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1, 4-Dioxane and the Need for EPA to Lead on Consistent National Guidance

In 2016, Congress passed amendments to the Toxic Substances Control Act (TSCA), with one key piece requiring the Environmental Protection Agency (EPA) to use the best available science and the weight of scientific evidence when evaluating new and existing chemicals. These amendments, called the Lautenberg Chemical Safety Act, clearly established the framework for a modern chemical management system to enhance public, industry, and government confidence in the federal chemical regulatory system.

The American Chemistry Council (ACC) and its member companies worked for nearly a decade, along with lawmakers from both parties and stakeholders from industrial, environmental, public health, animal rights, and labor organizations, to help pass this important piece of legislation.

“Best available science” means information that has been evaluated based on its strengths, limitations, and relevance. Factors that help determine the best available science include: peer review, statistical significance, objectivity, consideration of exposure, and reproducibility.

Weight of the scientific evidence means a systematic review method that uses pre-established protocols to comprehensively, objectively, transparently, and consistently identify and evaluate the evidence. That includes evaluating the strengths, limitations, and relevance of each study and integrating the evidence as necessary and appropriate based upon its strengths, limitations, and relevance. 

One of the first chemicals selected by EPA for risk evaluation under the revised TSCA process was 1, 4-dioxane, a substance previously used in a number of applications, but with limited current uses. It is, however, formed at very low levels as an unintended byproduct of the process used to make many soaps, body washes, and cleaning products that we use every day. Despite its limited use and low exposure potential, 1, 4-dioxane provides an excellent case study for EPA to apply the principles of best available science and weight of scientific evidence.

There have been multiple studies conducted within the past few years on 1,4-dioxane. While some studies have linked 1,4-dioxane exposure with cancer in rats and mice, tumors have only been reported after exposure to exceedingly high levels, suggesting that cancer only results after the exposure exceeds a “threshold.” This conclusion is supported by other studies of the chemical that have investigated the potential mechanisms of cancer and how it occurs in animals, including a recently completed study sponsored by ACC. As a result, governmental bodies around the world – including the World Health Organization (WHO), the Australian Health Ministry, the European Union, and Health Canada – have concluded that current, low-level exposure to 1, 4-dioxane does not present a health risk.

Despite this significant body of evidence that 1,4-dioxane does not present a health risk, EPA stated in an earlier 2013 assessment of 1,4-dioxane, under the Integrated Risk Information System (IRIS) program, that there is potential risk from low-level exposure. The agency’s IRIS assessment dismissed the conclusions reached by the majority of other countries that a potential health risk from 1,4-dioxane exposure only occurs if a threshold is exceeded, and it instead relied on its default and outdated “linear, low-dose” approach. This approach reasons that any exposure – no matter how small – increases the potential risk, which is increasingly at odds with what we know about how mammals react to chemicals.

Dioxane Could Have Been a Good Opportunity

EPA’s decision to include 1, 4-dioxane among the first chemicals to be evaluated in 2020 under the amended TSCA provides the Agency with an opportunity to update its data base, revise its approach to cancer mechanisms, and align its assessment of 1, 4-dioxane with the rest of the world.

EPA’s draft risk evaluation for 1, 4-dioxane is disappointing because it reaches the same outdated conclusion as the 2013 IRIS assessment – that low-level exposure to 1, 4-dioxane presents a cancer risk. Although the draft TSCA conclusion is slightly less conservative than the IRIS assessment, it still clings to the same default linear, low-dose approach. Numerous questions and concerns were raised about this linear assumption by members of the Science Advisory Committee on Chemicals (SACC) that reviewed the draft.

Barring a seismic shift at EPA in the next few weeks, the conclusions of the final TSCA risk evaluation for 1, 4-dioxane, when released, will mean that EPA remains at odds with many authoritative bodies around the globe as well as multiple studies that conclude current levels of exposure to 1, 4-dioxane do not present a potential health risk.

The direct impact of the TSCA evaluation for 1, 4-dioxane is expected to be minimal. Given the limited number of uses of the chemical, it’s unlikely that any resulting regulations will have broad impact on industry. But the impact for the chemical industry as a whole could be significant. EPA’s failure to incorporate the best available science in the TSCA evaluation may mean additional activity at the state level, creating an uneven patchwork of different and competing regulations across the country.

Make no mistake, the safety of the general public, of workers, and the environment is one of ACC’s top priorities. We believe that the principles of best available science and weight of the scientific evidence laid out by the TSCA amendments must be implemented in a clear, consistent, and transparent manner, which ensures a thorough and accurate risk assessment process that uses relevant data, rather than outmoded default assumptions.

We hope to see EPA honor the intent of the 2016 TSCA amendments for future risk evaluations, as it will help best protect both people and the environment and provide states with a clear set of criteria for their own regulatory activities.

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