| Model Name | Model Description | Emission and Transport | Transformation | Exposure Routes and Pathways |
|---|---|---|---|---|
| The Stochastic Human Exposure and Dose Simulation Model for Multimedia, Multipathway Chemicals: Residential Module (SHEDS-Residential) (EPA, 2021) | Probabilistic model to simulate population exposures to single or multiple chemicals in air, water, and surfaces through multiple exposure route. Model results can be used as input in physiological-based pharmacokinetic models. Variability and uncertainty can be characterized at the same time through Monte Carlo simulations. |
User-defined and scenario-based chemical emission. A single decay rate for each scenario, based on fugacity model. |
No built-in chemical transformation mechanisms. | Multimedia exposure through inhalation, ingestion, and dermal absorption. |
| Stochastic Human Exposure and Dose Simulation–High Throughput (SHEDS-HT) (Isaacs et al., 2014) | A “screening-tier” model in the SHEDS family for prioritization purpose. The model structure is similar to SHEDS-Residential (or Multimedia), but the model is more computationally efficient. SHEDS-HT is a probabilistic model to simulate population exposures to multiple chemicals in microenvironments through multiple exposure routes. Technically, SHEDS-HT estimates variability but does not characterize uncertainty directly. |
Two scenarios for chemical release—instantaneous release and constant release. One type of indoor surface (floor) is included. Decay rates are based on fugacity models. |
No built-in chemical transformation mechanisms. | Multimedia exposure through inhalation, ingestion, and dermal absorption. |
| USEtox (Rosenbaum et al., 2011) | Deterministic model with multiple scales (far field and near field) to characterize the impact of chemicals throughout their life cycles on human and freshwater systems. Variability across a population and the uncertainties are not simultaneously characterized by the model. |
Emission rate is user defined based on exposure scenarios. Chemical transfers among compartments are characterized by partitioning coefficients. |
Built-in equations to account for gas-phase degradation through reactions involving ozone, hydroxyl radicals, and nitrate radicals. | Multimedia and multipathway exposures through inhalation, ingestion, and dermal absorption. |
| Consumer Exposure Model (CEM) (EPA, 2019a) | Deterministic model for regulatory purpose to characterize human exposures in indoor environments to chemicals in consumer products and articles. Variability across a population and the uncertainties are not simultaneously characterized by the model. | Emission rate is user defined based on exposure scenarios. Chemical transfers among compartments are characterized by partitioning coefficients. |
No built-in chemical transformation mechanisms. | Multimedia user and non-user exposure through inhalation, ingestion, and dermal absorption. |
| Indoor Environmental Concentrations in Buildings with Conditioned and Unconditioned Zones (IECCU) (EPA, 2019b) | Deterministic model for regulatory purpose to characterize the concentration of airborne chemicals in a multizone indoor environment, due to emissions from articles, paints, etc. Variability across a population and the uncertainties are not simultaneously characterized by the model. |
Constant and variable source emissions are defined by user. Chemical transfers among compartments are characterized by partitioning coefficients. |
Built-in equations to account for limited number of gas-phase reactions. | Inhalation exposure. |
| CONTAM (NIST, 2018) | A multizone indoor air quality model to predict ventilation, indoor air pollutant concentration, and inhalation exposure. | Source emission profiles can be specified in the model. Ventilations, including indoor-outdoor air exchange and zone-to-zone airflows, due to pressure difference, temperature difference, and mechanical forces, can be modeled. Sorption and desorption are also accounted for in the model. |
Chemical transformations are modeled with kinetic reaction simulation. Radioactive species are modeled based on exponential decay constants. | Inhalation exposure. |
| Consumer Exposure and Uptake Models (ConsExpo) (National Institute for Public Health and the Environment, 2017) | A suite of models (the latest version is a web application), ranging from screening-level models to probabilistic models, to estimate exposure and resulting absorbed dose of chemicals due to consumer products’ use under various conditions, including emissions from vapor, spray, and solid materials; direct contact to products; and chemical migration from food packaging materials. | Chemical release is modeled based on product use conditions and chemical properties. There is limited consideration of chemical partition among compartments. Bulk air exchange rate and mass transfer coefficients are employed to account for chemical migration. |
Chemical transformation is not modeled. | Estimate exposure and absorbed dose through inhalation, ingestion, and dermal absorption. |
| Model Name | Model Description | Emission and Transport | Transformation | Exposure Routes and Pathways |
|---|---|---|---|---|
| Risk Assessment IDentification And Ranking Indoor and Consumer Exposure (RAIDAR-ICE) (Li et al., 2018) | A steady-state screening model, formulated in fugacity notation, predicting human exposure in the indoor environment to neutral organics, through estimating human external exposure and internal dose and comparing these metrics with health benchmark. | Chemical release is characterized by either a steady-state emission rate or a chemical application rate. Chemical transport among seven indoor compartments, including indoor air, polyurethane foam, carpet, vinyl floor, and organic films on vertical, up-facing, and down-facing surfaces. |
No built-in chemical transformation mechanisms. | Estimate exposure and internal dose through inhalation, ingestion, and dermal absorption. |
| Production-To-Exposure Model (PROTEX) (Health Environmental Assessment Team, n.d.) | A multipathway and multiscale model coupling near-field and far-field exposure with the capability to predict exposure and toxicokinetics. | User-defined emission rate; indoor environment comprises four compartments, including indoor air, carpet, vinyl floor, and organic film on indoor surfaces; mass transfer across indoor, urban, and rural environments. | No built-in chemical transformation mechanisms, but transformation can be quantified with a half-life time. | Estimate exposure and internal dose through inhalation, ingestion, and dermal absorption. |
| Fugacity-based INdoor Exposure (FINE) (Bennett and Furtaw, 2004) | A flexible framework to build multicompartment dynamic mass balance model in fugacity notation to predict near-field exposures to organics released in the indoor environment. | User-defined emission scenarios; diffusive and advective mass transfer across compartments, including but not limited to air, carpet, vinyl floor, ceiling, and wall. | No built-in chemical transformation mechanisms. | Estimate exposure through inhalation, hand-to-mouth ingestion, and dermal absorption. |
| Activity-Based Indoor Chemical Assessment Model (ABICAM) (Kvasnicka et al., 2020) | Multimedia residential indoor model, based on mass balance and in fugacity notation, to predict transient exposures and internal dose to semivolatile organic compounds. | User-defined personal activity–related emissions. Chemical mass transfer among nine compartments, including “skin-surface lipids in hands and the rest of skin, internal body, indoor air, polyurethane-foam (PUF) mattress pad, hard floor, carpet, upward-oriented surfaces coated by a thin layer of organic film and other film-coated surfaces of vertical and downward orientations.” |
No built-in chemical transformation mechanisms. | Estimate exposure and internal dose through inhalation, hand-to-mouth ingestion, and dermal absorption. |
REFERENCES
Bennett, D. H., and E. J. Furtaw. 2004. Fugacity-based indoor residential pesticide fate model. Environmental Science & Technology 38(7):2142–2152. https://doi.org/10.1021/es034287m.
EPA (U.S. Environmental Protection Agency). 2019a. Consumer Exposure Model (CEM) User Guide. https://www.epa.gov/sites/default/files/2019-06/documents/cem_2.1_user_guide.pdf.
EPA. 2019b. Indoor environmental concentrations in buildings with conditioned and unconditioned zones (IECCU): Simulation program for estimating chemical emissions from sources and related changes to indoor environmental concentrations in buildings with conditioned and unconditioned zones. In IECCU User’s Guide. https://www.epa.gov/sites/default/files/2019-06/documents/ieccu_1.1_users_guide.pdf.
EPA. 2021. Stochastic Human Exposure and Dose Simulation (SHEDS) to estimate human exposure to chemicals. https://www.epa.gov/chemical-research/stochastic-human-exposure-and-dose-simulation-sheds-estimate-human-exposure.
Health Environmental Assessment Team. n.d. Comprehensive Exposure Model, in PROTEX (PROduction-To-Exposure). Accessed February 2, 2022. https://lilienv.weebly.com/protex.html.
Isaacs, K. K., W. G. Glen, P. Egeghy, M. R. Goldsmith, L. Smith, D. Vallero, and H. Özkaynak. 2014. SHEDS-HT: An integrated probabilistic exposure model for prioritizing exposures to chemicals with near-field and dietary sources. Environmental Science & Technology 48(21):12750–12759. https://doi.org/10.1021/es502513w.
Kvasnicka, J., E. Cohen Hubal, J. Ladan, X. Zhang, and M. L. Diamond. 2020. Transient multimedia model for investigating the influence of indoor human activities on exposure to SVOCs. Environmental Science & Technology 54(17): 10772–10782. https://doi.org/10.1021/acs.est.0c03268.
Li, L., J. N. Westgate, L. Hughes, X. Zhang, B. Givehchi, L. Toose, and J. A. Arnot. 2018. A model for risk-based screening and prioritization of human exposure to chemicals from near-field sources. Environmental Science & Technology 52(24):14235–14244. https://doi.org/10.1021/acs.est.8b04059.
National Institute for Public Health and the Environment. 2017. ConsExpo Consumer Exposure Models Model Documentation. RIVM Report 2017–0197. https://www.rivm.nl/bibliotheek/rapporten/2017-0197.pdf.
NIST (National Institute of Standards and Technology). 2018. IAQ analysis and contaminant transport. https://www.nist.gov/el/energy-and-environment-division-73200/nist-multizone-modeling/applications-contam/iaq-analysis.
Rosenbaum, R. K., M. A. Huijbregts, A. D. Henderson, M. Margni, T. E. McKone, D. Van De Meent, and O. Jolliet. 2011. USEtox human exposure and toxicity factors for comparative assessment of toxic emissions in life cycle analysis: Sensitivity to key chemical properties. The International Journal of Life Cycle Assessment 16(8):710–727. https://doi.org/10.1007/s11367-011-0316-4.
