Transient Multimedia Model for Investigating the Influence of Indoor Human Activities on Exposure to SVOCs

Empirical evidence suggests that human occupants indoors, through their presence and activities, can influence the dynamics of semivolatile organic compounds (SVOCs). To better understand these dynamics, a transient multimedia human exposure model was developed (Activity-Based Indoor Chemical Assessment Model (ABICAM)). This model parametrizes mass-balance equations as functions of time-dependent human activities. As a case study, ABICAM simulated exposures of an archetypal adult and toddler over 24 h to diethyl phthalate (DEP), butyl benzyl phthalate (BBzP), and di-2-ethylhexyl phthalate (DEHP) that span a wide range of gas-particle partitioning tendencies. Under baseline (no activities beyond respiration), the toddler's time-average internal doses were three to four times higher than the adult's, due to differences in physical human attributes (e.g., inhalation rate). When time-dependent activities were considered, interindividual (e.g., adult vs toddler) variability was accentuated by up to a factor of 3 for BBzP. Activities with the greatest influence on time-average internal dose were showering (-71% for BBzP), cooking (+27% for DEHP), and sleeping (-26% for DEHP). Overall, the results support the hypotheses that (1) transient indoor activities can give rise to intraindividual variability in estimated internal doses of SVOCs, and (2) interindividual variability in such exposure can result from differences in activity patterns and physical human attributes, according to a compound's physical-chemical properties.