Methylhippuric Acid Research Articles

Mediating effect of oxidative stress on blood pressure elevation in workers exposed to low concentrations of benzene, toluene, and xylene (BTX).

To investigate the mediating effect of oxidative stress on the relationships between low-concentration benzene, toluene, and xylene (BTX) exposure and blood pressure in workers. A cross-sectional study involving 841 workers from a petroleum refining enterprise in Hainan, China, was conducted. Among the workers, 615 workers were exposed to low-concentration BTX, and 216 workers were in the control group. S-phenylmercapturic acid (S-PMA), hippuric acid (HA), and methyl hippuric acid (MHA, including the three isomers 2-MHA, 3-MHA, and 4-MHA) were measured in the urine of workers via high-performance liquid chromatography‒tandem triple quadrupole mass spectrometry to assess the internal BTX burden. Oxidative stress markers, blood pressure, and their correlations were analysed in both the exposed and control groups of workers. Mediation analysis was used to investigate the potential role of oxidative stress in the relationship between BTX exposure and blood pressure. The concentrations of BTX at the sampling points in the enterprise were all below the limits stipulated in China's national occupational health criteria: occupational exposure limits for hazardous agents. With respect to the internal burden of BTX, the concentrations of the benzene metabolite S-PMA, the toluene metabolite HA, and the xylene metabolites 3-MHA and 4-MHA in the urine samples in the exposure group were greater than those in the control group (P < 0.05). The correlation analysis results revealed that the concentration of the benzene metabolite S-PMA in workers' urine was positively correlated with diastolic blood pressure (DBP) (r = 0.265, P < 0.05). Compared with those in the control group, DBP was greater (β = 1.363, 95% CI 0.088 -2.639), serum superoxide dismutase (SOD) activity was lower (β = - 0.037, 95% CI - 0.060 to - 0.013), and the serum malondialdehyde (MDA) concentration was greater (β = 0.066, 95% CI 0.022-0.110) in the exposure group. Partial correlation analysis revealed a positive correlation between DBP and MDA (rs = 0.115, P < 0.01). The results of the mediation analysis indicated that MDA was a complete mediator between low BTX exposure and DBP (P < 0.05). Occupational exposure to low concentrations of BTX elevates blood pressure and oxidative stress among workers. A positive correlation between DBP and MDA was observed, with MDA acting as a complete mediator between low-concentration BTX exposure and DBP elevation.

Deep eutectic solvent-based dispersive liquid-liquid microextraction coupled with HPLC and central composite design for biological monitoring of hippuric acid and methyl hippuric acid in urine

Exposure assessment of toluene and xylene as two hazardous compounds in occupational settings are great of importance. Hippuric acid (HA) and methyl hippuric acid (MHA) are common urinary metabolites for biological monitoring of toluene and xylene exposure, respectively. In this study a dispersive liquid–liquid microextraction (DLLME) method based on a deep eutectic solvent (DES), was suggested to determine the urinary MHA and HA simultaneously. Optimizations of all parameters affecting the DLLME-DES were done using response surface methodology. In obtained optimized conditions, a linear calibration range of 0.024–20 µg mL−1 for HA and 0.033–20 µg mL−1 for MHA were achieved and R2 was above 0.99 for these two metabolites. The detection limit of HA and MHA was 0.008 and 0.010 µg mL−1 respectively. The quantification limit was reported as 0.024 and 0.033 µg mL−1 for HA and MHA respectively. The suggested analytical technique was used for quantitation of target biomarkers in urine samples of occupational workers with high accuracy (97–103.6% for HA and 92–104% MHA) and precision (RSD ≤ 4.5% for HA (RSD ≤ 6.2% for MHA). Applying the proposed method for urine sample analysis of exposed-workers and comparing with the standard method (National Institute for Occupational Safety & Health standard method) showed that HA and MHA can be pre-concentrated and quantified by a simple, fast and environmental friendly method.

HPLC analysis of biomarkers of Toluene and Xylene in human urine samples

Introduction: Urinary Hippuric acid (HA) and Methylhippuric acid (MHA) are considered reliable biomarkers for monitoring exposure to toluene and xylenes. A simple and robust HPLC method for simultaneous determination of HA and MHA in urine samples was developed and validated as per Internation Conference on Harmonization (ICH) Q2 guidelines. Methods: Mobile phase consisting of two solvents A &amp; B, solvent A was 0.1% TFA in water, and solvent B was 0.1% TFA in acetonitrile. Separation was performed in gradient elution mode and the time program was as follows - Time (min)/%B: 0/20, 4/20, 11/80, 11.1/90, 16/90, 16.1/20, 25/20. The detection wavelength was 205 nm. Results: The limits of detection (LOD) and quantification (LOQ) of HA in urine were 0.3 and 1.0 mg/L, and for MHA were 0.25 mg/L and 1.0 mg/L respectively and the recovery for HA and MHA were 95% and 98.9% respectively. Conclusion: The developed method was successfully applied for the analysis of urine samples.

Hematological Changes in Gas Station Workers.

(1) Background: Benzene, toluene, and xylene isomers (BTX) are present in gasoline. Exposure to benzene may lead to the appearance of a series of signs, symptoms, and complications, which are characterized by benzene poisoning, which is an occupational disease. This study evaluated the presence of signs and symptoms related to occupational exposure and whether occupational exposure to BTX is associated with the development of hematological changes. (2) Material and Methods: This cross-sectional epidemiological study included 542 participants, in which 324 were gas station workers (GSWs) and 218 were office workers (OWs) with no occupational exposure to benzene. To characterize the type of exposure (exposed and not exposed), trans,trans-Muconic acid (tt-MA), Hippuric acid (HA), and Methylhippuric acid (MHA) were used as exposure biomarkers. The tt-MA analysis revealed that the GSWs had 0.29 mg/g of urinary creatinine and the OWs had 0.13 mg/g of urinary creatinine. For HA, the GSWs presented 0.49 g/g of creatinine while the OWs presented 0.07. MHA analysis revealed that the GSWs had 1.57 g/g creatinine and the OWs had 0.01 g/g creatinine. Occupation habits and clinical symptoms were collected by questionnaire and blood samples were analyzed for hematological parameters. The persistence of hematological changes was evaluated with three serial blood collections every 15 days followed by laboratory hematological analysis. A descriptive analysis by the Chi-square test method was performed to evaluate the association between occupational exposure to fuels and the occurrence of changes in hematological parameters. (3) Results: In the GSWs, the most described signs and symptoms were somnolence (45.1%), headache (38.3%), dizziness (27.5%), tingling (25.4%), and involuntary movement (25%). Twenty GSWs that presented hematological alterations performed serial collections fifteen days apart. In addition, these workers presented total leukocyte counts above the upper limit and lymphocyte counts close to the lower limit. Leukocytosis and lymphopenia are hematological alterations present in chronic benzene poisoning. (4) Conclusions: The results found an initial change in different hematological parameters routinely used in clinics to evaluate health conditions. These findings reveal the importance of valuing clinical changes, even in the absence of disease, during the health monitoring of gas station workers and other groups that share the same space.

Determination of seven monoaromatic hydrocarbon metabolites by ultra performance liquid chromatography-tandem mass spectrometry

Monoaromatic hydrocarbons (MAHs) such as benzene, toluene, and xylene are important anthropogenic pollutants in the urban atmosphere. The detection of urinary MAH metabolites are included in human biomonitoring programs in several countries, including Canada, the United States, Italy, and Germany, because their evaluation is vital to monitor the exposure of humans to MAHs. To this end, herein, a method was developed for the determination of seven MAH metabolites through ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). An aliquot of 0.5 mL urine was fortified with an isotopic labeled internal standard solution before being hydrolyzed by 40 μL of 6 mol/L HCl solution, followed by extraction using a 96-well EVOLUTE®EXPRESS ABN solid-phase extraction plate. The samples were washed with 1.0 mL of methanol-water (10∶90, v/v) and eluted with 1.0 mL methanol. The eluate was diluted four times with water prior to use in instrumental analysis. Chromatographic separation was achieved using an ACQUITY UPLC HSS T3 column (100 mm×2.1 mm, 1.8 μm), with gradient elution using 0.1% formic acid as mobile phase A and methanol as mobile phase B. The detection of seven analytes was performed using a triple-quadrupole mass spectrometer equipped with a negative electrospray ionization source in the multiple reaction monitoring mode. The linear ranges of the seven analytes varied from 0.1-20 μg/L to 2.5-500 mg/L, with correlation coefficients greater than 0.995. The method detection limits were 1.5, 0.02, 0.1, 900, 0.6, and 4 μg/L for trans,trans-muconic acid (MU), S-phenylmercapturic acid (PMA), S-benzylmercapturic acid (BMA), hippuric acid (HA), 2-methyl hippuric acid (2MHA), and 3-methyl hippuric acid (3MHA)+4-methyl hippuric acid (4MHA), respectively. The limits of quantification were 5, 0.05, 0.4, 3000, 2, and 12 μg/L for MU, PMA, BMA, HA, 2MHA, and 3MHA+4MHA, respectively. The method was verified by spiking urine samples at three different concentration levels, with recovery rates ranging from 84% to 123%. The intra- and inter-day precisions were 1.8%-8.6% and 1.9%-21.4%, respectively. The extraction efficiencies were 68%-99%, and the matrix effects ranged from -11% to -87%. The urine samples obtained from the German external quality assessment scheme (round 65) were used to assess the accuracy of this method. Both high and low concentrations of MU, PMA, HA, and methyl hippuric acid were within the tolerance range. All analytes in the urine samples were found to be stable for up to seven days at room temperature (20 ℃, absence of light), with less than 15% change in concentration. Analytes in urine samples were found to be stable for at least 42 d at 4 ℃ and -20 ℃, or for six freeze-thaw cycles and up to 72 h in an autosampler (8 ℃). The method was applied to the analysis of 16 non-smokers' and 16 smokers' urine samples. The detection rates of MU, BMA, HA, and 2MHA were 100% in both non-smokers' and smokers' urine samples. PMA was detected in 75% non-smokers' and 100% smokers' urine samples. 3MHA+4MHA was detected in 81% non-smokers' urine and in all smokers' urine samples. Statistical differences were found for MU, PMA, 2MHA, and 3MHA+4MHA between the two groups (p<0.001). The established method has good robustness and can provide reliable results. The experiments were carried out in a high-throughput manner with large sample sizes, owing to the small sample volume, and allowed the successful detection of the seven MAH metabolites in human urine.

Effective extraction of the metabolites of toluene and xylene based on a postsynthetic-modified magnetic covalent organic polymer

Toluene and xylene are volatile organic compounds, and long-term exposure to toluene and xylene may cause brain structure and nervous system damage. To evaluate exposure to toluene and xylene in the environment, it is usually possible to monitor their metabolites in organisms, hippuric acid (HA) and methylhippuric acid (MHA). In this work, we designed a new magnetic solid phase extraction (MSPE) sorbent, zirconium postsynthetic-modified magnetic covalent organic polymer (Fe3O4@COP-COOZr), for purifying and enriching HA and 4-MHA. Zirconium ions were immobilized on the magnetic COP surface by postsynthetic modification without the use of additional coating layers or chelating ligands. The developed Fe3O4@COP-COOZr interacted with HA and 4-MHA through the π-π stacking effect and electrostatic interactions, as well as strong chelation with coordinatively unsaturated zirconium sites. The promising affinity material of Fe3O4@COP-COOZr in MSPE had high stability and recyclability. The established MSPE-HPLC-UV method showed low sorbent consumption (10 mg) and high sensitivity (LODs less than 0.1 μg L−1), and can be used for the analysis of HA and 4-MHA in real samples. The recoveries of the proposed method in real urine samples for the simultaneous determination of HA and 4-MHA were in the range of 83.5–103.2 %, and the RSDs were 0.9–7.1 %.

Exposure assessment of wastewater treatment plant employees to BTEX: a biological monitoring approach

To monitor employees' work safety and exposure against air contaminants, Trans, trans-muconic acid, Hippuric acid, Methyl hippuric acid, Mandelic acid and Phenylglyoxylic acid can be used as reliable biomarkers of exposure to benzene, toluene, ethylbenzene, and xylene (BTEX) compounds. This study aims to determine the level of urinary metabolites of BTEX compounds using biological monitoring in the employees of a wastewater treatment plant (WWTP) in the south of Iran. The study was performed on 56 employees of the WWTP of one of the southern cities of Iran in 2020. Urine samples (n total = 112) consisting of 60 samples of employees working in the operation section (exposed group) and 52 samples of employees working in the administrative section (control group) in the WWTP were collected before and at the end of their shift. The mean concentration of urinary metabolites of BTEX of both groups ranged from 546.43 (μg/g cr) for trans, trans-muconic acid to 0.006 (μg/g cr) for methyl hippuric acid, which indicates that most of the evaluated metabolites showed a higher concentration than their occupational threshold limit value urine (p < 0.05). Regression analysis results showed a significant correlation (p < 0.05) between age and utilization of flame heaters with changes in the measured BTEX metabolites in the urine. The results of this study illustrate that WWTPs should be considered as one of the workplaces with potential sources of BTEX exposure for employees. Future investigations are recommended to perform itemized appraisals of BTEX intake sources, particularly in employees of the operational sections of WWTP.

Investigation of some effective factors on urinary metabolites in biological monitoring of benzene, toluene, and xylene compounds

ABSTRACT The present study was performed to identify possible factors affecting the biological monitoring of benzene, toluene, and xylene (BTX) metabolites. Fifty persons with occupational exposure to BTX and 28 administrative employees were evaluated. Urinary trans, trans-muconic acid (t,t-MA), Hippuric Acid (HA) and Methyl Hippuric Acid (MHA) were determined as the biomarkers of exposure. The mean levels of t,t-MA, HA, and MHA in the exposed group were 541.90 (µg‧g creatinine−1), 0.0199, and 0.00205 (g‧g creatinine−1), respectively, which were higher than the non-exposed group (significant difference, Pvalue <0.001). In the regression model obtained from the amount of urinary t,t-MA, level of education, work experience, residence, length of work per shift, use of personal protective equipment (PPE), and habit of consuming industrial food or fruit juice had a significant effect. HA levels were affected by variables including education level, residence, consumption of industrial food or fruit juice in the past three days, and use of masks, gloves, and PPE. Due to the small amount of MHA in urine, there was a weak correlation between it and independent variables. Based on results, it was concluded that the health effects of exposure to BTX were significantly different between the two groups.

Blood serum levels of selected biomarkers of oxidative stress among printing workers occupationally exposed to low-levels of toluene and xylene.

Printing workers (PWs) are exposed to a mixture of solvents, yet the health risks associated with such exposuer are unknown. This study aimed to compare the serum levels of selected biomarkers of oxidative stress among occupationally exposed PWs to low-level of toluene and xylenes and unexposed controls. Associations between levels of such biomarkers and occupational exposures to toluene and xylene were also investigated. Urinary levels of hippuric acid (HA) and methyl hippuric acids (MHAs) as exposure biomarkers of toluene and xylenes, respectively, and serum levels of oxidative stress biomarkers, including total antioxidant capacity (TAC), malondialdehyde (MDA), and the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), were measured among the 84 subjects, comprising 44 PWs and 40 unexposed subjects. Mean concentrations of urinary HA and MHAs of PWs showed a significant increase compared with the unexposed controls. Although levels of urinary biomarkers of exposure to toluene (HA) and xylenes (MHAs) were well below the biological exposure indices (BEIs; ACGHI), PWs presented significantly increased serum levels of MDA, and significantly decreased serum activities of SOD and GPx compared to the unexposed controls. However, for serum TAC and CAT activity, no significant difference was observed between the two groups. Correlation analyses indicated that urinary levels of HA and MHAs were positively correlated with MDA levels and negatively correlated with GPx and SOD. Our study suggested that the alterations evidenced in serum levels of MDA, SOD, and GPx could be involved in the oxidative stress caused by co-exposure to low levels of toluene and xylene. Further investigation is needed to clarify the effect of low-level occupational exposure to solvents among PWs.

Comparison of urinary biomarkers concentrations in exposed and non-exposed petrol station workers in the Eastern Economic Corridor (EEC), Thailand.

The Thai government has been developing its Eastern Economic Corridor (EEC), which spans three provinces, with the aim of improving connections with other Asian nations. Since this strategic development, the number of trucks, private car, and passenger car registrations have continued to grow, with a corresponding increase in related to benzene, toluene, ethylbenzene, and xylene (BTEX). This study aims to compare the levels of trans, trans-muconic acid (t, t MA); toluene (TU); mandelic acid (MA); and methyl hippuric acid (MHA) in the urine of gas station employees, considering demographic and occupational factors. These employees worked either near or away from the fuel dispenser, and there 100 people in each group. Data were collected using interviews and testing environmental air and urine samples for benzene, toluene, ethyl benzene, and xylene (BTEX). The results showed that BTEX concentrations were just detectable in all 200 cases (100%). The mean (±SD) urine level of t, t MA was 449.28 (±213.32) μg/g creatinine, while the median (min-max) was 428.23 (95.58-1202.56) μg/g creatinine. The mean TU was 0.011 (0.001) mg/L, while the median (min-max) was 0.011 (0.010-0.013) mg/L. MA levels were higher inside the pollution control zone than they were outside the zone (p=.009). Employees who practiced poor personal hygiene had relatively high urinary toluene and MHA levels (p=.009) and those who did not wear personal protective equipment (PPE) had relatively high MA levels (p=.040). The results of this study revealed statistically significant biomarkers influencing the levels of t, t MA; TU; MA; and MHA in urine. The recommendations of this study are that employers should provide their employees with suitable PPE, check regularly to ensure that it is worn, and strongly encourage employees to take care of their sanitation. Employees should take appropriate breaks and days off to minimize their exposure to BTEX.

Investigation of kidney function changes in sea salt workers during harvest season in Thailand.

Occupational factors have previously been mentioned as contributing to decreased kidney function and the development of chronic kidney disease of unknown cause. Sea salt workers are one of the occupations facing high outdoor temperatures and a highly, intensive workload. The purpose of the study was to examine whether the kidney function of sea salt workers at the beginning of the harvest season differs from kidney function at the end of the harvest season and to identify factors that can predict the change of kidney function. Data were collected from salt workers (n=50) who were between 18–60 years of age without hypertension, diabetes, and kidney disease in Samut Sakhon province, Thailand. Urine specific gravity (USG) was used for hydration status and the estimated glomerular filter rate (eGFR) was used to measure kidney function. The mixed model was used to find differences over the harvest season and prediction of factors. On average, the eGFR was estimated to decrease by 15.2 ml/min/1.73 m2 over the harvest season. The decline in eGFR of sea salt workers with moderate and heavy workloads were significantly faster than their light workload counterparts after controlling for other covariates. Similarly, dehydration (USG ≥ 1.030) significantly accelerated the rate of kidney function loss. Our study confirmed exposure to heat over the harvest season leads to decreased eGFR in sea salt workers. The rate of change of eGFR could be predicted by workload and hydration status. Workers with dehydration who performed medium to heavy workloads in farms showed faster kidney function decline than those who performed light workload.

Analytical techniques for monitoring of toluene and xylene exposure biomarkers hippuric acid and methylhippuric acid in human urine samples.

Quantification of hippuric acid and methylhippuric acid in human urine matrices provides information on the toluene and xylene exposure conditions. High performance liquid chromatography coupled with UV detection is the preferable technique for hippuric acid and methylhippuric acid detection in human urine. This study was conducted to present analytical techniques developed for monitoring of hippuric acid and methylhippuric acid in human urine matrices during 2016-2021.

Determination of Hippuric Acid and Methylhippuric Acid Isomers in the Urine of Gas Stations Workers

The purpose of this study was to determine the concentration levels of hippuric acid and 2, 3, 4- methyl hippuric acid isomers as biological indicators of exposure to toluene and xylene isomers in the urine of the gas stations workers of Ahvaz, Iran. The urine sample was taken the first time in January and the second time in June. The mean concentration of hippuric acid, 2, 3 and 4- methyl hippuric acid in the investigated urine of the workers were 0.245, 0.017, 0.012, and 0.101g/g creatinine, respectively. There was no relationship between variable of season and levels of hippuric acid, 2, 3 and 4- methyl hippuric acid in the urine of exposed and control groups. There was no significant difference in the analyzed results of urine samples between control and exposure groups. There was at least one methyl hippuric acid isomer, indicating that all subjects were exposed to xylene, which was lower than the threshold limit value. In conclusion, the variable of season cannot cause a significant change in the metabolites of toluene and xylene isomers. Exposure of workers to toluene and xylene at gas stations are within acceptable limits.

Urinary metabolites as exposure biomarkers of benzene, toluene, ethylbenzene, and xylene in footwear workers and assessment of pulmonary function

Aim: This pilot cross-sectional study focused on biological monitoring of the benzene, toluene, ethylbenzene, and xylene (BTEX) urinary metabolites trans, trans-muconic acid (tt-MA), s-phenyl mercapturic acid (SPMA), hippuric acid (HA), mandelic acid (MA), and methylhippuric acid (MHA) and measured the effects of workplace BTEX exposure on pulmonary function of workers engaged in footwear manufacturing. Materials and Methods: Urinary metabolites tt-MA, SPMA, HA, MA, and MHA concentration in urine samples of study participants (N = 35) were analyzed by reverse-phase high-pressure liquid chromatography. Pulmonary function parameters were measured by spirometer and peak flow meter. Demographic information and work exposure information of study participants were collected by questionnaire interview. Results: In exposed workers, concentration of urinary SPMA, tt-MA, and HA was significantly higher (P < 0.01, in all) than the control group. Reduction in both force expiratory volume in 1 s (Forced expiratory volume in one second) and peak expiratory flow rate (PEFR) were inversely associated (P < 0.01) with growing years of age among all workers. Inverse association was measured between urinary tt-MA and decline in forced vital capacity and PEFR (P < 0.05, for each) in workers. Based on the questionnaire interview, workers were not found to be aware of workplace exposure hazards. Conclusions: Exposure biomarkers of benzene (tt-MA and SPMA) and toluene (HA) were significantly higher in workers than the control group. Study results evident the presence of occupational exposure to benzene and toluene in footwear workers. Deterioration in FEV1 and PEFR were also measured among all workers with growing years of age. The sample size was small in the present study, so further research required to confirm our results.

Petroleum and Chlorinated Solvents in Meconium and the Risk of Hypospadias: A Pilot Study.

Background: Hypospadias is a male congenital malformation that occurs in ~2 of 1,000 births. The association between hypospadias and fetal exposure to environmental chemicals has been studied, but the results are inconsistent. Although several petroleum and chlorinated solvents are suspected to have teratogenic effects, their role in the occurrence of hypospadias has been little studied and never using biomarkers of exposure. We aimed to evaluate the association between fetal exposure to petroleum and chlorinated solvents measured in meconium and the occurrence of hypospadias.Methods: We conducted a pilot case-control study in the maternity of the University Hospital of Rennes (France). Eleven cases of hypospadias and 46 controls were recruited between October 2012 and January 2014. Data from hospital records and maternal self-reported questionnaires, including socio-demographic characteristics and occupational and non-occupational exposure to chemicals, were collected. Meconium samples were collected using a standardized protocol. Levels of petroleum solvents (toluene, benzene, ethylbenzene, and p, m, and o xylene), certain metabolites (mandelic acid, hippuric acid, methylhippuric acid, S-phenylmercapturic acid, S-benzylmercapturic acid, and phenylglyoxylic acid), and two chlorinated solvents (trichloroethylene and tetrachloroethylene) were measured in meconium by gas and liquid chromatography, both coupled to tandem mass spectrometry. Associations between the concentration of each chemical and the occurrence of hypospadias were analyzed using exact logistic regressions adjusted for maternal age, educational level, pre-pregnancy body mass index, and alcohol, and tobacco consumption during pregnancy. Results are presented with odds ratios (ORs) and their 95% confidence intervals (CIs).Results: Quantification rates for petroleum and chlorinated solvents or metabolites ranged from 2.2% (for methylhippuric acid) to 77.1% (for trichloroethylene) of the meconium samples. We found a significant association between the quantification of phenylglyoxylic acid (metabolite of styrene and ethylbenzene) in the meconium and a higher risk of hypospadias (OR = 14.2, 95% CI [2.5–138.7]). The risk of hypospadias was non-significantly elevated for most of the other solvents and metabolites.Conclusion: This exploratory study, on a limited number of cases, suggests an association between petroleum solvents and hypospadias. Additional studies are needed to confirm these results and identify the determinants for the presence of these solvents in meconium.

Evaluation of Exposure to Toluene and Xylene in Gasoline Station Workers.

The main volatile organic compounds found at gasoline stations are benzene, toluene, ethylbenzene, and xylene isomers (BTEX). They cause several harmful effects on human health. Regulatory Norm 7 (1978) provides that, in Brazil, biological monitoring of toluene and xylene is carried out by measuring the urinary metabolites hippuric acid (HA) and methylhippuric acid (MHA), respectively. The objective of this study was to assess the exposure to toluene and xylene and to identify related signs and symptoms in gasoline station workers. A cross-sectional epidemiological study was conducted with workers occupationally exposed to fuels. These gasoline station workers were divided into two groups: 94 workers exposed mainly by inhalation (convenience store workers (CSWs)) and 181 workers exposed by inhalation and dermal route (filling station attendants (FSAs)). A comparison group was formed by 119 workers not occupationally exposed to fuels (office workers (OWs)). Workers exposed to fuels had higher average levels of these exposure biomarkers (HA and MHA), which were also higher in convenience store workers than in filling station attendants. In addition, individuals exposed to the solvents present in gasoline had altered mood/depression, cramps, dizziness, drowsiness, headaches, irritability/nervousness, weakness, weight loss, and other symptoms more frequently and had higher urinary levels of HA and MHA compared to the comparison group. Gasoline station workers showed high levels of HA and MHA, reflecting high occupational exposure to the solvents toluene and xylene present in gasoline, demonstrating that changes in the current legislation and in the work environment are necessary to ensure better health protection for these workers.

Use of urinary hippuric acid and o-/p-/m-methyl hippuric acid to evaluate surgical smoke exposure in operating room healthcare personnel

Toluene and xylene are common components of surgical smoke, whereas hippuric acid (HA) and methylhippuric acid (MHA) are the products of toluene and xylene metabolism in humans, respectively. HA and MHA can be used as indicators to evaluate the exposure hazards of toluene and xylene. In this study, we used liquid chromatography tandem mass spectrometry (LC-MS/MS) to simultaneously analyze the HA, o-/m-/p-MHA, and creatinine contents in the urine of healthcare personnel. Concentrations of HA and o-/m-/p-MHAs were normalized to those of creatinine and used to analyze urine samples of 160 operating room (OR) healthcare personnel, including administrative staff, surgical nurses, nurse anesthetists, and surgeons. The results showed that the five analytes could be accurately separated and exhibited good linearity (r > 0.9992). The rate of recovery was between 86% and 106%, and the relative standard deviation was less than 5%. Urine from administrative staff presented the highest median concentration of hippuric acid (0.25 g/g creatinine); this was significantly higher than that found in the urine of surgeons (0.15 g/g). The concentrations of urinary o-/m-/p-MHAs in surgical nurses were higher than those in administrative staff, nurse anesthetists, and surgeons. Furthermore, the type, sex, and age of healthcare personnel were associated with changes in urine HA and o-/m-/p-MHA concentrations. Healthcare personnel should be aware of the risk of exposure to surgical smoke.

Hepatotoxicological potential of P-toluic acid in humanised-liver mice investigated using simplified physiologically based pharmacokinetic models

p-Toluic acid, a metabolite of organic solvent xylene, has a high reported no‐observed‐effect level (NOEL, 1000 mg/kg) in rats, possibly because of direct glycine conjugation to methylhippuric acid. In this study, plasma levels of p-toluic acid and its glycine conjugate in mice and humanised-liver mice were evaluated after oral administrations. Although rapid conversion of p-toluic acid to its glycine conjugate was evident from mouse plasma concentrations, the biotransformation of p-toluic acid was slower in humanised-liver mice. The input parameters for physiologically based pharmacokinetic (PBPK) models were determined using fitting procedures to create PBPK-generated plasma concentration curves. The PBPK-modelled hepatic concentrations of p-toluic acid in humanised-liver mice were higher than those observed in plasma. PBPK-modelled hepatic and plasma concentrations of p-toluic acid also indicated slow elimination in humans. These results suggest that rapid conjugations of p-toluic acid reportedly observed in rats could result in overestimation of NOELs for conjugatable chemicals when extrapolated to humanised-liver mice or humans.

Combined effect of multiple exposure to low-level organic solvents on hepatotoxicity

Background/Aim Exposure to organic solvents is one of the most common health hazard in workplaces. We aimed to find an association of multiple exposure to low-level organic solvents with hepatotoxicity by Bayesian kernel machine regression(BKMR). Methods Korean special health screening data of 2013 was used. We used hippuric acid(g/g crea.), methyl hippuric acid(g/g crea.), and N-dimethylformamide(mg/L) concentrations for exposure variable and aspartate aminotransferase(AST, IU/L), alanine transaminase(ALT, IU/L), and gamma-glutamyltransferase(GGT, IU/L) for outcome variable. For statistical analysis, participants with the exposure concentration above the exposure limits of the Korea special health screening were excluded, and those with missing data were excluded. All exposure variables were log transformed and standardized prior to the analysis. We examined the association between single exposure and each outcome using multivariate linear regression. In addition, we estimated combined hepatotoxicity of three exposure variables using BKMR. All analyses were adjusted for age, sex, body mass index, smoking status, alcohol drinking habits, and physical activity. Results 615 workers’ data were included in the analysis. In the single exposure model, N-dimethylformamide concentrations were positively associated with AST (β=0.92, SE=0.35). In the BKMR analysis, increase of AST level was significantly associated with increase of combined three exposures. Posterior inclusion probabilities of the hippuric acid, methyl hippuric acid, and N-dimethylformamide were 0.148, 0.382, and 0.950, respectively. In addition, the results of BKMR represented the interactions among the three exposures and nonlinearity of each exposure. Conclusions The study found that simultaneous exposure to low-level organic solvents resulted in hepatotoxicity, and among the three exposures, N-dimethylformamide had the highest hepatotoxicity. BKMR can show combined effect, contribution of each exposure on the combined effect, nonlinear relationship, and interactions between exposures. Therefore, we should try to use this approache on occupational health study to obtain additional information not available from classical statistics.

Occupational exposure evaluation of Brazil university community to the volatile organic compounds

Occupational exposure to volatile organic compounds (VOC) might generate serious worker health damages. Therefore, biological monitoring is essential to evaluate exposure biomarkers from highly toxic chemicals, ensuring better attention to the worker health. In this study was developed and validated a bioanalytical method based on high-performance liquid chromatography coupled to photodiode array (HPLC-PDA) for the quantification of VOC biomarkers in urine samples from Federal University of Goias (UFG) workers. Samples were collected from 30 occupationally exposed subjects after application of a questionnaire survey. The following biomarkers hippuric acid, methyl-hippuric acid, mandelic acid, phenylglyoxylic acid and phenol were quantified, representing exposition to toluene, xylene, styrene, ethylbenzene, benzene and phenol solvents, respectively. Hippuric acid levels were found close to or above the reference values, although a subject had levels higher than preconized by Biological Limit Values (BLV) guideline of 4.0 mg/g creatinine. Five subjects had 3 and 4-methylhippuric acid ranging from 0.1 to 1.0 mg/g creatinine. These results indicate a moderate to high VOC exposure from UFG workers. Multivariate analysis generated four clusters and indicated that histotechnicians and graphic workers need especial attention on occupational VOC exposure. The results from this study reinforce the need for reliable methods able to the biological monitoring as an important tool for assessing occupational exposure.