The effect of workload on biological monitoring of occupational exposure to toluene and n-Hexane: contribution of physiologically based toxicokinetic modeling

A physiologically based toxicokinetic model was used to examine the impact of work load on the relationship between the airborne concentrations and exposure indicator levels of two industrial solvents, toluene and n-Hexane. The authors simulated occupational exposure (8 hr/day, 5 days/week) at different concentrations, notably 20 ppm and 50 ppm, which are the current threshold limit values recommended by ACGIH for toluene and n-hexane, respectively. Different levels of physical activity, namely, rest, 25 W, and 50 W (for 12 hr followed by 12 hr at rest) were simulated to assess the impact of work load on the recommended biological exposure indices: toluene in blood prior to the last shift of the workweek, urinary o-cresol (a metabolite of toluene) at the end of the shift, and free (nonhydrolyzed) 2,5-hexanedione (a metabolite of n-hexane) at the end of the shift at the end of the workweek. In addition, urinary excretion of unchanged toluene was simulated. The predicted biological concentrations were compared with the results of both experimental studies among human volunteers and field studies among workers. The highest predicted increase with physical exercise was noted for toluene in blood (39 microg/L at 50 W vs. 14 microg/L at rest for 20 ppm, i.e., a 2.8-fold increase). The end-of-shift urinary concentrations of o-cresol and toluene were two times higher at 50 W than at rest (for 20 ppm, 0.65 vs. 0.33 mg/L for o-cresol and 43 vs. 21 microg/L for toluene). Urinary 2,5-hexanedione predicted for 50 ppm was 1.07 mg/L at 50 W and 0.92 mg/L at rest (+16%). The simulations that best describe the concentrations among workers exposed to toluene are those corresponding to 25 W or less. In conclusion, toxicokinetic modeling confirms the significant impact of work load on toluene exposure indicators, whereas only a very slight effect is noted on n-hexane kinetics. These results highlight the necessity of taking work load into account in risk assessment relative to toluene exposure.

Quantitation of o-, m- and p-cresol and deuterated analogs in human urine by gas chromatography with electron capture detection

A gas chromatographic method for the analysis of cresol metabolites of toluene and [2H8]toluene in urine was developed. Cresol glucuronides and sulfates in urine were hydrolyzed with beta-glucuronidase and arylsulfatase. Following extraction with tert.-butyl methyl ether and solvent exchange into benzene, the cresols were derivatized with heptafluorobutyric anhydride to form the heptafluorobutyrate esters. The derivatives were analyzed by gas chromatography with electron capture detection. Chromatographic resolution was achieved between all cresol isomers and their 2H7 analogs. Calibration ranged from 0.001 to 500 microg/ml. Recoveries were 55-97% and showed no trend with respect to analyte concentration. Within-day precision of analyses of benchmark urine samples had a coefficient of variation of less than 4%. The assay sensitivity was limited by chromatographic background but was sufficient for quantification of the unlabeled cresols in urine from men with only environmental exposure to toluene. Average levels in urine samples from 45 men were 0.023, 0.054 and 37 microg/ml for o-, m- and p-cresol, respectively.

Dietary and ethanol induced alterations of the toxikokinetics of toluene in humans

This study was undertaken to evaluate the influence of a carbohydrate restricted diet, a subacute ethanol intake, and their combined effect on the kinetics of toluene in humans. Eight healthy male volunteers were exposed by inhalation at four different occasions to 200 mg/m3 2H8-toluene for two hours at a work load of 50 W after a one week low (30%) carbohydrate (CH) diet or high (60%) CH diet with (+EtOH) or without (-EtOH) ethanol consumption (47 g ethanol) on the evening before exposure. Deuterium labelled toleune was used to measure the excretion of hippuric acid originating from toluene separately from hippuric acid from other sources. The results indicated that subacute ethanol consumption combined with a carbohydrate restricted diet, may enhance the metabolism of toluene in humans at an exposure concentration of 200 mg/m3. The cumulative amount of hippuric acid excreted in the urine up to 20 hours after the end of exposure in % of the net uptake of toluene was enhanced by 22% (p = 0.05) in the low CH + EtOH compared with the low CH-EtOH experiment. The apparent blood clearance of toluene was 37% higher in the low CH + EtOH than in the low CH-EtOH experiment, but this effect was not statistically significant (p = 0.1). There were no significant changes in the kinetics of toluene as a result of a low carbohydrate diet alone. Neither did subacute ethanol intake without the combination with a carbohydrate restricted diet influence the kinetics of toluene.

Effects of smoking and drinking habits on urinary o-cresol excretion after occupational exposure to toluene vapor among Chinese workers

The relationship between the time-weighted average intensity of exposure to toluene and o-cresol concentration in shift-end urine was investigated in nearly 500 factory workers of both sexes in China, together with a similar number of nonexposed control subjects. Toluene concentration (25 ppm as geometric mean and 550 ppm as the maximum) was monitored by diffusive sampling using carbon cloth as adsorbent followed by gas chromatographic (GC) analysis. o-Cresol (up to 7 mg/l) was measured by GC after acid hydrolysis of samples. Urinary o-cresol levels correlated significantly (r = 0.69-0.77; p < 0.01) with toluene exposure in men, women and the two sexes in combination, regardless of correction for urine density. When compared with hippuric acid, however, o-cresol was less sensitive as an indicator of exposure to toluene and is not a suitable biological marker for detecting low level toluene exposure. Since urinary o-cresol level was significantly reduced by smoking, drinking, and the two habits combined, it cannot be considered reliable as an indicator of exposure to toluene.

Toxicokinetics of toluene and urinary excretion of hippuric acid after human exposure to 2H8-toluene

Nine male volunteers were exposed to 2H8-toluene (200 mg/m3 for two hours during a workload of 50 W) via inspiratory air with the aid of a breathing valve and mouthpiece. Labelled toluene was used to differentiate between hippuric acid originating from exposure to toluene and hippuric acid normally excreted in urine. The total uptake of toluene was 2.2 (standard deviation (SD) 0.2) mmol, or 50% of the amount inhaled. Four hours after the end of exposure 1.4 (SD 0.3) mmol or 65% of the total uptake had been excreted in urine as 2H-hippuric acid and 20 hours after the end of exposure the cumulative excretion of 2H-hippuric acid was 1.8 (SD 0.3) mmol, or 78% of the total uptake. By contrast the cumulative excretion of labelled plus unlabelled hippuric acid exceeded the total uptake of toluene already after four hours. The excretion rate of 2H-hippuric acid was highest, about 5 mumol/min, during exposure and the SD between the subjects was low. The background concentrations of unlabelled hippuric acid in urine were high, however, and there were large differences between subjects. These findings confirm earlier indications that for low exposure, urinary hippuric acid concentration cannot be used for biological monitoring of exposure to toluene.

Determination of aromatic hydrocarbons and their metabolites in human blood and urine

Methods for the biological monitoring of aromatic hydrocarbons and their metabolites in the human blood and urine are reviewed. For the determination of the unchanged aromatic hydrocarbon in blood, gas chromatographic head-space analysis is recommended. The metabolites can be monitored by photometric, thin-layer chromatographic, high-performance liquid chromatographic and gas chromatographic methods. For the assessment of health risks caused by aromatic hydrocarbons, reference values and occupational limit values, expressed as biological tolerance values and biological exposure indices, have to be considered.

Urinary excretion of o-cresol and hippuric acid after toluene exposure in rotogravure printing

In 62 male rotogravure printers, the time-weighted average (TWA) toluene exposure during one workweek ranged from 8 to 496 mg/m3 (median 96). Post-shift urinary excretion of hippuric acid showed a poor correlation with the air toluene concentration. Level of o-cresol excretion ranged from 0.08 to 2.37 mmol/mol creatinine and was associated with the exposure (rS = 0.57, P less than 0.0001), although the variation was considerable. However, this metabolite was significantly influenced by smoking habits, both in the workers (0.34 vs 0.10 mmol/mol creatinine after adjustment to zero exposure for the smokers and non-smokers, respectively; P = 0.03) and in 21 unexposed controls (0.18 vs 0.06 mmol/mol creatinine; P = 0.002). The excretion of these metabolites was followed during vacation, when the workers were unexposed. The shared one-compartment half-time was 44 h (+/- SE 30, 82). After 2-4 weeks of vacation, the concentration of o-cresol was significantly higher for the smokers than the non-smokers (0.14 vs 0.06 mmol/mol creatinine; P = 0.02). No smoking-associated difference was found for the urinary hippuric acid concentration. However, there was an association between alcohol consumption and hippuric acid excretion (P = 0.03); no such difference was shown for o-cresol. These results demonstrate that hippuric acid excretion is unsuitable for biological monitoring of toluene exposure when the exposure level is below 200 mg/m3. Also, in spite of the favourable excretion kinetics, the impact of smoking and the large interindividual variation warrant the same conclusion for o-cresol as a means of monitoring low level exposure in an individual worker.

Two cases of acute toluene intoxication

Two patients exposed to high concentrations of toluene in air (greater than 7000 mg/m3) were found at the bottom of a small swimming pool under construction. Their symptoms were stupefaction, paresis, and amnesia. Patient A had been exposed for three hours and patient B for two hours. Ninety minutes after the exposure, the toluene blood concentration in patient A was 4.1 mg/l and in patient B 2.2 mg/l. Urinary ortho-cresol secretion was shown to be a good index of exposure to toluene. After high level exposure, urinary meta-cresol excretion may also be used to monitor toluene exposure.

Health effects of the alkylbenzenes. I. Toluene

The alkylbenzenes, toluene being the most common example, represent a class of six-membered ring aromatic compounds that have a variety of alkyl groups attached. These chemicals are liquids with relatively low boiling points and are used primarily as solvents or as starting materials in the synthesis of other chemicals and drugs. They are also integral components of gasoline, distillate fuels and other petroleum products. These substituted aromatics are economically important in the chemical, petroleum, pharmaceutical, polymer, paint and dye industries. Alkylbenzenes such as toluene, xylene, ethylbenzene, styrene and cumene are toxicologically important since they are produced, used or disposed of in the largest quantities and therefore might pose significant and potential health risks to man and the environment. In general, the toxicity of alkylbenzenes has been found to be relatively low. Also, for the most part, human and environmental risks are low; however, there may be a few operations where the potential for high exposure could exist. These exposures are minimized by workplace controls or personal protective equipment. Furthermore, health risks for humans are minimized by guidelines for maximum allowable exposure concentrations which have been established for the workplace. This present paper reviews the toxicology and disposition of toluene in animals and humans.

Mutual metabolic suppression between benzene and toluene in man

The exposure intensity during a shift and the metabolite levels in the shift-end urine were examined in male workers exposed to either benzene (65 subjects; the benzene group), toluene (35 subjects; the toluene group), or a mixture of both (55 subjects; the mixture group). In addition, 35 non-exposed male workers (the control group) were similarly examined for urinary metabolites to define background levels. A linear relationship was established between the intensity of solvent exposure and the corresponding urinary metabolite levels (i.e. phenol, catechol and quinol from benzene, and hippuric acid and o-cresol from toluene) in each case when one of the three exposed groups was combined with the control group for calculation. Comparison of regression lines in combination with regression analysis disclosed that urinary levels of phenol and quinol (but not catechol) were lower in the mixture group than in the benzene group when the intensities of exposure to benzene were comparable, indicating that the biotransformation of benzene to phenolic compounds (excluding catechol) in man is suppressed by co-exposure to toluene. Conversely, metabolism of toluene to hippuric acid was suppressed by benzene co-exposure. Conversion of toluene to o-cresol was also reduced by benzene, but to a lesser extent. The significance of the present findings on the mutual suppression of metabolism between benzene and toluene is discussed in relation to solvent toxicology and biological monitoring of exposure to the solvents.

Toluene metabolism during exposure to varying concentrations combined with exercise

The urinary excretion of hippuric acid (HA) and ortho-cresol (O-cr) in man was measured in two studies of 7-h exposure to toluene in a climate chamber, either constant concentration of 100 ppm or varying concentrations containing peaks of 300 ppm but with a time-weighted average of 100 ppm. In Study A, four males were exposed to clean air and to constant and varying concentrations of toluene in combination with rest and with 100 W exercise in 140 min. Exercise increased end exposure excretion rate of HA and O-cr by 47 and 114%, respectively. After exposure, all excess HA was excreted within 4 h, while O-cr was eliminated with a half life of about 3 h. Alveolar air concentration of toluene varied between 21 and 31 ppm during constant exposure and between 13 and 57 ppm during varying exposure, but no difference in mean alveolar toluene concentration or in metabolite excretion was seen between the exposure schedules. In Study B, 32 males and 39 females aged between 31 and 50 years were exposed once to either clean air, constant or varying concentrations of toluene. Background excretion rate of HA was 0.97 +/- 0.75 mg/min (1.25 +/- 1.05 g/g creatinine) and rose to 3.74 +/- 1.40 mg/min (3.90 +/- 1.85 g/g cr) during the last 3 h of exposure to 100 ppm toluene. The corresponding figures for O-cr were 0.05 +/- 0.05 micrograms/min (0.08 +/- 0.14 mg/g cr), and 2.04 +/- 0.84 micrograms/min (2.05 +/- 1.18 mg/g cr). The individual creatinine excretion rate was considerably influenced by sex, body weight and smoking habits, thus influencing the metabolite concentration standardised in relation to creatinine. It is concluded that both metabolites are estimates of toluene exposure. O-cr is more specific than HA, but the individual variation in excretion of both metabolites is large, and when implementing either of them as biological exposure indices, the influence of sex, body size, age as well as consumption of tobacco and alcohol has to be considered.

Hippuric acid and ortho-cresol as biological indicators of occupational exposure to toluene

Industrial exposure to toluene was studied in a group of 18 subjects working in a printing plant, exposed only to this solvent. Environmental monitoring was carried out using personal samplers for the whole work-shift. Urine samples were collected for the determination of hippuric acid and ortho(o)-cresol before toluene exposure, at the end of the work-shift, and 5, 9, and 17 h after the end of the work-shift. The values of two metabolites in all the urinary samples were corrected for g creatinine and specific gravity (1.024). Toluene time weighted average (TWA) concentrations ranged from 51 to 221 mg/m3 (7-h samples; two samplings lasting 3.5 h each). Urinary hippuric acid and o-cresol values at the end of the work-shift were significantly higher than the prework-shift values. Both hippuricuria and o-cresoluria end-of-work-shift values, corrected for creatinine and specific gravity, were significantly related to the mean daily environmental concentration of toluene, the correlation being weaker for o-cresol. Correlation coefficients were 0.88 and 0.84 for hippuric acid and 0.63 and 0.62 for o-cresol after correction for creatinine and specific gravity, respectively. No significant relationship was observed between environmental exposure and the values of the two urinary metabolites 5, 9, and 17 h after the end of the work-shift. Extrapolated values from the linear regression analysis at 375 mg/m3 were in good agreement with the biological exposure index (BEI) suggested by ACGIH for hippuric acid.(ABSTRACT TRUNCATED AT 250 WORDS)

Occupational chronic exposure to organic solvents. XII. O-cresol excretion after toluene exposure

Thirty-five printing workers were investigated according to their external and internal exposure to toluene. The concentration of toluene in the air of the working place was determined using stationary air sampling and gas chromatography. To determine the levels of toluene in blood as well as the concentrations of o-cresol, hippuric acid, and phenol in urine, biological specimens were collected at the end of exposure. The parameters were determined by gas chromatography and gas chromatography/mass spectrometry. According to our results, o-cresol concentrations higher than 5.3 mg per litre of post-shift urine might indicate an external exposure higher than the present MAK-value of 200 ppm.

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

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.

Urinary excretion of hippuric acid and o-cresol after laboratory exposure of humans to toluene

The urinary excretion of hippuric acid and o-cresol was studied after respiratory exposure of human volunteers to approximately 80 ppm (306 mg/m3 +/- SD 13) of toluene for 2 h under different work loads (0, 50, 100, 150 W, respectively, during 30-min periods). The diet before and after exposure varied. An isotachophoresis method for the determination of hippuric acid is described. The correlation between the total urinary excretion, excretion rate and concentration of hippuric acid, and the respiratory uptake of toluene was poor or non-existing. The same was true for the excretion of o-cresol, which 4 h after exposure was concluded amounted to 0.03-0.26% of the toluene uptake. Thus, after a short-time exposure neither metabolite proved to be a reliable measure of individual toluene uptake at varying workloads or food intake in combination with low exposure levels.

Urinary hippuric acid and orthocresol excretion in man during experimental exposure to toluene

It is not known whether urinary excretion of hippuric acid (HA) or orthocresol (O-Cr) is to be preferred for the biological monitoring of workers with occupational exposure to toluene. To study this, 42 printing trade workers with more than 10 years' exposure to a mixture of organic solvents including toluene (0-20 ppm) and 43 control subjects matched by age, smoking habits, and living accommodation were investigated. Each matched pair was randomised to an experimental exposure of either 100 ppm or 0 ppm toluene for 6.5 hours under controlled conditions in an exposure chamber. Urinary excretion of HA and O-Cr was determined by high pressure liquid chromatography from samples obtained before exposure, during the first three hours, and during the last 3.5 hours of exposure. No difference in HA and O-Cr excretion was found between printing trade workers and controls. The median O-Cr excretion increased 29 times during exposure, whereas the HA excretion increased only five times. Thus only 3% of the O-Cr excretion originated from other sources than toluene whereas the corresponding value for HA was 19%. Standardisation of the concentrations of HA and O-Cr in relation to urinary creatinine reduced the relative variation by 29% and 56% respectively. This was not reduced further by expressing the excretions as average excretion rates based on total volume of urine collected. Background urinary O-Cr excretion was three to four times higher among smokers than non-smokers, probably due to the content of O-Cr in cigarettes. The O-Cr excretion in unexposed smokers was, however, 10 times lower that that of the non-smokers during the end of the experimental exposure to 100 ppm toluene.

Hippuric acid and o-cresol in the urine of workers exposed to toluene

Factory workers, 74 males and 56 females exposed predominantly to toluene up to 129 ppm, were examined for the urinary excretion of hippuric acid and o-cresol. The time-weighted averages (TWA) of toluene exposure were measured by personal sampling with carbon felt dosimeters. A preliminary study revealed that the concentrations of hippuric acid and o-cresol in urine increased during work and both reach their peaks at the end of the shift. Correlation coefficients between the TWA of toluene concentration in air and hippuric acid concentration in urine collected at the end of the shift were 0.803 for the 74 males, and 0.830 for the 56 females, while the counterpart correlation coefficients between toluene and o-cresol were 0.607 for the 74 males, and 0.627 for the 56 females, suggesting that hippuric acid is more reliable than o-cresol as an index of toluene exposure. In the urine samples (4 to 8 samples per subject) collected during 8-h worktime from 11 males and 13 females, the urinary levels of o-cresol increased as a function of exposure time in parallel with those of hippuric acid, and the correlation coefficients between o-cresol and hippuric acid were significant (r = 0.834 approximately 0.987; P less than 0.05) when the urine samples from the same subjects were examined. The comparison of the slopes of 24 regression lines between o-cresol and hippuric acid in urine revealed that the maximal slope was almost 8 times as large as the minimal one. From 8 female workers, five urine samples each were collected during 8-h worktime on two consecutive Mondays and analyzed for the two metabolites. The slopes of the regression lines between o-cresol and hippuric acid in the samples from the same subject were identical, regardless of variation in exposure intensity. The findings indicate that an individual difference exists in the pattern of toluene metabolism, and that the ratio between aliphatic and aromatic oxidation is presumably set congenitally. Possible toxicological significance is discussed.

Dose dependent induction of rat liver microsomal cytochrome P-450 and microsomal enzymatic activities after inhalation of toluene and dichloromethane

Sprague-Dawley rats were exposed, by inhalation, to toluene and dichloromethane (500, 1,500 or 3,000 p.p.m.) and to benzene (1,500 p.p.m.) for three days. Toluene and benzene increased the concentration of liver microsomal cytochrome P-450. A dose dependent increase in the in vitro liver microsomal formation of several metabolites of biphenyl and benzo(a)pyrene was observed for both dichloromethane and toluene. At the highest dose-level the increase in the vitro formation of benzo(a)pyrene-7,8-dihydrodiol was more than three-fold for both dichloromethane and toluene whereas the formation of benzo(a)pyrene-4,5-dihydrodiol increased more than five-fold following exposure to toluene but less than two-fold after exposure to dichloromethane. Our results suggest that dichloromethane and toluene can modify the metabolism and thereby the toxicity of other environmental contaminants.

Biomonitoring of occupational toluene exposure

Toluene 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 less than 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.

Determination of urinary hippuric acid and o-cresol, as indices of toluene exposure, by liquid chromatography on dynamically modified silica

Two simple and sensitive high-performance liquid chromatographic methods for the determination of hippuric acid and o-cresol in urine have been developed. The chromatographic system is the same for the two methods and is based on dynamically modified silica. The detection limits were found to be 0.05 mg/ml and 0.05 microgram/ml of urine for hippuric acid and o-cresol, respectively, when using UV detection at 254 nm. The recovery for hippuric acid was about 100% and for o-cresol 33-36%. The detection limit for o-cresol could be lowered by a factor of ten by using fluorescence detection. The methods were used for investigations of the urine from persons exposed to 100 ppm toluene for 6.5 h. The method for o-cresol may also be used for determination of other phenols in urine.

Experimental exposure to toluene: further consideration of cresol formation in man

In two separate experiments 10 healthy men each were exposed at rest in an exposure chamber to about 200 ppm toluene in the air. Hippuric acid, o-, m-, p-cresol, and phenol in urine were detected by capillary gas chromatography at the beginning and at the end of exposure, and at variable times after the cessation of exposure. In addition toluene in blood was determined at the same intervals. The results indicate that in addition to hippuric acid, o-, m-, p-cresol are metabolites of toluene; the detoxication lasting 24 hours at least.

Toluene-exposed workers and chromosome aberrations

Peripheral blood lymphocytes from 32 male rotogravure workers with daily exposure to toluene were studied for chromosome aberrations and sister chromatid exchange. Neither of these two cytogenetic parameters differed significantly from the correspondong frequencies in 15 unexposed control subjects. However, a significant increase in sister chromatid exchange was observed among smokers, both exposed and occupationally unexposed, compared to nonsmoking referents.