The weak link: gaps in exposure assessments

Protecting the public from the most concerning environmental chemicals and contaminants involves many individual steps. For example, when an agency like the US EPA or FDA evaluates a chemical used in consumer products, they want to evaluate: 

  • the hazards associated with that chemical,  
  • how that chemical causes harm,
  • how much of the chemical is released into the environment or enters the bodies of people, and
  • to what degree those exposure levels are anticipated to cause harm.  

Each of these steps is like a link in a chain, and a weakness in even a single one can break the entire chain.

Unfortunately, there are many weaknesses in one of the most important links in this chain: the approaches in exposure assessment. Exposure assessments use scientific approaches to understand and quantify exposures to chemicals. They might do this by measuring how much of a chemical is released by a pollution source, like a coal-fired power plant; or, they might calculate an exposure based on an equation looking at the amount of a pollutant found in a consumer product, like canned food, and an estimate of how much the average person consumes that product; or, they might measure the amount of the pollutant that is found in blood, urine, hair, or another bodily fluid or tissue and use that information to directly calculate a daily exposure.

A new approach

Of course, each of these approaches have some limitations, and those are important to understand and account for when quantifying exposures. Meanwhile, researchers in the field of exposure assessment continue to improve upon the scientific approaches they use to evaluate exposures and exposure sources. We took a different approach. In our recent publication, Addressing Systemic Problems with Exposure Assessments to Protect the Public’s Health, we focused on big-picture gaps in exposure assessments that weaken public health protections. Addressing these limitations in exposure assessments could have real-world benefits, especially for communities that are highly exposed to pollutants.

What’s really in your products shouldn’t be a secret

The first gap we identified is the massive number of chemicals currently in commerce, leaving many exposures entirely unknown. In some cases, the public remains in the dark because the identities of chemicals in consumer products are protected as trade secrets or confidential business information. In other cases, chemical pollution is suspected but cannot be quantified because the chemical manufacturers have not produced the chemical reagents that scientists need to measure the pollutant in products or in tissues and fluids collected from exposed people. Also challenging is that, even when exposures are assessed by a regulatory agency, they are typically examined one at a time instead of in the mixtures that are more relevant to environmental exposures.

The second gap we identified is that exposure assessments can quickly become out-of-date. For example, data use patterns for the herbicide glyphosate assumed that glyphosate was used to suppress weeds, and to support the growth of genetically modified crops that were designed to be resistant to the chemical. Yet, farmers also began to use glyphosate right before harvesting grains, which the current assessments didn’t account for. When they sprayed glyphosate on these crops, it helped them to dry out the grains, but it also left high residue levels on seeds, wheat, and oats. Updated exposure assessments would acknowledge that these new ways of herbicide use were significantly contributing to human exposure levels. 

The third gap we examined was the use of inadequate models and data in exposure assessments, and concerns that these assessments may not be based on the best available science. For example, when researchers first started studying how BPA is released from consumer products, they focused on canned food linings and hard, shatter-resistant plastics, since this is where BPA was known to be used by scientists. Yet, in the late 2000s, chemists discovered that industry was also using BPA in thermal receipt papers, a usage that was not originally disclosed to the public. With more and more studies recognizing that humans could be exposed to a significant amount of BPA just from handling receipt paper, there was similarly an acknowledgement that exposure assessments that did not account for this use were underestimating exposures.

Exposure assessments need to recognize the experience of frontline communities

These and other weaknesses in exposure assessments put communities at risk. Numerous communities, including those that live in or near Superfund sites, heavily polluted areas like Cancer Alley, and other fenceline communities are often rightly outraged when their concerns about exposures are not taken seriously. Even when people living in these communities report health concerns that they argue are due to their exposures, they often feel ignored or dismissed by public health officials. Thus, addressing gaps in exposure assessments would have immediate and measurable impact on communities like these, and for the public more generally. 

We’ve made a series of recommendations, some of which require relatively few resources to implement. These include the use of the precautionary principle in heavily polluted communities, and the use of the best available science to reduce contaminants to levels that are acceptable to the EPA and other regulatory agencies. We also recommend that agencies that evaluate exposures calculate how other aspects of the environment, including exposures to segregation, stress, racism and poverty can compound the effects of pollutants. Agencies also must acknowledge that chemical exposures occur in mixtures. Finally, we recommend that regulators recognize poorly studied sources of exposure and adjust for exposure uncertainties when calculating “safe” exposure levels. 

The methods that are used to protect the public from harmful environmental exposures is a chain with many interconnected links. Exposure assessments have been a weak link in this chain; it’s time for reinforcement.

This post is second in a series about our Roadmap papers, which provide scientific recommendations to update chemical risk assessment to better reflect exposures and hazards, guide decision-making, and protect the public’s health. Lead authors of the papers will discuss their recommendations on a webinar on Thursday, February 2nd. Register here:

Other blogs in this series:

About the Author

Laura Vandenberg, PhD is a professor of Environmental Health Sciences at the University of Massachusetts Amherst School of Public Health and Health Sciences. Trained as an endocrinologist and developmental biologist, Vandenberg’s research focuses on understanding the effects of endocrine disrupting chemicals after exposures occur during vulnerable periods of development.