Absorption, metabolism and elimination of N,N-dimethylformamide in humans

The potential health risks of N,N-dimethylformamide: An updated review

N,N-dimethylformamide (DMF) is a universally used industrial material with exponential growth in production and consumption worldwide. The frequently reported occupational DMF poisoning cases in some countries and the gradually recognized unavoidable health risks to the general population highlight that DMF should still be a matter of concern. Previous studies have demonstrated that the liver is the primary target organ of DMF exposure and multiple mechanisms have been revealed. However, most of these studies investigate the detrimental effects of acute and subacute DMF exposure, while the effects of chronic DMF exposure are rarely studied. Furthermore, the key mechanism for the acute hepatotoxicity of DMF remains to be elucidated. Future research may focus on the identification of efficient preventive measures against the toxicity of DMF to occupational workers, the investigation of the detrimental effects of DMF at environmentally relevant doses, and the studies on the elimination and recycling of DMF in industrial wastes. Herein, we present an updated review of the metabolism of DMF, the biomarker of DMF exposure, underlying molecular mechanisms of DMF-induced hepatotoxicity, and the toxicity of DMF to both occupational workers and general populations and discuss the possible directions in future studies.

Comparison of urinary mercapturic acid excretions in users of various tobacco/nicotine products

Urinary mercapturic acids (MAs) are detoxification products for electrophiles occurring in the human body. They are suitable biomarkers of exposure to directly acting electrophilic chemicals or to chemicals which generate the electrophile during its metabolism. We determined the urinary excretion of 19 MAs in habitual users of combustible cigarettes (CCs), electronic cigarettes (ECs), heated tobacco products (HTPs), oral tobacco (OT), and nicotine replacement therapy (NRT) products, and nonusers (NUs) of any tobacco/nicotine products. The 19 MAs are assumed to be physiologically formed primarily from 15 toxicants with three of them belonging to IARC Group 1 (human carcinogen), seven to Group 2A (probable human carcinogen), four to Group 2B (possible human carcinogen), and one to Group 3 (not classifiable as carcinogen). Smoking (CC) was found to be associated with significantly elevated exposure to ethylene oxide (or ethylene), 1,3-butadiene, benzene, dimethylformamide, acrolein, acrylamide, styrene, propylene oxide, acrylonitrile, crotonaldehyde, and isoprene compared with the other user groups and NU. Users of HTPs revealed slight elevation in the MAs related to acrolein, acrylamide, and crotonaldehyde compared with the other non-CC groups. Vaping (EC) was not found to be associated with any of the MAs studied. In conclusion, the determination of urinary MAs is a useful tool for assessing the exposure to toxicants (mainly potential carcinogens) in users of various tobacco/nicotine products. Our data also give cause to clarify the role of vaping (EC) in urinary excretion of DHPMA (precursor: glycidol).

Human Biomonitoring Initiative (HBM4EU): Human Biomonitoring Guidance Values Derived for Dimethylformamide

Within the European Joint Program on Human Biomonitoring HBM4EU, human biomonitoring guidance values (HBM-GVs) for the general population (HBM-GV_GenPop) or for occupationally exposed adults (HBM-GV_Worker) are derived for prioritized substances including dimethylformamide (DMF). The methodology to derive these values that was agreed upon within the HBM4EU project was applied. A large database on DMF exposure from studies conducted at workplaces provided dose–response relationships between biomarker concentrations and health effects. The hepatotoxicity of DMF has been identified as having the most sensitive effect, with increased liver enzyme concentrations serving as biomarkers of the effect. Out of the available biomarkers of DMF exposure studied in this paper, the following were selected to derive HBM-GV_Worker: total N-methylformamide (tNMF) (sum of N-hydroxymethyl-N-methylformamide and NMF) and N-acetyl-S-(N-methylcarbamoyl)cysteine (AMCC) in urine. The proposed HBM-GV_Worker is 10 mg·L⁻¹ or 10 mg·g⁻¹ creatinine for both biomarkers. Due to their different half-lives, tNMF (representative of the exposure of the day) and AMCC (representative of the preceding days’ exposure) are complementary for the biological monitoring of workers exposed to DMF. The levels of confidence for these HBM-GV_Worker are set to “high” for tNMF and “medium-low” for AMCC. Therefore, further investigations are required for the consolidation of the health-based HBM-GV for AMCC in urine.

Characterization of US population levels of urinary methylcarbamoyl mercapturic acid, a metabolite of N,N-dimethylformamide and methyl isocyanate, in the National Health and Nutrition Examination Survey (NHANES) 2005-2006 and 2011-2016

Methylcarbamoyl mercapturic acid (MCAMA, N-acetyl-S-(N-methylcarbamoyl)-L-cysteine) is a urinary metabolite of N,N-dimethylformamide and methyl isocyanate, which are volatile organic compounds that are harmful to humans. N,N-dimethylformamide exposure causes liver damage, and methyl isocyanate inhalation damages the lining of the respiratory tract, which can increase risk of chronic obstructive pulmonary disease and asthma. This study characterizes urinary MCAMA levels in the US population and explores associations of MCAMA concentrations with select demographic and environmental factors. We used liquid chromatography tandem mass spectrometry to measure MCAMA in urine collected from study participants ≥ 12 years old (N = 8272) as part of the National Health and Nutrition Examination Survey 2005-2006 and 2011-2016. We produced multiple regression models with MCAMA concentrations as the dependent variable and sex, age, fasting time, race/ethnicity, diet, and cigarette smoking as independent variables. Cigarette smokers and nonsmokers had median urinary MCAMA concentrations of 517 μg/g creatinine and 127 μg/g creatinine, respectively. Sample-weighted multiple regression analysis showed that MCAMA was positively associated with serum cotinine (p < 0.0001). Compared to non-exposed participants (serum cotinine ≤ 0.015 ng/mL), presumptive exposure to second-hand tobacco smoke (serum cotinine > 0.015-≤ 10 ng/mL and 0 cigarettes smoked per day) was associated with 20% higher MCAMA (p < 0.0001). Additionally, smoking 1-10 cigarettes per day was associated with 261% higher MCAMA (p < 0.0001), smoking 11-20 cigarettes per day was associated with 357% higher MCAMA (p < 0.0001), and smoking > 20 cigarettes per day was associated with 416% higher MCAMA (p < 0.0001). These findings underscore the strong association of tobacco smoke exposure with urinary MCAMA biomarker levels.

A review of the analysis of biomarkers of exposure to tobacco and vaping products

Quantification of exposure to different chemicals from both combustible cigarettes and vaping products is important in providing information on the potential health risks of these products. To assess the exposure to tobacco products, biomarkers of exposure (BOEs) are measured in a variety of biological matrices. In this review paper, current knowledge on analytical methods applied to the analysis of biomarkers of exposure to tobacco products is discussed. Numerous sample preparation techniques are available for the extraction and sample clean up for the analysis of BOEs to tobacco and nicotine delivery products. Many tobacco products-related exposure biomarkers have been analyzed using different instrumental techniques, the most common techniques being gas and liquid chromatography coupled with mass spectrometry (GC-MS, GC-MS/MS and LC-MS/MS). To assess exposure to emerging tobacco products and study exposure in dual tobacco users, the list of biomarkers analyzed in urine samples has been expanded. Therefore, the current state of the literature can be used in preparing a preferred list of biomarkers based on the aim of each study. The information summarized in this review is expected to be a handy tool for researchers involved in studying exposures to tobacco products, as well as in risk assessment of biomarkers of exposure to vaping products.

Association of urinary dimethylformamide metabolite with lung function decline: The potential mediating role of systematic inflammation estimated by C-reactive protein

Dimethylformamide (DMF) is a volatile organic compound listed as one of the four toxicants with the highest priority for human field study. However, the effect of DMF exposure on lung function and the underlying mechanisms remain unknown. We aimed to investigate the exposure-response relationship and possible mechanism between internal DMF exposure and lung function alteration. We studied 3701 Chinese adults from the Wuhan-Zhuhai cohort with a 3-year follow-up. The cross-sectional relationship between urinary biomarker of DMF exposure (N-Acetyl-S-(N-methylcarbamoyl)-L-cysteine, AMCC) and lung function, and the mediating role of plasma C-reactive protein (CRP) were assessed. We also convened a sub-cohort (N = 138) to assess the stability of AMCC in repeated urine samples collected for continuous 3 days and intervals of 1, 2 and 3 years. The longitudinal association between AMCC and lung function change in 3 years was further assessed. We found a dose-response relationship between AMCC and lung function reduction. Each 2-fold increase in AMCC was cross-sectionally associated with a 23.12-mL (95% CI: -36.68, -9.55) decrease in FVC and a 19.01-mL (95% CI: -31.08, -6.93) decrease in FEV₁. Increased CRP significantly mediated 5.39% and 5.87% of the AMCC-associated FVC and FEV₁ reductions, respectively. With 3-year follow-up, AMCC showed a fair to excellent stability (intra-class correlation coefficients were 0.88, 0.55, 0.60 and 0.50 for continuous 3 days, intervals of 1, 2 and 3 years, respectively) and was dose-dependently associated with longitudinal lung function decline. Compared with those with persistent low AMCC levels, participants with persistent high AMCC levels had a 101.09-mL/year (95% CI: -167.40, -34.77) decline in FVC and a 66.27-mL/year (95% CI: -114.14, -18.41) decline in FEV₁ in the sub-cohort. Similar results were found in the full-cohort. Our findings suggest that exposure of general population to environmental DMF may impair lung function, and systematic inflammation may be an underlying mechanism.

Association between CYP2E1 and GOT2 gene polymorphisms and susceptibility and low-dose N,N-dimethylformamide occupational exposure-induced liver injury

OBJECTIVE

To investigate the effects of the interactions between the CYP2E1 and GOT2 gene polymorphisms and N,N-dimethylformamide (DMF) on liver injury.

METHODS

A total of 672 DMF-exposed workers were randomly selected from two synthetic leather enterprises in Suzhou, China, for follow-up in a cohort study. Information on exposure to DMF in the air was collected through a fixed-point air sampler in the worker's breathing zone. The subjects were assessed every year during the period of 2010-2015, they underwent occupational health examinations. Alanine aminotransferase and aspartate aminotransferase levels were measured. Peripheral blood was collected and DNA was extracted. The genotypes rs2031920, rs3813867 and rs6413432 of the CYP2E1 gene and rs7204324 of the GOT2 gene were detected by PCR, and analyzed using the Chi-square test and logistic regression analysis.

RESULTS

Workers exposed to a high cumulative dose of DMF were significantly more likely than low-exposed workers to develop liver injury. No association was observed between rs2031920, rs3813867 and rs6413432 of the CYP2E1 gene and DMF-induced liver damage. However, the A allele of rs7204324 on the GOT2 gene may be a risk factor for susceptibility to DMF-induced liver injury.

CONCLUSION

Polymorphisms of rs7204324 on GOT2 may play an important role in susceptibility to liver injury following exposure to DMF.

Performance and kinetic model of degradation on treating pharmaceutical solvent wastewater at psychrophilic condition by a pilot-scale anaerobic membrane bioreactor

A pilot-scale anaerobic membrane bioreactor (AnMBR) was operated for 435 days in this study, aiming to treat pharmaceutical solvent wastewater containing m-Cresol (MC), isopropanol (IPA) and N,N-Dimethylformamide (DMF) pollutants at different temperatures of 35 ± 3 °C, 25 ± 3 °C, 15 ± 3 °C and 25 ± 3 °C, respectively. The reactor reached average total removal efficiencies of about 96%, 97.2% and 98% of MC, IPA and DMF at psychrophilic condition (15 ± 3 °C). Higher physical removal rate was obtained at 15 ± 3 °C due to the important contribution of membrane filtration. At this stage, the biogas production, methane content and specific methanogenic activity and extracellular polymeric substances of suspended sludge were observed with the lowest level. Moreover, the kinetic models for solvent degradation were established at different temperatures, results showed the smaller maximum specific substrate degradation rate of MC and IPA, besides, the lowest degradation rate of three solvents were obtained at 15 ± 3 °C.

Study on the potential way of hepatic cytotoxicity of N,N-dimethylformamide

The intermediate metabolites and redox status imbalance were supported as the two major points for N,N-dimethylformamide (DMF)-induced hepatotoxicity. However, the potential mechanism has not yet been concerned. By applying two inhibitors, this study tried to seek the major role in DMF-induced toxicity on HL7702 cell. We observed that DMF induced cell apoptosis through mitochondrial-dependent and p53 pathway. Inhibition reactive oxygen species by catalase remarkably attenuated the mitochondrial transmembrane potential (MMP), apoptotic proteins, and apoptosis. On the contrary, it reduced the biodegradation rate of DMF by coincubation with CYP2E1 antagonist (DDC) partially reduced late apoptosis. However, the change in MMP, the ratio of Bax to Bcl-xl, and cleaved-caspase 9 was not attenuated by DDC. The pathway in DDC coincubation groups was related to the p53 rather than the mitochondrial pathway. Restoring the redox balance during biodegradation is much more effective than attenuating the metabolite rate of DMF. This study may provide a suitable prevention method to occupational workers.

Occupational exposure to N,N-dimethylformamide in the summer and winter

We evaluated total body burden of N,N-dimethylformamide (DMF) taken through the lung and skin by personal exposure of workers to DMF and urinalysis of N-methylformamide (NMF) and N-acetyl-S(N-methylcarbamoyl)-cysteine (AMCC). A total of 270 workers were engaged in four different jobs in a workplace distant from main production lines emanating high levels of DMF. They were not required to wear any personal protective equipment including respirators or gloves. We found that log-transformed urinary levels of NMF and AMCC increased with an increase in log-transformed concentrations of exposure to DMF. Urinary levels of NMF and AMCC were significantly higher in the summer than the winter, although there was no significant seasonal difference in the concentrations of exposure to DMF. Our findings suggested that the increased urinary levels of NMF and AMCC in the summer resulted in increased skin absorption of DMF due to an increased amount of DMF absorbed by the moisturized skin under humid and hot conditions. Seasonal changes in the relative internal exposure index confirmed the present finding of enhanced summertime skin absorption of DMF. AMCC is thought to be a useful biomarker for assessments of cumulative exposure to DMF over a workweek and for evaluations of workers' health effects.

Short-term exposure to dimethylformamide and the impact on digestive system disease: an outdoor study for volatile organic compound

Occupational and experimental studies have revealed the organs most affected by dimethylformamide (DMF) are liver and gastrointestinal tract. However, few studies have focused on the potential effect of outdoor pollution of DMF. This study examined the health risk of hospitalization due to digestive system disease by time series studies in a case city Longwan, China. The urine metabolite of DMF was correlated well with DMF exposure concentration (EC). A 101.0-μg/m(3) (interquartile range) increase in the two-day moving average of DMF EC was associated with a 1.10 (1.01 ˜ 1.20), 1.22 (1.10 ˜ 1.35), and 1.05 (0.90 ˜ 1.22) increase in hospitalization for total digestive system diseases, liver disease, and gastrointestinal tract disease, respectively. The exposure-dose response between DMF and the relative risk of liver disease was linear only below 350 μg/m(3). These findings highlight a previously unrecognized health problem related to VOCs released into the outdoor environment.

Seasonal difference in percutaneous absorption of N,N-dimethylformamide as determined using two urinary metabolites

OBJECTIVE

We evaluated the percutaneous absorption of N,N-dimethylformamide (DMF) in DMF-exposed workers in the summer and winter by assessing their urinary levels of DMF metabolites.

METHODS

Breathing-zone concentrations of DMF and workers' urinary levels of N-methylformamide (NMF) and N-acetyl-S-(N-methylcarbamoyl)-cysteine (AMCC) were simultaneously measured in the summer and winter in 193 male workers wearing a respirator and chemical protective gloves.

RESULTS

The mean breathing-zone concentrations of DMF in both seasons were below the occupational exposure limit of 10 ppm. Although there was no significant seasonal difference in the breathing-zone concentrations of DMF, workers' urinary levels of NMF and AMCC were significantly higher in the summer than in the winter. Log-transformed urinary levels of the metabolites were significantly correlated with log-transformed breathing-zone concentrations of DMF in the summer, whereas no significant correlation between AMCC and DMF was found in the winter. The urinary levels of AMCC were dispersed more widely than those of NMF, suggesting that urinary AMCC reflected the cumulative exposure to DMF over a workweek.

CONCLUSIONS

Percutaneous absorption was the principal route of exposure to DMF for the respirator-wearing workers. Increased urinary levels of NMF and AMCC in the summer were attributed to increased percutaneous absorption of DMF resulting from the increased amount of water-soluble DMF absorbed by sweaty skin caused by the increased summertime room temperature and humidity.

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.

A framework incorporating the impact of exposure scenarios and application conditions on risk assessment of chemicals applied to skin

PURPOSE

1. To develop a framework for exposure calculation via the dermal route to meet the needs of 21st century toxicity testing and refine current approaches; 2. To demonstrate the impact of exposure scenario and application conditions on the plasma concentration following dermal exposure.

METHOD

A workflow connecting a dynamic skin penetration model with a generic whole-body physiologically-based pharmacokinetic (PBPK) model was developed. The impact of modifying exposure scenarios and application conditions on the simulated steady-state plasma concentration and exposure conversion factor was investigated for 9 chemicals tested previously in dermal animal studies which did not consider kinetics in their experimental designs.

RESULTS

By simulating the animal study scenarios and exposure conditions, we showed that 7 studies were conducted with finite dose exposures, 1 with both finite and infinite dose exposures (in these 8 studies, an increase in the animal dose resulted in an increase in the simulated steady-state plasma concentrations (C p,ss)), while 1 study was conducted with infinite dose exposures only (an increase in the animal dose resulted in identical C p,ss). Steady-state plasma concentrations were up to 30-fold higher following an infinite dose scenario vs. a finite dose scenario, and up to 40-fold higher with occlusion vs. without. Depending on the chemical, the presence of water as a vehicle increased or decreased the steady-state plasma concentration, the largest difference being a factor of 16.

CONCLUSIONS

The workflow linking Kasting's model of skin penetration and whole-body PBPK enables estimation of plasma concentrations for various applied doses, exposure scenarios and application conditions. Consequently, it provides a quantitative, mechanistic tool to refine dermal exposure calculations methodology for further use in risk assessment.

S-(acetamidomethyl)mercapturic acid (AMMA): a new biomarker for occupational exposure to N,N-dimethylacetamide

N,N-dimethylacetamide (DMA) is used in the textile and plastics industry as a solvent alternative to more toxic N,N-dimethylformamide. Here we studied toxicokinetics of two major urinary metabolites of DMA, namely, S-(acetamidomethyl)mercapturic acid (AMMA) and N-methylacetamide (NMA). Urine samples were collected from workers exposed to DMA in a factory manufacturing acrylic fibers. AMMA and NMA were determined by HPLC/MS and GC/MS, respectively. The working scheme in the factory consisted of periods of three consecutive working shifts alternated regularly with two days off work. In the first stage of the study, NMA and AMMA were determined in urine samples collected before, in the middle, and at the end of one working shift. In the second stage, urine was collected five times during three consecutive days after a two-day rest: before and at the end of the first and second working shifts and before the third shift. It was found that the end-of-shift NMA levels were several folds higher than the pre-shift levels of the same day and dropped significantly until the next shift. On the other hand, there were no significant differences in AMMA levels before and at the end of the same shift but a continuous rise during the three-day working period was observed. Median values of NMA concentrations at the end of working shifts were between 10.1 and 17.3 mg/g creatinine, median AMMA concentrations in the second or third day of the working period varied between 12.4 and 38.1 mg/g creatinine. The approximate half-lives of NMA and AMMA (means) in the exposed workers were about 9 and 29 h, respectively. Thus, while NMA in the end-of-shift urine samples remains a preferential biomarker of DMA exposure during that shift, AMMA determined at the end of a work-week reflects cumulative exposure over the last few days. Further studies are needed to determine AMMA concentrations corresponding to the threshold limit value of DMA.

Calculating the retention of volatile organic compounds in the lung on the basis of their physicochemical properties

In the workplace, deliberate or accidental exposure to volatile organic compounds (VOCs) may occur by ingestion, but more usually through inhalation or dermal contact. The basic model of occupational exposure assumes repeated inhalation exposure during long periods of time, such as 8-h daily, 40-h per working week. Evaluation of the systemic health effects of industrial chemicals can be based on biological levels or internal doses absorbed in dermal or inhalation exposures. The lungs are the primary route of absorption in exposure to gases, vapors, and aerosols. In inhalation exposure, the dose absorbed can be calculated using the following equation: [formula in text] where C, concentration in the air; T, duration of exposure; V, lung ventilation; R, lung retention expressed as % of intake. As lung retention of VOCs has been studied on human volunteers in costly and time-consuming chamber-type experiments, available data are limited. To calculate dosage for the purpose of risk assessment, the default value of 100% is used. As the lung retention of VOCs in lungs can vary from less than 20 to more than 90%, a possibility of predicting the retention values on the basis of blood/air partition coefficients (K(B)) has been investigated. Lung retention data for 36 compounds were obtained from the existing scientific literature. These values derive from human volunteer studies lasting at least 2h. The K(B) values were either the already published experimental data or were calculated based on their physicochemical properties using a published solvation equation. The compounds under study were divided arbitrarily into two groups: water soluble (>10 g/l) and slightly soluble in water (<10 g/l) compounds. For water soluble compounds, the correlation between K(B) and lung retention was high (r=0.75 and 0.73 respectively); this referred both to K(B) values obtained experimentally or calculated in this report. For the compounds slightly soluble in water, the respective values amounted to 0.79 and 0.82. The obtained results indicate that VOC retention in the lung can be calculated solely on the basis of the partition coefficient K(B). As the descriptors used in the solvation equation can be predicted from chemical structure, this finding indicates that it is possible to assess lung retention for any chemical structure of VOC. The model described in the present report can be a practical alternative to the necessity costly and long-lasting chamber-type experiments which are also questionable on ethical grounds.

Simultaneous determination of mercapturic acids derived from ethylene oxide (HEMA), propylene oxide (2-HPMA), acrolein (3-HPMA), acrylamide (AAMA) and N,N-dimethylformamide (AMCC) in human urine using liquid chromatography/tandem mass spectrometry

Mercapturic acids are highly important and specific biomarkers of exposure to carcinogenic substances in occupational and environmental medicine. We have developed and validated a reliable, specific and very sensitive method for the simultaneous determination of five mercapturic acids derived from several high-production chemicals used in industry, namely ethylene oxide, propylene oxide, acrylamide, acrolein and N,N-dimethylformamide. Analytes are enriched and cleaned up from urinary matrix by offline solid-phase extraction. The mercapturic acids are subsequently separated by means of high-performance liquid chromatography on a Luna C8 (2) column and specifically quantified by tandem mass spectrometric detection using isotopically labelled analytes as internal standards. The limits of detection (LODs) for N-acetyl-S-2-carbamoylethylcysteine (AAMA) and N-acetyl-S-2-hydroxyethylcysteine (HEMA) were 2.5 microg/L and 0.5 microg/L urine, while for N-acetyl-S-3-hydroxypropylcysteine (3-HPMA), N-acetyl-S-2-hydroxypropylcysteine (2-HPMA) and N-acetyl-S-(N-methylcarbamoyl)cysteine (AMCC) it was 5 microg/L. These LODs were sufficient to detect the background exposure of the general population. We applied the method on spot urine samples of 28 subjects of the general population with no known occupational exposure to these substances. Median levels for AAMA, HEMA, 3-HPMA, 2-HPMA and AMCC in non-smokers (n = 14) were 52.6, 2.0, 155, 7.1 and 113.6 microg/L, respectively. In smokers (n = 14), median levels for AAMA, HEMA, 3-HPMA, 2-HPMA and AMCC were 243, 5.3, 1681, 41.7 and 822 microg/L, respectively. Due to the simultaneous quantification of these mercapturic acids, our method is well suited for the screening of workers with multiple chemical exposures as well as the determination of the background excretion of the general population.

N-Methylcarbamoyl-lysine adduct in globin: A new metabolic product and potential biomarker of N,N-dimethylformamide in humans

Metabolism of the solvents N,N-dimethylformamide (DMF) and N-methylformamide (MF) results in the formation of N-methylcarbamoyl adducts at the N-terminal valine and lysine in blood protein globin, of which the lysine adduct has so far only been reported in rats given high doses of both solvents [Mráz, J., Simek, P., Chvalová, D., Nohová, H., Smigolová, P., 2004. Studies on the methyl isocyanate adducts in globin. Chem. Biol. Interact. 148, 1-10]. Here we examined whether the lysine adduct is produced, and accessible to analysis, in humans occupationally or experimentally exposed to DMF. Globin from exposed subjects (n=35) and unexposed controls (n=5) was analyzed by two methods. Edman degradation was used as a sensitive reference method to measure the valine adduct by converting it to 3-methyl-5-isopropylhydantoin (MVH). The MVH levels in globin of the exposed subjects were in the range of 1-441 nmol/g, in controls <1 nmol/g. The principal method of globin analysis consisted of enzymatic hydrolysis with pronase to release free N(epsilon)-(N-methylcarbamoyl)lysine (MLU) and N-methylcarbamoylvaline (MVU), which were determined by HPLC/MS/MS, with no clean-up or preconcentration steps needed. For MLU, the parent and product ions were m/z 204-->173, and the limit of detection was approximately 5 nmol/g globin. MLU was found in most globins from the exposed subjects but not in the controls. A close correlation between the MLU and MVH levels (nmol/g) was observed: MLU=7+0.48 MVH (R(2)=0.84, n=32). In conclusion, MLU can be easily measured in globin of workers exposed to DMF. The findings also indicate a long-term persistence of MLU in the human body, and consequently, its potential as a biomarker of chronic exposure to DMF.

The use of biomarkers of exposure of N,N-dimethylformamide in health risk assessment and occupational hygiene in the polyacrylic fibre industry

BACKGROUND

N,N-dimethylformamide (DMF) was recently prioritised for field studies by the National Toxicology Program based on the potency of its reproductive toxic effects.

AIMS

To measure accurately exposure to DMF in occupational settings.

METHODS

In 35 healthy workers employed in the polyacrylic fibre industry, N-methylformamide (NMF) and N-acetyl-S-(N-methylcarbamoyl)cysteine (AMCC) in urine, and N-methylcarbamoylated haemoglobin (NMHb) in blood were measured. Workplace documentation and questionnaire information were used to categorise workers in groups exposed to low, medium, and high concentrations of DMF.

RESULTS

All three biomarkers can be used to identify occupational exposure to DMF. However, only the analysis of NMHb could accurately distinguish between workers exposed to different concentrations of DMF. The median concentrations were determined to be 55.1, 122.8, and 152.6 nmol/g globin in workers exposed to low, medium, and high concentrations of DMF, respectively. It was possible by the use of NMHb to identify all working tasks with increased exposure to DMF. While fibre crimpers were found to be least exposed to DMF, persons washing, dyeing, or towing the fibres were found to be highly exposed to DMF. In addition, NMHb measurements were capable of uncovering working tasks, which previously were not associated with increased exposure to DMF; for example, the person preparing the fibre forming solution.

CONCLUSIONS

Measurement of NMHb in blood is recommended rather than measurement of NMF and AMCC in urine to accurately assess exposure to DMF in health risk assessment. However, NMF and AMCC are useful biomarkers for occupational hygiene intervention. Further investigations regarding toxicity of DMF should focus on highly exposed persons in the polyacrylic fibre industry. Additional measurements in occupational settings other than the polyacrylic fibre industry are also recommended, since the population at risk and the production volume of DMF are high.

Simultaneous determination of N-hydroxymethyl-N-methylformamide, N-methylformamide and N-acetyl-S-(N-methylcarbamoyl)cystein in urine samples from workers exposed to N,N-dimethylformamide by liquid chromatography-tandem mass spectrometry

N-Hydroxymethyl-N-methylformamide (HMMF) and N-methylformamide (NMF) in urine samples from workers exposed to N,N-dimethylformamide (DMF) cannot be distinguished by a gas chromatographic method because HMMF is converted to NMF at the injection port of gas chromatography (GC). Total NMF (HMMF+NMF) has been measured instead. Also, the determination of N-acetyl-S-(N-methylcarbamoyl)cystein (AMCC), which is supposed to be related to the toxicity of DMF, needs multiple treatments to convert to a volatile compound before GC analysis. There is no previous report of a simultaneous determination of three major metabolites of DMF in urine. The aim of this study is to develop a simple and selective method for the determination of DMF metabolite in urine. By using a liquid chromatography-tandem mass spectrometry, we can directly distinguish these three major metabolites of DMF in a single run. The diluted urine samples were analyzed on Capcell Pak MF SG80 column with the mobile phase of methanol in 2mM formic acid (10:90, v/v). The analytes were detected by an electrospray ionization tandem mass spectrometry in the multiple-reaction-monitoring mode. The standard curves were linear (r>0.999) over the concentration ranges of 0.004-8 microg/mL. The precision and accuracy of quality control samples for inter-batch (n=6) analyses were in the range of 1.3-9.8% and 94.7-116.8, respectively. The sum of each HMMF and NMF concentration determined by LC-MS/MS method shows high correlation (r=0.9927 with the slope of 1.0415, p<0.0001) with NMF included HMMF concentration determined by GC method for 13 urine samples taken from workers exposed to DMF. The excretion ratio of HMMF:NMF:AMCC is approximately 4:1:1 in molar concentration.

Total body burden arising from a week's repeated dermal exposure to N,N-dimethylformamide

BACKGROUND

Hazardous chemicals and their metabolites may accumulate in the body following repeated airborne exposures and skin contact.

AIMS

To estimate the contribution of skin absorption to total body burden of N,N-dimethylformamide (DMF) across a working week in two groups with similar levels of respiratory exposure but dissimilar skin contact.

METHODS

Twenty five workers in a synthetic leather (SL) factory, 20 in a copper laminate circuit board (CLCB) factory, and 20 age and sex matched non-DMF exposed subjects, were recruited. Environmental monitoring of DMF exposure via respiratory and dermal routes, as well as biological monitoring of pre-shift urinary N-methylformamide (U-NMF), were performed for five consecutive working days.

RESULTS

Environmental and biological monitoring showed no detectable exposure in controls. The average airborne DMF concentration (geometric mean (GM) 3.98 ppm, geometric standard deviation (GSD) 1.91 ppm), was insignificantly lower for SL workers than for CLCB workers (GM 4.49, GSD 1.84 ppm). Dermal DMF exposure and U-NMF values, however, were significantly higher for SL workers. A significant pattern of linear accumulation was found across a five day work cycle for SL workers but not for CLCB workers.

CONCLUSIONS

Dermal exposure to DMF over five consecutive days of occupational exposure can result in the accumulation of a significant DMF body burden. The long term exposure response under both repeated and intermittent conditions of substantial skin exposure is worthy of note.

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

General regulations and risk assessment regarding toxicants are single-compound oriented even though humans are exposed to multi-chemicals in the general environment. This study investigated the effects of different levels of N,N-dimethylformamide (DMF) and co-exposure levels of methyl ethyl ketone (MEK) and toluene (TOL) on two biomarkers of DMF exposure: non-metabolized urinary (U-)DMF and the DMF metabolite urinary N-methylformamide (NMF). Thirty-five workers were selected from a two-stage field investigation strategy and were classified into four groups based on DMF exposure and co-exposure levels. Breathing-zone air concentrations of DMF, MEK, and TOL as well as dermal DMF exposure were determined. Post-shift U-DMF and U-NMF levels were determined for each individual. U-DMF concentrations were significantly higher in high-DMF groups than in low-DMF groups, but U-NMF concentrations were significantly (P<0.05) lower in the high-DMF-high-co-exposure group than in the high-DMF-low-co-exposure group; there were no significant differences between two low-DMF groups. The ratio of U-NMF to U-DMF showed the biotransformation from DMF to NMF was significantly suppressed at high co-exposure (P<0.001) for high-DMF exposure groups, possibly because of competitive inhibition of CYP2E1, the responsible enzyme involved. Due to the ubiquity of MEK/TOL in DMF-exposed occupational settings, the biological exposure index for occupational DMF exposure should be re-evaluated at high co-exposure levels.

Evaluation of Current Biological Exposure Index for Occupational N, N-dimethylformamide Exposure From Synthetic Leather Workers

The aim of this study was (1) to investigate the correlation between external exposure to N, N-dimethylformamide (DMF) and urinary excretion of DMF and N-methylformamide; (2) to assess whether the correspondence between the current occupational exposure limit setting and recommended urinary biological exposure index is substantial; and (3) to evaluate whether coexposure to toluene, methyl ethyl ketone, and ethyl acetate has an effect on urinary excretion of DMF and N-methylformamide (NMF). Urinary DMF and NMF were significantly correlated (P < 0.01) with one another and also significantly correlated with airborne DMF (P < 0.01) over the range of 1.55 to 152.8 mg/m. Urinary DMF can be considered a complementary marker for short-term exposure. Urinary concentration of NMF and DMF, corresponding to the 8-hour exposure to airborne DMF at 30 mg/m, was estimated to 38.4 mg/L or 39.4 mg/g creatinine for NMF and to 0.92 mg/L or 0.96 mg/g creatinine for DMF.

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

The present study was initiated to examine whether urinary benzylmercapturic acid (or N-acetyl-S-benzyl cysteine, BMA), a mercapturate metabolite of toluene, increases in relation to the intensity of toluene exposure, and whether this metabolite is a better marker of occupational exposure to toluene than two traditional markers, hippuric acid and o-cresol. Accordingly, end-of-shift urine samples were collected from 122 printers and 30 office clerks (all men) in the second half of a working week. Solvent (toluene) exposure of the day (8 h) was monitored by means of diffusive sampling. Quantitative relation with toluene showed that BMA had a greater correlation coefficient with toluene (r = 0.7) than hippuric acid (r = 0.6) or o-cresol (r = 0.6). The levels in the urine of the non-exposed control subjects were below the detection limit of 0.2 microg/l for BMA, whereas it was at substantial levels for hippuric acid and o-cresol (239 mg/l and 32 microg/l as a geometric mean, respectively). Thus, BMA, hippuric acid and o-cresol could separate the exposed from the non-exposed when toluene was at < 1, 50 and 3 ppm, respectively. Overall, therefore, it appeared reasonable to conclude that BMA is superior to hippuric acid and o-cresol as a marker of occupational exposure to toluene.

The effects of co-exposure to methyl ethyl ketone on the biological monitoring of occupational exposure to N,N-dimethylformamide

OBJECTIVES

(1) To assess whether urinary N,N-dimethylformamide (U-DMF) is suitable as a biomarker when co-exposure to methyl ethyl ketone (MEK) exists, and to evaluate whether it is suitable as an exposure biomarker of DMF. (2) To examine whether the co-exposure to MEK affects the characteristics of U-NMF and U-DMF. (3) To investigate if the difference in creatinine-adjusted and non-adjusted measurements of urinary biomarkers of DMF exposure is substantial.

METHODS

Personal exposure monitoring of N,N-dimethylformamide (DMF) and MEK on 11 synthetic-leather workers was performed for 5 consecutive days. Daily post-shift urine for each individual was collected and was analyzed for urinary N-methylformamide (U-NMF) and U-DMF levels on both non-adjusted and creatinine-adjusted bases.

RESULTS

Both U-NMF and U-DMF showed significant associations with airborne DMF. Positive and significant associations between U-NMF and U-DMF on either a non-adjusted basis or a creatinine-adjusted basis were found. Satisfactory linear associations ( P<0.01) between all kinds of urinary biomarkers and DMF exposure were found. The co-exposure to MEK exerted more effect on the relationship of airborne DMF to U-DMF than to U-NMF.

CONCLUSIONS

U-DMF is detectable when occupational DMF exposure is near or below the occupational exposure limit of 10 ppm. In view of the performance of sensitivity, specificity, and positive predictive value, U-NMF, in general, is superior to U-DMF. However, on a par with other findings in this and previous studies, U-DMF might be considered as a complimentary biomarker of exposure to DMF in addition to U-NMF. No distinction between creatinine-adjustment or non-adjustment for urine specimens was found in the biological monitoring of DMF exposure. Further exploration of the influence of co-exposure to MEK at higher exposure is warranted.

Measurement of urinary N-acetyl-S-(N-methylcarbamoyl)cysteine by high-performance liquid chromatography with direct ultraviolet detection

A new high-performance liquid chromatographic (HPLC) method is described for the determination of urinary N-acetyl-S-(N-methylcarbamoyl)cysteine (AMCC), the final product of the conjugation reaction between a metabolic intermediate of N,N-dimethylformamide (DMF) and glutathione. Urine samples were purified by C(18) solid-phase extraction and then directly analysed by HPLC with an Aminex Ion Exclusion HPX-87H column maintained at 25 degrees C and a UV detector set at 196 nm. Under isocratic conditions (2.4 mM sulphuric acid, flow-rate=0.6 ml/min) AMCC eluted at 20.2 min. The reproducibility (C.V.%) was 1.3-2.7% (intra- and inter-assay, N = 5); the accuracy was 98.0+/-1.7% at 10 mg/l and 101.9+/-1.5% at 800 mg/l (mean+/-SD, N = 3). AMCC was measured in urine from 22 exposed subjects. A strong correlation was found between AMCC and environmental DMF [AMCC (mg/g creatinine)=3.40xDMF (mg/m(3)) + 3.07; r=0.95], while in the urine of 20 unexposed subjects the concentration of AMCC was constantly below the detection limit of the method (0.9 mg/l in urine). The method described appears to be useful for the biological monitoring of DMF exposure.

Improved gas chromatographic-mass spectrometric determination of the N-methylcarbamoyl adduct at the N-terminal valine of globin, a metabolic product of the solvent N,N-dimethylformamide

A sensitive method for determination of the N-methylcarbamoyl adduct at the N-terminal valine of globin, a new metabolic product of the industrial solvent N,N-dimethylformamide (DMF), has been developed and validated. The method includes conversion of the adduct by the Edman degradation to 3-methyl-5-isopropylhydantoin (MVH), which is followed by optimized gas chromatographic analysis with mass spectrometric detection at m/z 114. The recovery of MVH from terminal N-methylcarbamoylvaline was determined using a model dipeptide to be 90%. Calibration of the method is done with MVH, employing 3-methyl-5-isobutylhydantoin as the internal standard. The limit of detection is 0.2 nmol MVH/g globin when a 100-mg sample is used. Within- and between-day precision is 4-10%. The method has been used to determine the background levels of MVH in unexposed subjects. Further, toxicokinetic studies in volunteers laid the grounds for setting the reference value for biological monitoring of occupational exposure to DMF.

Analysis of urinary N-acetyl-S-(N-methylcarbamoyl)cysteine, the mercapturic acid derived from N,N-dimethylformamide

Human biotransformation of the industrial solvent N,N-dimethylformamide gives raise to N-acetyl-S-(N-methylcarbamoyl)cysteine (AMCC) which has the longest half-life (about 23 h) among urinary metabolites of N,N-dimethylformamide. It could be used for monitoring industrial exposure over several workdays, by measuring it in urine samples collected at the end of the working week. This is consistent with the suggestions of the American Conference of Governmental Industrial Hygienists, which established a limit of 40 mg/l for the year 2000. An easy, cheap and user-friendly method has been developed for determination of urinary AMCC. Unlike currently available methods, it requires neither a time-consuming preparation phase nor gas chromatographic analysis with a nitrogen-phosphorus or mass detector. The method uses high-performance liquid chromatography (HPLC), with an UV detector at 436 nm. A 10-microl volume of urine is added to a carbonate-hydrogen carbonate buffer and mixed with a dabsyl chloride solution in acetonitrile. The reaction between AMCC and the reagent is performed at 70 degrees C for 10 min. The 'dabsylated' product is stable for at least 12 h. After brief centrifugation, the solution is ready for HPLC analysis using a C18 column (250 x 4.6 mm, 5 microm). The method is sensitive (detection limit 1.8 mg/l) and specific. It identified urinary AMCC in urine of 40 subjects not exposed to N,N-dimethylformamide with a median concentration of 3.9 mg/l. In urine samples from 20 workers exposed to N,N-dimethylformamide (5-40.8 mg/m3), AMCC concentrations ranged from 16 to 170 mg/l. Industrial toxicology laboratories with limited instrumentation will be able to use it in the biological monitoring of workers exposed to N,N-dimethylformamide.

Simultaneous determination of two human urinary metabolites of N,N-dimethylformamide using gas chromatography-thermionic sensitive detection with mass spectrometric confirmation

Two human urinary metabolites of the industrial solvent N,N-dimethylformamide (DMF), N-hydroxymethyl-N-methylformamide (HMMF) and N-acetyl-S-(N-methylcarbamoyl)cysteine (AMCC), were assayed using a new analytical method (gas chromatography and thermionic sensitive detection). Clean-up of urine samples includes a liquid-liquid extraction step followed by a solid-phase extraction step to separate HMMF and AMCC from other urine components. During clean-up, AMCC is converted into ethyl-N-methylcarbamate (EMC), and during gas chromatography, HMMF is degraded in the injector to N-methylformamide (NMF). All the validation data necessary for a quantitative procedure are given. The method was applied to urine samples from workers exposed to DMF and from the general population. The results were confirmed by mass spectrometric determination. For this purpose a further liquid-liquid extraction step was introduced in the clean-up procedure. Background levels of AMCC in the general population were identified.

Influence of individual factors and personal habits on the levels of biological indicators of exposure

The progressive improvement of hygienic conditions in the workplace has increased the importance of obtaining detailed information on extra-occupational factors that might influence the levels of the biological indicators. This information is indispensable both when subjects belonging to the general population are selected for establishing 'reference values' and when subjects occupationally exposed to specific chemical substances are studied. In non-occupationally exposed subjects the biological indicator levels may be influenced by circumstances which enhance absorption of the substance in question. Examples of interference factors considered for biological indicators of main metals are: gender, age, smoking habits, alcohol consumption and dietary habits. In occupationally exposed subjects the levels of the biological indicators can be influenced by factors that interfere with the metabolism of the substances absorbed in the workplace. In particular, factors such as alcohol, drugs and tobacco appear to play an important role in modifying the biological indicator levels in the occupationally exposed. Ethanol can inhibit as well as induce the metabolism of solvents. Inhibition occurs after excessive ingestion of ethanol, whereas induction occurs in subjects who regularly consume alcohol. There are several examples of inhibition of the metabolism of solvents by alcohol in man, occurring at levels of exposure frequently encountered in the workplace, also within the 'occupational exposure limits', (OEL). Conversely, there are very few studies on the effects of induction, which presumably occur only when the exposure levels greatly exceed OEL. Among drugs, analgesics seem to play a particular role in interfering with the metabolism of solvents. Since cigarette smoking is frequently associated with alcohol ingestion at present it is difficult to extrapolate the isolated effect of smoking on the metabolism of solvents. In order to facilitate interpretation of the results of biological monitoring, we propose to prepare informative sheets for the main substances which will contain information on factors that can influence the levels of the indicators.

Biological monitoring of workers exposed to N, N-dimethylfomamide. I. Methods of analysis

Some methods for analysing N,N-dimethylformamide and its metabolites [hydroxymethyl-N-methylformamide, hydroxymethylformamide and N-acetyl-S-(N-methylcarbamoyl)cysteine] in the urine of exposed workers are described. Unchanged dimethylformamide was measured after pretreatment of urine (2 ml) with silica gel cartridges and elution with methanol. The gas chromatographic analysis using a nitrogen phosphor detector made it possible to detect N,N-dimethylformamide in urine even when workers were exposed to low concentrations of the solvent (about 1 mg/m3). N-Hydroxymethyl-N-methylformamide and N-hydroxymethylformamide were analysed as N-methylformamide and formamide respectively after direct injection of urine into the gas chromatograph. The injection port temperature played an important role in the gas chromatographic determination of these products. Reliable results were obtained when direct or split injections were performed at 250 degrees C. The splitless injection gave the same reliable results at 150 degrees C. In urine samples from occupationally non-exposed persons, N-methylformamide could not be detected. In contrast, formamide (or its precursor, hydroxymethylformamide) was present in every urine sample. Our results in respect of 19 urine samples analysed with the injection port of the gas chromatograph at 250 degrees C gave a mean of 8.6 mg/l of formamide. N-Acetyl-S-(N-methylcarbamoyl)cysteine was determined using a modified method for analysing organic acid in urine samples. The metabolite was extracted with ethyl ether in an acid environment, treated with a silylating reagent and measured by gas chromatography/mass spectrometry.

Biological monitoring of workers exposed to N-N-dimethylformamide. II. Dimethylformamide and its metabolites in urine of exposed workers

N,N-Dimethylformamide (DMF) exposure was monitored in a synthetic leather factory; at the same time, urinary dimethylformamide and its metabolites were measured in urine samples collected before and at the end of workshifts. The study was run during two different periods. During the first phase ten workers were observed for 3 days (Monday, Tuesday and Wednesday) in the same week. In the second phase 16 workers were involved in the study on a Friday and on the following Monday. Urinary DMF, as well as hydroxymethyl-N-methylformamide and hydroxymethylformamide [measured as N-methylformamide (NMF) and formamide, respectively], were measured as a "physiological" product in subjects not exposed to dimethylformamide. Environmental exposure to DMF ranged between 10 and 25 mg/m3. The unmodified solvent found in urine collected at the end of the exposure was significantly related to the environmental concentrations of DMF; its urinary concentrations were found to range between 0.1 and 1 mg/l. Higher concentrations of NMF (mean 23.3 mg/l) and formamide (24.7 mg/l) were measured in urine samples collected at the end of workshifts. The same concentrations were related to individual exposures to DMF. N-Acetyl-S-(N-methylcarbamoyl)cysteine in the urine of workers exposed to DMF showed a mean concentration of 40.4 mg/l on Friday (before and after the workshift) and a mean concentration of 10.3 mg/l on Monday. Its slow kinetic profile favours its body accumulation during the working week.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological monitoring of workers exposed to N,N-dimethylformamide by determination of the urinary metabolites, N-methylformamide and N-acetyl-S-(N-methylcarbamoyl) cysteine

Biological monitoring of workers exposed to N,N-dimethylformamide (DMF) was carried out by determination of the urinary metabolites, N-methylformamide (MF, mainly from N-hydroxymethylformamide) and N-acetyl-S-(N-methylcarbamoyl)cysteine (AMCC), which were derived from two different routes of metabolism of the solvent. The urinary levels of MF increased rapidly at the start of the work shift, and decreased almost to zero within 24 h after the beginning of the last exposure. The highest level was found between the end of the afternoon shift and bedtime. AMCC levels remained constant over the consecutive work days and increased after the cessation of exposure, with the peak concentration being observed at 16-40 h after the cessation of exposure. AMCC levels at the beginning of the next morning shift were closely correlated with personal exposure levels of DMF in air, although the correlation of MF and DMF in air was highest in the urine at the end of the shift. Hence urinary AMCC represents an index of the average exposure during several preceding work days and may indicate the internal dose. By contrast, MF represents an index of daily exposure.

Uptake, metabolism and elimination of cyclohexanone in humans

The metabolism and toxicokinetics of cyclohexanone (CH-one), an important solvent and chemical intermediate, have been studied in volunteers during and after 8-h exposures to CH-one vapour at a concentration of 101, 207 and 406 mg.m-3. The pulmonary ventilation in these experiments was typically 11 l.min-1 and retention in the respiratory tract was 58%. After exposure to CH-one, 207 mg.m-3, the metabolic yields of cyclohexanol (CH-ol), 1,2- and 1,4-cyclohexanediol (CH-diol) as determined in urine by a gas chromatographic method involving hydrolysis of glucuronide conjugate were 1.0% +/- 0.3%, 39% +/- 5% and 18% +/- 2% (n = 8), respectively. Peak excretion of CH-ol was achieved at the end of the exposure period, after which it decayed rapidly. Elimination of 1,2- and 1,4-CH-diol reached maximum values a few hours following exposure, with subsequent elimination half-times of 16 +/- 2 and 18 +/- 4 h, respectively. Repeated exposure to CH-one vapour (around 200 mg.m-3) for five consecutive days (8 h/day) resulted in cumulative excretion of CH-diols. The permeation rate of CH-one liquid through the skin was 0.037-0.069 mg.cm-2.h-1 (n = 3), indicating that the contribution of percutaneous absorption to total CH-one occupational intake is of minor importance. CH-diols are recommended as biomarkers of exposure to CH-one.