Comparative evaluation of biomarkers of occupational exposure to toluene

Objectives This study was initiated to make comparative evaluation of five proposed urinary markers of occupational exposure to toluene, i.e., benzyl alcohol, benzylmercapturic acid, o-cresol, hippuric acid and un-metabolized toluene. Methods In practice, six plants in Japan were surveyed, and 122 Japanese workers (mostly printers; all men) together with 12 occupationally nonexposed control subjects (to be called controls; all men) agreed to participate in the study. Surveys were conducted in the second half of working weeks. Time-weighted average exposure (about 8 h) to toluene and other solvents were monitored by diffusive sampling. End-of-shift urine samples were collected and analyzed for the five markers by the methods previously described; simultaneous determination of o-cresol was possible by the method originally developed for benzyl alcohol analysis. Results The toluene concentration in the six plants was such that the grand geometric mean (GM) for the 122 cases was 10.4 ppm with the maximum of 121 ppm. Other solvents coexposed included ethyl acetate (26 ppm as GM), methyl ethyl ketone (26 ppm), butyl acetate (1 ppm) and xylenes (1 ppm). By simple regression analysis, hippuric acid correlated most closely with toluene in air (r = 0.85 for non-corrected observed values) followed by un-metabolized toluene (r = 0.83) and o-cresol (r = 0.81). In a plant where toluene in air was low (i.e., 2 ppm as GM), however, un-metabolized toluene and benzylmercapturic acid in urine showed better correlation with air-borne toluene (r = 0.79 and 0.61, respectively) than hippuric acid (r = 0.12) or o-cresol (r = 0.17). Benzyl alcohol tended to increase only when toluene exposure was intense. Correction for creatinine concentration or specific gravity of urine did not improve the correlation in any case. Multiple regression analysis showed that solvents other than toluene did not affect the levels of o-cresol, hippuric acid or un-metabolized toluene. Levels of benzylmercapturic acid and un-metabolized toluene were below the limits of detection [limit of detections (LODs); 0.2 and 2 μg/l, respectively] in the urine from the control subjects. Conclusions In over-all evaluation, hippuric acid, followed by un-metabolized toluene and o-cresol, is the marker of choice for occupational toluene exposure. When toluene exposure level is low (e.g., 2 ppm), un-metabolized toluene and benzylmercapturic acid in urine may be better indicators. Detection of un-metabolized toluene or benzylmercapturic acid in urine at the levels in excess of the LODs may be taken as a positive evidence of toluene exposure, because their levels in urine from the controls are below the LODs. The value of benzyl alcohol as an exposure marker should be limited.     

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. We conclude that determination of hippuric acid in urine samples collected at the end of the work-shift can be used for routine biological monitoring of exposure to toluene, even at low levels. O-cresol seems to be a less reliable indicator of toluene exposure.     

Toluene itself as the best urinary marker of toluene exposure

Head-space gas chromatography (GC) and high-performance liquid chromatography (HPLC) (with fluorescence detectors) methods were developed for toluene (TOL-U) and o-cresol (CR-U) in urine, respectively. In order to identify the most sensitive urinary indicator of occupational exposure to toluene vapor (TOL-A) among TOL-U, CR-U, and hippuric acid in urine (HA-U), the two methods together with an HPLC (with untraviolet detectors) method for determination of HA-U were applied in the analysis of end-of-shift urine samples from 115 solvent-exposed workers (exposed to toluene at 4 ppm as geometric mean). Regression analysis showed that TOL-U correlated with TOL-A with a significantly higher correlation coefficient than did HA-U or CR-U. With regard to the TOL-A concentrations at which the exposed subjects could be separated from the nonexposed by the analyte, TOL-U achieved separation at < 10 ppm TOL-A, whereas both HA-U and CR-U did so only when TOL-A was 30 ppm or even higher. The ratio of the analyte concentrations at 50 ppm TOL-A to those at 0 ppm TOL-A was also highest for TOL-U. Overall, the results suggest that TOL-U is a better marker of exposure to toluene vapor than HA-U or CR-U.     

Occupational chronic exposure to organic solvents XVI. Ambient and biological monitoring of workers exposed to toluene

Object Ambient air and biological monitoring of an occupational toluene exposure was carried out on a group of 33 workers. Method The biological monitoring of the workers was based on determination of the concentration of toluene in blood and on quantification of the urinary metabolites o-cresol and hippuric acid. All blood and urine samples were collected post-shift. Results The average toluene concentration in the workplace air was 65?ppm, ranging from 13 to 151?ppm. An average concentration of toluene in blood of 911?μg/l was found, corresponding to an average urinary concentration of 2.9?mg/l (2.3?mg/g creatinine) o-cresol and 2.4?g/l (1.9?g/g creatinine) hippuric acid. Both urinary metabolites can be correlated with the concentration of toluene in ambient air and blood, respectively. Conclusions The results of our study indicate that the determination of the urinary o-cresol excretion represents a diagnostically specific and sensitive parameter for the estimation of an individual toluene uptake. In contrast, monitoring of the concentration of hippuric acid in urine cannot be recommended for assessment of individual exposure. To set up a biological tolerance value (BAT) for o-cresol, a urinary concentration of 3?mg/l o-cresol should be in accordance with the current MAK value of 50?ppm toluene.     

Biological monitoring of exposure to solvents using the chemical itself in urine: application to toluene

Objective Biomonitoring of solvents using the unchanged substance in urine as exposure indicator is still relatively scarce due to some discrepancies between the results reported in the literature. Based on the assessment of toluene exposure, the aim of this work was to evaluate the effects of some steps likely to bias the results and to measure urinary toluene both in volunteers experimentally exposed and in workers of rotogravure factories. Methods Static headspace was used for toluene analysis. o-Cresol was also measured for comparison. Urine collection, storage and conservation conditions were studied to evaluate possible loss or contamination of toluene in controlled situations applied to six volunteers in an exposure chamber according to four scenarios with exposure at stable levels from 10 to 50 ppm. Kinetics of elimination of toluene were determined over 24 h. A field study was then carried out in a total of 29 workers from two rotogravure printing facilities. Results Potential contamination during urine collection in the field is confirmed to be a real problem but technical precautions for sampling, storage and analysis can be easily followed to control the situation. In the volunteers at rest, urinary toluene showed a rapid increase after 2 h with a steady level after about 3 h. At 47.1 ppm the mean cumulated excretion was about 0.005% of the amount of the toluene ventilated. Correlation between the toluene levels in air and in end of exposure urinary sample was excellent (r = 0.965). In the field study, the median personal exposure to toluene was 32 ppm (range 3.6–148). According to the correlations between environmental and biological monitoring data, the post-shift urinary toluene (r = 0.921) and o-cresol (r = 0.873) concentrations were, respectively, 75.6 μg/l and 0.76 mg/g creatinine for 50 ppm toluene personal exposure. The corresponding urinary toluene concentration before the next shift was 11 μg/l (r = 0.883). Conclusion Urinary toluene was shown once more time a very interesting surrogate to o-cresol and could be recommended as a biomarker of choice for solvent exposure.     

Biological monitoring of controlled toluene exposure

Objectives: Widespread exposure to toluene occurs in the printing, painting, automotive, shoemaking, and speaker-manufacturing industries. The relationship between air concentrations and the absorbed dose is confounded by dermal exposure, personal protective devices, movement throughout the workplace, and interindividual differences in toluene uptake and elimination. Methods: To determine the best biological indicator of exposure we examined the blood and alveolar breath concentrations of toluene as well as the urinary excretion rates of hippuric acid and of o-, m-, and p-cresols from 33 controlled human inhalation exposures to 50 ppm for 2 h. Results: Among the metabolites, o-cresol was least influenced by background contributions, whereas the p-cresol and hippuric acid rates were obscured by endogenous and dietary sources. Toluene levels in alveolar breath proved to be the most accurate and noninvasive indicator of the absorbed dose. A physiologic model described blood and breath data using four measured anthropometric parameters and the fit values of extrahepatic metabolism and adipose-tissue blood flow. Conclusions: After breathing rate and extrahepatic metabolism had been set to conservative (protective) values (the 97.5th and 2.5th percentiles, respectively) the model predicted that pre-final-shift breath levels of ≤10 μmol/m³ and post-final-shift levels of ≤150 μmol/m³ corresponded to average workplace exposure levels of ≤50 ppm toluene. Alternately, we used the distributions and covariances of the measured and fit model parameters to yield conservative pre-final-shift levels of ≤7.3 μmol/m³ and post-final-shift breath levels of ≤120 μmol/m³ that were reflective of workplace exposure levels of ≤50 ppm toluene. Received: 30 December 1997 / Accepted: 12 June 1998     

Aromatic and polycyclic hydrocarbons in air and their urinary metabolites in coke plant workers

This study describes the exposure of coke plant workers to hydrocarbons. Aromatic hydrocarbons (AHs) and polycyclic aromatic hydrocarbons (PAHs) in the breathing zone air and their oxygenated metabolites in the urine of coke plant workers are qualitatively and quantitatively determined. Concentrations of benzene, toluene, naphthalene, m+p-xylene, o-xylene and 14 different PAHs were measured at the different workplaces by personal air sampling. O-cresol, 1- and 2-naphthol, methylhippuric acid, and 1-hydroxypyrene were determined in hydrolyzed urine of workers collected after the work shift. The gas chromatography–mass spectrometry (GC/MS) method was applied to identify AHs in air and in urine samples. Time-weighted values of exposure to aromatic hydrocarbons at a coke plant were: benzene (0.06–9.82 mg/m³), toluene (0.05–4.71 mg/m³), naphthalene (0.01–3.28 mg/m³), o-xylene (0.01–1.76 mg/m³) and m + p-xylene (0.01–2.62 mg/m³). At the coke batteries, the total concentration of PAHs ranged from 7.27 to 21.92 μg/m³. At the sorting department, the total concentration of PAHs were about half this value. Concentration of the urinary metabolites (naphthols and methylhippuric acid) detected in workers at the tar distillation department are three times higher than those for the coke batteries and sorting department workers. A correlation between inhaled toluene, naphthalene, xylene, and urinary excretion of metabolites has been found. Time-weighted average concentrations of AHs in the breathing zone air show that exposure levels of the workers are rather low in comparison to exposure limits. The 1-hydroxypyrene concentration is below 24.75 μmol/mol creatinine. The GC/MS analysis reveals the presence of AHs, mainly benzene and naphthalene homologues. It has been found that coke plant workers are simultaneously exposed to the mixture of aromatic and polycyclic hydrocarbons present in the breathing zone air of a coke plant. Exposure levels are significantly influenced by job categories. Compounds identified in the urine appear to be the products of the hydroxylation of AHs present in the air as well as unmetabolized hydrocarbons. Am. J. Ind. Med. 34:445–454, 1998. © 1998 Wiley-Liss, Inc.     

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

Summary 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.     

Self-collected urine sampling to study the kinetics of urinary toluene (and <Emphasis Type="Italic">o</Emphasis>-cresol) and define the best sampling time for biomonitoring

Purpose  To study the excretion kinetics of urinary toluene, TOL-U, and o-cresol, o-C, following occupational exposure to toluene in order to define the best time for sample collection, to apply a non-invasive approach based on self-collected urine sampling. Methods  Five rotogravure printing workers exposed to uncontrolled levels of toluene collected spot urine samples over three consecutive working days and the following day of rest. In each sample TOL-U and o-C were measured and kinetics of excretion evaluated. Results  Toluene exposure ranged from 48.3 to 75.3 mg/m³; TOL-U and o-C ranged from 1.4 to 34.6 μg/L and from 0.013 to 1.012 mg/L. A time course trend was obtained: TOL-U and o-C increased during the shift and peaked at the end of exposure and up to 2 h later, respectively; afterwards they rapidly decreased following apparent first order kinetics. Considering TOL-U, the elimination half-life for the first fast phase was 79 (±35 standard error) min, and for the second slow phase was 1,320 (±1,162) min. For o-C the elimination half-life for the first fast phase was 231 (±48) min. Considering a toluene uptake of 86%, TOL-U and o-C excreted in urine were about 0.0067 and 0.18% of the up taken. Conclusion  Our results support the use of end shift TOL-U as a short term biomarker of occupational exposure to toluene and show the feasibility of self-collected urine sampling to investigate the elimination kinetics of industrial toxics in humans.     

Urinary methylhippuric acid isomer levels after occupational exposure to a xylene mixture

Summary The quantitative relationship between exposure to xylene vapor and urinary excretion of methylhippuric acid (MHA) isomers were studied in the second half of a working week. The participants in the study were 121 male workers engaged in dip-coating of metal parts who were predominantly exposed to three xylene isomers. The intensity of exposure measured by diffusive sampling during an 8-h shift was such that the geometric mean vapor concentration was 3.8 ppm for xylenes (0.8 ppm for o-xylene, 2.1 ppm for m-xylene, and 0.9 ppm for p-xylene), 0.8 ppm for toluene, and 0.9 ppm for ethylbenzene. Urine samples were collected at the end of the shift and analyzed for metabolities by HPLC. The statistical analysis showed that there is a linear relationship between the intensity of exposure to xylenes and the concentration of MHA in urine, that the regression line passes very close to the origin, and that the increment in observed (i.e., noncorrected) MHA concentrations as a function of increasing xylene concentration was 17.8 mg × 1^–1 ppm^–1. Further examination on the basis on individual xylene isomers showed that the slopes of the regression lines for o- and m-isomers were similar (i.e., 17.1 and 16.6 mg l^–1 ppm^–1, respectively), whereas that for p-xylene was larger (21.3 mg l^–1 ppm^–1).     

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

Summary 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 (r _s = 0.57, P<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/mot 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 44h (± 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.     

High-pressure liquid chromatographic determination of toluenein urine as a marker of occupational exposure to toluene

Objective: To establish a convenient method by high-pressure liquid chromatography (HPLC) to measure toluene in urine as a marker of occupational exposure to toluene. Methods: As soon after sampling as possible, 1 ml of urine was mixed with an equal volume of acetonitrile in a 2.2-ml HPLC glass bottle, and the bottle was tightly sealed and stored at 4 °C. Immediately before HPLC determination, 100 μl methanol was added to the mixture to prevent confounding effects of glycosuria, and the bottle was spun to remove any suspended matter. An aliquot of the supernate was introduced into the HPLC system and analyzed on a PRODIGY column, with an acetonitrile – perchloric acid – phosphoric acid – water mixture serving as the mobile phase. The effluent was monitored at 191 nm. Results: The method can measure toluene in urine every 20 min; the detection limit was 2 μg/l, the coefficient of variation was less than 5%, and the recovery rate was 100%. No significant reduction in toluene concentration was observed for 1 week after storage at 4 °C. When the method was applied to end-of-shift urine samples from 13 male workers exposed to toluene at 18–140 ppm and also to urine samples from 10 nonexposed male controls, toluene in urine was linearly related to toluene exposure concentration, with a regression line passing close to the origin. The correlation coefficient was as high as 0.97 (n = 23). No toluene was detected in control urine samples. Calculations suggest that urinary toluene accounts for as little as less than 0.01% of the toluene absorbed via inhalation and that the absorbed toluene is converted almost quantitatively to hippuric acid and, by less than 0.1%, to o-cresol. Received: 25 August 1997 / Accepted: 13 February 1998     

Biological monitoring of occupational exposure to isopropyl alcohol vapor by urinalysis for acetone

Summary The relationship of the intensity of occupational vapor exposure to isopropyl alcohol (IPA) with urinary excretion of acetone and unmetabolized IPA was studied in 99 printers of both sexes, who were exposed to up to 66 ppm IPA (as time-weighted average), together with toluene, xylenes, methyl ethyl ketone and/or ethyl acetate. Acetone and IPA concentrations in urine were studied also in 34 non-exposed subjects. Acetone was detectable in the urine of most of the non-exposed, and the urinary acetone concentration increased in proportion to the IPA exposure intensity (r = 0.84 for observed, non-corrected values), whereas the correction for creatinine concentration or specific gravity of urine did not give a larger correlation coefficient. IPA itself was not found in the urine of the non-exposed, and was detectable in urine of only those who were exposed to IPA above a certain level, e.g. 5 ppm. The present study results suggest that urinary acetone is a valuable index for biological monitoring of occupational exposure to IPA as low as 70 ppm.A part of this work was presented at 62nd Annual Meeting of Japan Association of Industrial Health, held in Hirosaki, Japan, on 27th–30th, April, 1989     

Effect of ethanol,cimetidine and propranolol on toluene metabolism in man

Summary In a climatic exposure chamber four healthy volunteers were exposed to 100ppm toluene, 100ppm toluene + ethanol, 100ppm toluene + cimetidine, and 100ppm toluene + propranolol for 7h each at random over four consecutive days. A control experiment and 3.5 h of exposure to 200 ppm toluene were also performed. Ethanol inhibited toluene metabolism by 0.5 as expressed by the urinary excretion of two of the metabolites of toluene, namely o-cresol and hippuric acid. In agreement with this, the mean alveolar concentration of toluene was greater by 1.7 during ethanol exposure; 45 min after discontinuation of exposure the increase was by 3.3. Neither cimetidine nor propranolol changed toluene metabolism significantly. The results indicate that ethanol may prolong the time interval in which toluene is retained in the human body in persons simultaneously exposed to ethanol and toluene. When using o-cresol or hippuric acid in biological monitoring of persons occupationally exposed to toluene, the consumption of ethanol should be considered.Supported by grants from the Working Environment Fund, Denmark     

Mutual metabolic suppression between benzene and toluene in man

Summary 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.     

Comparative evaluation of blood and urine analysis as a tool for biological monitoring of n-hexane and toluene

Blood and urine samples were collected from 57 male Japanese solvent workers [exposed to n-hexane (Hex-A), ethyl acetate, and toluene (Tol-A) at 1.5, 2.3, and 2.3 ppm as GM-TWA, respectively] and also from 20 male nonexposed workers at the end of a 8-h shift, and analyzed for n-hexane (Hex-B) and toluene (Tol-B) in blood, and n-hexane (Hex-U), toluene (Tol-U), 2,5-hexanedione [both with (HD-U/cHYD) and without hydrolysis (HD-U/sHYD)] and hippuric acid (HA-U) in urine. Regression analysis showed that both Hex-B and Tol-B correlated significantly with corresponding exposure to the solvents. Solvents in urine (Hex-U and Tol-U) also correlated with solvents in air but with smaller correlation coefficients than the solvents in blood. Both HD-U/cHYD and HD-U/sHYD showed significant correlation with Hex-A, but HA-U failed to do so with Tol-A. Based on the correlation among biological exposure indicators and solvent concentration in air, sensitivity as an exposure indicator was compared between the solvent in blood and the metabolite in urine in terms of the lowest solvent concentration at which the exposed can be separated (with statistical significance) from the nonexposed (the lowest separation concentration; LSC). The LSC was 3.9 ppm for Hex-B, 1 to 2 ppm for HD-U/sHYD and 10 to 30 ppm for HD-U/cHYD, suggesting that HD-U/sHYD is superior even to Hex-B in detecting low n-hexane exposure; this high sensitivity of HD-U/sHYD is due to the absence of HD-U/sHYD in the urine from the nonexposed. In contrast, Tol-B (with LSC of 2.4 ppm) was more sensitive than HA-U; no LSC for HA-U could be obtained because of lack of correlation with Tol-A at low toluene exposure.     

Habitual and genetic factors that affect urinary background levels of biomarkers for organic solvent exposure

Urinary hippuric acid, phenol, and o-cresol, which are biomarkers for toluene, benzene, and phenol exposures, are usually present in a significant amount in urine collected from subjects who have not been occupationally exposed to the organic solvents. With the improvement of working enviroments, the urinary concentrations of the biomarkers have become lower and closer to the levels of urine from unexposed subjects. It is very useful to clarify the background levels of these biomarkers and the factors which effect the background levels of the biomarkers in order to make effective use of biological monitoring under low level exposure. In the present study, the effects of life habits and the genetic polymorphisms of the metabolizing enzymes on the background levels of urinary hippuric acid, phenol and o- and p-cresol were clarified, using 351 males (means age: 38.6, range: 19–71) who were not occupationally exposed to hazardous chemical materials. Their life habits, smoking, alcohol consumption, and dietary habits were examined by means of a questionnaire. The genotypes of five metabolizing enzymes, that is, low Km aldehyde dehydrogenase (ALDH2), polymorphic N-acetyl transferase (NAT2), cytochrome P-4501A1 (CYP1A1), cytochrome P-4502E1 (CYP2E1), and glutathione-S-transferase (GSTM1) were determined form peripheral blood samples. The urinary hippuric acid and creatinine were analyzed by HPLC and urinary phenol, o-, p- and m-cresol were determined by GC/MS. Recoveries and the coefficients of variance of phenol, o-cresol, and p-cresol ranged from 92.7 to 107.8% and 1.3% to 6.7%, respectively. Linear relationships between the concentrations of phenol, o- and p-cresol, and their peak area ratios were observed. As results, with advancing age, alcohol consumption increased, and the intake of greasy food, coffee, and tea was reduced. Smoking, alcohol consumption, and coffee and tea consumption were associated with each other. ALDH2 polymorphism was significantly associated with alcohol consumption and coffee and tea consumption, however, NAT2, CYP1A1, GSTM1, and CYP2E1 polymorphisms did not correlate with any of the smoking, alcohol consumption, and dietary habits. From a multiple regression analysis, the background level of urinary hippuric acid reduced according to alcohol consumption. Urinary phenol concentration was reduced by coffee and tea intake, and o-cresol concentration increased with the number of smoked cigarettes. No genetic polymorphisms of the five metabolizing enzymes were related to the urinary background levels of hippuric acid, phenol, o- and p-cresols.     

Occupational chronic exposure to organic solvents

Summary A group of printing workers (n = 34) exposed to toluene was examined according to the concentrations of hippuric acid, phenol, o-cresol, and (m+p)-cresol in urine. The average concentration in the air of the workroom was 23 ppm. It is shown that, besides hippuric acid, small amounts of o-cresol. which is not a normal constituent of urine, were formed from toluene. The occurrence of o-cresol could be proved by mass spectrometry. On account of the small amounts of benzene present in industrially used toluene—in this case 0.025%—the average concentration of phenol in urine of the exposed group was significantly higher statistically than in urine from the controls .     

Toluene in blood as a marker of choice for low-level exposure to toluene

The validity of two new biological exposure markers of toluene in blood (TOL-B) and toluene in urine (TOL-U) was examined in comparison with that of the traditional marker of hippuric acid in urine (HA-U) in 294 male workers exposed to toluene in workroom air (TOL-A), mostly at low levels. The exposure was such that the geometric mean for toluene was 2.3 ppm with a maximum of 132 ppm; the workers were also exposed to other solvents such as hexane, ethyl acetate, styrene, and methanol, but at lower levels. The chance of cutaneous absorption was remote. Higher correlation with TOL-A and better sensitivity in separating the exposed workers from the nonexposed subjects were taken as selection criteria. When workers exposed to TOL-A at lower concentrations (< 50 ppm, < 10 ppm, < 2 ppm, etc.) were selected and correlation with TOL-A was examined, TOL-B showed the largest correlation coefficient which was significant even at TOL-A of < 1 ppm, whereas correlation of HA-U was no longer significant when TOL-A was < 10 ppm. TOL-U was between the two extremes. The sensitivities of TOL-B and TOL-U were comparable; HA-U showed the lowest sensitivity. Thus, it was concluded that TOL-B is the indicator of choice for detecting toluene exposure at low levels.     

Evaluation of biomarkers of occupational exposure to toluene at low levels

Objectives The purpose of the present study was to compare validity of various biomarkers of occupational exposure to toluene (Tol) at low levels. The focus was placed on the comparison of un-metabolized toluene in urine (Tol-U) and peripheral blood (Tol-B) with hippuric acid in urine (HA-U). Methods Surveys were conducted in 16 workplaces on the second half of working weeks, with participation of male solvent workers. Urine and peripheral blood samples were collected at the end of the shifts. After exclusion of cases with dense or diluted urine samples, 473 valid sets of samples were obtained for statistical evaluation. Time-weighted average exposure (for about 8-h) were monitored by diffusive sampling for toluene and other four solvents. Blood samples were subjected to the analyses for Tol-B, whereas urine samples were analyzed for HA-U and Tol-U. Results The solvent exposures were low, i.e., a grand geometric mean (GM) Tol concentration was 1.6 ppm, and the GM for the SUM in the additiveness equation was 0.12. The correlation analyses of the biomarkers in urine and blood with Tol exposure showed that Tol-U and Tol-B were more closely [correlation coefficients (r) being 0.67 and 0.60, respectively] related than HA-U (r = 0.27). Results of receiver operator characteristic analyses were in agreement with the correlation analysis results. Conclusions Taking the non-invasive nature of sampling together, Tol in the end-of-shift spot urine sample appears to be the marker of choice for biological monitoring of occupational exposure to Tol at low levels such as <2 ppm as a geometric mean.