EPA’s IRIS Program Closure Signals a Major Shift in Chemical Risk Assessment

The U.S. Environmental Protection Agency’s (EPA) decision to dismantle its Integrated Risk Information System (IRIS) program marks one of the most consequential shifts in environmental health policy in decades. The move has immediate implications for chemical risk evaluation, regulatory consistency, and how environmental liabilities may be assessed moving forward.

For companies managing environmental exposures, remediation obligations, product stewardship programs, or emerging contaminant risks, this development deserves close attention.

What Was IRIS?

Established in 1985, EPA’s IRIS program served as the agency’s centralized repository for chemical hazard assessments. IRIS chronic toxicity values for cancer and noncancer health endpoints (cancer slope factors and reference values, respectively) have long informed regulatory and risk management decisions across multiple EPA programs, including:

• Superfund remediation
• Emissions standards for air toxics
• Drinking water standards
• Vapor intrusion evaluations
• State cleanup criteria
• Occupational and community exposure assessments

Although IRIS assessments were not themselves regulatory standards, they often became the scientific foundation underlying regulatory actions and risk-based screening levels. Multiple Federal programs such as the Air Toxics Screening Assessment and the Occupational Safety and Health Administration depend on IRIS values for their output.

Over time, IRIS also became deeply embedded in state environmental programs and private-sector risk assessment practices, and many states depend on IRIS values for their own risk assessments.

Why EPA is Closing IRIS?

According to EPA leadership, the agency is pursuing a broader restructuring of how risk assessments are developed and applied across regulatory programs. EPA officials have characterized the change as part of a “Gold Standard Science” initiative intended to improve transparency, consistency, and fitness-for-purpose in risk evaluation.

Critics of IRIS have argued for years that the program relied on overly conservative assumptions that produced toxicity thresholds disconnected from real-world exposure conditions. EPA leadership echoed those concerns in announcing the closure. Supporters of IRIS are concerned that the program’s end may weaken EPA’s ability to evaluate the risks of toxic chemicals.

The agency also indicated that individual program offices may now take greater ownership of chemical risk evaluations rather than relying on centralized hazard determinations developed through IRIS.

Why the Closure of IRIS Matters

The implications extend far beyond internal EPA structure.

1. Greater Regulatory Variability

One of IRIS’s primary functions was to provide a common scientific baseline across EPA programs and states. Without that centralized framework, regulatory offices may increasingly develop independent risk methodologies tailored to specific statutory programs.

This creates the potential for:

• Divergent toxicity values across programs
• Inconsistent cleanup thresholds
• Increased variability among states
• More uncertainty in risk-based decision making

For regulated entities, the result may be more fragmented compliance landscape.

Additionally, many state environmental agencies relied heavily on IRIS values because they lacked the internal resources to independently develop toxicological benchmarks. Former EPA officials have warned that the loss of IRIS could force states to create their own assessments or collaborate informally to fill scientific gaps. Over time, this could contribute to a patchwork regulatory environment where acceptable risk levels vary substantially across jurisdictions.

2. Increased Scrutiny of Existing Records

EPA leadership has directed program offices to review prior regulatory decisions that relied on IRIS assessments and determine whether updates are warranted.

This raises the possibility that some existing standards, guidance values, or remediation targets could face reevaluation – particularly for chemicals where IRIS assessments have historically driven aggressive risk estimates.

Ethylene oxide (EtO) is already emerging as an early example. EPA is reportedly reconsidering reliance on the 2016 IRIS assessment that significantly tightened perceived cancer risks associated with EtO exposure.

3. Reliance on Outdated Values

The EPA will continue to make IRIS assessments and other information available but will likely add disclaimer language to EPA’s IRIS website indicating that the values do not necessarily reflect the most up-to-date science and are not intended for use as regulatory levels.

What Are the Industry Implications Following IRIS’ Closure?

For companies operating in regulated industries, the transition creates both uncertainty and opportunity.

Organizations should expect:

• More case-specific risk evaluations (and more challenges to proposed values)
• Increased scrutiny of toxicological assumptions
• Potential reevaluation of remediation goals
• Greater importance of technical defensibility

At the same time, the absence of a centralized IRIS framework may create additional flexibility in certain contexts where conservative toxicity values previously constrained risk management options.

However, regulatory uncertainty itself can become a business risk – especially for long-term remediation projects, permitting strategies, transactional due diligence, and emerging contaminant management.

What Organizations Can Do Following IRIS Closure

Environmental and Environmental Health Science leaders should closely monitor:

• EPA program-specific guidance developments
• Changes to toxicity criteria for key chemicals
• State-level responses and independent criteria development
• Litigation trends involving risk methodology challenges
• Evolving expectations for risk assessment transparency

Companies with active remediation sites, air toxics exposure concerns, or chemicals under heightened scrutiny should also evaluate how changing federal methodologies could affect existing risk assumptions and future liabilities.

Looking Ahead

The closure of IRIS represents a significant change in how EPA may approach environmental health science and chemical risk assessment in the future.

Supporters of the change argue that integrating risk assessment more directly into individual program offices could improve efficiency, increase flexibility, and better align scientific evaluations with specific regulatory objectives. Critics, however, have raised concerns about the potential for reduced consistency across programs and states, as well as increased debate over how hazard and toxicity information are developed and applied.

Regardless of perspective, the transition is likely to reshape how chemical risks are evaluated across federal and state environmental programs. As EPA continues to define its revised approach, organizations should expect an evolving regulatory landscape with continued discussion around scientific methodologies, transparency, and the use of toxicity values in decision-making.

For regulated entities, maintaining awareness of these developments, and understanding how they may influence future risk evaluations, remediation strategies, and compliance obligations, will be increasingly important.

About RHP Risk Management

RHP Risk Management is an environmental and occupational health consulting firm of scientists, toxicologists, public health professionals, and risk assessors that cover practices including environmental engineering, industrial hygiene, exposure science, and human health interaction and risk assessment.

RHP works with clients to develop solutions to their most pressing concerns. Understanding exposures and risks through a grounding in a sound, defensible, state-of-the-art scientific approach gives our clients peace of mind. Empowered by a comprehensive understanding of exposure, we provide clients with reliable data and tools to recognize unseen business and liability risks, manage known risks, comply with regulations, and be better braced for regulatory or liability actions.

Contact RHP Risk Management by calling (866) 481-8188.