Understanding the Science to Better Protect the Public from Cumulative Impacts 

January 23, 2023 | 3:45 pm
Dr.s Devon Payne-Sturges and Richard H. Sprinkle
Kristie Ellickson
Kendall Fellow

An interview with two leading scientists in the emerging field of cumulative risks and impacts

Scientists call the many thousands of toxic chemicals that enter our environment “toxicants.” As they persist and mix, we’re exposed to them in ways both obvious and subtle. Do they accumulate in our bodies? Do they harm us? Do US environmental laws recognize “cumulative risks” and “cumulative impacts” as real and substantial? And are cumulative risks and impacts worse in communities that experience more social adversity? The answers to all these important questions increasingly seem to be yes. 

Working in this field has meant interacting with experts from various backgrounds, areas of study, and experiences who are working to enact more holistic and protective environmental policies. After participating in a workshop on this topic at the University of Maryland (UMD), I had a conversation with the two UMD professors who hosted and organized the event. We spoke about the science and regulatory authority to move beyond a one chemical-one source approach.  

Dr. Devon Payne-Sturges (pictured above left, and hereafter “DPS”) is a Doctor of Public Health (Dr. PH) at the UMD School of Public Health who specializes in cumulative environmental health risks and social disparities and has published on systems approaches to environmental health protections. Dr. Robert H. Sprinkle (above right, and hereafter “RHS”), an MD/PhD, works at the intersection of politics and the life sciences at the UMD School of Public Policy and has published on clinical medicine, health policy, bioethics, bioengineering, biosecurity, environmental health, environmental policy, and policy history. The two collaborate on the subject of cumulative risks and impacts and I had the chance to ask them some questions about their thoughts and perspectives.  

What are some of the key things people should know about US policies protecting them from cumulative risks and impacts? 

DPS: Cumulative risks and impacts represent the biggest silent regulatory policy failure that is robbing us of our physical, cognitive, and mental health and well-being. I compare it to a saying about counting calories… we’re often advised to “count calories” to maintain good body weight and prevent heart disease, diabetes, and cancer, but we aren’t similarly counting chemical exposures to prevent adverse health outcomes. 

RHS: We now realize that the “exposome” [the sum of all exposures experienced over the course of an individual’s life] is much bigger and more varied than previously realized. Within clinical medicine, it’s absolutely no problem to imagine that these exposures over time, complex rather than simple, have different morbidity and mortality impacts than they would have had individually, one at a time. 

Can you talk a bit about the science supporting cumulative risk and impacts policy? 

RHS: Years ago, I read a paper reporting reproductive anatomical abnormalities in male rat pups after gestational exposure to a mixture of different chemicals (antiandrogens) whose individual doses were assumed to be safe. Some of the tested mixtures injured the pups not just additively, as expected, but far more than additively—which was to say synergistically. We used the same principle therapeutically, hitting cancer cells at different vulnerable spots or stages simultaneously or in sequence, or using antibiotics with different mechanisms simultaneously. This was not a foreign concept from a life-sciences perspective. But it was already being greeted, or avoided, as a foreign and highly disruptive concept from regulatory, civil-liability, and public-health perspectives. That’s where I started. 

DPS: In addition, we have evidence that social conditions (non-chemical stressors) can act as an accelerant or a magnifier of harmful effects. Children from low-income households exposed to lead have worse outcomes than children from wealthier families. This contributes to intergenerational poor health.  

RHS: There are three mechanisms by which a non-chemical stressor may exacerbate the effect of a chemical stressor or a mixture of chemical stressors, even at low dose.

First, environmental effects may produce a stress response. Cortisol and adrenaline are released. Blood pressure goes up, and cardiovascular and renal risks rise. The assumption that a chronic stress response would have no impact on a toxicant’s effect — a chemical stressor’s effect — is fading

Secondly, an injury may be epigenetic, a modification of gene expression rather than an alteration of the genetic code itself. An epigenetic effect can be passed along through several generations. 

And third, many people live where they must instead of where they would wish. That means they often live in communities where land values are low, and where polluting industries are nearby. Individuals in these communities are exposed to more and different toxicants all the time. By “all the time,” I mean prior to conception, during embryonic and intrauterine life, while being breastfed, and while growing. 

DPS: An EPA research laboratory run by scientist, Dr. Earl Gray, has exposed animals to mixtures of chemicals, each below its “no observed-adverse-effect level.” His work shows that the combination of exposures to individual contaminants at these low levels can lead to adverse health outcomes, meaning they produce cumulative toxicity. Dr. Deborah Cory-Slechta’s research is also focused on animal models of exposures to both stress and metals; exposing animals prenatally and postnatally to chemicals and other toxic contaminants or conditions that interact and jointly impact the brain.  

I’m interested in cumulative risk because it is how you take all this evidence about the additive and synergistic effects [the combined effect being greater than the sum of individual effects] of multiple chemical and non-chemical stressor exposures and translate it into policy. 

RHS: The first studies (in the 1940s and 50s) with irrefutable evidence showing increased risk of lung cancer from smoking were significant, but the added risk identified seems low in retrospect. The reason is that, back then, everybody was exposed. That meant that there were many lung cancers in people who were not smokers. We’ve got a similar situation now with the chemical “exposome” issue: everybody’s exposed. In US government data from the National Health and Nutrition Examination Survey (NHANES), we see industrial chemicals in low concentrations but “pre-mixed” in pregnant women — in their blood, fat, and breast milk — and in their babies. 

What policies or laws are possible right now to address cumulative risks and impacts? 

RHS: You might wonder why we’re talking about cumulative risk as anything but obvious. It’s because risks have been assessed very carefully in laboratory settings delivering one chemical in one way to animals over the lifespan. In terms of professional culture within this field of expertise, it is quite foreign to do this any other way.  

But the accumulation of chemicals and exposures is contrary to the way litigation is advanced in court — in torts, in civil cases. As quoted in our paper, Dr. Ellen Silbergeld says, “to regulate mixtures, the law must be changed.” She’s right. 

Imagine toxicants flowing off a pasture in the rain. They are manufactured by different companies and used in different but supposedly safe amounts at different times. You couldn’t implicate one chemical individually without its manufacturer saying, “My chemical is well behaved. It just fell into a bad crowd.”  

The fact that we’re having this discussion is a consequence of the way this science has been done for a long time and the way laws have been written. To some degree, to protect the public, but to a great degree to protect chemical manufacturers. 

How do you regulate complexity?  

RHS: The answer has been for decades that you don’t go anywhere near it. And the reason being, you can’t do that. You regulate what you can pick up from complexity as if a laboratory bench or a laboratory animal were its true environment. This approach has been extremely successful, but it leaves many questions not just unanswered but un-askable.   

Regulating environmental mixtures chemical-by-chemical without simplifying complexity or ignoring low-concentration synergy is, let’s face it, impossible from a case-by-case impacts perspective. And, some would say then, pointless from a risk perspective. But let’s cut the Gordian knot here. Devon and I assert that impossibility is not the problem. Impossibility is the message. As we say in our paper, if toxicants cannot be accepted within the environment then toxicants must not be accepted into the environment. The policy prescription isn’t magical. It isn’t easy. But it is obvious. We need to minimize the exposome by, first, decelerating its expansion. Even that first step, deceleration, would be a high hurdle to clear technologically and politically. 

DPS: At EPA, I was involved in initiatives to move cumulative risk assessment into decision-making. It was a complete struggle. I have done a systematic research project to understand the internal barriers at environmental regulatory agencies that are important to address. 

RHS: The environmental justice non-chemical stressor argument has been pounding on the door of the science of chemical stress. The door has remained closed because the people on the other side have been saying, “We do chemicals here, not non-chemicals.” No surprise. 

DPS: Some of the barriers to progress have to do with this very traditional toxicological approach to environmental regulation. We need a broader perspective. 

What policies might we be able to implement 10 years from now?  

DPS: Cumulative risk and impacts is on the national agenda because of environmental justice and community advocacy work [read more about that here and here]. EPA has legal authority; they need to be creative about how to use it. We discussed at our workshop, that some regulatory language is written quite broad and there are windows of opportunity. 

I think opportunities include: 

  • Regulate chemicals that share a health effect. Regulate them as a class/group instead of one at a time, such as PFAS or phthalates.  
  • Incorporate evidence of vulnerability or susceptibility to non-chemical stressors into EPA health-based standards. 
  • Dedicate more resources to inspections and enforcement.  
  • More multi-media coordination [such as between regulations of air pollutants and water pollutants, etc.] 
  • Put as much energy toward solutions to reduce and prevent impacts as has been put into creating cumulative impacts mapping tools. 
  • Make every risk assessment a cumulative risk assessment.  
  • Adopt cumulative risk/impacts perspective broadly and consistently as part of the culture inside all levels of government.  

RHS: You must begin to decrease the exposome, first just by slowing its expansion, then by bending its curve down decisively. The EPA is not the only player (other federal agencies have a role). You need epidemiology, medicine, especially endocrinology, and other life-sciences fields. We need an overarching national director role to make sure that every logically involved life sciences discipline is incorporated to improve environmental health.  

Window of opportunity 

As these experts explain, there is a unique window of opportunity within the current EPA administration. The agency is paying attention to these issues right now, and despite the complexity, experts in the scientific, community, and environmental justice fields are ready and available to do the work. The benefits to public health from this type of a regulatory paradigm shift would be enormous! 

About the author

More from Kristie

Kristie Ellickson is a Kendall Fellow at the Center for Science and Democracy at the Union of Concerned Scientists. Her research focuses on the integration of the elements of cumulative risk and impacts into regulatory analyses and decisionmaking. In her role, Dr. Ellickson builds on past cumulative impacts work from her experience as a state scientist in Minnesota.