Comparison between urinary o-cresol and toluene as biomarkers of toluene exposure

Evaluation of environmental and biological monitoring methods for toluene exposure assessment in paint industry

The aim of this study was to assess the exposure to Toluene in paint industry and to evaluate the environmental and biological monitoring techniques for the assessment of occupational exposure to this aromatic hydrocarbon. In this study, personal active and passive air sampling for toluene measurements, blood and urine sampling respectively for B-Tol and HA or U-Tol analyses for eight workers from two paint and thinner production factories were collected during four successive working days. Correlations were analyzed between biological indicators and environmental toluene exposure levels. The concentration of Toluene measured in air samples ranged from 0.2 to 414.0 ppm (mean = 59.8 ppm), with high variability of atmospheric levels between activities and between days. No significant difference was found between airborne toluene concentrations measured by the two sampling methods. The correlation between air concentrations sampled by the diffusive sampling method and the biomarkers was the best for HA (r = 0.902, p < 0.01), followed by B-Tol (r = 0.820; p < 0.01), o-Cr (r = 0.691; p < 0.01) and U-Tol (r = 0.607; p < 0.05). The correlation was better between air concentrations and urinary metabolites HA and o-Cr for exposure levels higher than 50 ppm (r = 0.931; p < 0.01), and lower than 300 ppm (r = 0.827; p < 0.01), respectively. According to our results, workers in the studied industries are highly exposed to Toluene. Given the high correlation found between toluene concentrations in samples taken on dosimeters and those actively sampled on charcoal tubes, it may be assumed that both sampling methods are valuable. Despite the influencing factors, HA was found to be a reliable biological indicator for the monitoring of occupational exposure to toluene for high exposure levels. However, B-Tol seems to be an interesting alternative, since it is more specific and showed the best correlations with airborne toluene levels.

Biological monitoring and personal exposure to traffic-related air pollutants of elementary school-age children living in a metropolitan area

An ever-growing burden of scientific evidence links air pollution to different aspects of human health even at very low concentrations; the impact increases for those living in urban environments, especially the youngest and the elderly. This study investigated the exposure to air pollution of urban school children of Milan, Italy, by personal and biological monitoring, in the frame of the MAPS-MI project. A total of 128 primary school children (7-11 years) were involved in a two-season monitoring campaign during spring 2018 and winter 2019. Personal exposure to airborne VOCs and eBC, and biological monitoring of urinary benzene (BEN-U) and methyl-tert-butyl ether (MTBE-U) were performed. Time-activity patterns, environmental tobacco smoke (ETS), spatial, and meteorological information were evaluated as determinants in mixed effects regression analysis. Children personal exposure was mostly quantifiable with median (5th-95th percentile) levels 1.9 (0.8-7.5) μg/m³ for eBC, and 1.1 (<0.6-3.4) and 0.8 (0.3-1.8) μg/m³ for benzene and MTBE, respectively; with values 2-3-fold higher in winter than in spring. In urine, median (5th-95th) BEN-U and MTBE-U levels were 44.9 (25.7-98.6) and 11.5 (5.0-35.5) ng/L, respectively. Mixed effect regression models explained from 72 to 93 % of the total variability for air pollutants, and from 58 to 61 % for biomarkers. Major contributors of personal exposure were season, wind speed, mobility- or traffic-related variables; biomarkers were mostly predicted by airborne exposure and ETS. Our results suggest that traffic-mitigation actions, together with parents' educational interventions on ETS and commuting mode, should be undertaken to lower children exposure to air pollution.

Environmental and biological monitoring of personal exposure to air pollutants of adult people living in a metropolitan area

BACKGROUND

Human exposure to air pollutants, and specifically to particulate matter (PM) and volatile organic compounds (VOCs), may pose a relevant risk on human health.

AIM

To evaluate the personal exposure of adults living and working in Milan (Italy) by environmental and biological monitoring.

METHODS

Personal exposure of 51 volunteer adults to PM_2.5, PM_2.5-10 and selected VOCs, including benzene, toluene, ethylbenzene, o-xylene, m + p-xylene, methyl tert-butyl ether, naphthalene, hexane, cyclohexane, heptane, and limonene was assessed along a 24-h period via personal cascade impactors and radial diffusive samplers. Urine spot samples were collected to investigate the corresponding urinary biomarkers. Time-activity patterns were filled in by participants to explore the performed activities. Multiple regression models were applied to investigate the association between personal exposure, biomarker levels, and tobacco smoke, traffic exposure, commuting mode, cooking activities, and personal characteristics.

RESULTS

Median personal exposure to PM_2.5, PM_2.5-10, benzene, toluene, ethylbenzene o-xylene, m + p-xylene, methyl tert-butyl ether, naphthalene, hexane, cyclohexane, heptane, and limonene were 36.1, 7.8, 2.3, 7.8, 2.1, 1.8, 4.7, 0.8, 0.3, 1.4, 2.5, 1.6, and 59.9 μg/m³, respectively. Median levels of urinary benzene, toluene, ethylbenzene o-xylene, m + p-xylene, naphthalene, hexane, and heptane were 78.0, 88.1, 21.5, 15.2, 43.9, 21.0, 11.0, and 22.5 ng/L, respectively. For personal exposure, multiple regression models explained up to 67% (PM_2.5) and 61% (benzene) of variability, with major contribution from commuting mode and environmental exposure. For biological monitoring, multiple regression analysis explained up to 74% of urinary benzene, with a major contribution given by creatinine, and secondary contributions by commuting mode, personal exposure to airborne benzene and smoking.

CONCLUSIONS

Personal exposure to air pollutants was lower than that measured in the past in Milan. Personal exposure was mainly driven by traffic variables, while internal dose was mainly driven by personal characteristics and smoking habit.

Urinary biomonitoring of subjects with different smoking habits. Part I: Profiling mercapturic acids

BACKGROUND

While tobacco smoke contains thousands of chemicals, some of which are carcinogenic to humans, the content of electronic cigarette smoke is less known. This work aimed to assess and compare the exposure associated with different smoking habits by profiling urinary mercapturic acids as biomarkers of toxic compounds.

METHODS

In this pilot study, sixty-seven healthy adults with different smoking habits were investigated: 38 non-smokers (NS), 7 electronic cigarette users (ECU), and 22 traditional tobacco smokers (TTS). Seventeen urinary mercapturic acids, metabolites of 1,3-butadiene (DHBMA, MHBMA), 4-chloronitrobenze (NANPC), acrolein (3-HPMA), acrylamide (AAMA, GAMA), acrylonitrile (CEMA), benzene (SPMA), crotonaldehyde (CMEMA, HMPMA), ethylating agents (EMA), methylating agents (MMA), ethylene oxide (HEMA), N,N-dimethylformamide (AMCC), propylene oxide (2-HPMA), styrene (PHEMA), and toluene (SBMA), were quantified, along with urinary nicotine and cotinine.

RESULTS

Median urinary cotinine was 0.4, 1530 and 1772 μg/L in NS, ECU and TTS, respectively. Most mercapturic acids were 2-165 fold-higher in TTS compared to NS, with CEMA, MHBMA, 3-HPMA and SPMA showing the most relevant increases. Furthermore, some mercapturic acids were higher in ECU than NS; CEMA and 3-HPMA, in particular, showed significant increases and were 1.8 and 4.9 fold-higher, respectively.

CONCLUSIONS

This study confirms that tobacco smoking is a major source of carcinogenic chemicals such as benzene and 1,3-butadiene; electronic cigarette use is a minor source, mostly associated with exposure to chemicals with less carcinogenic potential such as acrylonitrile and acrolein.

Simultaneous determination of aromatic and chlorinated compounds in urine of exposed workers by dynamic headspace and gas chromatography coupled to mass spectrometry (dHS-GC-MS)

Mixed exposure to chemical products is a topical issue for occupational health and often includes exposure to volatile organic compounds (VOCs). As very few methods are available for evaluating these mixed exposures, the aim of this work was to develop a simple biomonitoring method to assess simultaneous occupational exposures to chlorinated and aromatic VOCs by analyzing the unmetabolized fraction of the VOCs in the urine of workers. Volatile organic compounds were analyzed using dynamic headspace gas chromatography coupled to mass spectrometry (dHS-GC-MS), and 11 unmetabolized urinary VOCs were measured into headspace phase, without any time-consuming pretreatment. Simultaneously, a standardized collection protocol was designed to avoid VOC losses or the contamination of urinary samples. The calibration samples were real urines, spiked with known amounts of the VOC mixtures studied. Test investigations were performed on potentially exposed workers in three factories in order to assess the effectiveness of both the collection protocol and analytical method. A satisfactory level of sensitivity was achieved, with limits of quantification (LOQ) between 10 and 15 ng/L obtained for all VOCs (except for styrene at 50 ng/L). Calibration curves were linear in the 0-20 μg/L range tested, with R² correlation coefficients of 0.991 to 0.998. At the lowest concentration tested (0.08 μg/L), within-day precision varied from 2.1 to 5.5% and between-day precision ranged from 2.7 to 8.5%. Sample stability at -20 °C required that urinary samples be analyzed within 3 months. Even though the urinary concentrations of VOCs used in the plants were mostly quite low, significant differences between post-shift and pre-shift were observed. In conclusion, a fast, sensitive, specific and easy-to-use method has been developed for extracting VOCs from human urine using dHS-GC-MS. The method described has proven to be reliable for assessing current occupational exposure to chlorinated and aromatic VOCs in France.

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.

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.

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.

Background, approaches and recent trends for setting health-based occupational exposure limits: a minireview

The setting of occupational exposure limits (OELs) are founded in occupational medicine and the predictive toxicological testing, resulting in exposure-response relationships. For compounds where a No-Observed-Adverse-Effect-Level (NOAEL) can be established, health-based OELs are set by dividing the NOAEL of the critical effect by an overall uncertainty factor. Possibly, the approach may also be used for carcinogens if the mechanism is epigenetic or the genetic effect is secondary to effect from reactions with proteins such as topoisomerase inhibitors, and mitotic and meiotic spindle poisons. Additionally, the NOAEL approach may also be used for compounds with weak genotoxic effect, playing no or only a minor role in the development of tumours. No health-based OEL can be set for direct-acting genotoxic compounds where the life-time risks may be estimated from the low-dose linear non-threshold extrapolation, allowing a politically based exposure level to be set. OELs are set by several agencies in the US and Europe, but also in-house in major chemical and pharmaceutical companies. The benchmark dose approach may in the future be used where it has advantage over the NOAEL approach. Also, more attention should be devoted to sensitive groups, toxicological mechanisms and interactions as most workplace exposures are mixtures.

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

OBJECTIVE

Biomonitoring of solvents using the unchanged substance in urine as exposure indicator is still relatively scarce due to some discrepancies between the results reported in the literature. Based on the assessment of toluene exposure, the aim of this work was to evaluate the effects of some steps likely to bias the results and to measure urinary toluene both in volunteers experimentally exposed and in workers of rotogravure factories.

METHODS

Static headspace was used for toluene analysis. o-Cresol was also measured for comparison. Urine collection, storage and conservation conditions were studied to evaluate possible loss or contamination of toluene in controlled situations applied to six volunteers in an exposure chamber according to four scenarios with exposure at stable levels from 10 to 50 ppm. Kinetics of elimination of toluene were determined over 24 h. A field study was then carried out in a total of 29 workers from two rotogravure printing facilities.

RESULTS

Potential contamination during urine collection in the field is confirmed to be a real problem but technical precautions for sampling, storage and analysis can be easily followed to control the situation. In the volunteers at rest, urinary toluene showed a rapid increase after 2 h with a steady level after about 3 h. At 47.1 ppm the mean cumulated excretion was about 0.005% of the amount of the toluene ventilated. Correlation between the toluene levels in air and in end of exposure urinary sample was excellent (r = 0.965). In the field study, the median personal exposure to toluene was 32 ppm (range 3.6-148). According to the correlations between environmental and biological monitoring data, the post-shift urinary toluene (r = 0.921) and o-cresol (r = 0.873) concentrations were, respectively, 75.6 microg/l and 0.76 mg/g creatinine for 50 ppm toluene personal exposure. The corresponding urinary toluene concentration before the next shift was 11 microg/l (r = 0.883).

CONCLUSION

Urinary toluene was shown once more time a very interesting surrogate to o-cresol and could be recommended as a biomarker of choice for solvent exposure.