Assessment of dermal exposure to drinking water contaminants - new measurements and models

Assessment of skin uptake in vivo relies largely upon parameters derived from in vitro steady-state experiments. These parameters may underestimate uptake for exposure events where steady-state conditions are not attained. This study employed two novel techniques to measure short-term (≤60 min) dermal uptake in vivo in humans. Saturated aqueous solutions of nitrophenol (NP) and cyanophenol (CP), spiked with 8.6±1.6 nCi ml^-1 of ¹⁴C-radiolabel, were applied under occlusion to the ventral forearms of human volunteers for 5, 15 and 60 min. After removal of the delivery system, multiple and sequential infra-red (IR) spectra and adhesive tape strippings of the stratum corneum (SC) were obtained. ¹⁴C-radiolabel in the tape strips was assayed with accelerator mass spectrometry (AMS), an isotope-ratio mass spectrometric method of quantifying radioisotopes independent of their decay times. Total absorbed doses of ¹⁴C-CP and NP at 5, 15 and 60 min were 0.014, 0.023±0.007 and 0.035±0.012, and 0.060, 0.067±0.048 and 0.070±0.012 ng cm^-2, respectively. Additionally, the in vivo IR spectra provided an alternative assay of the distribution of chemical as a function of SC depth. Results from the AMS tape strip analysis show good correlation with the spectral measurement of chemical penetration observed with IR.