The effects of simultaneous exposure to methyl ethyl ketone and toluene on urinary biomarkers of occupational N,N-dimethylformamide exposure

Vulnerable Factors Affecting Urinary N-Methylformamide Concentration among Migrant Workers in Manufacturing Industries in Comparison with Native Workers in the Republic of Korea (2012-2019)

BACKGROUND

Occupational studies on N-N-dimethylformamide (DMF) exposure among migrant workers in Korea are scarce. We determined the urine concentration of N-methylformamide (NMF) among migrant workers with DMF exposure and compared the data with those of native workers.

METHODS

Data were collected from Workers' Special Health Examination and Work Environment Monitoring databases during 2014-2019. Workers aged ≥20 years were eligible to participate in the special health examination for DMF exposure. Urine concentrations of NMF were determined and compared between migrant and native workers. We also evaluated the factors affecting the difference in the urine concentration of NMF between the migrant and native workers. Multiple logistic regression was performed by adding confounders step by step.

RESULTS

Among 9259 subjects, 504 (5.2%) were migrant workers. The mean urinary concentration of NMF was 6.73 mg/L in migrant workers, which was significantly higher than that in native workers (2.06 mg/L, p < 0.001). The odds of a urine concentration of NMF > 30 mg/L were significantly higher in migrant workers than in native workers after adjusting for sex and age (odds ratio [OR] = 7.31, 95% confidence interval [CI] = 4.66-11.45). However, the odds between the native and migrant workers were not significantly different when fully adjusted for confounders (OR = 1.12, 95% CI = 0.65-1.94).

CONCLUSIONS

The excessive exposure to DMF among migrant workers was attributed not to differences in biological characteristics but to their work environment. Workers must have awareness of the use of protective equipment and knowledge of hazardous chemicals that they may be exposed to, especially at the workplace.

Diazepam influences urinary bioindicator of occupational toluene exposure

In the present study, we investigated the influence of diazepam (DZP) on the excretion of TOL by examining their urinary metabolites, hippuric acid (HA) and ortho-cresol (o-C). Male Wistar rats were exposed to TOL (20ppm) in a nose-only exposure chamber (6h/day, 5days/week for 6 weeks) with simultaneous administration of DZP (10mg/kg/day). Urinary o-C levels were determined by GC-MS, while HA, creatinine (CR), DZP and its metabolite, nordiazepam, were analysed by HPLC-DAD. The results of a Mann-Whitney U test showed that DZP influenced the urinary excretion of o-C (p<0.05). This pioneering study revealed that there was an interaction between DZP and TOL, probably by the inhibition of the CYP isoforms (CYP2B6, CYP2C8, CYP2E1, and CYP1A2) involved in the oxidative metabolism of the solvent. This is relevant information to be considered in the biomonitoring of occupational toluene exposure.

Comparative Study on the EC50 Value in Single and Mixtures of Dimethylformamide, Methyl Ethyl Ketone, and Toluene

The aim of this research was to improve our understanding of human toxicity due to exposure to DMF, MEK, or TOL individually as compared to exposure to DMF-MEK or DMF-TOL mixtures, by comparing EC₅₀ values as well as the morphological changes in HepG2 cells treated with these substances. We found that there was marked cell necrosis in the groups treated with mixtures than in those treated with the compounds alone, and that the amount of cell death and the EC₅₀ value were more dependent on MEK and TOL than on DMF. Moreover, analysis of the changes in effective concentration curves revealed that MEK had an antagonistic effect on the human toxicity of DMF, whereas TOL had a synergistic effect. Accordingly, these results suggest that in workplaces involved in the manufacture of synthetic leather, mixtures of DMF and TOL should be avoided as much as possible in order to minimize environmental toxicity and protect the health of the workers.

Hepatotoxicity in rats treated with dimethylformamide or toluene or both

The effects of toluene in dimethylformamide (DMF)-induced hepatotoxicity were investigated with respect to the induction of cytochrome P-450 (CYP) and the activities of related enzymes. The rats were treated intraperitoneally with the organic solvents in olive oil (Single treatment groups: 450 [D1], 900 [D2], 1,800 [D3] mg DMF, and 346 mg toluene [T] per kg of body weight; Combined treatment groups: D1+T, D2+T, and D3+T) once a day for three days, while the control group received just the olive oil. Each group consisted of 4 rats. The activities of the xenobiotic metabolic enzymes and the hepatic morphology were assessed. The immunoblots indicated that the expression of CYP2E1 was considerably enhanced depending on the dosage of DMF and the CYP2E1 blot densities were significantly increased after treatment with both DMF and toluene, compared to treatment with DMF alone. The activities of glutathione- S-transferase and glutathione peroxidase were either decreased or remained unaltered after treatment with DMF and toluene, whereas the lipid peroxide levels were increased with increasing dosage of DMF and toluene. The liver tissue in the D3 group (1,800 mg/kg of DMF) showed signs of microvacuolation in the central vein region and a large necrotic zone around the central vein, in rats treated with both DMF (1,800 mg/kg) and toluene (D3T). These results suggest that the expression of CYP2E1 is induced by DMF and enhanced by toluene. These changes may have facilitated the accelerated formation of Nmethylformamide (NMF) from toluene, and the generated NMF may directly induce liver damage.

Saliva as an analytical tool to measure occupational exposure to toluene

OBJECTIVE

To describe a sensitive and rapid method for the determination of toluene in saliva. Biomonitoring of toluene exposure is commonly performed by determination of urinary hippuric acid, o-cresol or toluene itself. The analysis of blood toluene has been verified as another method for biomonitoring. However, drawing blood is invasive and can often not be performed at the workplace for hygienic reasons. Sampling of saliva may be non-invasive, easy to perform and a viable alternative for biomonitoring in the workplace.

METHODS

We measured the solvent concentration in saliva specimens of 5 healthy volunteers studied in the laboratory and a group of 36 workers exposed to toluene in the synthetic leather industry. Saliva was collected into Salivette (Sarstedt, Germany) devices by sterile cotton rolls placed in the mouth and then squeezed into pre-weighted vials. Environmental toluene was collected for the duration of a work-shift by Radiello (FSM, Italy) passive samplers. Toluene in urine and saliva (head space analysis) and in environmental samples was measured by GC-MS.

RESULTS

Environmental toluene levels ranged from 0.22 to 57.20 mg/m(3), while the concentrations of the solvent in saliva and urine ranged from 0.12 to 18.30 microg/L, and from 0.47 to 26.64 microg/L, respectively. The correlation coefficients (r) between biological and environmental levels of toluene were 0.77 and 0.93, respectively, for saliva and urine samples.

CONCLUSION

This preliminary study suggests that saliva may offer many advantages over 'classical' biological fluids such as blood as it is readily accessible and collectible: therefore saliva toluene may be considered as a possible biomarker of exposure to toluene.