Re-visioning TSCA: Address the cumulative impacts of chemical exposures

Richard Denison, Ph.D., is a Lead Senior Scientist.

Part 4 of a 4-part series see Part 1, Part 2, and Part 3 here

This series of blog posts is looking ahead toward opportunities to advance a more robust and holistic vision for implementing the Toxic Substances Control Act (TSCA) as reformed in 2016.

We discussed in the preceding installments of this series the importance of ensuring that combined exposures to a chemical from multiple sources and the greater exposures and susceptibilities of certain groups are accounted for.  But it is critical to also recognize that many other factors influence the impacts chemical exposures have on our health.  This final installment in our series will discuss how TSCA can and should take into account all of these factors – that is, account for cumulative impacts.

Recognition of the need to address cumulative impacts has been around for many years but rarely acted on.  EPA has a framework for cumulative risk assessment dating back to 2003, but its use has been limited and it may need to be updated.

There is every reason for the Biden EPA to start applying cumulative approaches to its chemical assessments under TSCA – something that EPA’s own Children’s Health Protection Advisory Committee (CHPAC) recently recommended.

In 2008, the National Research Council of the National Academies published a report titled Phthalates and Cumulative Risk Assessment:  The Tasks Ahead that provided a roadmap to conducting just such an assessment on just such chemicals.  One near-term opportunity to advance a cumulative risk approach under TSCA is to conduct such a risk evaluation for the six chemicals in the phthalates category for which risk evaluations were recently initiated.

While further advances in the science will help strengthen the application of cumulative approaches to chemical assessments, there is every reason for the Biden EPA to start doing so now under TSCA.  EPA’s own Children’s Health Protection Advisory Committee (CHPAC) recently recommended just that.

Why is a cumulative impact approach so critical? 

We know that we are not exposed to one chemical at a time, but rather to complex mixtures of chemicals, whether in our air or water, materials in our homes and workplaces, or products we use.  These “co-exposures” can amplify the effects of exposure to a chemical being assessed.  Different chemicals can lead to the same or similar health effects, and exposure to one chemical can increase the likelihood of another chemical having an adverse effect.  And compromised health status due to prior chemical exposures can make a person more susceptible to the effects of another.

Scientific studies (see, for example, here, here and here) have also identified non-chemical “stressors” that can exacerbate the effects of chemical exposures.  These factors may be individual, socio-economic or environmental.  Genetic differences (e.g., variation across the population in genes that affect how well we can metabolize toxic chemicals) can increase an individual’s susceptibility to the effects of a chemical; so too can pre-existing health conditions.  Life stage (e.g., in utero or infancy vs. adulthood) impacts susceptibility.  We noted in the preceding installment in this series above how social determinants of health such as proximity to sources of pollution, access to health care, and racism can alter groups’ risk, by increasing exposure or susceptibility.  Exposure to air pollution or excessive heat are examples of environmental stressors.

Some people are subject to more of these stressors than others, and it is the combined effect of all stressors to which individuals or groups are subject that comprises the cumulative impact of chemical exposures.  If we are serious about addressing health inequities we must do a better job of considering the cumulative impact of these multiple determinants of health.  Moreover, all of these factors are relevant as EPA identifies, evaluates, and mitigates risks to “potentially exposed or susceptible subpopulations” under TSCA.

The Trump EPA gave short shrift to such factors in its risk evaluations.  It repeatedly failed to explicitly quantify or characterize the increased risk individuals face because of increased susceptibility due to genetic factors or pre-existing health conditions.  It also failed even to identify, let alone assess, the heightened risks faced by fence-line and other communities whose residents are disproportionately exposed or experience multiple stressors on top of exposure to the chemical being evaluated.

An opening under TSCA

Looking forward, TSCA presents both challenges and opportunities to robustly address cumulative impacts.  One challenge inherent to TSCA is that the entry point into its processes and procedures is through an individual chemical or a category of related chemicals.  Prioritization, evaluation and regulatory decision-making are focused on that chemical or category.

But despite that constraint, there is ample room for EPA to use TSCA to advance the practice of cumulative risk assessment.  Such approaches are allowed, and one could argue are in some respects mandated, by TSCA requirements discussed in our previous posts in this series:  the requirement that EPA identify, assess and protect against risks to subpopulations subject to greater exposure or greater susceptibility, which demands that EPA consider all factors that could increase exposure to or a chemical’s effect on an individual or group; and TSCA’s requirement that EPA use best available science, which supports if not requires a cumulative risk approach wherever possible.



The past four years wreaked considerable damage on TSCA’s implementation and there is a clear need for the Biden EPA to take steps to undo as much of that damage as possible and sharply depart from the legally and scientifically flawed approaches taken by the Trump EPA.  But even as it works to right the ship, EPA’s new leadership – and the nation – can’t afford to lose the opportunity to advance a more robust and holistic vision for this law, the seeds of which are embedded deeply in some of its core provisions.

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