The Exposure Event module of TRIM (TRIM.Expo), similar to most human exposure models, provides an analysis of the relationships between various chemical concentrations in the environment and exposure levels of humans. Because multiple sources of environmental contamination can lead to multiple contaminated media, including air, water, soil, food, and indoor air, it is useful to focus on the contaminated environmental media with which a human population will come into contact. These media typically include the envelope of air surrounding an individual, the water and food ingested by an individual, and the layer of soil and/or water that contacts the surface of an individual. The magnitude and relative contribution of each exposure pathway must be considered to assess total exposure to a particular chemical. Currently, the focus of TRIM.Expo development is on inhalation and ingestion exposure; however, dermal exposure may be added in the future.

The exposure analysis process consists of relating chemical concentrations in environmental media (e.g., air, surface soil, root zone soil, surface water) to chemical concentrations in the exposure media with which a human or population has contact (e.g., air, drinking water, foods, household dusts, and soils).

TRIM.Expo is currently comprised of two components, one for inhalation exposure and one for ingestion exposure. The inhalation component (also called APEX) predicts inhalation exposures of many individuals randomly selected to represent an area's population by tracking the movement of each individual through locations where chemical exposure can occur according to specific activity patterns. In a typical application, the inhalation component can combine either processed air monitoring data or air dispersion modeling results with the activity patterns of the individuals and micro-environment concentration relationships to estimate exposures. The movements of an individual are defined as an exposure-event sequence that can be related to time periods for which exposure concentrations are estimated. Each exposure event places the individual in contact with one or more environmental media within a specified microenvironment (e.g., inside a home, along a road, inside a vehicle) in an exposure district (i.e., a defined physical or political region) for a specified time interval. In addition to the location assignments, the exposure event can also provide information relating to the potential for pollutant uptake (e.g., respiration rate). Exposures associated with these events are aggregated to predict an exposure concentration for the time period of interest.

The primary purpose of the ingestion component of TRIM.Expo (to be available in the future) is for the assessment of ingestion exposure to air pollutants that are persistent and/or bioaccumulative. The ingestion component calculates the ingestion exposure (in units of milligrams of constituent per kilogram of body weight per day) to human receptor groups from media and food concentrations. In a typical application, the ingestion component will accept TRIM.FaTE output data or other pollutant concentration data for media and biota to estimate human exposure. TRIM.FaTE can be used to provide an inventory of chemical concentrations in environmental media and in biota across the ecosystem at selected time intervals (e.g., days, hours). A farm food chain module will also be available to provide livestock and produce contaminant estimates from air and soil concentrations and air deposition estimates provided by TRIM.FaTE or from an external file.

In addition to directly providing human population exposure estimates, the TRIM.Expo module is intended to contribute to a number of health-related assessments, including risk assessments and status and trends analyses.