TRI National Analysis

Hazard and Risk of TRI Chemicals in the 2015 TRI National Analysis

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Among other information, the Toxics Release Inventory (TRI) provides data about environmental releases of toxic chemicals from industrial facilities throughout the United States, measured in pounds. Pounds of releases, however, is not an indicator of any health risks posed by the chemicals. Although TRI data generally cannot indicate to what extent individuals have been exposed to toxic chemicals, TRI can be used as a starting point to evaluate exposure and the potential risks TRI chemicals pose to human health and the environment.

The human health risks resulting from exposure to toxic chemicals are determined by many factors, as shown in the figure below. TRI contains some of this information, including what chemicals are released from industrial facilities; the amount of each chemical released; and the amounts released to air, water, and land.

Overview of Factors that Influence Risk

Overview of factors that influence risk (emissions, fate, exposure, toxicity, and risk of adverse effect)

It is important to keep in mind that while TRI often includes information on a large portion of the toxic chemicals used by industry, it does not cover all facilities, all toxic chemicals, or all sources of TRI chemicals in communities. For example, potential sources of chemical exposure that are not covered by TRI include exhaust from cars and trucks, chemicals in consumer products, and chemical residues in food and water.

Helpful Concepts

The hazard of a toxic chemical is its ability to cause an increased incidence of adverse health effects (e.g., cancer, birth defects). Toxicity is a way to measure the hazard of a chemical.

The risk of a toxic chemical is the chance of adverse health effects occurring as a result of exposure to the chemical. Risk is a function of hazard and exposure.

To provide information on the potential hazard and risk posed by disposal or other releases of TRI chemicals, the TRI Program uses EPA’s publicly available Risk-Screening Environmental Indicators (RSEI) model, a screening-level model that uses simplifying assumptions to fill data gaps and reduce the complexity of calculations in order to quickly evaluate large amounts of data. RSEI includes TRI data for on-site releases to air and water, transfers to Publicly Owned Treatment Works (POTWs), and transfers for off-site incineration. RSEI does not currently model other release pathways, such as land disposal.

RSEI produces hazard estimates and unitless risk “scores,” which represent relative chronic human health risk. Each type of result can be compared to other results of the same type.

RSEI: Risk-Screening Environmental Indicators

RSEI results consider more than just chemical quantities released.

  • RSEI hazard results also consider:
    • Toxicity of the chemical
  • RSEI scores also consider:
    • Location of releases
    • Toxicity of the chemical
    • Fate and transport
    • Human exposure pathway

Note that the RSEI model should be used for screening-level activities such as trend analyses that compare relative risk from year to year, or ranking and prioritization of chemicals or industry sectors for strategic planning. RSEI does not provide a formal risk assessment, which typically requires site-specific information, more refined exposure information, and detailed population distributions.

Top chemicals released§ in 2015, ranked in order by...

Pounds Released RSEI Hazard
RSEI Score
(estimated dose*toxicity*exposed population)
1. Nitrate compounds 1. Chromium and compounds 1. Chromium and compounds
2. Methanol 2. Cobalt and compounds 2. Nickel and compounds
3. Ammonia 3. Arsenic and compounds 3. Cobalt and compounds
4. Sulfuric acid 4. Nitroglycerin 4. 1,3-Butadiene
5. Hydrochloric acid 5. Nickel and compounds 5. Arsenic and compounds
Why are the rankings different?
  • The top five chemicals by pounds are released in large amounts and are comparatively less toxic than the top chemicals by hazard or score. None of them are known carcinogens - cancer effects usually drive RSEI hazard and RSEI scores.
  • The top five chemicals by RSEI hazard have very high toxicity weights and all of them are carcinogens.
  • For a chemical to have a high RSEI score, it must be either very toxic, have a large number of people potentially exposed, or have potential for very high exposures (or some combination).
  • Nitroglycerin is in the top five chemicals by RSEI hazard but not by RSEI score because the two releases driving the hazard results are large off-site transfers to wastewater treatment and incineration. RSEI hazard is calculated using the pounds transferred, while RSEI score uses the amount of the chemical released into the environment after treatment, which is substantially smaller. 
  • 1,3 Butadiene is in the top five chemicals by RSEI score but it is not in the top five chemicals by RSEI hazard because of a small number of releases with a large number of people potentially exposed. Exposure is only a component of RSEI score.

§This includes chemicals released on-site to air and water by TRI facilities, or transferred and released off-site to air and water by POTWs and incinerators.
Note: RSEI is commonly used to quickly screen and highlight situations that may potentially lead to chronic human health risks. More information about the model can be accessed at the RSEI webpage.

This page was published in January 2017 and uses the 2015 TRI National Analysis dataset made public in TRI Explorer in October 2016.

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