Liver injury in workers exposed to dimethylformamide

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.

The effects of dimethylformamide exposure on liver and kidney function in the elderly population: A cross-sectional study

Dimethylformamide (DMF) is widely used as a solvent in the production of synthetic leather. Previous studies have focused on workers exposed to DMF in leather factories; however, little attention has been paid to the general population. This study was conducted to examine the effects of DMF exposure on elderly residents living near synthetic leather factories. A total of 962 subjects over 60 years of age in proximity to these factories (monitoring points) were enrolled as the exposure group, and 1924 permanent residents living distant from the factories were enrolled as the control group. The exposure group was divided into 3 groups according to their distance from the monitoring points. Physical examination, routine blood tests, and liver and renal function data were collected, and the DMF concentration in the air was analyzed by gas chromatography-mass spectroscopy. The prevalence of abnormal heart rhythm, electrocardiogram and B-mode ultrasound results in the exposure group was significantly greater than in the control group. Aspartate transaminase (AST), alanine transaminase (ALT), and blood urea nitrogen (BUN) levels in the exposure group also were higher than those in the control group (P < .01). There was an effect of distance from leather factories on liver and kidney dysfunction in the 3 exposure groups. Compared with the exposure group at >3 km distance from the source, the prevalence of increased AST, ALT, and BUN in the exposure group at <1 km was significantly greater (P < .001). It was concluded that DMF exposure was related to an increased risk of a cardiac injury and liver and kidney dysfunction.

Polyvinylpyrrolidone as additive for perovskite solar cells with water and isopropanol as solvents

The recent years have witnessed a fast-paced development of perovskite solar cells (PSCs). Unfortunately, the vast majority of PSCs relies on the use of highly polar aprotic solvents during the preparation process, such as dimethylformamide (DMF), which is toxic and detrimental to both humans and the environment. Here, we describe the preparation of PSCs under ambient conditions from an aqueous solution of lead nitrate, to which polyvinylpyrrolidone (PVP) was added in order to enhance the photoelectric performance of the PSCs. By a combination of SEM, EIS, PL and UV spectroscopy and other characterization approaches, we show that the PVP additive is effective in inhibiting carrier recombination, enhancing composite resistance and reducing film defects. Ultimately, we achieved an outstanding photoelectric performance of the PVP-doped PSCs shown by a power conversion efficiency (PCE) of 15.19% and an average steady-state PCE of 14.55% under AM 1.5G simulated solar irradiation with a shadow mask of 0.1 cm². The PCE continued to be over 80% of the initial PCE after 60 days of storage. FInally, the introduced PVP-doped PSCs present a low-cost and low-toxicity way to commercialize perovskite solar cells.

Oxidative stress-related DNA damage and homologous recombination repairing induced by N,N-dimethylformamide

The intensified anthropogenic release of N,N-dimethylformamide (DMF) has been proven to have hepatotoxic effects. However, the potential mechanism for DMF-induced toxicity has rarely been investigated. Our research implicated that DMF induced a significantly dose-dependent increase in reactive oxygen species (ROS) in HL-7702 human liver cells. Moreover, oxidative stress-related DNA damage, marked as 8-hydroxy-2'-deoxyguanosine, was increased 1.5-fold at 100 mmol l(-1) . The most severe DNA lesion (double-strand break, DSB), measured as the formation of γH2AX foci, was increased at/above 6.4 mmol l(-1) , and approximately 50% of cells underwent DSB at the peak induction. Subsequently, the DNA repair system triggered by molecules of RAD50 and MRE11A induced the homologous recombination (HR) pathway by upregulation of both gene and protein levels of RAD50, RAD51, XRCC2 and XRCC3 at 16 mmol l(-1) and was attenuated at 40 mmol l(-1) . Consequently, cellular death observed at 40 mmol l(-1) was exaggerated compared with exposure at 16 mmol l(-1) . Although the exact mechanism relying on the DMF-induced hepatotoxicity needs further clarification, oxidative stress and DNA damage involved in DSBs partially explain the reason for DMF-induced liver injury. Oxidative stress-induced DNA damage should be first considered during risk assessment on liver-targeted chemicals. Copyright © 2015 John Wiley & Sons, Ltd.

Efficient perovskite solar cells fabricated using an aqueous lead nitrate precursor

A novel, aqueous precursor system (Pb(NO₃)₂ + water) is developed to replace conventional (PbI₂ + DMF) for fabricating methylammonium lead iodide (MAPbI₃) perovskite solar cells (PSCs).

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.

Co-exposure to noise, N,N-dimethylformamide, and toluene on 24-hour ambulatory blood pressure in synthetic leather workers

Independent exposure to noise, N,N-dimethylformamide (DMF), or toluene has been associated with cardiovascular effects, but the combined effects are not clear. This study investigated ambulatory systolic blood pressure (SBP) and diastolic blood pressure (DBP) in workers co-exposed to noise, DMF, and toluene. Twenty workers in a synthetic leather manufacturing company were recruited as study subjects. Personal noise exposure and ambulatory blood pressure were measured concomitantly for 24 hr; airborne co-exposure to DMF and toluene during the working period was also analyzed to identify solvents exposure. Linear mixed-effects regressions were used to estimate effects on ambulatory blood pressure by controlling potential confounders. Four high-combined-exposure workers (83 +/- 8 dBA; DMF: 3.23 +/- 2.15 ppm, toluene: 1.09 +/- 1.13 ppm) had the higher means of 16 +/- 7 mmHg in 24-hr DBP (p = 0.027) and 21 +/- 8 mmHg in working-time DBP (p = 0.048) than seven low-combined-exposure workers (73 +/- 12 dBA; DMF: 0.41 +/- 0.02 ppm, toluene: 0.12 +/- 0.01 ppm). Three high-noise-exposure workers (84 +/- 7 dBA) also had a marginal increase of 13 +/- 6 mmHg in DBP at work (p = 0.076) compared with the control group. No significant differences in SBP and DBP were found between six high-solvent-exposure workers (DMF: 1.24 +/- 1.25 ppm, toluene: 2.63 +/- 1.29 ppm) and office workers during any periods. After the Bonferroni correction, there were no significant differences in ambulatory blood pressure between three high-exposure groups and the low-exposure groups. Our findings suggest no interactive effects of co-exposure to noise, DMF, and toluene on workers' ambulatory blood pressure.

Field survey on types of organic solvents used in enterprises of various sizes

OBJECTIVE

To examine (1) common types of organic solvent work and prevalent types of solvent used, and (2) possible association of high solvent concentration with types of solvent work and with enterprise size.

METHODS

The present survey was conducted in Kyoto, Japan, in April 2004 to March 2005. Air samples were collected in 1,010 solvent workplaces (SWPs) (>or=5 samples/SWP) in 156 enterprises of various sizes, and analyzed for 47 legally designated organic solvents by flame-ionization detector-equipped gas-liquid chromatography. The geometric mean value of the concentrations (after summation by use of the additiveness formula) in the >or=5 samples were taken as a representative value for the SWP. Solvent works were classified into 11 categories according to the Japanese regulation. Enterprises were classified in terms of number of employees.

RESULTS

Degreasing (including cleaning and wiping) was the most common type of solvent work, followed by painting and printing, and toluene was the most often detected solvent (i.e., in 42% of the 1,010 SWPs). Further observation by types of solvent work disclosed that toluene was most common in printing (61%), painting (78%), and adhesive spreading/adhesion SWPs (47%), whereas isopropyl alcohol was the leading solvent in cases of surface coating (51%) and degreasing/cleaning/wiping SWPs (42%). Use of methyl alcohol was also high (36% of all cases). In contrast, use of hexane in adhesives was limited (12%). There was a reverse size-dependency in solvent concentrations in air of SWPs, being five times higher in enterprises with <or=50 employees as compared with the level in enterprises with >or=501 employees. Among SWPs, concentrations tended to be high in printing workplaces especially in small enterprises. In contrast, the levels were much lower in testing and research laboratories irrespective of enterprise size. Comparison with the results in a previous survey in 1996 (Ukai et al. 1997) showed that use of toluene and xylenes was reduced and use of isopropyl alcohol and methyl alcohol was increased. The need of continuous updating of the target analyte list was stressed in relation to the limitation of the present study.

CONCLUSIONS

Solvent levels were about five times higher in small enterprises as compared with the levels in large enterprises. There was a gradual shift in solvent use from aromatics to other solvents, typically alcohols. The use of hexane in adhesives was reduced. Solvent levels were relatively high in solvent-drying and printing workplaces and low in degreasing/cleaning/wiping workplaces and testing/research laboratories.

Carcinogenicity and Chronic Toxicity after Inhalation Exposure of Rats and Mice to N,N ‐Dimethylformamide

Carcinogenicity and chronic toxicity of N,N-Dimethylformamide (DMF) were examined by inhalation exposure of groups of 50 rats and 50 mice of both sexes to DMF vapor at a concentration of 0, 200, 400 or 800 ppm (v/v) for 6 h/d, 5 d/wk, for 104 wk. In rats, incidences of hepatocellular adenomas and carcinomas significantly increased in the 400 and 800 ppm-exposed groups and in the 800 ppm-exposed group, respectively. The hepatocellular adenoma did not increase significantly in the 400 ppm-exposed female rats, but its incidence exceeded a range of historical control data in the Japan Bioassay Research Center (JBRC). In mice, incidences of hepatocellular adenomas and carcinomas significantly increased in all the DMF-exposed groups. Incidence of hepatoblastomas significantly increased in the 200 and 400 ppm-exposed male mice, and 4 cases of hepatoblastomas in the 400 ppm-exposed female mice and the 800 ppm-exposed male mice exceeded the range of historical control data of the JBRC. Incidences of altered cell foci increased in the liver of exposed rats and mice in an exposure concentration-related manner, and those foci were causally related to the hepatocellular tumors. Liver weights increased in both rats and mice exposed to DMF at 200 ppm and above. Increased levels of gamma-GTP, ALT, AST and total bilirubin in exposed rats of both sexes and AST and ALT in exposed mice of both sexes were noted. It was concluded that 2-yr inhalation exposure to DMF increased incidences of hepatocellular adenomas and carcinomas in rats and incidences of hepatocellular adenomas, carcinomas and hepatoblastomas in mice, and that hepatocarcinogenicity of DMF was more potent in mice than in rats.

Toxicity due to 2‐ and 13‐wk Inhalation Exposures of Rats and Mice to N , N ‐Dimethylformamide

In order to better characterize the toxicity of N,N-dimethylformamide (DMF) and to provide its basic toxicity data for risk assessment of workers exposed to DMF, F344 rats and BDF1 mice of both sexes were exposed by inhalation (6 h/d x 5 d/wk) to 100, 200, 400, 800 or 1,600 ppm DMF for 2 wk, and 50, 100, 200, 400 or 800 ppm DMF for 13 wk. Three male and 7 female rats died during the 2-wk exposure to 1,600 ppm DMF, but no death of the exposed rats or mice occurred under any other exposure conditions. Massive, focal and single cell necroses were observed in the liver of DMF-exposed rats and mice. The massive necrosis associated with the centrilobular fibrosis occurred at the highest exposure concentration. The single cell necrosis was associated with fragmentation of the nucleoli as well as an increased mitotic figure. The 13-wk exposures of rats and mice to DMF were characterized by increases in the relative liver weight and the incidence of the centrilobular hepatocellular hypertrophy as well as increased serum levels of AST, ALT, LDH, total cholesterol and phospholipid. Lower confidence limits of the benchmark dose yielding the response with a 10% extra risk (BMDL10) were determined for the relative liver weight and the incidence of hepatocellular hypertrophy of the 13-wk exposed animals. The BMDL10 resulted in 1 ppm for the increased relative liver weight of male rats and mice and 17 ppm for the hepatocellular hypertrophy of male mice.

Inactivation of rat liver cytochrome P450 (P450) by N,N-dimethylformamide and N,N-dimethylacetamide

N,N-dimethylformamide (DMF), an organic solvent widely used in industry, is bioactivated by cytochrome P450 (P450) to reactive metabolites which are believed to be responsible for the hepatotoxicity observed in animals and humans. A decrease of the activating enzyme has been reported in rats treated with DMF, although the specific P450 isoform(s) involved and the nature of the reactive species responsible for this and the other toxic effects are still being investigated. In the present work, the effect of DMF and of the structurally related N,N-dimethylacetamide (DMAc) on the activating enzyme and the nature of the reactive species involved in the mechanism of P450 inactivation by the two chemicals were investigated in vitro. Incubation of liver microsomes from pyridine-induced rats with either substrate resulted in a dose-dependent (0-20 mM) loss of P450 (up to 28 and 24% for DMF and DMAc, respectively), microsomal haem (up to 24 and 20% for DMF and DMAc, respectively), but not protoporphyrin IX content. Moreover, bubbling of CO through the incubation mixture gave almost complete protection against substrate-dependent P450 inactivation, and the spin trapping agent N-tert-butyl-alpha-phenylnitrone, but neither glutathione nor vitamin C, provided a significant protection against DMF- or DMAc-dependent haem loss. Finally, electron spin resonance analysis of microsomal incubations in presence of DMF or DMAc showed spectral evidence for a carbon centered radical intermediate. The results indicate, overall, that both compounds are metabolized in vitro by P450, probably CYP2E1, to free radical metabolites which attack the haem prosthetic group, leading to suicidal enzyme inactivation.

Serum hepatic biochemical activity in two populations of workers exposed to styrene

OBJECTIVE

To determine whether hepatic biochemical changes, as measured by routinely available tests indicative of hepatocellular necrosis, cholestasis, or altered hepatic clearance of bilirubin, occur in association with low to moderate exposure to styrene commonly experienced in industrial production.

METHODS

Two independent cross sectional studies were performed comparing serum hepatic transaminases (alanine aminotransferase (ALT) and aspartate aminotransferase (AST)), cholestatic enzymes (alkaline phosphatase (AP) and gamma glutamyl transpeptidase (GGT)), and bilirubin in (a) 47 workers of fibreglass reinforced plastics who were exposed to styrene and (b) 21 boat and tank fabricators, with separate referent groups of unexposed workers. Exposure to styrene was assessed in air by dosimetry, and in venous blood by headspace analysis. Hepatic biochemical variables were assessed across strata of exposure to styrene defined as 25 ppm in air, or 0.275 mg/l in blood, adjusting for age, sex, body mass index, and ethanol consumption.

RESULTS

A consistent and significant linear trend for increasing direct bilirubin and direct/total bilirubin ratio was found in association with increasing exposure to styrene, by both air and blood monitoring, in both studies. Mean direct bilirubin concentrations increased from 0.05-0.08 mg% in referents to 0.12-0.19 in workers exposed above 25 ppm, with a significant exposure-response trend (p<0.005). Significantly increased direct/total bilirubin ratios, ranging from 0.22 to 0.35 were associated with exposure to styrene (p<0.001), indicating diminished hepatic clearance of conjugated bilirubin. Also, a significant linear association between the hepatic transaminases ALT and AST and exposure to styrene was found in pooled regression analyses, with an increase in AP of about 10 IU/ml in workers exposed above 25 ppm air or 0.275 mg/l blood styrene in pooled analyses from both studies.

CONCLUSIONS

The consistent finding of increased direct bilirubin and AP concentrations in these two independent studies provides evidence for diminished hepatic clearance of conjugated bilirubin with associated cholestasis in workers exposed to styrene. The finding of a significant linear association between hepatic transaminase concentrations and exposure to styrene in pooled analyses is consistent with mild hepatic injury and associated metabolic dysfunction.

The diagnosis and management of solvent-related disorders

Millions of workers in the United States are recurrently exposed to solvents throughout their working lives. Members of this class of compounds share the ability to dissolve waxes, fats, and oils as their common characteristic. This review offers the health practitioner a practical approach to the diagnosis, management, and prevention of solvent-related disorders that result from exposures to these compounds in the workplace. A description of commonly used solvents is provided, along with a brief review of the literature that documents their acute and chronic effects on health.

N,N-Dimethylformamide modulates acid extrusion from murine hepatoma cells

N,N-Dimethylformamide (DMF) affects cellular differentiation, causes hepatotoxicity and gastric irritation, and may be carcinogenic. Since these processes involve changes in cellular pH homeostasis, we investigated the effects of DMF on H+ extrusion and cytosolic pH (pHi) of mouse hepatoma cells (Hepa 1C1C7). Extracellular pH was monitored using a silicon-based sensor system (Cytosensor microphysiometer) and pHi was monitored by fluorescence spectrophotometry. Superfusion of cells with DMF (0.25 to 0.5 M) suppressed the extracellular acidification rate (ECAR) below baseline. Following washout of DMF there was a rapid, concentration-dependent, prolonged overshoot of ECAR above baseline rates. Removal of extracellular Na+ or superfusion with amiloride abolished the overshoot in acidification rate, indicating involvement of Na+/H+ exchange. The overshoot was dependent on extracellular glucose, suggesting that it arises from an increase in metabolic acid production. Fluorescence measurements showed that DMF did not change pHi. Furthermore, DMF did not alter the rate of pHi recovery of cells acid loaded using nigericin, indicating that DMF does not directly alter Na+/H+ exchange activity in these cells. In summary, these data suggest that suppression of acidification rate by DMF is likely due to decreased metabolic acid production. Washout of DMF is then accompanied by increased glucose metabolism and H+ efflux via Na+/H+ exchange. It is possible that alterations in H+ production and transport contribute to the hepatotoxicity of DMF and its effects on cellular differentiation.

Health surveillance using an occupational medical database

This pilot study sought associations between liver function tests (LFTs) and membership in homogeneous exposure groups (HEGs) at a target plant as pre-clinical indications of possible future occupational health problems. A large company database yielded linear models for each of six LFTs (total bilirubin, alkaline phosphatase, gammaglutamyl transferase, lactate dehydrogenase, aspartate transaminase, and alanine transaminase) in terms of sex, body mass index, age, race (white/non-white), alcohol and cigarette consumption, and production/non-production (P/NP) job, permitting control for these in analyses of LFTs vs HEGs at the plant. These analyses, with HEG substituted for P/NP in the large group model, resulted in loosely "suspect" associations significant at P < 0.10. Collapsed HEG variable (containing "suspects" separately and all other non-significant HEG levels pooled) yielded "confirmed suspects" at P < 0.05 in the analysis of an independent LFT set taken at the plant approximately one year later.

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.

Disease clusters in occupational medicine: a protocol for their investigation in the workplace

Disease clusters have been an important source of epidemiologic and medical information in the history of occupational medicine. Many accepted disease-exposure linkages were first observed and investigated as disease clusters in the workplace setting. Recent interest in disease cluster methodology has focused on traditional environmental settings. There has been very little work on a similar methodology for the investigation of disease clusters in the workplace, despite the many advantages of workplace cluster investigations for recognizing new etiologic associations. In this paper, a protocol is proposed and discussed which can be implemented in both acute and chronic disease cluster outbreaks in the workplace, where no obvious previously recognized cause is identified. A standardized approach to occupational disease cluster investigation will lead to increased efficiency, decreased social-political tensions, and a greater yield of scientific information.

Increase in sister chromatid exchange rates in association with occupational exposure to N,N-dimethylformamide

The effects of occupational exposure to N,N-dimethylformamide (DMF) on sister chromatid exchange (SCE) rates were studied in peripheral lymphocytes from 22 DMF-exposed women (aged 22-52 years) in comparison with 22 sex-, age-, and residence-matched controls. All subjects were nonsmokers and nondrinkers as confirmed by medical interview. The 22 pairs were divided by the intensity of exposure to DMF into 3 subgroups of high-exposed (8 pairs with mean DMF exposure at 5.8 ppm), middle-exposed (5 pairs with DMF at 0.7 ppm in combination with toluene at 0.9 ppm), and low-exposed (9 pairs with DMF at 0.3 ppm). The SCE rates were significantly higher in the high (P less than 0.005) and middle (P less than 0.01) exposed than in their matched pairs, and the increase was related to the intensity of DMF exposure.

Occupational dimethylformamide exposure. 1. Diffusive sampling of dimethylformamide vapor for determination of time-weighted average concentration in air

A diffusive sampling method with water as absorbent was examined in comparison with 3 conventional methods of diffusive sampling with carbon cloth as absorbent, pumping through National Institute of Occupational Safety and Health (NIOSH) charcoal tubes, and pumping through NIOSH silica gel tubes to measure time-weighted average concentration of dimethylformamide (DMF). DMF vapors of constant concentrations at 3-110 ppm were generated by bubbling air at constant velocities through liquid DMF followed by dilution with fresh air. Both types of diffusive samplers could either absorb or adsorb DMF in proportion to time (0.25-8 h) and concentration (3-58 ppm), except that the DMF adsorbed was below the measurable amount when carbon cloth samplers were exposed at 3 ppm for less than 1 h. When both diffusive samplers were loaded with DMF and kept in fresh air, the DMF in water samplers stayed unchanged for at least for 12 h. The DMF in carbon cloth samplers showed a decay with a half-time of 14.3 h. When the carbon cloth was taken out immediately after termination of DMF exposure, wrapped in aluminum foil, and kept refrigerated, however, there was no measurable decrease in DMF for at least 3 weeks. When the air was drawn at 0.2 l/min, a breakthrough of the silica gel tube took place at about 4,000 ppm.min (as the lower 95% confidence limit), whereas charcoal tubes could tolerate even heavier exposures, suggesting that both tubes are fit to measure the 8-h time-weighted average of DMF at 10 ppm.

Occupational dimethylformamide exposure. 3. Health effects of dimethylformamide after occupational exposure at low concentrations

A factory survey was conducted in a plant where N,N-dimethylformamide (DMF) was in use during the production of polyurethane plastics and related materials. In all, 318 DMF-exposed workers (195 men and 123 women) and 143 non-exposed controls (67 men and 76 women) were examined for time-weighted average exposure (to DMF and other solvents by diffusive sampling), hematology, serum biochemistry, subjective symptoms, and clinical signs. Most of the exposed workers were exposed only to DMF, whereas others were exposed to a combination of DMF and toluene. DMF exposure in the former group was up to 7.0 ppm (geometric mean on a workshop basis), whereas it was up to 2.1 ppm in combination with 4.2 ppm toluene. Both hematology and serum biochemistry, results (including aspartate and alanine aminotransferases, gamma-glutamyl transpeptidase and amylase) were essentially comparable among the 3 groups. There was, however, a dose-dependent increase in subjective symptoms, especially during work, and in digestive system-related symptoms such as nausea and abdominal pain in the past 3-month period. The prevalence rate of alcohol intolerance complaints among male (assumedly) social drinkers was also elevated in relation to DMF dose.