Science, Policy & Risk Perspectives: Sound Science and Transparent Scientific Methods Must Be the Foundation for Cumulative Risk Assessments
The American Chemistry Council’s (ACC) Science, Policy & Risk Perspectives blog series provides recommendations to improve EPA’s TSCA risk evaluation process and the Agency’s continued implementation of the law. This series will focus on several key science areas, such as application of systematic review, understanding workplace exposures, utilizing new approach methods, incorporation of mode of action information, all of which are critical for science-based decision-making.
Assessing cumulative risk is a very complex scientific endeavor. In chemical risk assessment policy discussions, cumulative risk is a term generally used to describe co-exposures to multiple chemicals, and/or non-chemical stressors, from multiple sources. As you might expect from that description, whether used in regulatory, community-based, or broad disease causation investigation contexts, cumulative risk involves understanding multiple pieces of scientific information to draw conclusions about human health risk.
The scientific complexity in assessing cumulative risk, however, hasn’t stopped federal and state lawmakers from proposing requirements for cumulative risk assessments (CRAs). Recently, CRAs have been proposed to address environmental justice (EJ) concerns. These proposals aim to address cumulative impacts on minority and low-income communities from disproportionate levels of co-exposures to multiple chemicals from multiple environmental sources, including industrial facilities. Some of these proposals would require cumulative impact assessments to inform facility permitting decisions and site remediation actions under federal and state air/water/waste laws. While the broad EJ objectives of these proposals are well intended, the difficulties of implementing CRAs on this scale cannot be ignored.
While certain cumulative screening methods, like EPA’s Risk-Screening Environmental Indicators (RSEI) model, have been developed to help identify potential priorities for more in-depth evaluation, such models, and RSEI in particular, do not calculate scientifically accurate levels of actual risks of adverse effects or disease outcomes. In fact, EPA clearly states that “RSEI Scores do not describe a level of risk (such as the number of excess cancer cases)” and “RSEI does not perform a risk assessment, but is rather a screening-level tool to help identify situations of potential concern. Additional investigation should always be performed before any conclusions regarding risk are made …” Cumulative risk analysis, as noted above, is scientifically complex, and considerable care needs to be taken to avoid misuse and miscommunication of results from screening approaches such as RSEI.
There has been a recent call by some to implement the use of CRAs in TSCA risk evaluations, particularly when evaluating the risks posed by multiple TSCA chemicals to fenceline communities near industrial facilities. Setting aside for a moment the question of whether fenceline communities are subpopulations envisioned under TSCA, their hope is that EPA’s Office of Pollution Prevention and Toxics will use TSCA risk evaluations and determinations to force other EPA program offices to strengthen air/water/waste regulations under other federal environmental laws to protect fenceline communities.
The 2016 TSCA amendments require EPA to address risks to potentially exposed and susceptible subpopulations (e.g., infants, children, pregnant women, etc.) when these subpopulations are relevant to a TSCA risk evaluation. And while TSCA doesn’t require EPA to consider cumulative risk in TSCA risk evaluations, it also doesn’t prohibit the agency from doing so either.
It is important to develop science-based approaches for appropriately assessing cumulative risk before applying it to TSCA for a few reasons. First and foremost, the more recent fenceline CRA proposals are very light on the science that would be needed to conduct a CRA in the TSCA risk evaluation context. They propose simplistic approaches -- like just adding together disparate impacts and potential risk factors in ways that are not based on best available science. Simplistic and flawed approaches, based on unsupported assumptions – assumptions that fall well short of the legal mandate under TSCA for the Agency to use best available science – would likely lead to flawed conclusions that raise undue concerns about the potential impacts of chemical uses and industrial facilities.
If EPA decides to pursue CRAs in certain TSCA risk evaluations, it must rely upon scientifically-established procedures to evaluate cumulative risk that do not group all chemicals together inappropriately.
Further, EPA must evaluate all determinants of health effects and impacts – biological, behavioral, environmental, and social. Each of these factors can play important roles in the health outcomes of a fenceline community. EPA would need to document and rely upon scientific understanding of cause and effect, strength of association, and the quality of the available data to understand the contribution of each of these factors. Unless EPA uses scientific procedures that consider all these factors for CRAs in the fenceline community context, its TSCA risk evaluation decisions, based on these CRAs, will not meet the best available science requirements under TSCA. As a result, EPA’s risk determinations would be neither scientifically sound nor sufficiently credible to provide the foundation for reasonable and defensible risk management decision making under TSCA.