Modeling use phase chemical releases, fate, and disposal for modeling longitudinal human exposures to consumer products

摘要

The US EPA's Human Exposure Model (HEM) is an integrated modeling system to estimate human exposure to chemicals in household consumer products. HEM consists of multiple modules, which may be run either together, or independently. The Source-to-Dose (S2D) module in HEM uses a compartmental mass partitioning approach that models the release and transport of chemicals during product use as a series of stages including the initial use phase release, transfers during the use phase, end of the direct use phase, and direct exposure to residual chemicals. In the first stage, the fractional mass releases of chemicals that occur during the use of a product are determined for 11 possible compartments (indoor/outdoor air, indoor/outdoor surface, skin, gut, other body parts, solid waste, drain, appliance and retained solid product). The mass releases to each compartment vary by the type of product. Products are categorized into 17 different product categories based on the physical processes involved in their use (sprays, liquids, dusts etc.) and on their application location (body, indoor, outdoor surfaces, among others). The second stage determines the transfers between compartments during the time the product is used by processes such as, but not limited to, volatilization and settling. The third stage determines the movement of chemicals to household trash and residential waste water from wipe-off and rinse-off events. Some products have a fourth stage for modeling direct exposure to any residual chemical left on the skin or in the nearby area. The mass of chemicals in the indoor air and surface compartments at the end of the fourth stage are used as inputs to a fugacity module to determine the time series of post-use chemical concentrations in the home's indoor air and surfaces. This approach allows for the efficient calculation of population-based residential human exposures and releases in support of mid-tier assessments and life-cycle analyses.