart from 2,5-dimethylfuran determination for which the variation coefficient was 15%. The detection limits ranged between 0.2 and 0.7 mg/1 and between 0.05 and 0.1 mg/1 when a packed or capillary column was used. Results obtained from a packed and capillary column are discussed.

Urinary excretion of n-hexane metabolites

Exposure to n-hexane, a component of many industrial solvent mixtures, is known to cause polyneuropathy in man. The concentration of metabolites in urine following exposure may be useful in biological monitoring. In a comparative study experimental animals (rat, rabbit and monkey) were subjected to single inhalatory treatments of 6, 12 and 24 h with 5,000 ppm of pure n-hexane. At the end of the treatments and at intervals thereafter, urine, and in rats also blood, were collected and analyzed for n-hexane and its metabolites. While the urine of rats contained 2-hexanol, 3-hexanol, methyl n-butyl ketone, 2,5-dimethylfuran, γ-valerolactone and 2,5-hexanedione, rabbit and monkey urine were found to contain only 2-hexanol, 3-hexanol, methyl n-butyl ketone and 2,5-hexanedione. Within 72 h of the end of exposure, the principal metabolite was 2,5-dimethylfuran in rats and 2-hexanol in rabbits and monkeys. In all three species the excretion rates of methyl n-butyl ketone, 3-hexanol and 2-hexanol peaked several hours earlier than 2,5-hexanedione (and γ-valerolactone and 2,5-dimethylfuran in rats). In all species 2,5-hexanedione was still detectable in urine 60 h following exposure. n-Hexane metabolites in rat blood were 2-hexanol, methyl-n-butyl ketone, 2,5-dimethylfuran and 2,5-hexanedione. The first two, as well as n-hexane itself, were found in maximum concentration immediately after termination of exposure, while 2,5-dimethylfuran and 2,5-hexanedione, with the longer exposure times, peaked some hours later. The data from urine collected at the end of exposure were compared with those obtained in a parallel study in humans occupationally exposed to a mixture of hexane isomers. Humans chronically exposed to 10–140 ppm n-hexane had 2,5-hexanedione concentrations in urine ranging from 0.4 to 21.7 mg/l, i.e., in the same proportion as rats exposed once for 6 or 12 h to 5,000 ppm.

Lung uptake and metabolism of cyclohexane in shoe factory workers

SummaryCyclohexane in environmental air, alveolar air, and blood, and urinary cyclohexanol were determined in shoe factory workers occupationally exposed to cyclohexane. All the parameters studied correlated well with each other. The mean alveolar cyclohexane corresponded to 78% of the environmental cyclohexane. Blood cyclohexane corresponded to 53–78% of alveolar cyclohexane concentration. Urinary cyclohexanol corresponded to 0.1–0.2% of the cyclohexane absorbed.The results suggest that biological monitoring of cyclohexane via alveolar air and urine can be reliably used in the evaluation of occupational exposure. It is likely that the urinary cyclohexanol test, from the practical viewpoint, represents the simplest way of monitoring cyclohexane exposure in industrial plants.

Alveolar air and blood dichloromethane concentration in shoe sole factory workers.

SummaryThe dichloromethane (CH2 Cl2 ) concentration at the fourth working hour has been tested in alveolar air and blood of 14 workers, and in the environmental air of a shoe sole factory using polyurethane resin.A mean lung uptake of respectively 0.31, 0.62 and 1.43 mg/min has been found with respect to a mean environmental concentration equivalent to 74, 122, and 333 mg/m3.It results that the CH2 C12 solubility in the blood is equivalent to 9.8, correlated to the triglycerides concentration in blood.