A Linear Pharmacokinetic Model Predicts Usefulness of N‐Methyl‐2‐Pyrrolidone (NMP) in Plasma or Urine as a Biomarker for Biological Monitoring for NMP Exposure

Quantitative risk analysis for N-methyl pyrrolidone using physiologically based pharmacokinetic and benchmark dose modeling

Establishing an occupational exposure limit (OEL) for N-methyl pyrrolidone (NMP) is important due to its widespread use as a solvent. Based on studies in rodents, the most sensitive toxic end point is a decrease in fetal/pup body weights observed after oral, dermal, and inhalation exposures of dams to NMP. Evidence indicates that the parent compound is the causative agent. To reduce the uncertainty in rat to human extrapolations, physiologically based pharmacokinetic (PBPK) models were developed to describe the pharmacokinetics of NMP in both species. Since in utero exposures are of concern, the models considered major physiological changes occurring in the dam or mother over the course of gestation. The rat PBPK model was used to determine the relationship between NMP concentrations in maternal blood and decrements in fetal/pup body weights following exposures to NMP vapor. Body weight decrements seen after vapor exposures occurred at lower NMP blood levels than those observed after oral and dermal exposures. Benchmark dose modeling was used to better define a point of departure (POD) for fetal/pup body weight changes based on dose-response information from two inhalation studies in rats. The POD and human PBPK model were then used to estimate the human equivalent concentrations (HECs) that could be used to derive an OEL value for NMP. The geometric mean of the PODs derived from the rat studies was estimated to be 350 mg h/l (expressed in terms of internal dose), a value which corresponds to an HEC of 480 ppm (occupational exposure of 8 h/day, 5 days/week). The HEC is much higher than recently developed internationally recognized OELs for NMP of 10-20 ppm, suggesting that these OELs adequately protect workers exposed to NMP vapor.

A cross-sectional observation of effect of exposure to N-methyl-2-pyrrolidone (NMP) on workers' health

This study was aimed at clarifying the effect of exposure to N-methyl-2-pyrrolidone (NMP) on workers' health. Fifteen male NMP-exposed workers and 15 referent male workers were recruited for this study. Exposure concentrations were assessed by determining NMP in the breathing zones and urinary NMP. Clinical examinations, motor and sensory nerve conduction velocities in the dominant arm, and neurobehavioral tests were carried out. The subjects were asked to complete self-administered questionnaires for subjective symptoms and psychological assessment. The mean NMP exposure concentrations ranged from 0.14 to 0.26 ppm, and urinary NMP levels at the end of each workday ranged from 0.17 to 0.22 mg/l, throughout the work week. In terms of clinical data, motor and sensory nerve conduction velocities, neurobehavioral tests, and subjective symptom assessments, there were no differences and no dose-dependent changes in either the means or the prevalence of abnormal findings between NMP-exposed and referent workers.

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

OBJECTIVES

The exposure of seven workers and three on-site study examiners to N-methyl-2-pyrrolidone (NMP) was studied in an adhesive bonding compound and glue production facility.

METHODS

Airborne NMP was analysed by personal and stationary sampling on activated charcoal tubes. NMP and its main metabolites, 5-hydroxy-N-methyl-2-pyrrolidone (5-HNMP) and 2-hydroxy-N-methylsuccinimide (2-HMSI), were analysed in pre-shift and post-shift spot urine samples by gas chromatography-mass spectrometry. The workers were examined with respect to irritation of the eyes, the mucous membranes and the skin, and health complaints before and after the work-shift were recorded.

RESULTS

The time-weighted average concentration of NMP in most work areas varied between 0.2 and 3.0 mg/m3. During the manual cleaning of stirring vessels, valves and tools, 8-h TWA exposures of up to 15.5 mg/m3 and single peak exposures of up to 85 mg/m3) were observed. NMP and its metabolites were detected in two pre-shift urine specimens. NMP and 5-HNMP concentrations in post-shift urine samples of five workers and three on-site study examiners were below 125 microg/g creatinine and 15 mg/g creatinine, respectively, while two vessel-cleaning workers showed significantly higher urinary NMP concentrations of 472 and 711 microg/g creatinine and 5-HNMP concentrations of 33.5 and 124 mg/g creatinine. 2-HMSI was detectable in four post-shift samples (range: 1.6-14.7 mg/g creatinine). The vessel cleaner with the highest NMP exposure reported irritation of the eyes, the upper respiratory tract and headaches.

CONCLUSIONS

The results of this study indicate a relatively low overall exposure to NMP in the facility. An increased uptake of NMP occurred only during extensive manual vessel cleaning. Health complaints associated with NMP exposure were recorded in one case and might be related to an excessive dermal exposure due to infrequent and inadequate use of personal protective equipment.