Learn About RSEI
Watch a short introduction to EPA's Risk-Screening Environmental Indicators (RSEI) model.
- What is RSEI?
- How RSEI works
- Using RSEI to explore TRI data
- Some limitations of RSEI
- Types of simplifying assumptions RSEI uses
What is RSEI?
EPA’s Risk-Screening Environmental Indicators (RSEI) is a screening-level model that helps policy makers, researchers, and communities explore data on toxic chemicals being managed by industrial and federal facilities. RSEI can be used to help establish priorities for further investigation and to look at changes in potential chronic human healthThe RSEI model addresses both chronic effects and chronic exposures related to human health. Chronic effects are those that generally persist over a long period of time whether or not they occur immediately after exposure or are delayed. Chronic exposure refers to multiple exposures occurring over an extended period of time, or a significant fraction of an individual's lifetime. impacts over time.
RSEI incorporates information from EPA’s Toxics Release Inventory (TRI), which tracks certain toxic chemical environmental releases and other waste management activities at federal facilities and larger industrial facilities across the United States. Find out more about the TRI Program.
By analyzing TRI data on the amount of toxic chemicals released or transferred off site for further waste management, together with risk-related factors such as the chemical’s fate and transport through the environment, each chemical’s relative toxicity, and the number of people potentially exposed, RSEI calculates different metrics and numerical results that are designed to be compared and analyzed from a relative perspective.
RSEI is a screening-level model, and uses worst-case assumptions about toxicity and potential exposure where data are lacking, and simplifying assumptions to reduce the complexity of the calculations involved. A more refined or site-specific assessment should be conducted before any conclusions about potential health impacts can be determined. RSEI does not produce a risk assessment, nor can RSEI results be used to determine whether a facility is in compliance with federal or state regulations.
How RSEI Works
RSEI incorporates over 30 years of TRI chemical reporting data, three U.S. decennial Censuses, toxicity and physicochemical properties for more than 400 chemicals, and geographical information for more than 100,000 facilities and thousands of streams and other waterbodies. All of this information is used to model each chemical release through the environment and the potential human exposure and relative impacts that may result.
RSEI first locates each facility geographically. For water releases, chemical concentrations are calculated in each segment of the stream or river downstream from the discharging facility. RSEI calculates potential human exposures that could result from eating contaminated fish caught in the stream or river, or if a drinking water intake is located downstream of the chemical release, from drinking contaminated water.
For air releases, RSEI calculates chemical concentrations in air up to 49 kilometers from the emitting facility using an EPA dispersion model called AERMOD. RSEI then calculates potential exposures that could result for residents from breathing in contaminated air within the 49-kilometer radius.
RSEI estimates the potentially exposed population using U.S. block-level Census data for 1990, 2000, and 2010, and estimates the dose, or how much of the chemical a person might take into their body, based on the calculated concentration in air and water. For each chemical with available toxicity data, separate toxicity weights are calculated for oral ingestion and for inhalation. Risk-related result values (RSEI Scores) are then calculated for each modeled chemical release by multiplying the toxicity weight of the chemical by the estimated dose and the number of potentially exposed people. More information on understanding RSEI results.
RSEI results are provided in a web dashboard called EasyRSEI. Experienced users can also download the RSEI Queries database, which provides direct access to RSEI data for more complex data applications. Disaggregated RSEI results are also available in the RSEI Geographic Microdata for other data user needs.
RSEI updates all years of reported TRI data once a year, usually around December. Users should select the most recent RSEI model version available that contains the desired data years needed for their analysis. Check the ways to get RSEI results page for the latest version.
Using RSEI to Explore TRI Data
RSEI helps users to:
- Look at trends in potential health-related impacts over time and across sectors, chemicals, facilities, and locations;
- Screen and prioritize chemicals, industry sectors, and locations for strategic planning purposes;
- Support community-based projects and analysis; and
- Highlight situations with higher relative RSEI model results that may warrant further investigation to better assess and characterize potential health-related impacts.
Some Limitations of RSEI
As with any model, RSEI is subject to the limitations of the underlying data sources and models that it incorporates, in addition to its own limitations:
- RSEI relies exclusively on TRI-reported data (TRI-listed chemicals reported by TRI-regulated facilities) for environmental release and transfer quantities; the TRI Program does not include all toxic chemicals or all sources of environmental pollution. (Read about factors to consider when using TRI data.)
- A low RSEI Score (relative to other RSEI Scores) indicates lower potential concern from reported TRI information, but other kinds of environmental risk may also be present.
- RSEI does not provide RSEI Scores for all TRI-listed chemicals or chemical categories because information required for modeling, such as toxicity or physicochemical property data, is not available for every chemical.
- RSEI does not cover all potential exposure routes or all health effects.
- RSEI toxicity weights are based only on chronic human toxicity and do not address acute human toxicity or ecological toxicity.
- Dermal and food ingestion (other than for fish consumption) exposure and other environmental exposure pathways are not evaluated.
- RSEI does not produce risk estimates such as the number of excess cancer cases. Risk-related result values (RSEI Scores) are unitless and are only meant and designed to be compared to provide context from a relative risk-related perspective.
- RSEI uses a number of simplifying assumptions.
Types of Simplifying Assumptions RSEI Uses
Screening-level calculations, like those in RSEI, frequently require simplifying assumptions. These assumptions are used to fill data gaps or reduce the complexity of the calculations involved. Some examples of simplifying assumptions used by RSEI include:
- When facility-specific information is available, the median parameter values for all stacks at that facility are used to model all of the facility's stack air releases.
- When facility-specific information is not available, RSEI uses median stack parameter values by industry sector.
- Data for representative chemical substances are assigned to some TRI chemical categories, e.g., metal compounds, polycyclic aromatic compounds.
- Air concentrations are the same both indoors and outside.
- People are assumed to be home all day and are continuously exposed.
- Assumptions are made about fishing behavior and fish consumption, and that a fixed percentage of people with fishing licenses consume caught fish as a major part of their diet.
- Tap water ingestion rates and breathing rates are estimated by sex and age groups.