Stochastic Human Exposure and Dose Simulation (SHEDS) to estimate human exposure to chemicals

What are the Stochastic Human Exposure and Dose Simulation (SHEDS) Models?

The SHEDS models are probabilistic models that can estimate exposures people face from chemicals encountered in everyday activities. The models are able to generate predictions of aggregate and cumulative exposures over time to inform risk assessments that protect human health. SHEDS can estimate the range of total chemical exposures in a population from different exposure pathways over different time periods given a set of demographic characteristics. SHEDS can also help identify critical exposure pathways, factors and uncertainties.

What are the benefits of using SHEDS?

SHEDS enhances estimates of exposure in many contexts. It has been used to inform EPA human health risk assessments and risk management decisions. SHEDS models have been successfully used by EPA to

Improve pesticide-related risk assessments (e.g., n-methyl carbamates, pyrethroids);
Evaluate risks to children posed by wood play-sets treated with chromated copper arsenate;
Improve risk assessment for chemicals in food;
Prioritize chemicals for further study on the basis of risk; and
Prioritize data needs

Who uses the SHEDS Models?

The SHEDS models have registered users in 26 countries and more than 20 U.S. states. The model is used by representatives from academia, industry, government, and consulting firms.

How does SHEDS work?

SHEDS models estimate the range of total chemical exposures in a population from four exposure pathways: inhalation, skin contact, and dietary and non-dietary ingestion. These estimates are calculated using available data such as dietary consumption surveys; human activity from the Consolidated Human Activity Database (CHAD); and observed or modeled levels in food, water, air and on surfaces like counters and floors. The data on chemical concentrations and exposure factors used in SHEDS are based in measurements collected in EPA field studies and published literature.

SHEDS Models:

EPA has developed a number of different SHEDS models and modules that address specific research questions about chemical exposure.

SHEDS-Multimedia, v3 is currently available via free download. It 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. SHEDS-Multimedia uses both the SHEDS-Residential and SHEDS-Dietary models 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.

SHEDS-High throughput (SHEDS-HT) — currently in beta form — can produce exposure estimates for thousands of chemicals in a rapid and cost-effective manner. It offers more flexibility for inputs than SHEDS-Multimedia, and can quickly provide exposure estimates for new chemicals that have limited data, and can provide information to help prioritize chemicals for future study on the basis of risk.

What is Required to run SHEDS?

The SHEDS model runs on a personal computer and requires that SAS 9.1 or higher be installed prior to the installation of SHEDS.

Download Now:

SHEDS-Multimedia (version 3):

SHEDS-Dietary (version 1.1):

SHEDS-Residential (version 4.1):

SHEDS-HT:

SHEDS-HT R package and default input files