How and Why to Close the Exposure Assessment Gap

Quantitative risk assessments underpin most of our federal regulations related to chemicals. Therefore, it is important to understand how and why risk assessments can go astray.

Risk assessment brings together concepts of hazard (an inherent property of a chemical, such as carcinogenicity) and exposure. Combining multiple sources of information and applying a variety of assumptions, a risk assessment produces an estimate of expected health or environmental harm, or excess burden of disease and disability. For example, a risk assessment may yield an estimate of how many extra people will get cancer each year from the use of one chemical of concern. 

Risk assessments can yield wildly varying results depending on the assumptions that are used. Well-intentioned risk assessors using the same data can generate risk estimates that vary from one another by orders of magnitude. One key source of variability comes from exposure assessments. How do we estimate how much of a chemical or chemical mixture people are exposed to? And what groups of people do we prioritize when creating that estimate? 

What’s wrong with exposure assessments

A recent study by Laura Vandenberg and colleagues provides insight into the exposure piece of the puzzle.

Vandenberg et al. lay out four major problems with exposure assessments:

1. Many exposures are simply unknown, due in part to lack of transparency about chemical use in products and processes;
2. Exposure patterns and quantities change over time;
3. Assessments rely on inadequate models and assumptions; and
4. Our knowledge of toxicokinetics (what a chemical does once it’s in our body) is incomplete.

These and other related deficiencies lead regulators to underestimate exposures; in turn, this leads to underregulation. 

Underestimating exposure: Atrazine; BPA

These methodological problems have direct consequences for our health, as illustrated by examples in the study: 

When assessing exposure to the hormone-disrupting herbicide atrazine, researchers failed to examine the full range of atrazine metabolites that could be detected in the human body. They concluded people were minimally exposed to this widely used chemical. This incorrect assumption might have contributed to the failure to regulate it adequately in the US. Meanwhile, atrazine has been banned in the EU. (For more about atrazine, see the talk by Dr. Tyrone Hayes in CHE’s recent webinar on scientific integrity.)

Similarly, exposure assessments for the hormone-disrupting chemical bisphenol A (BPA) rely on unrealistic and inadequate assumptions. One important source of BPA exposure is the powdery coating on thermal paper receipts, such as those used at supermarkets and restaurants. Existing exposure assessments for BPA use the unrealistic assumption that people touch receipts just once per day, using just three fingers. This estimate isn’t realistic for most shoppers - and certainly not for cashiers who handle hundreds of receipts a day. 

Disproportionate exposures: The example of phthalates

Faulty assumptions about exposure can lead to inadequate regulation that fails to protect public health. As discussed in a recent webinar co-hosted by CHE and the Program on Reproductive Health and the Environment, EPA is currently evaluating seven phthalates under the Toxic Substances Control Act. The agency has noted that it lacks key information about people’s exposure to these chemicals. 

Phthalates are used widely in plastic and personal care products, and in many scented products such as air fresheners. We have known for many years that phthalates are harmful to human health. For example, exposure during pregnancy can alter fetal development, leading to incomplete masculinization of the developing male fetus. 

Phthalates also pose a major environmental justice concern. Black and Latina women are disproportionately exposed to phthalates and other endocrine disrupting chemicals in personal care and other consumer products. 

The community-based Taking Stock study, which is gathering information on the effects of beauty products on the health of Black and Latina women in California, has found that even when women make efforts to avoid phthalates and other chemicals of concern in their personal care products, they still have biomarkers of exposure to these chemicals. These findings are particularly significant for EPA's phthalate risk evaluations because women of color are often exposed to other stressors, including racial discrimination, that can exacerbate the effects of toxic chemicals and leave them more susceptible to harm.

Supporting informed individual choices 

In the absence of regulatory protections, there are some ways to help people reduce exposures. Letting people know about hazards in the products they buy can open up opportunities for people to start protecting themselves. For example, Silent Spring Institute and Resilient Sisterhood Project worked with influencers to develop social media posts on toxics in personal care products marketed to Black women. The posts reached more than 100,000 followers. 

Meanwhile, researchers have been documenting the benefits of reduced exposures. The HERMOSA study showed that adolescent girls could reduce phthalate metabolites measured in urine by eliminating certain personal care products for just a few days. And CHE’s recent webinar on breast cancer prevention featured a study that examined benefits of eliminating personal care products containing phthalates or parabens for a month.

Health care providers could help by providing patients with guidance on how to protect themselves. But even with the best of efforts, individual product choices can only go so far; protective policies are necessary to prevent health harms from toxic chemicals. 

Protective policies 

Risk assessment is not the only way to make regulatory decisions. Hazard-based decision-making regulates chemicals based on their inherent properties and eliminates the need for time-consuming and often flawed exposure assessments. However, under current laws, most federal regulations involving toxic chemicals and pollutants within the US require some form of risk assessment. 

As long as risk assessments are the basis for our regulatory decisions, it’s important to make them as robust and reliable as possible. As the webinar panelists explained, it is urgent that EPA conduct adequate exposure assessments that take account of the people who are the most highly exposed. This is necessary for EPA’s assessment of phthalates and, more generally, for EPA to meet its goals related to health and environmental justice.

For more information

• Read Laura Vandenberg’s blog to learn more about gaps in exposure assessment methodology.
• Read the consensus statement and full set of studies from the Program on Reproductive Health and the Environment.
• Watch the joint CHE/PRHE webinar, Closing the Exposure Assessment Gap: A Case Study of Phthalates, with Jonathan Kalmuss-Katz, Dr. Bhavna Shamasunder, Dr. Astrid Williams, and Dr. Micaela Martinez.

Thanks to Jon Kalmuss-Katz for reviewing and commenting on a draft of this blog.