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.     

Urinary excretion of hippuric acid and m- or p-methylhippuric acid in the urine of persons exposed to vapours of toluene and m- or p-xylene as a test of exposure

Ogata, M., Tomokuni, K., and Takatsuka, Y. (1970).Brit. J. industr. Med.,27, 43-50. Urinary excretion of hippuric acid and m- or p-methylhippuric acid in the urine of persons exposed to vapours of toluene and m- or p-xylene as a test of exposure. Twenty-three male volunteers were exposed in groups of four or five to toluene and m- and p-xylene vapour for periods of 3 hours or of 7 hours with one break of an hour. Urine was collected at hourly intervals for several hours, and thereafter all urine was collected until 18 hours after the end of the exposure period, and was analysed for hippuric and methylhippuric acids. It was shown that hippuric acid was excreted equivalent to 68% of the toluene absorbed, and m-methylhippuric acid equivalent to 72% of the m-xylene absorbed. Up to hydrocarbon concentrations of 200 ppm the total quantity of hippuric acids excerted was proportional to the total exposure (ppm × hours). In descending order of precision the following were also related to exposure: rate of excretion during the exposure period; concentrations of hippuric acid in urine corrected to constant urine density; and concentrations in urine uncorrected for density. The last could not be used to calculate exposure, but the others could be to give screening tests to show whether workmen could have been exposed to concentrations greater than the maximum allowable.

The effects of exposure on blood pressure, pulse rate, flicker value, and reaction time were measured. There were some variations which suggested that the MAC of toluene should be set higher than 200 ppm.

     

Dose-response relationship for trichloroethylene in man

Summary Twelve volunteer students were experimentally exposed to 0, 27, 81 or 201 ppm trichloroethylene for 4 hours, and suffered from irritation to mucous membrane of eyes and throat at over 27 ppm trichloroethylene. No headache or physiological responses were reported at 27 ppm; headache occurred at levels over 81 ppm. Accumulated urinary excretion of total trichloro-compounds, trichloroacetic acid and trichloroethanol for 6 days after trichloroethylene exposure increased linearly with environmental trichloroethylene concentration in volunteers experimentally exposed to 0–315 ppm trichloroethylene.In 39 trichloroethylene workers also no changes were observed in the metabolic pattern of trichloroethylene in relation to environmental concentration corresponding to excretion of total trichloro-compounds in urine of 0–180 mg/4 hours namely.Those data might support a threshold limit value of 50 ppm for trichloroethylene. This conclusion, however, is based only on the appearance of toxic symptoms, but not on critical changes in trichloroethylene metabolism above 50 ppm.Presented before the 45th Annual Meeting of Japanese Association of Industrial Health at Tokyo on April 9, 1972, and the 43rd Annual Meeting of Japan Society for Hygiene at Sapporo on May 6, 1973     

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.     

Chronic occupational exposure to toluene

Summary Chronic occupational exposure to toluene was studied in a factory preparing tarpaulins. Seventy-eight workers were studied; 46 were exposed to various concentrations of toluene in air (20–200 ppm), 32 were unexposed workers in the same factory. In many cases the exposure had lasted for 10–20 years. The urinary hippuric acid excretion at the end of work shift showed good correlations to toluene concentrations in air, and it seems to be a good measure of exposure. The hippuric acid in urine samples collected overnight showed that elimination of toluene still occurs several hours after exposure. Most of the biological parameters measured showed no correlation to toluene exposure. The blood leukocyte count did show slight positive correlations to toluene exposure, but even this parameter stayed inside the range of normal values. The occurrence of chronic diseases, drug using habits, and drinking and smoking habits did not show any correlations to toluene exposure.This study has been supported by the grant of Y. Jahnsson Foundation in Finland     

Biological monitoring for occupational exposure to toluene

A study was undertaken to examine the relationship between exposure of workers to toluene in the work environment and biological indicators of toluene exposure. The biological indicators studied were toluene in expired air, toluene in blood obtained by the finger prick method, and urinary hippuric acid. The study was undertaken in a factory in Singapore that manufactures speakers for audio systems. A total of 86 female workers exposed to toluene at the workplace and a control group of workers not exposed to toluene were examined. All of them were teetotalers, were nonsmokers, and gave no history of chronic drug usage. The 8-hr time-weighted average exposure level of toluene ranged from 1.6 ppm to 263 ppm. The study showed the expected toluene levels in finger prick blood was 1.4 micrograms/mL after an 8-hr exposure to 100 ppm of toluene. Toluene concentration in expired air of 16 ppm after an 8-hr exposure to 100 ppm compared favorably with other studies. The toluene in blood/expired air ratio was observed to be lower than in other studies. In this study, the expected urinary hippuric acid level for a 100-ppm exposure to toluene was 2.7 g/g creatinine. This level is higher than that recorded in other studies. The results showed that at low levels of toluene, urinary hippuric acid is not a valuable indicator of exposure. Toluene in expired air is the most reliable biological indicator of exposure to toluene.     

Urinary hippuric acid concentration after occupational exposure to toluene.

The results of industrial investigations have shown a correlation between the rate of hippuric acid excretion in a single urine sample collected after daily occupational exposure and the amount of toluene absorbed. The rate of hippuric acid excretion and the average concentration of toluene vapour during exposure time were also related. The quantitative range of the test has been limited to amounts exceeding 425 mg of toluene and concentrations exceeding 69 ppm of toluene in the air because of the physiological presence of hippuric acid in urine. The rate of hippuric acid excretion in urine depends on diuresis and is constant for urinary fractions with diuresis of 30 ml/h. The physiological excretion rate was 20 mg/h with a standard deviation +/- 4.3 mg/h, maximal physiological level 33 mg/h.     

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     

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.     

Experimental human exposure to toluene

Summary The relationship between the individual toluene uptake and the urinary hippuric acid excretion was studied under experimental conditions. Six healthy male subjects were exposed to various concentrations in inspired air (50, 100, 125, 150, and 200 ppm) at rest or under different levels of physical effort.The hippuric acid excretion near the end of the exposure appeared under all circumstances directly proportional to the time-weighted uptake rate of toluene. The correlation between respiratory uptake rate and the rate of metabolite excretion near the end of the exposure period proved not to be systematically influenced by personal factors such as body weight, amount of body fat, urine flow rate and urinary pH. The relatively pronounced differences in background excretion of hippuric acid and, perhaps, distribution phenomena of toluene between different tissues under heavy workload conditions, can partly explain the greater variability in metabolite excretions as compared to the individual uptake rates.The correlation between the individual uptake rate of toluene and the hippuric acid excretion proved substantially better when using the end exposure excretion rate as exposure parameter as compared with the end exposure hippuric acid concentration, even after correcting the latter for urine density.Reasonable biological limit values complying to an acceptable time-weighted toluene dose were found to be 3000–3500 mg/l and 2.0–2.5 mg/min, resp. for average hippuric acid concentrations and excretion rates in spot samples during the second half of a complete work shift.     

Effects of smoking and drinking on excretion of hippuric acid among toluene-exposed workers

Summary In order to investigate possible effects of smoking and drinking on the metabolism of toluence in occupational settings, 206 toluene-exposed men (mean age: 31.4 years) in shoemaking, painting, or surface-coating workshops together with 246 nonexposed control men (36.8 years) were studied for the time-weighted average intensities of exposure to toluene, hippuric acid concentration in shift-end urine samples, and the two social habits of smoking and drinking. The mean daily consumptions of cigarettes and ethanol were about 20 pieces and 10 g among smokers and drinkers, respectively. The geometric mean toluene concentration among the exposed subjects was about 20 ppm, with a maximum of 521 ppm. Regression analysis after classification of the subjects by smoking and drinking clearly demonstrated that the two social habits, when combined, markedly reduce the hippuric acid level in the urine of workers exposed to was a significant association between smoking and drinking habits, which hindered separate evaluation of the effects of the two habits on toluene metabolism. Comparison of the present results with the findings reported in the literature, however, suggested that the observed effects may be attributable to smoking rather than to drinking habits.     

Effect of repeated exposure to methanol and toluene vapor on the metabolism of rats

Wistar male rats were repeatedly exposed to methanol and toluene vapors individually and simultaneously by inhalation 6 hours a day, five days a week for 4 weeks. Blood was obtained from the tail of the rats up to 23 hours after the end of 4-week exposure and the methanol and toluene concentrations were measured. Major metabolites of methanol and toluene, that is, formic acid and hippuric acid in urine were measured up to 6 days after the end of 4-week exposure. The biological half time of toluene in blood in the simultaneous exposure group was shorter than that in the toluene exposure group. This tendency was almost the same as that for one-day exposure, although the biological half time of solvents in the rat blood was prolonged. The half times of methanol were also longer than those for one-day exposure.     

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     

Effects of ethanol and phenobarbital treatments on the pharmacokinetics of toluene in rats.

Rats were exposed to toluene at a wide range of concentrations from 50 to 4000 ppm for six hours, and the effects of ethanol and phenobarbital (PB) treatments on the pharmacokinetics of toluene metabolism were investigated. Ethanol treatment influenced toluene metabolism mainly at low exposure concentrations. Thus ethanol accelerated the clearance of toluene from blood only when the blood concentration of toluene was not high (less than 360 microM), and ethanol increased hippuric acid (HA) excretion in urine more significantly at low (less than 250 ppm) than at high atmospheric toluene concentrations. Ethanol also expressed a similar effect on p-cresol excretion as on HA, but had little effect on o-cresol. Phenobarbital treatment promoted the urinary excretion of all of the metabolites of toluene, especially after exposure to high toluene concentration. As well as HA, benzoylglucuronide (BG) and free benzoic acid were found in urine. These are the products of the side chain metabolism of toluene. Amounts of BG could be detected when the urinary excretion of free benzoic acid exceeded 5 mumol/kg/6 h, indicating that a great deal of benzoic acid is required for the formation of BG. The Michaelis constant (Km) and the maximum rate of metabolic excretion in urine during six hours exposure (Vmax) of isozymes involved in the excretion of toluene metabolites were calculated, and correlated with the subtypes of cytochrome P-450. The significance of the result was suggested in the biological monitoring of exposure to toluene.     

Effects of ethanol and phenobarbital treatments on the pharmacokinetics of toluene in rats.

Rats were exposed to toluene at a wide range of concentrations from 50 to 4000 ppm for six hours, and the effects of ethanol and phenobarbital (PB) treatments on the pharmacokinetics of toluene metabolism were investigated. Ethanol treatment influenced toluene metabolism mainly at low exposure concentrations. Thus ethanol accelerated the clearance of toluene from blood only when the blood concentration of toluene was not high (less than 360 microM), and ethanol increased hippuric acid (HA) excretion in urine more significantly at low (less than 250 ppm) than at high atmospheric toluene concentrations. Ethanol also expressed a similar effect on p-cresol excretion as on HA, but had little effect on o-cresol. Phenobarbital treatment promoted the urinary excretion of all of the metabolites of toluene, especially after exposure to high toluene concentration. As well as HA, benzoylglucuronide (BG) and free benzoic acid were found in urine. These are the products of the side chain metabolism of toluene. Amounts of BG could be detected when the urinary excretion of free benzoic acid exceeded 5 mumol/kg/6 h, indicating that a great deal of benzoic acid is required for the formation of BG. The Michaelis constant (Km) and the maximum rate of metabolic excretion in urine during six hours exposure (Vmax) of isozymes involved in the excretion of toluene metabolites were calculated, and correlated with the subtypes of cytochrome P-450. The significance of the result was suggested in the biological monitoring of exposure to toluene.     

Urinary benzylmercapturic acid as a marker of occupational exposure to toluene

OBJECTIVE: To examine if benzylmercapturic acid (or N-acetyl- S-benzyl cysteine) in urine can be used as a marker of occupational exposure to toluene. METHODS: A factory survey was conducted in the latter half of a working week. A group of 46 men, who volunteered for the study, was engaged in ink preparation, surface coating or printing work. Diffusive samplers were used to measure average solvent exposure in an 8-h shift. End-of-shift urine samples were analyzed for benzylmercapturic acid (BMA) by a modification of an HPLC method originally developed for phenylmercapturic acid determination. RESULTS: The workers were exposed primarily to toluene [TOL; 13 ppm as the geometric mean (GM) and 86 ppm at the maximum] together with isopropyl alcohol (<1 and 4 ppm), ethyl acetate (2 and 127 ppm) and methyl ethyl ketone (2 and 142 ppm). BMA in urine correlated closely [correlation coefficient ( r) =0.7] with TOL in air, irrespective of correction for urine density. The lowest TOL concentration at which urinary BMA increased to a measurable level was approximately 10 ppm, and urinary BMA could separate the exposed from the non-exposed when TOL exposure was 15 ppm or higher. CONCLUSIONS: BMA in end-of-shift urine samples is a good marker of occupational TOL exposure. Urinalysis for BMA is sensitive enough to detect TOL exposure at 15 ppm, and therefore BMA appears to be more sensitive than hippuric acid and possibly o-cresol as a urinary marker of TOL 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.     

Exposure to toluene and urinary hippuric acid excretion in a group of heliorotagravure printing workers

Summary The influence of a number of factors possibly affecting the relation between urinary hippuric acid excretion and the exposure level to toluene was studied in a population of heliorotagravure printers. It was observed that the hippuric acid excretion rates, after 4 h and 8 h from the onset of the exposure, were in better agreement with the average toluene concentrations in work room air than either the urinary metabolite concentrations alone or corrected for urine density. Apart from differences in exposure level, a substantial proportion of the interindividual variability in hippuric acid excretion could be explained by differences in energetical load during the exposure. It was thereby not possible to elucidate the full extent to which this factor influences the metabolite excretion.In good agreement with previous experimental findings, the hippuric acid excretion rate apparently does not depend on the time of urine sampling during the exposure, provided that at least 4 h have elapsed from the onset.     

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.     

Occupational exposure to solvent mixtures: effects on health and metabolism.

Exposure monitoring by personal diffusive samplers, biological monitoring of toluene exposure by urinary hippuric acid determination, haematology, serum biochemistry for liver function, and a subjective symptom survey by questionnaire were conducted on 303 male solvent workers. They were exposed to a mixture of solvents including toluene (geometric mean 18 ppm), methyl ethyl ketone (MEK; 16 ppm), isopropyl alcohol (IPA; 7 ppm), and ethyl acetate (9 ppm). The intensity was mostly below unity using the additiveness formula based on current Japanese occupational exposure limits, but more than eight times unity at the maximum. The results were compared with the findings in 135 non-exposed male workers of similar ages. Haematology and liver function tests did not show any exposure related abnormality, and subjective symptoms were mostly related to central nervous system depression and local irritation. Further analysis suggested that the irritation effects were not related to exposure to MEK. Analysis of the relation between toluene exposure and hippuric acid excretion in urine showed that there was no metabolic interaction between MEK and toluene, or between IPA and toluene. Overall, therefore, it is concluded that there was no sign or symptom detected to suggest anything other than toluene toxicity, that there was no evidence to indicate any modification of toluene toxicity or metabolism due to coexposure, and that the additiveness assumption is reasonable for risk assessment for the combination of solvents under these exposure conditions.