Important Caveats of the RSEI Model
The following caveat should be considered regarding the release component of the model:
- RSEI uses facility-reported TRI data which is known to contain some reporting errors. Since facility management must certify reports to be accurate, the TRI program does not change any reported data until the reporting facility submits an official correction. Therefore, there are some releases in the TRI data that are thought to be erroneous but are still included because facilities have not submitted corrected reporting forms by the time of the annual public data release that RSEI uses. Some of these releases are associated with large risk-related impacts. One erroneous release warrants special note: a 2002 fugitive air release of 184,770 pounds of nickel in Johnstown, PA probably overstates the release amount and may be assigned to the wrong media. Even small reporting errors may lead to substantial risk scores depending on the chemical's toxicity, the exposed population, and the exposure scenario.
The following caveats should be considered regarding the toxicity component of the model:
- Toxicity weights are not designed to (and may not) correlate with statutory criteria used for listing and delisting chemicals in TRI. RSEI risk-related model results account for estimated exposure and may not correlate with listing/de-listing decisions.
- RSEI only addresses chronic human toxicity (cancer and noncancer effects, e.g., developmental toxicity, reproductive toxicity, neurotoxicity, etc.) associated with long-term exposure and does not address concerns for either acute human toxicity or environmental toxicity.
- Toxicity weights are based upon the single, most sensitive chronic human health endpoint for inhalation or oral exposure pathways, and do not reflect severity of effects or multiple health effects.
- Estimated Reference Doses and Reference Concentrations for noncancer effects incorporate uncertainty factors which are reflected in toxicity weights that are based upon these values.
- Several significant assumptions are made regarding metals and metal compounds, because important data regarding these chemicals are not subject to TRI reporting. Metals and metal compounds are assumed to have the same toxicity weight, although the chronic toxicity of some metal compounds may be higher. Metals and metal compounds are assumed to be released in the valence (or oxidation state) associated with the highest chronic toxicity. The only exception is chromium and chromium compounds, for which it is assumed that facilities may release some combination of hexavalent chromium and trivalent chromium. SIC-code specific estimates from the 2002 National Emissions Inventory are used to estimate the fraction of each type (available from EPA's Technology Transfer Network). As trivalent chromium has a very low toxicity, only the hexavalent fraction is modeled, using a toxicity weight specifically for that valence state.
The following caveats should be considered regarding the exposure component of the model:
- Like other exposure models, RSEI estimates exposure levels (it does not yield actual exposures). The model provides estimated air concentrations in each grid cell.
- The model uses some generic assumptions, e.g., default median stack heights, diameters, and exit gas velocities related to 2- or 3-digit Standard Industrial Classification (SIC) codes, or a nationwide median, where facility-specific median stack height, diameter, and exit gas velocity data are unavailable.
- In the current version of the model, only air and direct surface water exposures are fully modeled.
- The model does not account for population activity patterns.
- The model has greater uncertainty when examining disaggregated results at the local or facility level.
- RSEI does not model deposition of air releases. This may significantly underestimate the risk from releases of some chemicals.
The following caveats should be considered regarding the population component of the model:
- Population values for years in which Census data are not available are estimated based on linear interpolations at the block level between the 1990 and 2000 US Census dates, and on extrapolations back to 1988 and forward to 2006.
- Drinking water populations are estimated by using the total drinking water populations associated with individual downstream drinking water intakes. Estimated populations for the fish ingestion pathway are based upon US Fish and Wildlife Service surveys.
- Because RSEI results reflect changing population size at the local level, a facility's relative contribution could increase or decrease even without changes in its releases over time. While the model is designed to reflect the overall risk-related impacts on the local population, such population changes should be considered when examining a facility's environmental management practices.
Review strengths and limitations associated with RSEI.