The fraction of total hand surface area involved in young childrenʹs outdoor hand-to-object contacts

Information on the fraction of total hand surface area touching a contaminated object is necessary in accurately estimating contaminant (e.g., pesticides, pathogens) loadings onto the hands during hand-to-object contacts. While several existing physical–stochastic human exposure models require such surface area data to estimate dermal and non-dietary ingestion exposure, there are very limited data sets. This paper provides statistical distributions of fractional surface areas (FSAs) for childrenʹs outdoor hand contacts. These distributions were constructed by combining information collected from two distinct studies exploring childrenʹs activity patterns and quantifying hand contact surface area. Results show that for outdoor contacts with “All Objects”, a range of 0.13–0.27 captured median FSAs, while a range of 0.12–0.24 captured time-weighted FSAs. Overall, an FSA of 0.31 captured 80–100% of FSAs involved in each childʹs outdoor hand contacts, depending upon the object of interest. These values are much lower than the often conservative assumptions of up to 1 (i.e., the entire hand) that researchers currently make regarding FSAs involved in indoor and outdoor contacts [USEPA, 1997. Standard operating procedures (SOPs) for residential exposure assessments. Contract no. 68-W6-0030. http://www.epa.gov/pesticides/trac/science/trac6a05.pdf ].