Benzylmercapturic acid is superior to hippuric acid and o-cresol as a urinary marker of occupational exposure to toluene

Association of metabolites of benzene and toluene with lipid profiles in Korean adults: Korean National Environmental Health Survey (2015-2017)

Background

Environmental exposure to benzene and toluene is a suspected risk factor for metabolic disorders among the general adult population. However, the effects of benzene and toluene on blood lipid profiles remain unclear. In this study, we investigated the association between urinary blood lipid profiles and metabolites of benzene and toluene in Korean adults.

Methods

We analyzed the data of 3,423 adults from the Korean National Environmental Health Survey Cycle 3 (2015–2017). We used urinary trans,trans-muconic acid (ttMA) as a biomarker of benzene exposure, and urinary benzylmercapturic acid (BMA) as an indicator of toluene exposure. Multivariate logistic regression analyses were performed to explore the association between blood lipid profiles and urinary metabolites of benzene and toluene. Additionally, we examined the linear relationship and urinary metabolites of benzene and toluene between lipoprotein ratios using multivariate regression analyses.

Results

After adjusting for covariates, the fourth quartile (Q4) of ttMA [odds ratio (OR) (95% confidence interval, CI = 1.599 (1.231, 2.077)] and Q3 of BMA [OR (95% CI) = 1.579 (1.129, 2.208)] were associated with an increased risk of hypertriglyceridemia. However, the Q4 of urinary ttMA [OR (95% CI) = 0.654 (0.446, 0.961)] and Q3 of urinary BMA [OR (95% CI) = 0.619 (0.430, 0.889)] decreased the risk of a high level of low-density lipoprotein cholesterol (LDL-C). Higher urinary ttMA levels were positively associated with the ratio of triglycerides to high-density lipoproteins [Q4 compared to Q1: β = 0.11, 95% CI: (0.02, 0.20)]. Higher urinary metabolite levels were negatively associated with the ratio of low-density lipoprotein to high-density lipoprotein [Q4 of ttMA compared to reference: β = -0.06, 95% CI: (-0.11, -0.01); Q4 of BMA compared to reference: β = -0.13, 95% CI: (-0.19, -0.08)].

Conclusion

Benzene and toluene metabolites were significantly and positively associated with hypertriglyceridemia. However, urinary ttMA and BMA levels were negatively associated with high LDL-C levels. These findings suggest that environmental exposure to benzene and toluene disrupts lipid metabolism in humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-022-14319-x.

Exposure to benzene, toluene and polycyclic aromatic hydrocarbons in Nunavimmiut aged 16 years and over (Nunavik, Canada) - Qanuilirpitaa 2017 survey

There are numerous volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs) that Inuit may be exposed to from combustion, cooking, heating, vehicle exhaust, active and passive smoking and other local sources of contaminants such as oil spills or open-air burning in landfills. To better assess the levels of exposure to these non-persistent chemicals, we measured a suite of benzene, toluene (two VOCs) and PAHs metabolites in pooled urine samples from youth and adults aged 16 years old and over who participated in the Qanuilirpitaa? 2017 Inuit Health Survey (Q2017), a population health survey conducted in Nunavik. A cost-effective pooling strategy was established and 30 different pools from individual urine samples (n = 1266) were created by grouping individual urine samples by sex, age groups and regions. To assess smoking and exposure to second-hand smoke, cotinine levels were measured in individual urine samples. We found that benzene, toluene, all detected PAHs metabolites and cotinine levels were significantly higher in Q2017 compared to adults in the Canadian Health Measure Survey Cycle 4 (2014-2015) or the general U.S population (2015-2016). Moreover, mean levels of one benzene metabolite, S-phenylmercapturic acid, and several PAHs metabolites, 1-naphthol, 2-and 3-hydroxyfluorene, and 4- and 9-hydroxyphenanthrene, known to be associated with smoking habits, were higher in Q2017 compared to reference values (RV₉₅) established for non-smokers in the general Canadian population. Furthermore, benzene and PAHs metabolites were all correlated with cotinine levels. Our results suggest that the high smoking prevalence in Nunavik is an important contributor to the elevated benzene and PAHs exposure. Other local sources may add to that exposure, although we were not able to account for their contribution. These data highlight the importance of regional and community efforts for reducing smoking and to encourage smoke-free homes in Nunavik, while continuing to investigate and reduce other possible local sources of exposure to benzene, toluene and PAHs.

Estimation of toluene exposure in air from BMA (S-benzylmercapturic acid) urinary measures using a reverse dosimetry approach based on physiologically pharmacokinetic modeling

This study aimed to use a reverse dosimetry PBPK modeling approach to estimate toluene atmospheric exposure from urinary measurements of S-benzylmercapturic acid (BMA) in a small group of individuals and to evaluate the uncertainty associated to urinary spot-sampling compared to 24-h collected urine samples. Each exposure assessment technique was developed namely to estimate toluene air exposure from BMA measurements in 24-h urine samples (24-h-BMA) and from distributions of daily urinary BMA spot measurements (DUBSM). Model physiological parameters were described based upon age, weight, size and sex. Monte Carlo simulations with the PBPK model allowed converting DUBSM distribution (and 24-h-BMA) into toluene air levels. For the approach relying on DUBSM distribution, the ratio between the 95% probability of predicted toluene concentration and its 50% probability in each individual varied between 1.2 and 1.4, while that based on 24-h-BMA varied between 1.0 and 1.1. This suggests more variability in estimated exposure from spot measurements. Thus, estimating toluene exposure based on DUBSM distribution generated about 20% more uncertainty. Toluene levels estimated (0.0078-0.0138 ppm) are well below Health Canada's maximum chronic air guidelines. PBPK modeling and reverse dosimetry may be combined to interpret urinary metabolites data of VOCs and assess related uncertainties.

Requirement Prediction for Toluene Detox with Foods Intake Rich in CYP2E1 Enzyme and Glycine to Prevent Nerve and Kidney Damage at Shoe Home Industry Workers in Romokalisari Surabaya

BACKGROUND:

Toluene was an organic compound used in chemical and drug industries, the main source of toluene emissions from fires. To reduce and even eliminate toluene toxins in chemical component could be using detoxification by foods.

AIM:

This research aimed to calculate the intake of foods rich in CYP2E1 enzyme and glycine to improve toluene detoxification.

METHODS:

The type of research was a descriptive study. The subject of the study was 51 workers in Romokalisari Surabaya who had worked for more than or equal to 10 years. Variables were body weight, duration of working (years), working time per week (days), and working time per day (hours). The breathing rate, intake of non-carcinogen per respondent, can be calculated by variables before. Then, the effective dose of food rich in CYP2E1 enzyme and glycine will be obtained.

RESULTS:

Majority respondents had toluene concentrations below the threshold limit value (TLV). The highest effective dose of foods rich in CYP2E1 enzymes such as beef liver, beef brain, and salmon was 239.61 g, 745.45 g, and 203.3 g. Also, foods rich in glycines such as seaweed, tuna, and spinach were 432.98 mg, 934.41 mg, and 2070.71 mg.

CONCLUSION:

The level of adequacy of the CYP2E1 enzyme and glycine of each person was different and varied. The effective dose required by each respondent depending on weight, length of work, and concentration of benzene in the workplace. The greater the toluene concentration, the greater the needs for foods rich in CYP2E1 enzymes and glycine. Body weight can also be another factor in differences in individual intake. Weight, length of working, and toluene concentration can affect the intake of non-carcinogen in each which can affect the effective dose of foods.

Integrated evaluation of solvent exposure in an occupational setting: air, dermal and bio-monitoring

The assessment of dermal exposure to volatile organic compounds (VOCs) is becoming increasingly important in industrial settings. The study aimed to evaluate the overall exposure (inhalation and dermal) of workers to VOCs, and to assess the suitability of activated charcoal cloth (ACC) patches for the evaluation of the contribution of dermal exposure (vs. inhalation exposure) to the whole body burden, as reflected by human biomonitoring. Inhalation exposure to toluene, acetone and styrene (passive 3 M organic vapour monitors, OVMs) and dermal exposure (ACC patches on the index finger, thumb and neck) were measured simultaneously in 37 subjects performing different tasks in a factory of thermoplastic panels. Systemic exposure was assessed in urine by quantification of mandelic acid (MA) and phenyl glyoxylic acid (PGA), as biomarkers for styrene, as well as acetone and hippuric acid (HA) as biomarkers for acetone and toluene, respectively. High styrene (range 30.66-302 mg/m³) and acetone (range 11-644 mg/m³) concentrations were found in the air of the workplace, while toluene was less abundantly present (range 0.05-2.6 mg/m³). On the ACC patches, considerable amounts of these VOCs were found. For employees manually handling styrene, dermal exposure on the index finger and thumb were substantially higher compared to the neck ACC patch. A good correlation between air and urinary levels of acetone exposure was found. MA and PGA levels in urine, markers for styrene exposure, were correlated with both air and dermal exposure. These data suggest that there is a substantial benefit from assessing dermal exposure in the work place in addition to the more conventional air monitoring and urinary biomonitoring.

Effects of xylene and formaldehyde inhalations on renal oxidative stress and some serum biochemical parameters in rats

In this study, it was aimed to demonstrate the possible renal oxidative stress and some serum biochemical parameters and their alterations caused by the exposure to xylene and formaldehyde (HCHO) in rats. Weighing 150—200 g, 12-week-old, 24 female Sprague-Dawley rats were used. The rats were randomly divided into four groups: Group 1 (control), Group 2 (300-ppm technical xylene), Group 3 (6-ppm HCHO) and Group 4 (150-ppm technical xylene + 3-ppm HCHO). The animals were exposed to gases eight hours per day for six weeks. Superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) activities, glutathione (GSH) and malondialdehyde (MDA) levels were measured. In addition, serum total protein, albumin, urea and creatinine levels were evaluated. Compared with the control animals, urea levels increased significantly in all groups ( P < 0.001). GSH activities and MDA levels increased in xylene and xylene + HCHO groups ( P < 0.05). No statistically considerable differences were found in SOD, CAT and GSH-Px activities, total protein, albumin and creatinine levels among all groups ( P > 0.05). The present study indicates but not statistically confirms the renal toxicity of the exposures to xylene, HCHO and a mixture of them.

Metabolomics reveals effects of maternal smoking on endogenous metabolites from lipid metabolism in cord blood of newborns

INTRODUCTION

A general detrimental effect of smoking during pregnancy on the health of newborn children is well-documented, but the detailed mechanisms remain elusive.

OBJECTIVES

Beside the specific influence of environmental tobacco smoke derived toxicants on developmental regulation the impact on the metabolism of newborn children is of particular interest, first as a general marker of foetal development and second due to its potential predictive value for the later occurrence of metabolic diseases.

METHODS

Tobacco smoke exposure information from a questionnaire was confirmed by measuring the smoking related metabolites S-Phenyl mercapturic acid, S-Benzyl mercapturic acid and cotinine in maternal urine by LC-MS/MS. The impact of smoking on maternal endogenous serum metabolome and children's cord blood metabolome was assessed in a targeted analysis of 163 metabolites by an LC-MS/MS based assay. The anti-oxidative status of maternal serum samples was analysed by chemoluminiscence based method.

RESULTS

Here we present for the first time results of a metabolomic assessment of the cordblood of 40 children and their mothers. Several analytes from the group of phosphatidylcholines, namely PCaaC28:1, PCaaC32:3, PCaeC30:1, PCaeC32:2, PCaeC40:1, and sphingomyelin SM C26:0, differed significantly in mothers and children's sera depending on smoking status. In serum of smoking mothers the antioxidative capacity of water soluble compounds was not significantly changed while there was a significant decrease in the lipid fraction.

CONCLUSION

Our data give evidence that smoking during pregnancy alters both the maternal and children's metabolome. Whether the different pattern found in adults compared to newborn children could be related to different disease outcomes should be in the focus of future studies.

Co-exposure to polycyclic aromatic hydrocarbons, benzene and toluene and their dose-effects on oxidative stress damage in kindergarten-aged children in Guangzhou, China

Polycyclic aromatic hydrocarbons (PAHs), benzene and toluene (BT) are ubiquitous toxic pollutants in the environment. Children are sensitive and susceptible to exposure to these contaminants. To investigate the potential oxidative DNA damage from the co-exposure of PAHs and BT in children, 87 children (aged 3-6) from a kindergarten in Guangzhou, China, were recruited. Ten urinary PAHs and four BT metabolites, as well as 8-hydroxy-2'-deoxyguanosine (8-OHdG, a biomarker of oxidative DNA damage)in urine, were determined using a liquid chromatography tandem mass spectrometer. The results demonstrated that the levels of PAHs and BT in children from Guangzhou were 2-30 times higher than those in children from the other countries based on a comparison with recent data from the literature. In particular, the difference is more substantial for pyrene and volatile BT. Co-exposure to PAHs and BT could lead to additive oxidative DNA damage. Significant dose-effects were observed between the sum concentration of urinary monohydroxylated metabolites of PAHs (∑OH-PAHs), the sum concentration of the metabolites of BT (∑BT) and 8-OHdG levels. Every one percent increase in urinary PAHs and BT generated 0.33% and 0.02% increases in urinary 8-OHdG, respectively. We also determined that the urinary levels of PAHs and BT were negatively associated with the age of the children. Moreover, significant differences in the levels of ∑OH-PAHs and ∑BT were determined between 3- and 6-year-old children (p<0.05), which may be caused by different metabolism capabilities or inhalation frequencies. In conclusion, exposure to PAHs or BT could lead to oxidative DNA damage, and 8-OHdG is a good biomarker for indicating the presence of DNA damage. There exists a significant dose-effect relationship between PAH exposure, BT exposure and the concentration of 8-OHdG in urine. Toddlers (3-4 years old) face a higher burden of PAH and BT exposure compared with older children.

Biomass fuels and coke plants are important sources of human exposure to polycyclic aromatic hydrocarbons, benzene and toluene

Large amounts of carcinogenic polycyclic aromatic hydrocarbons (PAHs), benzene and toluene (BT) might be emitted from incomplete combustion reactions in both coal tar factories and biomass fuels in rural China. The health effects arising from exposure to PAHs and BT are a concern for residents of rural areas close to coal tar plants. To assess the environmental risk and major exposure sources, 100 coke plant workers and 25 farmers in Qujing, China were recruited. The levels of 10 mono-hydroxylated PAHs (OH-PAHs), four BT metabolites and 8-hydroxy-2'-deoxyguanosine (8-OHdG) in the urine collected from the subjects were measured. The 8-OHdG levels in the urine were determined to evaluate the oxidative DNA damage induced by the PAHs and BT. The results showed that the levels of the OH-PAHs, particularly those of 1-hydroxynathalene and 1-hydroxypyrene, in the farmers were 1-7 times higher than those in the workers. The concentrations of the BT metabolites were comparable between the workers and farmers. Although the exact work location within a coke oven plant might affect the levels of the OH-PAHs, one-way ANOVA revealed no significant differences for either the OH-PAHs levels or the BT concentrations among the three groups working at different work sites. The geometric mean concentration (9.17 µg/g creatinine) of 8-OHdG was significantly higher in the farmers than in the plant workers (6.27 µg/g creatinine). The levels of 8-OHdG did not correlate with the total concentrations of OH-PAHs and the total levels of BT metabolites. Incompletely combusted biomass fuels might be the major exposure source, contributing more PAHs and BT to the local residents of Qujing. The estimated daily intakes (EDIs) of naphthalene and fluorene for all of the workers and most of the farmers were below the reference doses (RfDs) recommended by the U.S. Environmental Protection Agency (EPA), except for the pyrene levels in two farmers. However, the EDIs of benzene in the workers and local farmers ranged from 590 to 7239 µg/day, and these levels were 2- to 30-fold higher than the RfDs recommended by the EPA. Biomass fuel combustion and industrial activities related to coal tar were the major sources of the PAH and BT exposure in the local residents. Using biomass fuels for household cooking and heating explains the higher exposure levels observed in the farmers relative to the workers at the nearby coal tar-related industrial facility.

Biomarkers of toluene exposure in rats: mercapturic acids versus traditional indicators (urinary hippuric acid and o-cresol and blood toluene)

1. Toluene (TOL) is a neurotoxic, ototoxic and reprotoxic solvent which is metabolized via the glutathione pathway, producing benzylmercapturic, o-, m- and p-toluylmercapturic acids (MAs). These metabolites could be useful as biomarkers of TOL exposure. 2. The aims of this study were (1) to provide data on MAs excretion in rat urine following TOL exposure by inhalation, (2) to compare them to data from traditional TOL biomarkers, i.e. TOL in blood (Tol-B), and urinary hippuric acid (HA) and o-cresol (oCre) and (3) to establish a relationship between these different indicators and the airborne TOL concentration (Tol-A). 3. Sprague-Dawley rats were exposed to a range of TOL concentrations. Blood and urine were collected and analyzed to determine biomarker levels. 4. Levels of the four MAs correlate strongly with Tol-A (comparable to the correlation with Tol-B). 5. MAs are thus clearly superior to oCre and HA as potential markers of exposure to TOL.

External quality assessment scheme for biological monitoring of occupational exposure to toxic chemicals

Objectives

In this study, we summarized the External Quality Assessment Scheme (EQAS) for the biological monitoring of occupational exposure to toxic chemicals which started in 1995 and continued until a 31^st round robin in the spring of 2010. The program was performed twice per year until 2009, and this was changed to once a year since 2010. The objective of the program is to ensure the reliability of the data related to biological monitoring from analytical laboratories.

Methods

One hundred and eighteen laboratories participated in the 31^st round robin. The program offers 5 items for inorganic analysis: lead in blood, cadmium in blood, manganese in blood, cadmium in urine, and mercury in urine. It also offers 10 items for organic analysis, including hippuric acid, methylhippuric acid, mandelic acid, phenylglyoxylic acid, N-methylformamide, N-methylacetamide, trichloroacetic acid, total trichloro-compounds, trans,trans-muconic acid, and 2,5-hexanedione in urine. Target values were determined by statistical analysis using consensus values. All the data, such as chromatograms and calibration curves, were reviewed by the committee.

Results

The proficiency rate was below 70% prior to the first round robin and improved to over 90% for common items, such as PbB and HA, while those for other items still remained in the range of 60-90% and need to be improved up to 90%.

Conclusion

The EQAS has taken a primary role in improving the reliability of analytical data. A total quality assurance scheme is suggested, including the validation of technical documentation for the whole analytical procedure.

Glutathione pathway in ethylbenzene metabolism: novel biomarkers of exposure in the rat

Glutathione pathway was specifically studied in rats exposed by inhalation to a range of ethylbenzene vapours (5-2000 ppm). Urines were collected during exposure (6h) and over the 18 h following the exposure. The potential metabolites coming from either side-chain or ring oxidation were synthesized: 1-, 2-phenylethylmercapturic acids (1-, and 2-PEMA) and 2-, 3- and 4-ethylphenylmercapturic acids (2-, 3-, and 4-EPMA). Their synthesis was fully described and the molecules characterized. Urine samples were analysed using a selective HPLC-fluorescence method. Among the five metabolites, 2-PEMA was never observed in any urine sample. By contrast, 1-PEMA was discovered in its two diastereomeric forms, and it was shown that one of them was mainly present. 2-EPMA, 3-EPMA and 4-EPMA (in the ratio 1:2:6) were also found, and their combined excretion levels were similar to that of 1-PEMA. The atmospheric concentrations and urinary excretions yielded very close correlations which allow us to consider these mercapturic acids as novel ethylbenzene exposure biomarkers.

Validation of urine density correction in cases of hippuric acid and un-metabolized toluene in urine of workers exposed to toluene

To investigate if it is appropriate to apply urine density correction when a urine sample is dense or dilute. Data on hippuric acid (HA-U), toluene (Tol-U), creatinine (CR) and specific gravity (SG) in end-of-shift urine samples and exposure to air-borne toluene were cited from previous publications. In practice, 837 cases were available, and they were classified into dense, intermediate and dilute groups taking 0.3 and 3.0 g/l of CR and 1.010 and 1.030 of SG as cut-off points. Lines of regression of HA-U and Tol-U (as observed, CR-corrected or SG-corrected) with air-borne toluene were calculated for each density groups, and correlation coefficients (CCs) were compared. The dense groups gave CCs similar to those of the intermediate groups. Dilute versus intermediate group comparison also gave promising results. These conclusions were however based primarily on the findings with observed values, because the numbers of cases in the dilute or dense group were limited when CR- or SG-correction was applied. Literature survey showed that urine density correction does not always improve the correlation between solvents in air and exposure makers in urine. It was concluded that no correction for urine density may be necessary in evaluating HA-U and Tol-U in dense (and probably also dilute) urine samples as markers of occupational toluene exposure. Just in case when correction for urine density is desired for any reason, SG-correction may be recommended.

Validity of new biomarkers of internal dose for use in the biological monitoring of occupational and environmental exposure to low concentrations of benzene and toluene

OBJECTIVES

This study analyzes the validity of new, more sensitive and specific urinary biomarkers of internal dose, namely, urinary benzene for benzene and urinary toluene and S-benzylmercapturic acid (SBMA) for toluene, to assess their efficacy when compared to traditional biomarkers for biological monitoring of occupational exposure to low concentrations of these two toxic substances.

METHODS

Assessment was made of 41 workers occupationally exposed to benzene and toluene, 18 fuel tanker drivers and 23 filling-station attendants, as well as 31 subjects with no occupational exposure to these toxic substances (controls). Exposure to airborne benzene and toluene was measured using passive Radiello personal samplers worn throughout the work shift. In urine samples collected from all subjects at the end of the workday, both the traditional and the new internal dose biomarkers of benzene and toluene were assessed, as well as creatinine so as to apply suitable adjustments.

RESULTS

Occupational exposure to benzene and toluene resulted significantly higher in the fuel tanker drivers than the filling-station attendants, and higher in the latter than in controls. Significantly higher concentrations of t,t-muconic acid (t,t-MA), S-phenylmercapturic acid (SPMA), urinary benzene, SBMA and urinary toluene were found in the drivers than the filling-station attendants or the controls. Instead, urinary phenol and hippuric acid were not different in the three groups. In the entire sample, airborne benzene and toluene values were significantly correlated, as were the respective urinary biomarkers, showing coefficients ranging from 0.36 to 0.98. Subdividing the subjects by smoking habit, higher coefficients were evident in non-smokers than in smokers; at multiple regression analysis t,t-MA, SPMA and urinary benzene and toluene were dependent on the number of cigarettes smoked daily and on airborne benzene and toluene, respectively. Instead, SBMA was dependent only on airborne toluene.

CONCLUSIONS

Our research confirmed the validity of t,t-MA and SPMA for use in the biological monitoring of exposure to low concentrations of benzene. Urinary benzene showed comparable validity to SPMA; both parameters are affected by smoking cigarettes in the hours before urine collection, so it is best to ask subjects to refrain from smoking for 2 h before urine collection. Urinary toluene was found to be a more specific biomarker than SBMA.

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.

Methyl mercapturate synthesis: an efficient, convenient and simple method

A safe and simple method for methyl S-arylmercapturate synthesis is described. Thirteen such compounds, to be used afterwards in metabolism studies, have been obtained with yields ranging from 71 to 99.6%. These compounds were obtained using a sulfa-Michael addition and synthesized by adding the corresponding thiophenols to a mixture composed of methyl 2-acetamidoacrylate (MAA), potassium carbonate and a phase transfer catalyst, Aliquat 336. MAA, the initial synthon, was itself isolated in quasi quantitative yield following a fully described synthesis.

Limited validity of o-cresol and benzylmercapturic acid in urine as biomarkers of occupational exposure to toluene at low levels

This study was initiated to evaluate o-cresol and benzylmercapturic acid in urine in comparison with other biomarkers, as tools to estimate the intensity of occupational exposure to toluene at low levels. In total, 108 solvent exposed workers (engaged in tape production) and 17 non-exposed controls (all men) participated in the study. The surveys were conducted in the second half of working weeks. Diffusive sampling was conducted to measure 8-h time-weighted average intensity of occupational exposure to toluene. Blood and urine samples were collected at the end of a working shift. Blood samples were subjected to analysis for toluene (Tol-B), and urine samples were analyzed for benzyl alcohol (BeOH-U), benzylmercapturic acid (BMA-U), o-cresol (o-CR-U), hippuric acid (HA-U) and toluene (Tol-U) by the methods previously described. The toluene concentrations in workplaces were low in general, with a geometric mean (GM) and the maximum concentration of 1.9 ppm and 8.8 ppm, respectively. The statistical analyses of the six biomarkers for correlation with air-borne toluene showed that both Tol-B and Tol-U gave a high correlation coefficient of 0.58 to 0.61 (p<0.01), whereas the coefficients for BeOH-U and BMA-U together with HA-U were all low (up to 0.22, depending on the correction for urine density) and statistically insignificant (p>0.10) in most cases. o-CR-U had an intermediary coefficient of 0.20 (p<0.05). Comparison with previous publications disclosed that BeOH-U, BMA-U and HA-U correlate with toluene in air when the exposure is intense (e.g., 50 ppm or above), but no longer proportional to air-borne toluene when the exposure is low, e.g., 2 ppm. Such appeared to be also the case for o-CR-U. In over-all evaluation, the validity of o-CR-U in monitoring occupational exposure to toluene at low levels (e.g., 2 ppm) appear to be limited, and BMA-U is not an appropriate biomarker. BeOH-U and HA-U are also inappropriate for this purpose. Only Tol-B and Tol-U may be employed to estimate toluene exposure at low levels.

Fast determination of urinary S-phenylmercapturic acid (S-PMA) and S-benzylmercapturic acid (S-BMA) by column-switching liquid chromatography-tandem mass spectrometry

Benzene and toluene are important industrial chemicals and ubiquitous environmental pollutants. The urinary mercapturic acids of benzene and toluene, S-phenylmercapturic acid (S-PMA) and S-benzylmercapturic acids (S-BMA) are specific biomarkers for the determination of low-level exposures. We have developed and validated a fast, specific and very sensitive method for the simultaneous determination of S-PMA and S-BMA in human urine using an automated multidimensional LC-MS-MS-method that requires no additional sample preparation. Analytes are stripped from urinary matrix by online extraction on a restricted access material, transferred to the analytical column and subsequently determined by tandem mass spectrometry using isotopically labelled S-PMA as internal standard. The lower limit of quantification (LLOQ) for both analytes was 0.05 microg/L urine and sufficient to quantify the background exposure of the general population. Precision within series and between series for S-PMA and S-BMA ranged from 1.0% to 12.2%, accuracy was 108% and 100%, respectively. We applied the method on spot urine samples of 30 subjects of the general population with no known exposure to benzene or toluene. Median levels (range) for S-PMA and S-BMA in non-smokers (n=15) were 0.14 microg/L (<0.05-0.26 microg/L) and 8.2 (1.6-77.4 microg/L), respectively. In smokers (n=15), median levels for S-PMA and S-BMA were 1.22 microg/L (0.17-5.75 microg/L) and 11.5 microg/L (0.9-51.2 microg/L), respectively. Due to its automation, our method is well suited for application in large environmental studies.

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, omicron-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 omicron-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 omicron-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 microg/l, respectively] in the urine from the control subjects.

CONCLUSIONS

In over-all evaluation, hippuric acid, followed by un-metabolized toluene and omicron-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.

Effects of Xylene and Formaldehyde Inhalations on Oxidative Stress in Adult and Developing Rats Livers

In this study, it was aimed to demonstrate the possible oxidative stress caused by exposure of xylene and formaldehyde (HCHO) on liver tissue, and on body and liver weights in adult as well as developing rats. The rats (96 female Sprague-Dawley) were randomly divided into four groups: embryonic day 1 (Group 1), 1-day-old infantile rats (Group 2), 4-week-old rats (Group 3) and adult rats (Group 4). The animals were exposed to gases of technical xylene (300 ppm), HCHO (6 ppm) or technical xylene + HCHO (150 ppm + 3 ppm), 8 hours per day for 6 weeks. Superoxide dismutase (SOD) and catalase (CAT) activities, and glutathione (GSH) and malondialdehyde (MDA) levels were evaluated. In addition, body and liver weights were determinated. Compared to the control animals, body and liver weights were decreased in the embryonic day 1 group (P < 0.001, P < 0.01, respectively) and the 1-day-old infantile group (P < 0.001). Liver weight was increased in the 4-week-old group (P < 0.01). SOD activities were decreased in the 4-week-old rats exposed to HCHO (P < 0.01). CAT activities increased in the embryonic day 1 group (P < 0.05). GSH levels were decreased in the 1-day-old infantile group (P < 0.01), and MDA levels was increased in the embryonic day 1 group (P < 0.05) as compared with the respective control groups. As to GSH and MDA levels in adult and 4-week-old animals, no statistically significant differences were observed (P > 0.05). The present study indicates that exposures to xylene, HCHO and a mixture of them are toxic to liver tissue, and developing female rats are especially more adversely affected. Furthermore, the results of this study show that adult female rats could better tolerate the adverse effects of these toxic gases.

Benzyl alcohol as a marker of occupational exposure to toluene

Benzyl alcohol (BeOH) is a urinary metabolite of toluene, which has been seldom evaluated for biological monitoring of exposure to this popular solvent. The present study was initiated to develop a practical method for determination of BeOH in urine and to examine if this metabolite can be applied as a marker of occupational exposure to toluene. A practical gas-liquid chromatographic method was successfully developed in the present study with sensitivity low enough for the application (the limit of detection; 5 microg BeOH /l urine with CV=2.7%). Linearity was confirmed up to 10 mg BeOH/l, the highest concentration tested, and the reproducibility was also satisfactory with a coefficient of variation of 2.7% (n=10). A tentative application of the method in a small scale study with 45 male workers [exposed to toluene up to 130 ppm as an 8-h time-weighted average (8-h TWA)] showed that BeOH in the end-of-shift urine samples was proportional to the intensity of exposure to toluene. The calculated regression equation was Y=50+1.7X (r=0.80, p<0.01), where X was toluene in air (in ppm as 8-h TWA) and Y was BeOH in urine (in microg/l of end-of-shift urine). The levels of BeOH in the urine of the non-exposed was about 50 microg/l, and ingestion of benzoate as a preservative in soft drinks did not affect the BeOH level in urine. The findings as a whole suggest that BeOH is a promising candidate for biological monitoring of occupational exposure to toluene.

Mercapturic acids of styrene in man: Comparability of the results obtained by LC/MS/MS and by HPLC-fluorimeter, and stability of samples under different storage conditions

Two analytical methods (HPLC-fluorimeter [HPLC-FLD] and tandem mass spectrometry LC/MS/MS) are available to assay phenyl-hydroxyethylmercapturic acids (PHEMAs), the mercapturic acids of styrene in humans. In the past, each method was used to check different populations of subjects, but until now no attempt has been made to compare the two methods. This study was designed to verify whether the two methods actually give comparable results. The influence of different conditions of sample storage in altering the concentration of PHEMAs was also investigated. Urine samples were collected at the beginning and at the end of the workshift from 10 workers exposed to different levels of styrene. Each sample was analysed both by LC/MS/MS after storage under different conditions (respectively, at -20 and +4 degrees C, and after repeated freezing-thawing cycles), and by HPLC-FLD (in the same conditions of storage). Strong correlations were found between the two methods both for total PHEMAs and for each of the isomers measured, including the minor (S,R)-M1. Also an alternative approach, the Bland-Altman test, confirmed the agreement between the two methods. The different storage conditions tested did not decrease the concentration of PHEMAs but, surprisingly, a clear trend to increase was shown, particularly for (R,R)-M1, (S,R)-M2 and (R,R)-M2 in samples stored at +4 degrees C for 1 week. In conclusion, the study demonstrates that the methods give comparable results. Indirectly, this confirms also the main characteristics of PHEMAs, showed in the previous experiments: low biotransformation rates of styrene into PHEMAs; large inter-individual variability; and the presence of a clear preference in the excretion of the isomers deriving from (S)-styrene oxide. PHEMAs appear stable under different storage conditions, but further studies are needed to explain the increase of levels that occurs when samples are not kept frozen. To avoid pre-analytical errors, samples collected for biomonitoring or research purposes should be frozen as soon as possible, and thawed only one time just before the analysis.

An experimental model for the determination of immunomodulating effects by volatile compounds

An in vitro exposure system was developed to enable simultaneous exposure of primary cells or cell lines to defined concentrations of volatile organic compounds (VOC) without the necessity of a constant-flow exposure system. Toluene was used as model VOC and administered via the gas phase. CD3/CD28-stimulated human peripheral blood mononuclear cells (PBMC) were used as indicator cells. Vitality/proliferation of PBMC was tested using the MTT assay and their functional reactivity using cytokine ELISA for interferon-gamma (IFN-gamma), interleukin-4 (IL-4), IL-13, and tumor-necrosis-factor-alpha (TNF-alpha). Chemical analysis using headspace gas chromatography confirmed that this new method guaranties reproducible VOC exposure (R2 = 0.995 for the correlation between external toluene concentration and toluene in the cell culture). While cytotoxic effects were not observed, dose-dependent toluene effects on functional reactivity of PBMC were found. The secretion of IFN-gamma, IL-4, and IL-13 was inhibited at concentrations of 72.5 g/m3 and above, whereas the TNF-alpha production was increased. Since the presented in vitro model ensures toluene exposure in concentrations comparable to the real situation, and allows the investigation of dose-dependent immunomodulatory toluene effects in concentrations without cytotoxicity, this method first described here is introduced as useful tool in analysis of VOC-triggered effects on immune cells.

Effect of hippuric acid on the gaschromatographic retention of S-phenylmercapturic acid

S-phenylmercapturic acid (PMA) is one specific urinary biomarker of low-level benzene exposure. It is used for biological monitoring of benzene-exposed workers in the petrochemical industry and normally ranges from non-measurable to 10 microg/l levels in non-exposed non-smoking subjects. Benzene-exposure caused by workplace or lifestyle sources is frequently accompanied by toluene exposure, which can cause the occurrence of high levels (from 10 mg/l to more than 2000 mg/l) of hippuric acid (HA) in urine. Both solvents are toxic, and benzene is classified as a human carcinogen. The biological monitoring of benzene and toluene is therefore required for preventive care of exposed workers health. In this study a GC-MS method was adopted for measuring urinary PMA, which involved liquid-liquid extraction (LLE) with ethyl acetate from acidified urine and esterification with 0.5 N hydrochloric acid in methanol. The method evidenced a GC effect in a conventional HP-5 (30 m x 0.25 mm i.d., 0.25 microm film-thickness) methyl-phenylsilicone capillary column produced by HA on PMA. The results demonstrate that HA at concentrations as low as 250 mg/l can delay the elution of PMA and labelled internal standard from the column. The recognition and discussion of this particular GC phase soaking effect may be of help for those who are occupied in the determination of PMA and of urinary acidic metabolites by GC.

Mercapturic acids revisited as biomarkers of exposure to reactive chemicals in occupational toxicology: a minireview

A minireview is presented concerning the use of mercapturic acids as biological exposure index for electrophilic chemicals. Besides pure analytical aspects, this minireview considers possible issues in relation to (a) the added value of mercapturic acids as compared to other well validated biomarkers of exposure and (b) the high inter-individual variability in mercapturic acids excretion. Recent field and/or experimental studies confirm the usefulness of mercapturic acids as biological exposure index for electrophilic chemicals and suggest the interest of a toxicogenetic approach for a better interpretation of the results of biological monitoring.

Inhibition of cyclooxygenase activity, platelet aggregation and thromboxane B2 production by two environmental toxicants: m- and o-cresol

Cresol is a well-known environmental pollutant, toluene metabolite, uremic toxicant and accidental poisoning product. Formocresol, a preparation of formalin and cresol, is also used as a root canal medicament and for pulpotomy of primary teeth. However, little is known about its effect on cardiovascular system. In this study, m-cresol inhibited the AA-induced platelet aggregation by 43-97% at concentrations ranging from 0.25 to 1 mM. Collagen-induced platelet aggregation was also inhibited by 0.25-1 mM of m-cresol by 47-98%. Accordingly, o-cresol (0.1-0.5 mM) also inhibited the AA-induced platelet aggregation by 46-96% and the collagen-induced platelet aggregation by 35-88% at concentrations of 0.1-1 mM. AA- and collagen-induced platelet thromboxane B(2) (TXB(2)) production was inhibited by even 0.1 mM of m-cresol with 88 and 54% of inhibition, respectively. The o-cresol (0.1 mM) also inhibited the AA- and collagen-induced platelet TXB(2) production with 91 and 97% respectively. Although m- and o-cresol (<1 mM) showed little effect on thrombin-induced platelet aggregation, they effectively inhibited the thrombin-induced platelet TXB(2) production. The m-cresol (2 and 5 mM) inhibited the COX-1 activity by 55-99%, but showed little effect on COX-2 enzyme activity. Moreover, o-cresol (0.5 and 1 mM) inhibited the COX-1 activity by 40-95%. COX-2 enzyme activity was inhibited by 68% at a concentration of 5 mM o-cresol. These results indicate that acute cresol-poisoning, direct root canal medication with formocresol or long-term occupational exposure to cresol and toluene may potentially suppress blood clot formation and lead to tissue hemorrhage via inhibition of platelet aggregation, TXB(2) production and COX enzyme activity.