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-dimethylf ormamide (DMF) (CAS No. 68-12-2) vapor. and the appropriate adjustment meth od and the half-lives of urinary concentrations of N-methylformamide (NMF) as the biological exposure item of DMF, Methods: Thirteen healthy male volu nteers (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, t he recommended occupational exposure limit set by the Japan Society for Occ upational Health, the American Conference of Governmental and Industrial Hy gienists, and Deutsche Forschungsgemeinschaftl under conditions of 27 degre esC and 44% humidity. Each volunteer was exposed to DMF via the skin in a w hole-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 sample s were collected at every opportunity until 72 h after exposure; and NMF, a s well as volume, creatinine, and specific gravity were measured. Dermal an d inhalation intakes were compared after adjusting concentrations. Results and Conclusions: DMF vapor absorptions via the skin and the lung were estim ated to be 40.4 and 59.6%, respectively. Workers need to be aware of the ri sk of dermal absorption of DMF vapor as well as of the liquid. Though NMF c oncentrations 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 correlate d better than the others. The biological half-life of urinary NMF after der mal exposure, 4.75 +/- 1.63 h, was longer than that after respiratory expos ure, 2.42 +/- 0.63 h.