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.     

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.     

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.     

Urinary mandelic acid concentration after occupational exposure to styrene and its use as a biological exposure test.

Excretion of mandelic acid from workers in the reinforced polyester plastic industry was studied with the determination of urinary mandelic acid concentrations. The styrene exposure level at the workplaces was evaluated with measurements of the styrene concentration in the ambient air. Three different groups (I, II and III) were studied. In group I [n=9, median of the time-weighted average (TWA) of exposure = 23 ppmof styrene, postexposure observation period = 64 h] two excretion slopes were observed, the first with a median half-time of 9.4 h (postexposure period 0--18 h) and a second with a median half-time of 16.6 h (postexposure period 19--64 h). For group II (n=9, median TWA exposure = 248 ppm, postexposure observation period = 15 h) a half-time of 6.4 h was found. These results suggest that the excretion rate of mandelic acid is dependent on the styrene exposure level. In addition the mandelic acid concentrations of 29 workers (group III) before and after the work shift were analyzed. The urinary mandelic acid concentrations of groups I, II and III, sampled immediately after the 8-h work shift, correlated with the 8-h TWA of styrene exposure (n=47, r=0.93). Accordingly about 2,300 mg of mandelic acid per gram of creatinine corresponded to 100 ppm of styrene.     

Urinary excretion of hippuric acid and m-methylhippuric acid after administration of toluene and m-xylene mixture to rats

Summary Male Wistar rats were injected intraperitoneally (i.p.) with toluene alone, m-xylene alone, and in combination with both of them. Urinary excretion of hippuric acid or m-methylhippuric acid of rats injected with solvents of various concentrations was investigated from the end of the injections up to 48 h later, at appropriate intervals. The amounts of increased excretion of HA and m-MHA in 0–24h urine samples of the rats given simultaneous injections of toluene and m-xylene were not lower than those of the rats given single injections of toluene alone or m-xylene alone, in the same amount. Data indicated that simultaneous administration of toluene and m-xylene did not significantly interfere with the metabolism of toluene or m-xylene.Read before the 50th Annual Meeting of Japan Industrial Health Association, Kurume, April 5, 1977The work was supported in part by grant No. 357188 of the Ministry of Education Agency     

Thin-layer chromatography of hippuric and m-methylhippuric acid in urine after mixed exposure to toluene and xylene.

The separation of hippuric and m-methylhippuric acid as toluene and m-xylene metabolites present in urine of people exposed simultaneously to toluene and xylene is described. Chloroform was used for hippuric and m-methylhippuric acid extraction. Satisfactory separation of these metabolites was obtained on TLC plates covered with silica gels and developed in chloroform acetic acid-water (4:1:1);p-dimethylaminobenzaldehyde in acetic acid anhydride was applied to develop the colour. The sensitivity of the method was 6 micrograms hippuric acid per 1 ml urine and recovery was 100% (+/- 1).     

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.     

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).     

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     

Significance of urinary hippuric acid determination as an index of toluene exposure

Ikeda, Masayuki, and Ohtsuji, Hatsue (1969).Brit. J. industr. Med.,26, 244-246. Significance of urinary hippuric acid determination as an index of toluene exposure. Urine samples from 118 male workers in photogravure printing factories were analysed for hippuric acid. The urinary levels of hippuric acid were proportional to the environmental concentrations of toluene, although within wide variations. The urinary concentration of hippuric acid corresponding to 200 p.p.m. of toluene was 3·5 g./litre (specific gravity 1·016) or 4·3 g./g. creatinine.     

Urinary trans-trans muconic acid (exposure biomarker to benzene) and hippuric acid (exposure biomarker to toluene) concentrations in Mexican women living in high-risk scenarios of air pollution

This study aimed to determine t,t-muconic acid (t,t-MA; exposure biomarker for benzene) and hippuric acid (HA; exposure biomarker for toluene) concentrations in the urine of women living in Mexico. In a cross-sectional study, apparently healthy women (n = 104) were voluntarily recruited from localities with a high risk of air pollution; t,t-MA and HA in urine were quantified using a high-performance liquid chromatography (HPLC) technique. Mean urinary levels of t,t-MA ranged from 680 to 1,310 μg/g creatinine. Mean values of HA ranged from 0.38 to 0.87 g/g creatinine. In conclusion, compared to data recently reported in literature, we found high urinary levels of t,t-MA and HA in assessed women participating in this study. We therefore deem the implementation of a strategy aimed at the reduction of exposure as a necessary measure for the evaluated communities.     

Urinary excretion of hippuric acid after consumption of nonalcoholic beverages

To investigate the types and quantities of beverages that increase urinary hippuric acid (HA) excretion, the authors recruited 137 healthy medical students and divided them into quintiles according to consumption of benzoic acid (BA) in beverages. Using chromatography, urinary HA before and 1.5 hours and 3 hours after consumption of various beverages and BA consumption in the beverages were measured. The mean age of the group was 24.2 years; 21 were female. The range of BA in 13 beverages was 0-1.02 mg/mL. The geometric means of urinary HA before consuming them in five groups were 0.276, 0.270, 0.207, 0.262, and 0.316 g/L, respectively (p = 0. 567); 1.5 hours after consuming the beverages, they were 0.210, 0. 603, 1.026, 1.066, and 1.688 g/L, respectively, and significantly increased after adjustment for urinary HA before ingestion (p < 0. 001). Three hours after ingestion, the geometric means were 0.160, 0. 232, 0.306, 0.287, and 0.337 g/L, respectively (p < 0.001). The authors estimate that beverages that contain more than 100 mg BA could increase urinary HA excretion significantly, up to 1.12 g/L without toluene exposure. Checking dietary and beverage-intake histories is essential in the interpretation of urinary HA concentrations in population studies.     

Hormone status in occupational toluene exposure.

Twenty toluene-exposed rotogravure printers, without signs of solvent-induced toxic encephalopathy, had lower median plasma levels of follicle stimulating hormone (FSH) (3.2 vs. 4.9 IU/L; p = .02) and luteinizing hormone (LH) (6.4 vs. 7.2 IU/L; p = .05) and also lower serum levels of free testosterone (7.8 vs. 86.8 pmol/L; p = .05), respectively, than 44 unexposed referents. The individual time-weighted toluene levels in air were 36 (median; range 8-111) ppm. The printers' median toluene levels in blood were 1.7 (1.0-6.6) mumol/l, and in subcutaneous adipose tissue 5.7 (2.5-21) mg/kg fat. There was a negative association between blood toluene and plasma levels of prolactin. In eight printers, the levels of FSH and LH increased during a 4 week vacation, while the levels of thyroid stimulating hormone, free triiodothyronine, and free thyroxine decreased during the same period. The results indicate a slight, reversible effect of toluene on the cortical level or on the hypothalamic-pituitary axis at exposures well below the permissible levels, possibly mediated through an effect on catecholamine neurotransmission.     

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.     

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.     

Measurement by gas chromatography of urinary hippuric acid and methylhippuric acid as indices of toluene and xylene exposure.

A gas chromatographic method was applied to the determination of the urinary glycine conjugates, hippuric, o-, m- and p-methylhippuric acids. These were extracted with ethyl acetate from urine after acidification with hydrochloric acid. The internal standard solution (heptadecanoic acid methanol solution) was added before extraction and a diazomethane-ether-ethanol solution was subsequently added to the dried extracts. The methylated residues were dissolved in methanol and injected into a gas chromatograph as described by Buchet and Lauwerys (1973). By the combined use of gas chromatography and mass spectrometry the methyl esters of hippuric acid and m-methylhippuric acid were identified in the urine of a volunteer who had been exposed to toluene and m-xylene vapours. When the urine specimen contained salicyluric acid (a urinary metabolite of salicylic acid) two sharp peaks were observed. The faster peak coincided with m- or p-methylhippuric acid. The upper limit of urinary hippuric acid concentration in healthy subjects with no occupational exposure was calculated by this method to be 1.026 microgram/ml (fiducial limit 5%) after correction to 1.024 for variation in urinary density.