Fall 2023

Cumulative Risk Assessment and Environmental Justice: A Growing Partnership

By Ari S. Lewis, M.S.

The critical role that cumulative risk assessment could play in environmental justice initiatives is clear, but the road forward has proven to be a long and complicated one.

While much of our understanding of chemicals and how they affect human health and the environment has developed one chemical at a time, the United States Environmental Protection Agency (US EPA) has been steadily developing strategies to better quantify multi-chemical, multi-exposure risks for more than two decades (Lewis et al., 2011).  Progress on this cumulative risk approach has mainly manifested as the assessment of similar chemicals with an overlapping toxic mode of action.  For example, in 2001, US EPA conducted a cumulative risk assessment for organophosphate (OP) pesticides, a class of pesticides that have a common, primary mechanism of action (US EPA, 2004).  In a recent example, however, the agency reflects its current thinking on this topic in its draft Toxic Substances Control Act (TSCA) priority risk assessment of phthalates, which was released in February 2023 and is currently under US EPA review.  The document emphasizes an expansive consideration of multi-pathway exposures, but, notably, restricts the analysis to similar chemicals and does not consider “non-chemical stressors” (see below for further discussion on non-chemical stressors) (US EPA, 2023a).

In addition to developing methodologies to quantify human health risk for multi-chemical exposures, the US EPA has an agency-wide objective to characterize risk in vulnerable populations.  While the agency defines vulnerability as “[c]haracteristics of individuals or populations that place them at increased risk of an adverse health effect,” it clarifies this definition further to address a whole host of factors (US EPA, 2023b).  These factors include more traditional biological aspects that may make an individual or group more susceptible to disease, such as youth, advanced age, and pregnancy, as well as aspects that have not been routinely addressed in quantitative human health risk assessment, such as psychological and social factors.  Of late, other factors as diverse as noise, radiation, crime, and nutritional deficits are being introduced into the vulnerability conversation.  Collectively, aspects of vulnerability that can contribute to disease are referred to as “non-chemical stressors.”

While the connection between cumulative risk assessment and EJ initiatives has been strategically visualized, the science-based application of cumulative risk assessment principles in EJ communities has been hampered by its complexity.”

The objective to more holistically understand chemical exposures and vulnerability has become integrated within the discipline of cumulative risk assessment.  According to US EPA guidance, cumulative risk assessment is “an analysis, characterization, and possible quantification of the combined risks to health and/or the environment from multiple agents and/or stressors.”  Though the idea to incorporate non-chemical risk stressors into the cumulative risk paradigm was first mentioned as early as 1997, US EPA’s “Framework for Cumulative Risk Assessment” report in 2003 was the first to formalize the connection between more traditional chemical-related health evaluations and non-chemical stressors (US EPA, 2003).  Although the report did not offer specific methodology, it did explicitly promote the consideration of non-chemical stressors in the risk assessment process.  Non-chemical stressors, including the impacts of low income, having limited access to health care, and experiencing psychosocial stress, were not commonly within US EPA’s regulatory purview at that time.

The growing interest in the interplay between multi-chemical exposures in vulnerable populations has bridged a connection between cumulative risk assessment and environmental justice (EJ) initiatives.  There are two key principles to EJ:

  • Enhancing community engagement in the regulatory process; and
  • Ensuring that communities receive fair treatment with respect to environmental laws.

The second principle focuses largely on ensuring underserved communities (i.e., communities with myriad vulnerabilities) are not overburdened with chemical exposures (i.e., multiple exposures).  Given these objectives, it is clear why cumulative risk assessment has emerged as a tool to address EJ concerns.  In fact, the National Environmental Justice Advisory Council (NEJAC), a US EPA advisory group, made the explicit connection between cumulative risk principles and EJ initiatives in a 2004 report (NEJAC, 2004).  In addition, subsequent US EPA documents echo this connection, as does the landmark National Research Council (NRC) 2009 report Science and Decisions:  Advancing Risk Assessment (NRC, 2009).

While the connection between cumulative risk assessment and EJ initiatives has been strategically visualized, the science-based application of cumulative risk assessment principles in EJ communities has been hampered by its complexity.  For example, as late as 2016, the US EPA’s “Technical Guidance for Assessing Environmental Justice in Regulatory Analysis,” noted that “[e]stablished methods are not available for modeling the effects of many non-chemical stressors that are important to an analysis of potential EJ concerns.  Such stressors (e.g., nutritional deficits, stress) may interact with chemical stressors to exacerbate or mitigate health outcomes; the ability to model such interactions is still in the nascent stages of development” (US EPA, 2016).  In the face of this complexity, US EPA has dedicated significant resources to develop tools that help provide perspective on the intersection between cumulative risk and EJ.  These tools, however, produce screening-level results that cannot replace community- and issue-specific assessments that are meant to occur under a cumulative risk framework.

Despite limited gains throughout the early 2000s, the Biden-Harris Administration has prioritized environmental initiatives and, in doing so, has dedicated significant resources to developing the science and strategies for cumulative risk assessment.  In fact, after much delay, the US EPA released its draft “Guidelines for Cumulative Risk Assessment Planning and Problem Formulation” in May 2023 (US EPA, 2023b).  In addition to this document, US EPA has released a series of documents over the past year that promise to shape how cumulative impacts and risk assessment interplay with regulatory initiatives (see Figure).  Note that some of the documents refer to “cumulative impacts,” potentially a more qualitative assessment, rather than cumulative risk, which may represent a more quantitative assessment, though the distinction is not clearly articulated.  One particular area where cumulative risk considerations will intersect with regulations is during facility and infrastructure permitting, such as projects subject to the National Environmental Policy Act (NEPA).  These assessments require an explicit demonstration that prospective projects will not cause disproportionate impacts in vulnerable communities.

Key Recent US EPA Guidance Documents Related to Cumulative Risk Assessment

Illustration of urban area with buildings and cars depicting various low-cost sensor icons

Click to Enlarge Figure.

The notable increase in guidance documents released in the past year highlights the commitment by regulators to consider cumulative risk assessment principles in their decisions.  How the rubber meets the road, however, is still to be determined.  The next few years will be formative for cumulative risk assessment, and the application of its principles will likely take root in various forms across an array of regulatory initiatives.  At this point in time, engaged practitioners and stakeholders should play a large role in shaping this important risk assessment advancement.

Contact Info

The author can be reached at alewis@gradientcorp.com.


Lewis, AS; Sax, SN; Wason, SC; Campleman, SL. 2011. “Non-chemical stressors and cumulative risk assessment: An overview of current initiatives and potential air pollutant interactions.” Int. J. Environ. Res. Public Health. 8:2020-2073. http://www.mdpi.com/1660-4601/8/6/2020/pdf.

National Environmental Justice Advisory Council (NEJAC), Cumulative Risks/Impacts Work Group. 2004. “Ensuring Risk Reduction in Communities with Multiple Stressors: Environmental Justice and Cumulative Risks/Impacts.” Submitted to US EPA. 178p. December.

National Research Council (NRC), Committee on Improving Risk Analysis Approaches Used by the US EPA. 2009. Science and Decisions: Advancing Risk Assessment. [The Silver Book.] National Academies Press (Washington, DC). 421p. Accessed on August 9, 2023, at https://nap.nationalacademies.org/catalog/12209/science-and-decisions-advancing-risk-assessment.

US EPA, Risk Assessment Forum (Washington, DC). 2003. “Framework for Cumulative Risk Assessment.” EPA/630/P-02/001F. 109p. May. Accessed on May 28, 2003, at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm.

US EPA, National Center for Environmental Assessment (NCEA), Superfund Health Risk Technical Support Center. 2004. “Provisional Peer Reviewed Toxicity Values for Benzothiazole (CAS No. 95-16-9).” 24p. November 23.

US EPA. 2016. “Technical Guidance for Assessing Environmental Justice in Regulatory Analysis.” 120p. June.

US EPA, Office of Chemical Safety and Pollution Prevention. 2023a. “Draft Proposed Principles of Cumulative Risk Assessment Under the Toxic Substances Control Act.” EPA-740-P-23-001. 22p. February.

US EPA, Risk Assessment Forum. 2023b. “Guidelines for Cumulative Risk Assessment Planning and Problem Formulation.” 73p. May.