On September 7, 2022, the Environmental Defense Fund (EDF) held a webinar to introduce a cumulative risk assessment (CRA) framework that takes into account multiple exposures to chemical and non-chemical stressors. Sarah Vogel, Senior Vice President for Health at EDF, moderated the webinar. According to Vogel, for decades, environmental justice leaders have documented disproportionate chemical exposures to disadvantaged communities. These chemical and social stressors (e.g., racism and lack of access to healthcare) contribute to adverse health outcomes. Vogel stated that the U.S. Environmental Protection Agency (EPA) ignores this reality, however, evaluating each chemical under the Toxic Substances Control Act (TSCA) in isolation. EDF is concerned that continuing this practice will perpetuate the injustices to these communities and other susceptible populations. As amended by the Frank R. Lautenberg Chemical Safety for the 21st Century Act (Lautenberg Act) in 2016, TSCA requires a holistic consideration of chemical risk and consideration of those at higher risk. To address this, EDF developed a CRA framework that provides a practical pathway for developing assessments under the framework of TSCA. The framework describes how EPA can scale up to yield fully inclusive and just assessments of chemical risk. EDF has posted a recording of the webinar.
Dr. Lariah Edwards presented an overview of the CRA framework. According to Edwards, chemical exposures amplify existing health inequities, and communities experiencing higher exposures are often more susceptible to the effects of a chemical. The Lautenberg Act amended TSCA to include explicit protection of vulnerable subgroups and to call for the holistic consideration of chemical risks. TSCA also requires the use of the best available science.
EDF’s CRA framework, which is available online as an interactive model, conceptualizes how EPA’s current risk evaluations can be incrementally scaled up to be more comprehensive and more protective. The framework is presented as an inverted pyramid, with a series of sequential steps. It includes five levels that begin with the least effective (Level 1) and advance to the most effective (Level 5) for performing risk evaluations. The levels consist of the following:
- Level 1 — Single-use risk from a single chemical: Limited evaluation of risk from specific uses of a single chemical substance, where numerous exposure sources are excluded and combinations of exposure are not addressed. Ultimately, according to EDF, these assessments are incomplete and serve to underestimate risk.
- Level 2 — Limited risk from a single chemical: Evaluation of risk from combined exposures to a single TSCA chemical. It considers all vulnerable subpopulations. An example of this type of assessment would include evaluating communities in the Greater Houston area that are disproportionately exposed to 1,3-butadiene.
- Level 3 — Aggregate risk from a single chemical: Expanded evaluation of risk from aggregate exposures to a single chemical accounting for background exposures from sources outside of the TSCA conditions of use (COU) or other unidentified sources. Risks are evaluated across the full lifecycle of the chemical substance. An example would be evaluated exposures to bis(2-ethylhexyl) phthalate (DEHP), a phthalate, from its use in electronics and paints/coatings (TSCA) and foods and medical devices (the U.S. Food and Drug Administration (FDA)).
- Level 4 — Cumulative risk from multiple chemicals: Complete evaluation of risk from exposure to multiple chemicals (or categories of chemicals) associated with the same health outcome(s). A CRA approach is consistent with the best available science as required under TSCA. A relevant example is ortho-phthalates, which have similar sources of exposure and many are linked to male reproductive effects.
- Level 5 — Cumulative impacts from chemicals and non-chemical stressors: Comprehensive evaluation of risk from both multiple chemicals and non-chemical stressors linked to the same health effects as the chemical undergoing risk evaluation. Noted above, this level ensures the protection of vulnerable subgroups by considering all their stressors, both chemical and non-chemical. An example of cumulative impacts would be an assessment of high stress among pregnant women and co-exposures to phthalates, which potentially leads to stronger associations with preterm birth.
Dr. Devon Payne-Sturges described how EPA, which is currently conducting separate risk evaluations for seven phthalates, could take this opportunity to incorporate CRA as part of its current risk evaluation. According to Payne-Sturges, to date, EPA has not signaled that it plans to do so. Payne-Sturges stated that a CRA of phthalates is warranted because the general population is exposed to a mixture of phthalates; the seven phthalates are similar in chemical structure, metabolism, and biological activity, including disruption of endocrine systems, and have common health outcomes; and the interactive effects of phthalate mixture exposures and with other chemicals have already been documented. Payne-Sturges noted that EDF is not the first group to make this argument, and that this is not the first time the argument has been made about phthalates. In its 2008 report, the National Academies recommended CRA of phthalates.
The webinar concluded with a question and answer session. Dr. Deborah Cory-Slechta joined Edwards and Payne-Sturges in responding to questions. The panelists emphasized the importance of considering the biology of different stressors and that the focus should be on common biological outcomes as an important and organizing principle. They also acknowledged the challenges with quantitatively assessing non-chemical stressors, which could possibly be addressed by the use of additional uncertainty factors (UF). Despite these challenges, the panelists noted that the CRA Framework is aligned with the steps in the risk evaluation process and will serve to allow for better use of science and avoid underestimating risks.
Commentary
Bergeson & Campbell, P.C. (B&C®) applauds EDF’s initiative in developing its CRA Framework. This body of work aims to address the limitations of regulatory risk assessments on chemical substances that have primarily applied a “one chemical, one risk assessment” approach (i.e., Level 1 from the CRA Framework). EDF’s introduction of cumulative impacts (i.e., Level 5 of the CRA Framework) provides a pathway for ultimately quantifying potential susceptibilities of subpopulations not just from multiple chemical exposures, but also from non-chemical stressors. The combination of these stressors may disproportionally enhance the susceptibility of subpopulations to single or multiple chemical exposures. Below, we provide a discussion of TSCA and offer considerations on the applicability and legality of the CRA Framework under TSCA.
B&C notes several aspects of the CRA Framework that would have significant implications for EPA and the regulated community as EPA evaluates chemical substances under TSCA. The threshold inquiry is, however, one that EPA must make. For example, TSCA defines the term “potentially exposed or susceptible subpopulations” (PESS) as:
[A] group of individuals within the general population identified by the Administrator who, due to either greater susceptibility or greater exposure, may be at greater risk than the general population of adverse health effects from exposure to a chemical substance or mixture, such as infants, children, pregnant women, workers, or the elderly [emphasis added].
EPA’s Office of Pollution Prevention and Toxics (OPPT) has the delegated authority of administering TSCA. Therefore, OPPT’s management would have to identify susceptible subpopulations that may be at greater risk. This could potentially be aligned with the CRA Framework. For example, EPA could focus on including the following considerations in its risk evaluations when identifying PESS: (1) subpopulations with higher exposures to individual chemical substances (i.e., Levels 1-3 of the CRA Framework), (2) subpopulations with multiple chemical exposures at variable levels that may collectively have the potential to cause effects equivalent to or greater than higher exposures to individual chemical substances (i.e., Level 4 of the CRA Framework), and (3) subpopulations with non-chemical stressors that enhance their vulnerability to individual and multiple chemical exposures (i.e., Level 5 of the CRA Framework).
At present, OPPT has taken steps to identify PESS that are consistent with the first consideration, in part, by issuing its “Draft TSCA Screening Level Approach for Assessing Ambient Air and Water Exposures to Fenceline Communities” document. Once finalized, this document has the potential to improve OPPT’s risk evaluations in a manner comparable to going from a Level 1 to a Level 2 assessment under the CRA Framework.
OPPT also has the authority under TSCA to perform risk evaluations in a manner consistent with Level 3 of the CRA Framework (i.e., aggregate risk). Though such an approach would be consistent with the scientific standards under TSCA Section 26, the issue with OPPT’s consideration of aggregate risk (i.e., quantified risk from exposures to a chemical from TSCA COUs and non-TSCA COUs regulated by other agencies) is that OPPT is limited with taking risk management action on unreasonable risk determinations from aggregate exposures that only occur from TSCA COUs. Performing an aggregate risk assessment would, however, give OPPT an opportunity to coordinate with other federal agencies under TSCA Section 9, if for example, OPPT did not identify unreasonable risks from exposures via TSCA COUs, but it did when considering aggregate exposures for TSCA COUs and non-TSCA COUs (e.g., food packaging or personal care products).
B&C also acknowledges that OPPT has taken steps consistent with the second consideration (i.e., Level 4 of the CRA Framework). The webinar panelists noted that other offices within EPA perform CRAs (i.e., Level 4 of the CRA Framework). We also note that OPPT has performed cumulative-like risk assessments. For example, OPPT’s original cyclic aliphatic bromide cluster included two forms of hexabromocyclododecane and 1,2,5,6-tetrabromocyclooctane. This supports the view that OPPT does have the established technical expertise with considering exposures from multiple chemical substances that may be associated with common health effects. We further note that OPPT could use its TSCA Section 4 Test Order authority to improve its understanding of common health effects caused by multiple chemical stressors in a manner consistent with OPPT’s recent issuance of its first TSCA Section 4(a)(1) Test Order on 6:2 fluorotelomer sulfonamide betaine.
B&C views the third consideration (i.e., Level 5 of the CRA Framework) as the most challenging for EPA’s identification of PESS. The webinar panelists mentioned several peer-reviewed studies that inform the impact that non-chemical stressors may have. They also acknowledged the lack of consensus on how to account for non-chemical stressors in CRAs. One of the panelists noted the possibility of addressing this through the use of UFs. B&C notes that if OPPT decides to consider non-chemical stressors in its evaluations under TSCA, it will have to consider including evaluation criteria within its current draft systematic review protocol for studies of this type. We further note that addressing non-chemical stressors through the use of UFs represents a pragmatic path forward, given the scientific uncertainties associated with non-chemical stressors and identification of PESS. OPPT will have to decide as a matter of science policy, however, whether it will include an additional UF in its risk assessments for non-chemical stressors. Alternatively, OPPT could, for example, change the magnitude of a default value used for one of its current UFs (e.g., intraspecies UF, default of 10). Regardless of its decision, OPPT will have to provide the scientific justification for the value used for a new UF or a modified existing UF.
B&C encourages readers to read EDF’s CRA Framework Report. It provides greater details on the underlying scientific support that went into developing this groundbreaking document. We are confident that OPPT will consider EDF’s CRA Framework as it moves forward with prioritizing and performing risk evaluations under TSCA, especially as the underlying science matures. We suspect, however, that given OPPT’s workforce and resource constraints, its consideration of the CRA Framework will require stepwise considerations, along with active engagement with members of the public on the most critical elements of the CRA Framework to incorporate in the near- versus long-term chemical risk evaluations.