N , N ‐Dimethylformamide ( DMF )

Abstract

The major routes of chemical exposure for the subjects in the occupational environment are through respiratory tract and through dermal tract. However, continuous improvement exerted in the respiratory protection these days in the occupational setting has substantially reduced the absorbed amount via respiratory route. Dermal exposure, thus, has become increasingly important with respect to the protection of the workers from the chemical hazards. The purposes of this study were to determine the relative contribution of dimethylformamide (DMF) exposure via dermal route and via respiratory route, respectively, and to determine the separate kinetic behaviors of skin vapor exposure and skin vapor plus respiratory exposure, respectively, by using a semi-actual exposure approach in a synthetic leather factory. Six healthy volunteers were designated to closely follow the actual DMF-exposed employees across a whole work shift for two exposure scenarios: with (skin vapor exposure only) and without (skin vapor plus respiratory exposure) wearing respiratory protection equipment. Their airborne and dermal exposures to DMF were determined on the individual basis. Airborne exposure assessment was conducted by integrating real-time DMF monitoring and time-activity pattern (TAP) for each individual. Dermal exposure assessment was performed by using taped method by both cross-sectional and cumulative measures on the palm and dorsal palm of both hands, both forearms and 7th cervical neck at pre-, during- and post-shifts, respectively. Biological monitoring was achieved to collect each participant’s urine at pre-, during- and post-shifts, respectively. Moreover, 36-hr consecutive urine samples were collected since the termination of the exposure to elaborate the kinetics. Urinary DMF and N-methylformamide (NMF) were determined as biological exposure markers for DMF exposure. We found the time-weighted average of airborne DMF concentrations among all participants by the integration of real-time monitor and TAP were 8.10 (2.75) and 9.52 (3.47) ppm (GM(GSD)), respectively, for skin vapor exposure only and skin vapor plus respiratory exposure. The dermal exposure concentrations for whole hand (forearm plus hand) for both hands among all participants were 51.85 (2.26) μg/cm2 and 75.20 (1.62) μg/cm2, respectively, for cross-sectional basis and for cumulative basis, indicating the estimates based on cross-sectional measure probably result in the underestimation of the actually dermal exposure to DMF vapor. Area under curve (AUC) of urinary NMF throughout 36 hrs showed 47% and 53% of excretory NMF contributed to respiratory exposure and dermal exposure, respectively, indicating that the absorbed dose of DMF via dermal vapor exposure was even greater than that via respiratory exposure. The excretory kinetics of urinary NMF also showed that the half-life estimate for skin vapor plus respiratory exposure (6.36 hrs) was shorter than that for skin vapor exposure only (7.49 hrs), suggesting the longer half-life for the DMF exposure via dermal route. We suggested that skin exposure protection should be enhanced for those who occupationally exposed to DMF in addition to the respiratory protection.