Implications of Using Steady-State Conditions in Estimating Dermal Uptake of Volatile Compounds in Municipal Drinking Water: An Example of THMs

Dermal exposure to volatile compounds (VC) in municipal water while showering is typically estimated using a steady-state condition between VC in water impacting on skin and skin exposed to water. The lag times to achieve steady-state between VC and skin can vary in the range of 7.5-218.3 min, while shower duration is often less than these values. Estimates of dermal exposure to VC using steady-state while showering may misinterpret exposure. This study developed models and estimated exposure to some disinfection byproducts (DBPs) through dermal pathway by considering lag times while showering. Dermal uptakes of VC were compared using different approaches. In the proposed approach, uptakes of trihalomethanes were estimated between 9.55 × 10^-10-1.43 × 10^-8 mg/cm² of skin during the lag times from exposure to water with trihalomethanes of 50 μg/L. These values were higher than the steady-state estimates (1.37 × 10^-10-4.34 × 10^-9 mg/cm²), and lower than the average exposure analysis (4.12 × 10^-8-1.93 × 10^-6 mg/cm²). Using the Drinking Water Surveillance Program data in Ontario, chronic daily intakes of trihalomethanes were estimated to be 9.40 × 10^-7 (1.85 × 10^-7-1.65 × 10^-6), 3.89 × 10^-6 (7.11 × 10^-7-2.33 × 10^-5), and 1.40 × 10^-6 (4.0 × 10^-7-1.77 × 10^-6) mg/kg/day in Toronto, Ottawa, and Hamilton, respectively. The findings can be useful in understanding THMs exposure and risk through dermal pathway.