How RSEI Should Be Used

EPA's Risk-Screening Environmental Indicators (RSEI) is a screening-level model that helps you use Toxics Release Inventory (TRI) data. RSEI results allow you to focus on chemicals, industry sectors, facilities, and geographic areas with the greatest potential for chronic human health impacts. 

Common uses for RSEI include:

• Identifying high-scoring chemicals and industry sectors for further investigation and pollution prevention opportunities.
• Highlight areas which may have higher pollution burden and health-related impacts involving toxic chemical releases from a relative standpoint.
• Examining trends over time for facilities, industry sectors, or geographic areas. In some cases, the potential for chronic human health impacts can increase even though fewer total quantities of toxic chemicals are released.
• Helping to prioritize issues for communities relating to toxics management. RSEI can help identify chemicals, facilities, and types of waste management activities that may be of most interest and require further investigation.
• Looking at environmental justice issues. Combining RSEI data with demographic and income data can help communities and policymakers identify areas of potential concern.

Understanding RSEI results provides more details on what the results mean. All RSEI results should be followed up with additional analysis before drawing conclusions or making decisions about the potential health impacts or risks posed to any particular population.

RSEI uses simplified data for modeling, and this can affect the results. RSEI is designed to represent a worst-case scenario in most situations. In many cases, additional investigation and analysis will indicate less potential for concern, such as in the following cases:

• Actual facility stack heights are much higher than the RSEI model assumes, leading to lower potential air concentrations around the facility.
• The metal compound actually released to the environment is less toxic than what RSEI assumes and models. 
• The facility location is actually further away from residential populations than modeled.
• The water discharge is to a larger stream or river than modeled.

What to do after an analysis using RSEI

Because RSEI often uses simplifying assumptions, high RSEI Scores can only indicate a potential need for further investigation. There are a number of ways to investigate how RSEI assumptions may affect results and risk-related impacts. For each facility and chemical release, users are able to review the specific input parameters used to generate the RSEI model results. Users may want to research those parameters to determine if they represent the best estimate for a specific facility. Examples of steps one might take include:

• Verify reported information (e.g., check EPA's Envirofacts database for corrected TRI reporting forms). Facilities occasionally submit corrections to reported data that may not be reflected in RSEI before the next update version.
• Determine what specific chemical substance is being released when chemicals are reported as TRI chemical categories (metal compounds, diisocyanates, polycyclic aromatic compounds, etc.). For screening-level purposes, RSEI generally assumes all releases for the chemical category are of the chemical with the greatest chronic toxicity, with some noted exceptions.
• Verify other RSEI simplifying assumptions, for example:
  • Parameters related to air releases such as stack heights – If actual stack heights are greater than the modeled stack heights, ambient concentration will be below the RSEI modeled concentration and therefore potential concerns are lessened.
  • Water releases – Is the discharge outfall location correct- on the correct stream or river and on the correct segment?
• Compare TRI sources of chemicals of concern with other sources (mobile sources, area sources, non-TRI point sources, indirect exposure to TRI sources) and assess the relative contribution of TRI releases. If the direct exposure to the TRI source is a minimal contributor, further efforts should focus on other sources of those chemicals. Other sources of environmental information provides links and information to help assess situations of potential concern.
• Consider more detailed modeling using appropriate air and water dispersion models, or, if resources permit, monitor ambient concentrations (air, water, fish tissue) to see if pollutant levels rise above a level of concern (reference dose or reference concentration, or acceptable cancer risk levels).