Ambient monitoring and biomonitoring of workers exposed to N-methyl-2-pyrrolidone in an industrial facility

Workplace environmental exposure level guide: n-Methyl-2-pyrrolidone

n-Methyl-2-pyrrolidone (NMP) is a widely used solvent with a mild amine-like odor that can exist in a vapor or aerosol at moderate temperatures. In humans, NMP was reported to induce weak and transient eye irritation and headache. NMP was not a dermal sensitizer and has a low acute toxicity via oral, dermal, and inhalation routes. NMP was not genotoxic/mutagenic in a battery of in vitro and in vivo studies. Furthermore, NMP was not carcinogenic in rats although species-specific liver tumors were identified in mice. Chronic studies in the rat provided a NOAEL of 10 ppm (40 mg/m³) causing only minor effects in males (slightly reduced mean body weight) at 100 ppm (400 mg/m³). Developmental toxicity was considered the critical endpoint (decreased fetal body weights at non-maternally toxic doses). Benchmark dose and PBPK models were utilized to derive an internal dose of 350-470 mg·h/L as a NOAEL for this response and a human equivalent air concentration of 350-490 ppm. With the application of adjustment factors, an 8-h time-weighted average WEEL value of 15 ppm (60 mg/m³) was derived and is expected to provide a significant margin of safety against any potential adverse health effects in workers. To address the potential for respiratory irritation, a short-term exposure level of 30 ppm (120 mg/m³) was derived, and a skin notation is assigned because of the contribution of dermal absorption to the systemic toxicity of NMP.

Human Biomonitoring of Environmental and Occupational Exposures by GC-MS and Gas Sensor Systems: A Systematic Review

Environmental chemicals and contaminants coming from multiple external sources enter the human body, determining a potential risk for human health. Human biomonitoring (HBM), measuring the concentrations of biomarkers in human specimens, has become an emerging approach for assessing population-wide exposure to hazardous chemicals and health risk through large-scale studies in many countries. However, systematic mapping of HBM studies, including their characteristics, targeted hazardous pollutants, analytical techniques, and sample population (general population and occupationally exposed workers), has not been done so far. We conducted a systematic review of the literature related to airborne hazardous pollutants in biofluids to answer the following questions: Which main chemicals have been included in the literature, which bodily fluids have been used, and what are the main findings? Following PRISMA protocol, we summarized the publications published up to 4 February 2021 of studies based on two methods: gas-chromatography/mass spectrometry (GC/MS) and electronic noses (e-noses). We screened 2606 records and 117 publications were included in the analysis, the most based on GC/MS analysis. The selected HBM studies include measurements of biomarkers in different bodily fluids, such as blood, urine, breast milk, and human semen as well as exhaled air. The papers cover numerous airborne hazardous pollutants that we grouped in chemical classes; a lot of hazardous and noxious compounds, mainly persistent organic pollutants (POPs) and volatile organic compounds (VOCs), have been detected in biological fluids at alarming levels. The scenario that emerged from this survey demonstrates the importance of HBM in human exposure to hazardous pollutants and the need to use it as valid tool in health surveillance. This systematic review represents a starting point for researchers who focus on the world of pollutant biomonitoring in the human body and gives them important insights into how to improve the methods based on GC/MS. Moreover, it makes a first overview of the use of gas sensor array and e-noses in HBM studies.

Novel Metabolic Pathway for N-Methylpyrrolidone Degradation in Alicycliphilus sp. Strain BQ1

The molecular mechanisms underlying the biodegradation of N-methylpyrrolidone (NMP), a widely used industrial solvent that produces skin irritation in humans and is teratogenic in rats, are unknown. Alicycliphilus sp. strain BQ1 degrades NMP. By studying a transposon-tagged mutant unable to degrade NMP, we identified a six-gene cluster (nmpABCDEF) that is transcribed as a polycistronic mRNA and encodes enzymes involved in NMP biodegradation. nmpA and the transposon-affected gene nmpB encode an N-methylhydantoin amidohydrolase that transforms NMP to γ-N-methylaminobutyric acid; this is metabolized by an amino acid oxidase (NMPC), either by demethylation to produce γ-aminobutyric acid (GABA) or by deamination to produce succinate semialdehyde (SSA). If GABA is produced, the activity of a GABA aminotransferase (GABA-AT), not encoded in the nmp gene cluster, is needed to generate SSA. SSA is transformed by a succinate semialdehyde dehydrogenase (SSDH) (NMPF) to succinate, which enters the Krebs cycle. The abilities to consume NMP and to utilize it for growth were complemented in the transposon-tagged mutant by use of the nmpABCD genes. Similarly, Escherichia coli MG1655, which has two SSDHs but is unable to grow in NMP, acquired these abilities after functional complementation with these genes. In wild-type (wt) BQ1 cells growing in NMP, GABA was not detected, but SSA was present at double the amount found in cells growing in Luria-Bertani medium (LB), suggesting that GABA is not an intermediate in this pathway. Moreover, E. coli GABA-AT deletion mutants complemented with nmpABCD genes retained the ability to grow in NMP, supporting the possibility that γ-N-methylaminobutyric acid is deaminated to SSA instead of being demethylated to GABA.IMPORTANCEN-Methylpyrrolidone is a cyclic amide reported to be biodegradable. However, the metabolic pathway and enzymatic activities for degrading NMP are unknown. By developing molecular biology techniques for Alicycliphilus sp. strain BQ1, an environmental bacterium able to grow in NMP, we identified a six-gene cluster encoding enzymatic activities involved in NMP degradation. These findings set the basis for the study of new enzymatic activities and for the development of biotechnological processes with potential applications in bioremediation.

[Guide values for 1-methyl-2-pyrrolidone in indoor air. Report of the German Ad-hoc Working Group on indoor Guidelines of the Indoor Air Hygiene Committee and of the States' Supreme Health Authorities]

The German Ad-hoc Working Group on Indoor Guidelines of the Indoor Air Hygiene Committee and the States' Supreme Health Authorities is issuing indoor air guide values to protect public health. No human studies of sufficient quality are available for health evaluation of 1-methyl-2-pyrrolidone in air. In a well-documented chronic inhalation toxicity study in rats significant impairment of weight gain development has been observed (LOAEC = 400 mg/m(3)). The Working Group used this LOAEC as the point of departure for the derivation of guide value II. The conversion of repeated inhalation to continuous exposure (6-24 h; 5-7 days) used a factor of 5.6. By applying an interspecies factor of 2.5 for toxicodynamics, a factor of 10 to account for individual differences and an additional factor of 2 to include sensitive subgroups, results in a health hazard guide value (RW II) of 1 mg 1-methyl-2-pyrrolidone/m(3) indoor air (rounded). By using the NOAEC of 40 mg/m(3) from the same study and applying the same assessment factors as above a precautionary guide value (RW I) of 0.1 mg 1-methyl-2-pyrrolidone/m(3) is calculated.

Biomonitoring of exposure to N-methyl-2-pyrrolidone in workers of the automobile industry

N-methyl-2-pyrrolidone (NMP) is an important organic solvent for varnishes in industry. NMP has been previously shown to be a developmental toxicant in rodents. This study reports current exposures to NMP in the spraying department of an automobile plant using biological monitoring. Two specific metabolites, 5-hydroxy-N-methyl-2-pyrrolidone (5-HNMP) and 2-hydroxy-N-methyl-succinimide (2-HMSI), were analyzed in 69 urine samples of 14 workers exposed to NMP and 9 nonexposed controls. Three different working tasks ('loading' and 'cleaning' of the sprayer system and 'wiping/packing' of the sprayed materials) and three sampling times (preshift, postshift, and preshift of the following day) were studied in exposed workers. Median exposures of 5-HNMP and 2-HMSI in postshift urine of exposed workers were 0.91 and 0.52mg g(-1) creatinine, respectively, whereas median levels in controls were below the limit of detection. Decreased levels of 5-HNMP were observed in preshift urine samples on the following day (0.39mg g(-1) creatinine) in exposed workers, while the concentration of 2-HMSI did not change (0.49mg g(-1) creatinine). Highest exposures occurred during sprayer cleaning with a maximum level of 8.31mg g(-1) creatinine of 5-HNMP in postshift urine. In contrast to 'wipers/packers', no decrease in 5-HNMP could be observed in preshift urine samples on day 2 of the 'loaders' and 'cleaners'. Overall, exposure in terms of 5-HNMP postshift and 2-HMSI preshift of the following day were well below the current biological limit values of the European Union (70 and 20mg g(-1) creatinine). Our results provide initial data on NMP exposure in the automobile industry and suggest that the analysis of 5-HNMP in preshift samples also provides essential information, particularly in situations involving direct handling of liquid NMP-containing formulations.

Determination of N-methyl-2-pyrrolidone and its metabolites in urine by micellar electrokinetic chromatography

A fast and accurate micellar electrokinetic capillary chromatography (MEKC) method was developed for monitoring N-methyl-2-pyrrolidone (NMP) exposure. Baseline separation of NMP and its main metabolites: 5-hydroxy-N-methyl-2-pyrrolidone (5HNMP), N-methylsuccinimide (MSI), 2-hydroxy-N-methylsuccinimide (2HMSI), and 2-pyrrolidone (2P) was obtained within 6 min in an uncoated fused silica capillary using 5 mM phosphate buffer and 140 mM sodium dodecyl sulfate (pH 7.1) as background electrolyte (BGE). On-line UV-detection was performed at 200 nm and the applied electric field was 400 V cm−1. Possible interference of BGE-induced system peaks on separation was investigated by computer simulation and no such interference was observed. The developed MEKC method combined with solid phase extraction for sample preparation was successfully applied to the analysis of urine of rats exposed to NMP. The urinary excretion was determined in 0–6 h and 6–24 h specimens collected after an intragastic administration of 308 mg NMP / kg rat body weight. The results of NMP disposition kinetics in rat urine are reported for NMP and metabolites.

Human volunteer study on the inhalational and dermal absorption of N-methyl-2-pyrrolidone (NMP) from the vapour phase

N-Methyl-2-pyrrolidone (NMP) is a versatile organic solvent frequently used for surface cleaning such as paint stripping or graffiti removal. Liquid NMP is rapidly absorbed through the skin but dermal vapour phase absorption might also play an important role for the uptake of the solvent. This particular aspect was investigated in an experimental study with 16 volunteers exposed to 80 mg/m(3) NMP for 8 h under either whole-body, i.e. inhalational plus dermal, or dermal-only conditions. Additionally, the influence of moderate physical workload on the uptake of NMP was studied. The urinary concentrations of NMP and its metabolites 5-hydroxy-N-methyl-2-pyrrolidone (5-HNMP) and 2-hydroxy-N-methylsuccinimide (2-HMSI) were followed for 48 h and analysed by gas chromatography-mass spectrometry (GC-MS). Percutaneous uptake delayed the elimination peak times and the apparent biological half-lives of NMP and 5-HNMP. Under resting conditions, dermal-only exposure resulted in the elimination of 71 +/- 8 mg NMP equivalents as compared to 169 +/- 15 mg for whole-body exposure. Moderate workload yielded 79 +/- 8 mg NMP (dermal-only) and 238 +/- 18 mg (whole-body). Thus, dermal absorption from the vapour phase may contribute significantly to the total uptake of NMP, e.g. from workplace atmospheres. As the concentration of airborne NMP does not reflect the body dose, biomonitoring should be carried out for surveillance purposes.

SPE–GC/FTD determination of N-methyl-2-pyrrolidone and its metabolites in urine

An analytical method using a combination of solid-phase extraction (SPE) and gas chromatography with a flame thermionic detector (GC/FTD) was developed for determination of N-methyl-2-pyrrolidone (NMP), N-methylsuccinimide (MSI), and 2-hydroxy-N-methylsuccinimide (2-HMSI) in human urine. The SPE cartridge of poly(divinylbenzene/hydroxymethacrylate) used was directly loaded with urine sample, followed by elution with methyl isobutyl ketone (MIBK) and subsequent centrifugation, and the supernatant was injected into the capillary GC using a DB1701. This method allowed efficient separation of NMP, MSI, and 2-HMSI, which were nearly free of interference by other GC peaks arising from urine. Recoveries of NMP, MSI, and 2-HMSI from the SPE cartridge were about 98, 101, and 67%, respectively, with limits of detection of 0.04, 0.02, and 0.06 mg/L, respectively, which met the regulatory requirements. The present method was used for assay in biological monitoring of workers exposed to NMP in their occupational environment.

Comparative developmental toxicities of the three major metabolites ofN-methyl-2-pyrrolidone after oral administration in rats

The developmental toxicity of the three main metabolites of N-methyl-2-pyrrolidone (NMP) was studied in Sprague-Dawley rats. Pregnant rats were given 5-hydroxy-N-methyl-2-pyrrolidone (5-HNMP; 0, 250, 500, 750 or 1000 mg kg(-1) day(-1)), N-methylsuccinimide (MSI; 0, 500, 750, 1000 or 1250 mg kg(-1) day(-1)), or 2-hydroxyN-methylsuccinimide (2-HMSI; 0, 250, 500, 1000 or 1500 mg kg(-1) day(-1)), by gavage, on gestational days (GD) 6-20. No evidence of maternal toxicity was observed in dams given 5-HNMP. Administration of 2-HMSI resulted in overt maternal toxicity at 500 mg kg(-1) day(-1) and higher doses, as indicated by a significant reduction in weight gain and food consumption at the beginning of treatment. There was no evidence of embryo/fetal toxicity in any of the groups treated with 5-HNMP or 2-HMSI. MSI produced marked developmental toxicity in the presence of maternal effects. Maternal body weight gain and food consumption were affected at 750 mg kg(-1) day(-1) MSI, and above. A significant increase in post-implantation loss occurred at 1250 mg kg(-1) day(-1) MSI, and the incidence of fetuses with external or with visceral malformations was significantly increased at 1000 and 1250 mg kg(-1) day(-1) MSI. Malformations mainly consisted of anasarca, cardiovascular defects and diaphragmatic hernia. Fetal weight was significantly reduced at 1000 and 1250 mg kg(-1) day(-1). The incidence of skeletal variations (predominantly cervical ribs, and delayed ossification of skull bones and sternebrae) was significantly elevated at 750 mg kg(-1) day(-1) and higher doses. However, MSI was much less potent than the parent compound. These results indicate that the embryotoxic and teratogenic effects of NMP are not attributable to these metabolites.

Human experimental exposure study on the uptake and urinary elimination of N-methyl-2-pyrrolidone (NMP) during simulated workplace conditions

A human experimental study was carried out with 16 volunteers to examine the elimination of N-methyl-2-pyrrolidone (NMP) after exposure to the solvent under simulated workplace conditions. The NMP concentrations were 10, 40 and 80 mg/m(3) for 2 x 4 h with an exposure-free interval of 30 min. Additionally, a peak exposure scenario (25 mg/m(3) baseline, 160 mg/m(3) peaks for 4 x 15 min, time-weighted average: 72 mg/m(3)) was tested. The influence of physical activity on the uptake and elimination of NMP was studied under otherwise identical exposure conditions but involving moderate workload on a bicycle ergometer (75 W for 6 x 10 min). The peak times and biological half-lives of urinary NMP and its main metabolites 5-hydroxy-N-methyl-2-pyrrolidone (5-HNMP) and 2-hydroxy-N-methylsuccinimide (2-HMSI) in urine were analysed as well as the interrelationships between exposure and biomarkers. All analytes showed a close correlation between their post-shift peak concentrations and airborne NMP. An exposure to the current German workplace limit value of 80 mg/m(3) under resting conditions resulted in urinary peak concentrations of 2,400 microg/L NMP, 117 mg/g creatinine 5-HNMP and 32 mg/g creatinine 2-HMSI (workload conditions: 3,400 microg/L NMP, 150 mg/g creatinine 5-HNMP, 44 mg/g creatinine 2-HMSI). Moderate workload enhanced the total uptake of NMP by approximately one third. Differences between the estimated and the observed total amount of urinary metabolites point to a significant contribution of dermal absorption on the uptake of NMP. This aspect, together with the influence of physical workload, should be considered for the evaluation of a biological limit value for NMP.

Human volunteer study on the influence of exposure duration and dilution of dermally applied N-methyl-2-pyrrolidone (NMP) on the urinary elimination of NMP metabolites

OBJECTIVES

N-Methyl-2-pyrrolidone (NMP) is a versatile solvent used in various industrial processes and applications. Apart from its mildly irritating effects on the eyes, the mucous membranes and the skin, NMP has revealed prenatal toxicity in animal experiments after the oral administration of high doses. The dermal absorption of NMP and the urinary elimination of its main metabolites were investigated within an experimental exposure study.

METHODS

Four male volunteers were exposed to liquid NMP under occlusive conditions on the back of one hand with varying exposure times and solvent concentrations. Urine was collected before, during and after the exposure and analysed for the main NMP metabolites 5-hydroxy-N-methyl-2-pyrrolidone (5-HNMP) and 2-hydroxy-N-methylsuccinimide (2-HMSI).

RESULTS

The urinary concentration of the metabolites upon exposure to undiluted NMP for 2 h increased rapidly with 5-HNMP reaching a maximum at 4-5 h and 2-HMSI after 26-29 h. The application of aqueous NMP solutions resulted in a delay of the peak time for 5-HNMP of approximately 6 h as compared with the undiluted solvent. An average dermal absorption of 5.4+/-1.5 mg NMP cm(-2) h(-1) was calculated for a 2 h exposure to undiluted NMP (6.5+/-2.0 mg NMP cm(-2) h(-1) for a 30 min exposure). Aqueous dilution of NMP to 50% was followed by a decrease of the absorption to 0.9+/-0.5 mg NMP cm(-2) h(-1). NMP metabolite concentrations in the range of the detection limits were found only in isolated urine samples after exposure to 10% NMP in aqueous dilution.

CONCLUSIONS

NMP is rapidly absorbed across the skin and the dermal route may contribute significantly to the uptake of the solvent. Therefore, a biomonitoring of NMP exposed workers is essential for occupational-medical surveillance. Both urinary metabolites reflect the internal dose after a dermal absorption of NMP and thus qualify as suitable biomarkers for NMP exposure.