Toward a Definition of Unreasonable Risk of Injury to Health or the Environment

As I have noted in previous articles, “How Does TSCA Define ‘unreasonable risk of injury to health or the environment’?” and “More Musings on Unreasonable Risk,” perhaps the most important term in the Toxic Substances Control Act (TSCA) is “unreasonable risk of injury to health or the environment,” or simply “unreasonable risk.” After all, the Environmental Protection Agency’s (EPA) determination that a chemical presents unreasonable risk triggers a suite of risk management measures that can include an outright ban of an existing chemical. For new chemicals, an unreasonable risk determination can significantly hinder market entry.    

Yet, neither TSCA nor EPA’s implementing regulations define the term. This omission prompted the TSCA Improvement Coalition – a group of companies advocating for sensible TSCA reform and managed by Keller and Heckman – to propose its own definition of unreasonable risk: 

The term “unreasonable risk of injury to health or the environment” means actual or reasonable potential for significant, irreversible adverse acute or chronic human health effects from known exposure to the chemical substance undergoing risk evaluation. With respect to the environment, unreasonable risk means actual or reasonable potential for significant, irreversible adverse changes in the diversity, productivity or stability of an ecological community from known exposure to the chemical substance undergoing risk evaluation. Unreasonable risk does not include risks that are speculative, transient, insubstantial, or similar to risk levels attributed to natural background levels of the chemical substance (from normal human metabolism or natural formation in the environment). In assessing unreasonable risk, EPA shall consider human health or environmental benefits attributed to the chemical substance under evaluation.  

Although earlier this year, the Senate Environment and Public Works Committee issued draft TSCA legislation that includes a laudatory attempt at elucidating unreasonable risk, the Senate did not go far enough, and its efforts still fall short of a definition:  

The term ‘unreasonable risk’ does not include risks that may arise from common, well-understood hazards, such as irritation, corrosion, flammability, unreactive dust, and other physical effects. The term ‘unreasonable risk’ includes consideration of both the hazard of a substance and the quantity, frequency, and duration of the exposure to the environment.

For its part, the House stayed clear of defining unreasonable risk in its draft TSCA legislation. 

Once again, Congress appears poised to avoid tackling unreasonable risk in ongoing legislative reform efforts. EPA, however, does not need Congress to craft a definition. Indeed, in 2017, when EPA initially proposed a risk evaluation procedural rule mandated by the 2016 TSCA amendments, EPA solicited comments on how to define unreasonable risk. Regrettably, EPA ultimately abandoned the effort in the final rule. The farthest EPA was willing to go was to delineate “factors” that EPA considers in determining whether unreasonable risk is present. These factors include, for example, the severity of the hazard, the confidence in the information EPA relied on to assess hazard and exposure values, among others. But none of these factors get us any closer to a definition. In fact, these factors have only underscored the need for a definition. Peruse any risk evaluation issued since the 2016 TSCA amendments, and you will see how EPA essentially equates unreasonable risk with any risk, effectively eviscerating the word “unreasonable” from “unreasonable risk” (https://www.khlaw.com/insights/more-musings-unreasonable-risk). 

Fast forward nearly 10 years in EPA’s most recent 2025 proposal to revise the risk evaluation procedural rule – EPA once again solicited public comments on whether EPA should define the term.   

The passage of time has not diminished the need for a definition of unreasonable risk that gives practical and functional meaning to the term “unreasonable. Under EPA’s current leadership, there is still an opportunity to remedy this pressing need in the forthcoming revisions to the risk evaluation procedural rule.