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EPA’s proposed rule on transparency in regulatory science gets it right when it comes to the best available science and non-linear modeling approaches

At ACC we’re still doing a deep dive in our review of EPA’s recently proposed rule: Strengthening Transparency in Regulatory Science. We look forward to submitting comments to help the agency ensure the final rule increases transparency and public confidence in the agency’s regulations while protecting personal privacy, confidential business information, proprietary interest and intellectual property rights. That said, one thing we already know they got right is the rule’s focus on dose response data and models.

For far too long and far too often EPA has relied on default linear dose-response models that have frequently resulted in inflated risk estimates. These inflated risks create misperceptions and confusion about true risks and can lead to unwarranted and costly risk management decisions. The good news is that EPA’s proposed rule calls on agency scientific staff and decision makers to give appropriate consideration to non-linear models or threshold models (i.e. dose models that show a level of exposure to a substance below which no harm is expected to occur). In other words, to use the best available science by presenting non-linear modeling approaches consistent with the available data and scientific understanding of endogenous exposures and mode of action, in lieu of, or at a minimum in addition to, the linear default.

EPA shall evaluate the appropriateness of using default assumptions, including assumptions of a linear, no-threshold dose response, on a case-by-case basis. EPA shall clearly explain the scientific basis for each model assumption used and present analyses showing the sensitivity of the modeled results to alternative assumptions. When available, EPA shall give explicit consideration to high quality studies that explore: A broad class of parametric dose-response or concentration-response models; a robust set of potential confounding variables; nonparametric models that incorporate fewer assumptions; various threshold models across the dose or exposure range; and models that investigate factors that might account for spatial heterogeneity.”

The proposed provision has been characterized in some corners of the environmental NGO blogosphere as granting industry an “ask.” Wrong. It’s simply a recognition by EPA that old default assumptions may not always represent the most up to date science.  Notably, it is an approach a strong bi-partisan majority of Congress supported in the 2016 amendments to Section 26 of the Toxic Substances Control Act:  When it comes to the science, EPA should “show its work.”

Backed by the best available 21st century science, ACC has long advocated for use of non-linear, threshold models in cases where available data and scientific understanding support such models. In fact mode of action and non-linear models are integral components in our well-known Risk Principles, found here and here.

UTILIZE MODERN SCIENTIFIC INFORMATION AND TOOLS RATHER THAN CONTINUING TO RELY ON OUTDATED ASSUMPTIONS: Reliance on defaults should be minimized. In many cases, government hazard and risk assessment programs rely on assumptions and default approaches developed in the 1970s [i.e., linear, no-threshold dose response]. Today’s scientists and health professionals have a wealth of knowledge including 21st-century understanding of how the human body works and the way chemicals interact with the body [i.e., mode of action and non-linear dose response] and the environment at different levels of exposure. This modern-day knowledge must be applied when determining chemical safety.

CHARACTERIZE HAZARDS AND RISKS FULLY AND ACCURATELY: Hazards and risks must be objectively characterized and presented in a manner understandable to stakeholders and risk managers. The characterization should provide a full picture of what is known and what has been inferred and should also present results based on alternative plausible assumptions [i.e., not just the default, but also scientifically plausible modes of action and non-linear dose response]. When a screening level assessment indicates potential concern, prior to initiating additional risk management actions, a refined assessment should be conducted to more accurately determine hazards or risks. When going beyond screening level, assessments should include central estimates and ranges; it is not sufficient to rely on theoretical maximum exposure estimates to characterize potential risk.

EPA got it right. We welcome this aspect of the Strengthening Transparency in Regulatory Science proposed rule and look forward to working with the agency to help ensure that it continues to recognize and act on advances in scientific knowledge and the best available, most relevant scientific data and integrates this into its regulatory decision making processes.

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