Raw release volume alone does not tell you which chemical releases actually matter most for human health. EPA built a tool specifically to answer that harder question. The Risk-Screening Environmental Indicators model, known as RSEI, layers toxicity data, exposure modeling and population information on top of raw Toxics Release Inventory numbers to produce a genuinely useful relative risk picture.
For chemical buyers trying to understand which substances in their portfolio draw the most regulatory and community attention, RSEI is worth understanding directly rather than relying only on headline TRI release totals.
What RSEI Actually Calculates
RSEI takes the same TRI release data covered in EPA's annual reporting and combines it with several additional layers of information: each chemical's fate and transport through the environment, its relative toxicity, and the number of people potentially exposed to a given release.
The model incorporates more than 30 years of TRI chemical reporting data, four decades of U.S. Census information, toxicity and physicochemical properties for more than 400 chemicals, and geographic details for over 100,000 facilities along with thousands of streams and water bodies. That scale of integrated data is what separates RSEI from a simple release volume ranking.
How the Model Actually Works
RSEI starts by locating each facility and its chemical release geographically. For releases to water, the model calculates chemical concentrations moving downstream through each segment of the affected stream or river, then estimates potential human exposure through eating contaminated fish or drinking water drawn from an affected intake point.
For air releases, RSEI uses an EPA dispersion model called AERMOD to calculate chemical concentrations extending up to 49 kilometers from the emitting facility. The model then estimates potential exposure for residents breathing air within that radius, using block level Census data from 1990, 2000, 2010 and 2020 to estimate how many people actually live within the affected area.
From there, RSEI calculates separate toxicity weights for oral ingestion and inhalation exposure routes wherever data exists for a given chemical. The resulting RSEI Score multiplies that toxicity weight by the estimated dose and the number of potentially exposed people, producing a unitless number designed purely for relative comparison rather than absolute risk measurement.
What RSEI Scores Are Actually Useful For
EPA describes several practical applications for this modeling output. RSEI helps users look at trends in potential health related impacts over time and across different sectors, chemicals, facilities and locations. It supports screening and prioritization work for strategic planning purposes, and it backs community based projects examining local pollution burden.
Perhaps most usefully for buyers and compliance teams, RSEI highlights situations with comparatively higher scores that may warrant further investigation, functioning as a genuine early flag for where a more detailed, site specific assessment might be worth pursuing.
The Limitations EPA Itself Flags
RSEI comes with a substantial list of stated limitations that are worth understanding before drawing conclusions from any specific score. EPA is explicit that RSEI is a screening-level model, not a risk assessment, and results cannot be used to determine whether a facility is in compliance with any federal or state regulation.
A few specific limitations stand out for anyone using this data seriously:
RSEI relies exclusively on TRI reported data, so it excludes any toxic chemical or pollution source not captured by the TRI program in the first place.
The model does not produce scores for every TRI listed chemical or category, since some substances lack the toxicity or physicochemical data needed to run the calculation.
RSEI toxicity weights address only chronic human toxicity and do not cover acute toxicity or ecological toxicity at all.
Dermal exposure and most food ingestion routes, aside from fish consumption, are not evaluated by the model.
RSEI does not estimate actual health outcomes, such as a specific number of excess cancer cases. Scores exist purely for relative comparison.
Simplifying Assumptions Baked Into Every Score
Because RSEI operates at screening scale rather than site specific detail, it relies on a set of standardized assumptions to fill data gaps. When facility specific stack information is unavailable, the model substitutes median values by industry sector. Some TRI chemical categories, such as metal compounds or polycyclic aromatic compounds, get assigned data from a single representative chemical standing in for the whole category.
The model also assumes air concentrations are identical indoors and outside, that people remain home and continuously exposed throughout the day, and applies standardized assumptions about fishing behavior and fish consumption rates among people holding fishing licenses. None of these assumptions are unreasonable for a screening tool, but they mean a single RSEI Score should never substitute for a genuine site specific risk assessment.
Why This Matters for Chemical Buyers
A chemical or facility carrying an elevated RSEI Score is not automatically in regulatory trouble, but it does signal where community concern and further scrutiny are statistically more likely to concentrate. Buyers sourcing from facilities with unusually high RSEI results for their release chemistry should treat that as a prompt for closer supplier due diligence, not as a compliance verdict on its own.
Because RSEI updates its underlying TRI data once a year, typically around December, with new model results following in the following spring, buyers tracking a specific chemical or facility over time can use this annual refresh cycle to monitor whether relative risk signals are trending up or down.
Practical Ways to Access RSEI Results
EPA offers several entry points depending on how deep a user needs to go. The EasyRSEI dashboard provides an accessible web interface for visualizing results without specialized technical skills. Experienced users needing more complex data applications can download the RSEI Queries database directly, and disaggregated results are also available through RSEI Geographic Microdata for other specialized use cases.
The Bottom Line for Procurement Teams
RSEI turns raw TRI release numbers into something genuinely more useful for prioritization, a relative chronic health risk signal built from decades of integrated environmental and demographic data. Its limitations are real and clearly documented by EPA itself, which means the smartest use of RSEI is as a screening flag that points toward further investigation, not as a final judgment on any single chemical or facility.
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Reference Link:
https://www.epa.gov/toxics-release-inventory-tri-program
