EPA Risk Evaluation for 1,4-Dioxane: What it Means for Water Systems


Final Risk Evaluation Released for 1,4-Dioxane

In July 2023, the U.S. Environmental Protection Agency (EPA) released the 2023 Draft Revised Risk Determination for 1,4-Dioxane and the 2023 Draft Supplement to the Risk Evaluation for 1,4-Dioxane, finding that the chemical presents an unreasonable risk of injury to human health. Together, these documents present the EPA's updated stance on the public health risks associated with exposure to this substance. The new risk evaluation includes significant changes from the previous evaluation conducted in December 2020, and may even lead to the development of updated EPA guidelines for 1,4-dioxane in the near future. The release of this risk evaluation is a significant event that could set regulatory action into motion.

While the 2020 risk evaluation for 1,4-dioxane recognized some health risks to workers in direct contact with the chemical, it did not fully account for the dangers of exposure through air and water contamination. By taking these additional pathways into consideration in the 2023 update, as well as 1,4-dioxane generated as a byproduct, the EPA determined that the potential hazards of exposure to the contaminant were much more severe than previously stated.  

After assessing the impact of 1,4-dioxane on workers, occupational non-users, consumers, bystanders, the general public, and fenceline communities, the EPA found that exposure to the chemical through inhalation, skin contact, or drinking water contamination could lead to increased risk of liver toxicity, negative effects in the olfactory epithelium, and cancer.

Drinking water and wastewater systems, municipalities, and others should pay close attention to the latest EPA updates, as they may be the first steps down the path to 1,4-dioxane regulation. By taking the initiative to assess contaminant levels and explore treatment options and potential cost recovery solutions early, systems may be able to avoid undue stress and financial concerns if and when regulations are enforced.

Sources of 1,4-Dioxane Contamination

1,4-dioxane is a synthetic chemical, meaning that it is human-made and not found in nature. It is generally used as a stabilizer in industrial and cleaning products such as solvents and detergents. The U.S. Food and Drug Administration (FDA) has noted that the chemical is sometimes also produced as a byproduct during the manufacturing process of certain ingredients used in cosmetic and personal care products.  

1,4-dioxane can enter the environment through manufacturing waste and spills. Due to the bio-persistent nature of this substance, it does not break down significantly through traditional wastewater treatment methods. This can lead to contamination of the surrounding environment and local water sources.  Increased water quality testing has revealed that 1,4-dioxane contamination is much more prevalent than previously thought. In fact, the nation’s ten largest wastewater facilities reported 1,4-dioxane concentrations as high as 11,500 μg/L in the 2020 risk evaluation report.

EPA Risk Evaluation Process

The EPA’s release of its updated risk evaluation for 1,4-dioxane is the result of a careful process that the agency follows for chemicals of concern. The Toxic Substances Control Act (TCSA) requires the EPA to follow a three-stage process to gauge the safety of known chemicals and establish regulations to control their use, providing opportunities for public comment during each phase. The three stages are prioritization, risk evaluation, and risk management.


The first step of the EPA’s risk evaluation process is to prioritize each chemical according to its likelihood of causing undue harm to public health. Substances that present a low hazard level to the public, or that rarely result in exposure at levels that may endanger human health, are categorized as Low-Priority Substances. These chemicals are taken out of consideration for further assessment, although they may be re-evaluated in subsequent years.

During the prioritization phase, the TSCA prohibits EPA from considering non-risk factors such as the costs and benefits of a chemical. This means that dangerous chemicals cannot be excluded from consideration simply because they are commonly used in products with high economic or convenience benefits. In order to be classified as a Low-Priority Substance, the chemical must not present a significant health threat.

If a chemical is found to present a public health hazard, then it is categorized as a High-Priority Substance, and it immediately proceeds to the risk evaluation phase.

Risk Evaluation

Once a chemical is deemed a High-Priority Substance, the EPA must conduct a risk evaluation to gauge its risk to human health and the environment under its typical conditions of use. Throughout this phase, EPA researchers must consider the risks to the general population as well as to more sensitive groups. For example, children may experience negative health effects when exposed to lower concentrations of a contaminant, and workers may be frequently in closer contact with a chemical than most members of the public.

The risk evaluation phase begins with the release of a scope document that explains the focus of the research to be done, and why it is important. From there, the EPA conducts hazard and exposure assessments and a risk characterization to determine the extent of the danger presented by the chemical in question. Finally, a risk determination is released, announcing to the public whether or not the substance presents an unreasonable risk if used as expected.

Risk Management

After a risk determination has been released for a chemical, as occurred for 1,4-dioxane in July 2023, the substance proceeds to the risk management phase under the TSCA. At this point, the EPA may implement new federal regulations to protect public health. The manufacture, processing, distribution, use, or disposal of the chemical may become subject to new rules soon after this phase.

Looking Forward: Potential Regulatory Changes for 1,4-Dioxane

If the EPA continues to follow the typical risk evaluation process described above, then it may soon begin work on risk management for 1,4-dioxane. This may include the development of federal regulations to protect the environment and public health from the dangerous effects of exposure to this chemical.

The progression from increased awareness, to EPA assessment, to proposed regulatory action has already been seen in 2023 with the response to water contamination from per- and polyfluoroalkyl substances (PFAS). 1,4-dioxane and PFAS have many similarities in that they are both highly persistent and pervasive in water sources and require specialized treatment technology to remove them from water supplies. The EPA has already proposed federal maximum contaminant levels (MCLs) for several PFAS chemicals. If finalized, water systems across the country will be required to take action to ensure that PFAS concentrations in their water supplies are below these levels. If the regulatory process of 1,4-dioxane continues to echo that of PFAS, then it is possible that MCLs could be proposed for this chemical as well.

1,4-dioxane is causing heightened concern among the public as well as regulatory bodies for its widespread presence and threat to public health. In fact, several states have already implemented maximum contaminant levels for 1,4-dioxane in drinking water. If new EPA water regulations for 1,4-dioxane are enacted in the future, both drinking water and wastewater systems may find themselves in need of costly updates to maintain compliance and ensure the safety of their ratepayers and communities.

As water systems wait to see what action the EPA may take to regulate 1,4-dioxane, lessons may be learned from those who took early action to manage their PFAS situations. Systems that took the initiative to remove contaminants from their water benefited from improved public trust and compliance with state and proposed federal PFAS regulations.

While it cannot be confirmed at this time that 1,4-dioxane will follow in the footsteps of PFAS with regard to regulations, a proactive approach may be beneficial. If the contaminant is detected, the necessary treatment facility upgrades may be costly. By seeking to pass those costs on to the manufacturers responsible for 1,4-dioxane pollution, systems may be able to protect ratepayers from paying the price for treatment.

Get Answers to Your 1,4-Dioxane Questions

The EPA’s release of its final risk evaluation for 1,4-dioxane is a clear indication of its stance that the chemical presents an unreasonable risk to human health and the environment. While it remains to be seen what federal regulations may be enforced based on this risk determination, you may benefit from taking early action to manage the contaminantion.

By taking a proactive approach to testing and treatment for 1,4-dioxane, you can show your ratepayers and community that you are committed to protecting public health. Beginning the process of upgrading treatment facilities to remove contaminants before regulations are in place may also reduce the stress of maintaining compliance if standards are enforced later. Additionally, by acting now, you may benefit from exploring your options to cover the cost of your 1,4-dioxane solutions through litigation.

If you suspect that your water supply or treated wastewater may be contaminated with 1,4-dioxane, you may consider legal action to recover the costs of treatment to remove the chemical and protect the health of ratepayers. To learn more about your options for 1,4-dioxane treatment cost recovery, schedule a free consultation with the team at SL Environmental Law.