The US Environmental Protection Agency (EPA) is charged with the Herculean and crucial task of assessing which chemicals are innocuous and which ones need to be banned or restricted because they pose a threat to our health or the environment. But assessing thousands of chemicals one at a time is not efficient and it doesn’t acknowledge that we are exposed to multiple chemicals at a time or in sequence.
Fortunately, EPA has begun a slow pivot toward assessing multiple chemicals at once. Enacting strong regulations on chemicals by class, rather than individually, can help protect people and the environment from serious harm while still making sure that scientific integrity is upheld and the best available science guides the process.
Here’s what’s entailed and how it can help.
Focus on impacts
There are a lot of chemicals in the world—some 6,000 based on 99 percent of the volume used today in commerce. However, counting based on volume tells us nothing about health hazards. Chemicals are produced for many uses, to: keep our food fresh, color frosting on our birthday cakes, hold together medical equipment, and make our jackets rain resistant. But some can make us very ill or make our existing illnesses worse. Moreover, the production of even non-toxic chemical end-products might involve toxic emissions during manufacture. And the people who benefit from chemical production aren’t always the ones who have to bear the burden from their manufacture. The concept of focusing on chemicals’ cumulative impacts expands beyond the paradigm of a one-source-one-chemical-at-a-time approach to environmental regulations.
Group chemicals into classes
Those of us who were college chemistry majors likely remember that there are known themes and tendencies, codified in the periodic table, that inform chemical and physical parameters. As I progressed in my education, I became fascinated with how some chemicals behave similarly when they interact in the environment, such as organic chemicals in salt marshes or mercury in the atmosphere.
Some chemical compounds have the same atoms, but because they are arranged somewhat differently, they can have different properties. Graphite (pencil lead) and diamonds are a classic example. (You can play this game to learn more). Structures are one factor that inform chemical-physical traits such as whether the compound is soluble in water or if it can hang out in the air at room temperature. Some chemicals can be grouped together because they are formed by similar environmental processes, such as during combustion of fuels or when chlorinated tap water is heated and sprayed in a shower. When chemicals are ingested, inhaled, or absorbed through the skin, some travel through the body similarly or result in similar adverse health outcomes, such as respiratory irritation or certain cancers. Any of these shared characteristics can be effectively used to group chemicals into classes.
Understanding the Toxic Substances Control Act
To understand how grouping chemicals might work in regulations, let’s talk about the Toxic Substance Control Act, or TSCA, the primary law safeguarding the public from exposures to non-pesticide chemicals. TSCA requires EPA to determine if existing or new chemicals should be regulated (banned or limited) or if they pose no unreasonable risk.
The basic steps in TSCA to evaluate whether existing actively manufactured chemicals pose ‘unreasonable risk’ are: prioritization, evaluation for potential impacts to human health or the environment, and developing a plan to eliminate potential impacts. This is a sequential process and each step is dependent on the step prior to it.
For new chemicals, the EPA process starts when manufacturers submit something called a pre-manufacture notice (PMN). It is worth noting that manufacturers can get PMN exemptions with shorter review times and less EPA scrutiny when a new chemical is: regulated by another agency, manufactured only for export, manufactured in quantities of less than 10,000 kilograms per year, made only for a test market, only formed in a chemical reaction, or other exclusion criteria listed here. If a chemical is not exempt or excluded, it is added to the TSCA Inventory. This list comprises 86,000 known chemical substances in US commerce including public and non-publicly disclosed substances, and active chemicals (currently manufactured) as well as those that were never or are no longer manufactured. EPA then must do an evaluation to determine if there is unreasonable risk or insufficient data to make this determination. The evaluation can result in a regulatory ban, approval, requirement for more testing, or restriction.
Strengthening TSCA for susceptible populations
A TSCA risk evaluation determines whether a chemical substance presents an unreasonable risk of injury to public health or the environment, including to any potentially exposed or susceptible subpopulation (PESS) that experiences greater risks because of increased chemical exposures or increased susceptibility to harm. This requirement in TSCA regulations is important, because there is evidence that populations are more susceptible to harm from exposure to pollutants when they also experience social adversity like systemic racism or poverty. This language in TSCA requires protection for environmental justice communities that tend to be more highly exposed to pollution, and improvements in EPA’s assessment of risks to PESS are needed.
One study by scientists at the Natural Resources Defense Council provides a methodology, where publicly available data were pulled together to identify highly exposed or more susceptible populations. The authors used the air pollutant formaldehyde as an example and pulled in other pollutants associated with the same health effect (respiratory cancer) into the analysis. This approach groups chemicals by health effect resulting in improved protections since it reflects more than one chemical exposure.
Cumulative risk for grouped chemicals
The term “category of chemical substances” is defined in TSCA in such a way that chemicals can be grouped based on similar molecular structure, or similar physical, chemical, or biological properties, or if they enter the human body or the environment in the same way. This is a broad definition. A recent study by scientists from University of Maryland and University of Rochester School of Medicine provides a science-based process to evaluate seven phthalates (chemicals used to make plastics more flexible and durable) under TSCA using cumulative risk assessment principals. EPA has proposed to evaluate six phthalates under TSCA using the justification that people are exposed to them at the same time and because of the similarity in effects on the reproductive systems of male children before and after birth. EPA has also published draft guidance on cumulative risk assessment principles such as grouping chemicals based on similar toxicity or exposures, and then adding the potential responses from the exposures.
EPA is already treating some chemicals as a class
The grouping of chemicals into classes is an important step toward providing regulatory protections that reflect real life chemical exposures. The good news is that methods for doing so are already in place for some substances that the EPA regulates. PFAS chemicals present a particularly interesting and important case study. These chemicals contain carbon and fluorine atoms; they are widely used; and they break down very slowly over time, if at all. There is a lot of evidence that the thousands of PFAS chemicals should be regulated as a class, and EPA recently proposed regulating four PFAS together in drinking water. Not all EPA offices agree on the definition of what constitutes a PFAS chemical and at least one EPA office is out of step with the scientific consensus on a definition. This is an important issue to watch since definitions inform how to group these chemicals and which ones are included in regulations.
The bottom line is that grouping chemicals in regulatory work is not new and that treating chemicals as a class can provide more adequate health protections. Regulating chemical classes instead of individual chemicals avoids regrettable substitutions when manufacturers switch from a newly regulated toxic product to one that is also toxic but has less restrictions. Our current method addresses each chemical individually which can often lead to the mistaken assumption that a lack of data means the chemical is not toxic. Grouping chemicals with similar properties together can help prevent these harmful scenarios and ensure that people and the environment are protected.