Water Adherence Factors for Human Skin

On incidental dermal exposure to chemicals in water, a key exposure factor is the amount of water adhering to skin. Although soil adherence factors have been developed for risk assessment, measurements of water adherence on human skin have not been described. In the Environmental Protection Agency's (EPA's) dermal risk assessment guidance, dermal dose from environmental exposures is based upon the flux rate across the skin, which assumes that an unlimited amount of chemical is available for absorption. This assumption is applicable to certain exposure scenarios such as swimming and bathing. However, exposures to contaminated water frequently involve scenarios where the available chemical is limited by the amount of water adhering to the skin, for example, during accidental splashes. We conducted studies in human volunteers to investigate water adherence per unit area of skin after brief contact with water. In two sets of experiments, either water was applied with a micropipette to 10‐cm2 areas of the lower leg, foot, and hand, or the foot and hand were briefly immersed in water. In males, using a micropipette, water adherence ranged from 1.93 (foot) to 7.13 μL/cm2 (lower leg). In females, it ranged from 1.10 (lower leg) to 4.83 μL/cm2 (hand). Hand and foot immersion resulted in relatively higher values of 6.89 and 5.17 μL/cm2, respectively, in males, and 5.40 and 6.39 μL/cm2 in females. Water adherence was affected by amount of body hair and type of exposure. Water adherence factors can be used to calculate the applied dose per unit area for exposures involving intermittent water contact.