Assessing multimedia/multipathway exposure to arsenic using a mechanistic source-to-dose modeling framework
S.W. Wang, V.M. Vyas, Y.C. Yang, P.G. Georgopoulos (EOHSI, UMDNJ - R.W. Johnson Medical School and Rutgers University); H. Ozkaynak (U.S. EPA - NERL)
A series of case studies is presented focusing on multimedia/multipathway population exposures to arsenic, employing the Population Based Modeling approach of the MENTOR (Modeling Environment for Total Risks) framework. This framework considers currently five exposure routes: inhalation, food intake, drinking water consumption, non-dietary ingestion, and dermal absorption. The simulation consists of the following steps: (1) Estimation of the multimedia background levels of environmental arsenic (air, water, and food) for the area where the population of interest resides through either environmental model predictions and/or measurement studies; (2) Estimation of multimedia levels (indoor air, drinking water, and food concentrations) and temporal profiles of environmental arsenic in various microenvironments such as residences, offices, restaurants, vehicles, etc. through microenvironmental mass-balance model simulations using the SHEDS (Stochastic Human Exposure and Dose Simulation) modeling methodology; (3) Selection of a fixed-size sample population in a way that it statistically reproduces essential demographics (age, gender, race, occupation, education) of the population unit used in the assessment (e.g., a sample of 500 people is typically used to represent the demographics of a given census tract); (4) Development of activity event sequences for each member of the sample population by matching his/her attributes to entries of USEPA's CHAD (Consolidated Human Activity Database); (5) Calculation of inhalation and intake rates for the members of the sample population, reflecting/combining the physiological attributes of the study subjects and the activities pursued during the individual exposure events; (6) Combination of inhalation, absorption and oral intake rates with the corresponding multimedia concentrations of the environmental arsenic for each activity event to assess exposures; (7) Estimation of target tissue does (e.g., kidney, liver) through physiologically based pharmacokinetic (PBPK) modeling based on inhaled, dermal, and ingested doses of environmental arsenic for the members of the sample population.
This work had been funded in part by the US Environmental Protection Agency under Cooperative Agreement # EPAR-827033 to Environmental and Occupation Health Sciences Institute. It has been subjected to Agency review and approved for publication.