The relegation of EPA’s Integrated Risk Information System (IRIS) marks a significant shift in the way EPA addresses the evaluation of the toxicity of environmental contaminants. For decades, IRIS has served as the primary resource for broadly applicable toxicity values. This shift transfers management of this information to EPA program offices, which may have varying priorities in assessing toxicity. It also places responsibility for applying and documenting appropriate values in the hands of regulated parties, which could set the stage for differing application of values and sow confusion among stakeholders.
A regressive shift
The toxicity values developed for the IRIS program presented succinct, standardized values applicable across people and environments. However, because of the need to cover most foreseeable potential applications and uncertainties in chemical databases, these values have been widely recognized as conservative. Derivation of new values under IRIS was also a lengthy process, often entailing many years of back-and-forth on formulation of the values and stakeholder input.
The change aims to eliminate these challenges by placing development and maintenance of toxicity values back in the hands of their respective program offices. This includes EPA’s Office of Pesticide Programs, the Office of Water, and potentially the Office of Air and Radiation and other programs.
Multiple states also have been known to derive their own in-house toxicity values (e.g., California, Massachusetts). In states with their own established toxicity values, it is likely that the state guidance will continue to prevail over federal.
Knowing your limits
While IRIS is no longer being updated with new values, the resource will remain available to those who choose to reference it, and the established numbers will not change. Many EPA program offices may continue to use IRIS values while determining whether the needs of their office justify the establishment of other values that may be considered better “fit for purpose.”
As they do, interested parties may find themselves with a new level of uncertainty around regulatory compliance for risk assessment and other applications where toxicity values are used (e.g., screening levels). The good news is that if your approach uses the currently identified toxicity hierarchy, which puts IRIS at the top level, your site or program will likely continue to meet, and even exceed, hazard management requirements. For risk assessment, practitioners will most likely continue to rely on existing guidance, which includes EPA guidance that specifies that risk assessments under Superfund should use IRIS as the “Tier 1” source for toxicity information, followed by EPA’s Provisional Peer-Reviewed Toxicity Values in Tier 2, and other values in Tier 3.
Compliance and risk assessment will, however, become more complicated as regulated parties adopt new values through program offices, since this introduces a degree of uncertainty regarding which values should have primacy.
From another perspective, this may also suggest an opportunity to explore the potential for some flexibility in the application of toxicity values. For example, if a technically sound toxicological assessment is available from a source other than IRIS and is considered to represent an applicable toxicity value for risk assessment, the choice could be made to use this value in lieu of the IRIS value and justify that decision with a robust technical rationale.
Due for review
Because the new values being established through program office will be specific to that office, EPA recommends that external entities review their existing approaches to assess the applicability of previous reliance upon IRIS values, including documentation of the decision to use IRIS values and the associated rationale. This goes beyond simply confirming an existing approach or finding an alternative toxicity value.
This shift requires closer analysis, ensuring values were or are adopted based on regulatory acceptance. Regulated parties should also anticipate greater scrutiny, meaning documentation should be thorough and reinforce defensible rationale for the applied values.
Organizations without strong internal human and environmental health risk expertise should consider partnering with a consultant. With our extensive experience assisting industry, public agencies, and even other consultants with their risk assessment needs, Woodard & Curran is one of the premier providers of risk assessment services in the United States.
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