CRAs can help EPA more accurately estimate risks from toxic chemical exposures

When a nail salon worker heads home after work, she’s probably carrying more than her paycheck. She is also carrying phthalates — a class of toxic chemicals that contaminates people via nail polish, cosmetics, cleaning supplies, plastics, and food. One nail salon worker is exposed to multiple chemicals from many different sources, yet regulators like EPA typically evaluate chemicals for risk one chemical at a time and one exposure at a time, an approach that fails to reflect real-world exposures.

Fortunately, methods exist to capture the impact of exposure to multiple chemicals. They’re called “cumulative risk assessment” or “CRA” and experts, including the National Academies of Sciences, Engineering, and Medicine (NASEM) and the UCSF Program on Reproductive Health and the Environment (PRHE), have been calling on EPA to adopt these methods for years. Recently, EPA followed these recommendations, proposing to evaluate multiple chemicals at a time in a cumulative risk assessment for phthalates.

In addition to being used in a wide range of personal care products, phthalates are used to make plastics soft so they can also be found in plastic bottles, vinyl flooring, garden hoses, and medical tubing. Since they are used in so many products that we use all the time, they are in the bodies of almost all people tested in the U.S. Studies have shown that people who frequently eat takeout food or food from restaurants or those who use beauty products marketed to Black and Latino populations have higher levels of phthalates (and other harmful chemicals).

EPA’s proposed cumulative risk assessment approach examines the combined effect of multiple phthalates that act on similar outcomes (specifically, problems with male reproductive tract development). However, it does not include other chemicals that can increase the risk of similar outcomes nor does it incorporate social factors (such as type of work, income level, or exposure to violence) that can influence exposure levels or severity of health outcomes. Not including other chemical exposures and social factors can underestimate the impact that widespread exposure can have, particularly for people like our nail salon worker and other vulnerable populations.

EPA decided to focus on problems with the developing male reproductive system because there is extensive data on this outcome. However, cumulative risk assessment can be done with much less data than EPA had for phthalates. This means that EPA can use existing data to combine chemical exposures with similar outcomes in future chemical risk assessments. Additionally, evaluating the risk of multiple chemicals at a time can make it easier for EPA to regulate the long list of chemicals they have to evaluate since they would be doing them in groups rather than chemical by chemical.

To estimate risk of exposure, EPA has typically calculated a Hazard Index – a ratio of the estimated exposure by the calculated risk for the adverse health effects being considered. This results in a rather useless measure that gives the false assumption that there is a “safe level” of exposure. A better approach is to use the relative potency factor approach, which combines the exposures for multiple chemicals based on how strong the effect is of each chemical and how much each individual is exposed to per day. This is important because we can then estimate the impact of exposure at lower doses. As we have shown, adverse health outcomes can occur at levels below which EPA considers “safe.”

EPA’s proposal to use cumulative risk assessment for phthalates is a step in the right direction. EPA needs to continue their work to upgrade their science by fully accounting for real-world exposures to better protect vulnerable populations via improved cumulative risk assessment methods.

About the Author

Jessica Trowbridge, MPH, PhD  is an Associate Research Scientist for the Science & Policy team. She studied Environmental Health Sciences at the University of California, Berkeley, before joining PRHE. Through her research, Jessica aims to fill critical evidence gaps, to improve policies and education to reduce toxic exposures to vulnerable populations.