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Human Exposure and Atmospheric Sciences

SHEDS-Multimedia User Information

EPA’s Stochastic Human Exposure and Dose Simulation model for multimedia, multipathway chemicals (SHEDS-Multimedia) is a physically-based, probabilistic model, that can simulate cumulative (multiple chemicals) or aggregate (single chemical) exposures over time for a population via residential and dietary routes of exposure for a variety of multimedia, multipathway environmental chemicals.

SHEDS-Multimedia has been used by EPA exposure and risk assessors to help address U.S. Food Quality Protection Act mandates for registration of pyrethroid pesticides. The model has also been used by EPA for cumulative exposure assessments to support regulatory decisions regarding organophosphate and carbamate pesticides.

Current and earlier versions of SHEDS-Multimedia have been used in EPA, academia, government, and industry for a variety of regulatory and research purposes. Additionally, SHEDS-Multimedia has registered users in more than nine countries and 12 U.S. states including representatives from academia, industry, consulting firms, and individual citizens.

Public Availability
SHEDS-Multimedia materials, including the accompanying SHEDS-Dietary and SHEDS-Residential modules, are available for free download off this web page. Please follow the links to the right. Users are asked to register at the link to the right prior to downloading SHEDS materials and software. This way, EPA can keep you informed of software modifications, revisions and improvements.

Background
On a daily basis, people come in contact with a variety of chemicals that enter the body through multiple routes and pathways. Implementation of the U.S. Food Quality Protection Act necessitated developing new methodologies to assess residential and dietary exposures.

SHEDS-Multimedia, and the model’s dietary and residential modules (SHEDS-Dietary and SHEDS-Residential) are able to generate predictive data on aggregate and cumulative exposures over space and time that inform risk assessments to protect human health. SHEDS-Multimedia and its accompanying modules predicts — for user-specified population cohorts — exposures incurred via inhaling contaminated air, touching contaminated surfaces, and ingesting residues from food, drinking water, hand-to-mouth activities, and object- to-mouth activities. The model can be used to predict ranges of exposure in a population; identify critical pathways, factors, and uncertainties; and enhance dose model estimates.

SHEDS-Dietary v.1 is a probabilistic, population-based dietary exposure assessment module of SHEDS-Multimedia. It can simulate individual exposures to chemicals in food and drinking water over different time periods (e.g., daily, yearly).

SHEDS-Residential v. 4 is a probabilistic, population-based residential exposure assessment module of SHEDS-Multimedia. It can simulate cumulative (multiple chemicals) or aggregate (single chemical) residential exposures over time via multiple routes of exposure for different types of chemicals and scenarios. These models are linked together with structure-based physiologically-based pharmacokinetic (PBPK) models and are used together to quantify target tissue dose, and conduct linked exposure-dose model evaluations.

Model Evaluation
Because of various types of uncertainty in models, it is important to evaluate or “ground truth” them to the extent possible, including modules within them as well as overall model predictions. This is particularly important for models used in regulatory decision-making. Without changing model structure or calibrating inputs, SHEDS-Multimedia aggregate estimates and its residential and dietary modules have compared well against other models and measurements data, including duplicate diet and biomarkers from different studies, for several metals (arsenic and methyl mercury), and pesticides (permethrin and chlorpyrifos). These multifaceted evaluation results provide confidence in SHEDS-Multimedia as an exposure assessment tool that can enhance human health risk assessments and human health research.

External Peer Review
SHEDS-Multimedia has been externally peer-reviewed by EPA’s Federal Insecticide, Fungicide, Rodenticide Act Scientific Advisory Panel. The current versions of the models (SHEDS-Residential 4.1 and SHEDS-Dietary 1.1) incorporate comments from peer reviews.

The August 14-15, 2007, Scientific Advisory Panel reviewed version 3 (aggregate residential version) methodology, code, and documentation, and provided consult on the dietary module structure and approach, and planned methodologies to extend version 3 to version 4.

The July 20-22, 2010, EPA Scientific Advisory Panel Review consisted of

  • A formal review of SHEDS-Multimedia version 4 (including dietary and applicator/post-application residential exposures);
  • A peer consult on refinements to the published PBPK models and how SHEDS outputs are introduced into and used by PBPK models; and
  • Demonstration of the application of the linked SHEDS-PBPK models with a permethrin case study. The overall goal of this Scientific Advisory Panel was to review these individual and linked state-of-the-science exposure and dose assessment tools with a permethrin case study to support a cumulative assessment of selected pyrethroids.

Quality Assurance
In developing SHEDS-Multimedia, EPA scientists placed emphasis on quality assurance for algorithms, code, and user interface by cross-checking all components; conducting one-person, event-by-event simulations for residential code verification; and conducting model-to-model and model-to-data comparisons.

Peer-reviewed Publications

Technical Contacts

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