How to Use—and Not Use—RSEI
- How should RSEI be used?
- How should RSEI not be used?
- What risk factors does RSEI consider?
- What health endpoints does RSEI consider?
- What are some of the limitations of RSEI?
- What types of simplifying assumptions does RSEI use?
- How has RSEI been appropriately used?
- What is a RSEI score?
- What does a high RSEI score mean?
- What are examples of further investigation warranted by high RSEI scores?
RSEI should be used for screening-level activities, such as:
- ranking regions, states, counties, industries, chemicals, facilities, or release pathways;
- trend analysis.
Note that detailed, local results involve the most uncertainty as a result of small sample size. All RSEI results should be followed up with additional analysis if detailed conclusions are desired.
RSEI does not provide a risk assessment so it is inappropriate to use it to:
- conclude that a particular chemical release is causing harm to a specific population or location;
- draw conclusions or make decisions about the risk posed by any particular facility;
- draw conclusions about individual risk or generate quantitative risk estimates.
RSEI incorporates a number of components of risk assessment including the amount of chemical released, the fate and transport of the chemical, the route and extent of human exposure to the chemical, the number of people affected, and the toxicity of the chemical.
RSEI considers both cancer and non-cancer chronic human health endpoints. Acute human health effects and ecological effects are not addressed. RSEI does not address all potential exposure pathways of TRI-reported releases and does not address all sources of toxic chemical exposure.
As with any model, RSEI is subject to the limitations of the underlying data sources and models that it incorporates, in addition its own limitations:
- RSEI relies exclusively on TRI-reported data for release estimates.
- TRI data do not cover all sources of TRI chemicals; they only include industrial releases from certain industries that meet specific reporting thresholds.
- TRI does not include all toxic chemicals.
- RSEI does not provide scores for all TRI chemicals because information required for modeling, such as toxicity data, is not available for every chemical.
- RSEI does not cover all exposure routes or all chronic health effects.
- Toxicity weights are based only on chronic human toxicity.
- Toxicity weights do not address acute human toxicity or environmental toxicity.
- Dermal and food ingestion pathways (other than fish consumption) and other indirect exposure pathways are not evaluated.
- RSEI uses a number of simplifying assumptions.
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 calculation. Some examples of simplifying assumptions used by RSEI:
- Median stack heights are used when facility-specific information is not available.
- When facility-specific information is available, stack parameters are averaged and the median for all stacks at that facility is used for all releases from that facility.
- Representative chemical substances are used for reports for chemical categories, e.g., metals and metal compounds.
- Air concentrations are the same both indoors and out.
- People are home all day and are continuously exposed.
When analyses using simplifying assumptions of this nature are applied in a small sample situation, such as local analyses (e.g., a facility-level analysis), the error associated with these assumptions is likely to be more significant than in the larger sample situation of a larger geographic area. In that case, assumptions of this nature tend to better reflect the population.
EPA Offices at Headquarters and in the Regions, and outside analysts have used RSEI to investigate:
- industry sector- and facility-based targeting for further investigation and strategic planning;
- analysis of trends;
- impact of regulations on cross-media risk transfers;
- environmental justice (EJ) issues;
- prioritization for community-based environmental protection.
RSEI starts with TRI releases. For each exposure pathway from each chemical release, the model generates an "Indicator Element." This Indicator Element is a risk-related score that is a unitless value proportional to the potential risk-related impact of the release. This score is the product of the estimated dose of a chemical multiplied by the chemical's assigned toxicity weight multiplied by the exposed population. Indicator Elements are specific to each exposure pathway, chemical, release medium, facility, and year. Indicator Elements are summed to provide the outputs requested by the user.
High scores identify areas for further investigation. They do not conclusively demonstrate sources of risk. If a facility receives a high RSEI score one cannot identify that facility as the predominant source of chronic human risk. RSEI points to releases that may be a problem that warrant further investigation. However, RSEI scores are directly comparable to each other. A RSEI score 10 times higher than another RSEI score suggests that the potential for risk is 10 times higher. Relatively small releases may lead to high risk scores if the toxicity weight is particularly high or if the estimated exposed population is large. Conversely, large releases may lead to low risk scores if the toxicity weight is low or if the estimated exposed population is small.
Because of the simplifying assumptions in the RSEI model, high RSEI scores can only identify potential problems. Further investigation is warranted in order to conclude that a particular facility is a source of high chronic human risk. There are a number of ways to investigate how RSEI assumptions may affect risk-related results. For each facility and release, users are able to review the specific parameters used to generate the estimates. 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 releases (e.g., check EPA's Envirofacts database for corrected TRI reports). Companies occasionally submit corrections to reported releases that may not be reflected in RSEI before the next update.
- For category reporting (metals and metal compounds, diisocyanates, polycyclic aromatic compounds, etc.), determine what specific chemical substance is being released. For screening-level purposes, RSEI assumes all releases in the category are for the chemical with the greatest chronic toxicity with the exception of chromium for which RSEI applies a speciation model.
- 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 estimated concentration and therefore potential concerns are lessened.
- Water releases - Are assumptions about the effluent point correct? Are there drinking water intakes downstream of the effluent point? RSEI uses the closest stream reach as the effluent point, which may locate the effluent point directly upstream of a drinking water intake. If the effluent point is actually downstream of the intake, the potential concern from the effluent would be substantially less.
- To assess the contribution of TRI releases to other sources of release, compare TRI sources of substances of concern with other sources (mobile sources, area sources, non-TRI point sources, indirect exposure to TRI sources). If the direct exposure to the TRI source is a minimal contributor, further efforts should focus on other sources of those substances.
- 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 the level of concern (reference dose or reference concentration, or acceptable cancer risk levels).