N, N-Dimethylformamide: Significance of dermal absorption and adjustment method for urinary N-methylformamide concentration as a biological exposure item

Objectives: To clarify the potential for dermal absorption of N, N-dimethylformamide (DMF) (CAS No. 68-12-2) vapor, and the appropriate adjustment method and the half-lives of urinary concentrations of N-methylformamide (NMF) as the biological exposure item of DMF. Methods: Thirteen healthy male volunteers (mean age: 22.7 years, range: 20-27) were exposed to DMF vapor twice, via both the skin and the lung, for 4 h at concentrations below 10 ppm, the recommended occupational exposure limit set by the Japan Society for Occupational Health, the American Conference of Governmental and Industrial Hygienists, and Deutsche Forschungsgemeinschaft, under conditions of 27 °C and 44% humidity. Each volunteer was exposed to DMF via the skin in a whole-body type exposure chamber and, outside the chamber, via the lung by a respirator connected to the chamber. Exposure levels were 6.2 ± 1.0 ppm in dermal exposure and 7.1 ± 1.0 ppm in inhalation exposure. Urine samples were collected at every opportunity until 72 h after exposure; and NMF, as well as volume, creatinine, and specific gravity were measured. Dermal and inhalation intakes were compared after adjusting concentrations. Results and conclusions: DMF vapor absorptions via the skin and the lung were estimated to be 40.4 and 59.6%, respectively. Workers need to be aware of the risk of dermal absorption of DMF vapor as well as of the liquid. Though NMF concentrations adjusted by creatinine, specific gravity, and urinary volume showed good correlation with total NMF excretion and the absolute amount of NMF at each sampling time, creatinine-adjusted NMF concentration correlated better than the others. The biological half-life of urinary NMF after dermal exposure, 4.75 ± 1.63 h, was longer than that after respiratory exposure, 2.42 ± 0.63 h.