Risk Evaluation for 1,3-Butadiene

In December 2025, EPA released the final risk evaluation under the Toxic Substances Control Act (TSCA) for 1,3-butadiene. EPA designated 1,3-butadiene as a high priority chemical in December 2019.

Find other information about other chemicals undergoing risk evaluations under TSCA.

On this page:

What is 1,3-Butdiene?
Risk Evaluation
Detailed Findings
Frequently Asked Questions
EPA’s Commitment to Gold Standard Science
Further Background on Risk Evaluation
Changes from Draft to Final
Risk Evaluation and Supporting Documents
Draft Risk Evaluation and Supporting Documents

What is 1,3-Butadiene?

1,3-Butadiene (CASRN 106-99-0), a colorless, flammable gas used in manufacturing polymers like plastic and synthetic rubber which are used to make products like:

Car tires
Adhesives and sealants
Paints and coatings
Automotive care products
Lubricants

Consumer products only contain tiny amounts of this chemical (less than 0.001%), which is safe for everyday use.

Unreasonable risks are found in industrial settings where workers may be exposed to much higher levels. In these industrial workplaces where 1,3-butadiene is manufactured or used to make products, high levels of exposure can be unsafe and can cause health risks such as reduced birthweight pregnancies, anemia, leukemia, and bladder cancer. These risks are not seen when people use consumer products.

Risk Evaluation

EPA completed a thorough review of 1,3-butadiene using gold standard science. We used the best research, data, and information to evaluate this chemical that's used to make many products we use every day. We also listened carefully to input from the public and independent expert reviewers.

EPA evaluated direct workplace exposure because that's where the highest potential exposures occur. The agency followed standard scientific practices by evaluating 1,3-butadiene exposures to provide clear results about this specific chemical's risks.

Our robust scientific review found that there are NO unreasonable risks for consumers or the general population (including people living near facilities), nor are there risks to environmental receptors.

EPA found that there could be health risks for workers who may breathe in this chemical at their jobs. This finding doesn't include any protective gear like masks, respirators or other safety equipment that workers might already be using.

As required by law under TSCA (Toxic Substances Control Act), EPA will now develop a rule to protect workers from the risks we identified. The agency will carefully consider health effects, exposure levels, how the chemical benefits society, and economic impacts. Input from workers, companies, and the public will be crucial to make sure our final rule protects health while being protective of vulnerable populations like women who are pregnant or of childbearing age and practical for businesses.

This next step, when finalized, will give companies clear rules to follow and provide workers with the protections they need to stay safe on the job.

Detailed Findings

EPA’s risk evaluation found that there are health risks for workers who breathe in this chemical in 11 types of work scenarios. These include factories that make or use 1,3-butadiene to create rubber, plastics, and other products. Our findings don't include protections that workers might already be using, like masks or special equipment.

We found NO unreasonable risks to:

Consumers using products with this chemical
People living near facilities that use 1,3- butadiene
The environment

This evaluation will help inform protections for American workers while allowing U.S. companies to continue making important products safely.

EPA will now develop a rule to protect workers from the unreasonable risks we identified. This process will include:

Careful consideration of health effects and exposure levels
Analysis of economic impacts
Input from workers, companies, and the public
Practical solutions that protect health while allowing important manufacturing to continue

The final rule will give companies clear direction and ensure workers have the protection they need while these important products continue to be made safely.

Frequently Asked Questions

Q: Why did EPA focus on direct workplace exposure?

A: TSCA requires us to evaluate the manufacturing, processing, distribution, use, and disposal of chemicals in a risk evaluation. We evaluated all these uses. We found that the highest risks occur in the workplace. Our gold standard science approach requires us to look at all sources of exposure covered by TSCA.

Q: What about communities near facilities using 1,3-butadiene?

A: We understand these communities have concerns, and we take them seriously. Our thorough analysis using the best available science shows that the chemical does not pose unreasonable risks to people living near facilities (fenceline communities). We considered air, water, and soil to reach this conclusion.

Q: Why did some of your findings change from the draft to the final evaluation?

A: We improved our evaluation by using real-world data, removing flawed assumptions from our first draft, and strengthening our methods and approaches. We also received updated information about how companies actually use this chemical. This made our science more accurate and reliable.

Q: Will workers be protected even though you found risks?

A: Yes. Part of EPA’s statutory obligations include the requirement to develop rules to protect workers from the unreasonable risks we identified. These rules will ensure that companies’ workers are kept safe.

EPA’s Commitment to Gold Standard Science

We made our evaluation better based on:

Updated data informing actual workplace conditions
Public comments that helped us understand how the chemical is really used
New reporting from companies about their current uses
Expert peer review to make sure our methods were sound

EPA removed flawed assumptions from our first draft and used real-world data, including widely accepted approaches used by EPA’s Office of Air and Radiation, to strengthen our risk evaluation.

Further Background on Risk Evaluation

EPA evaluated 30 conditions of use (COU) and determined that 11 were significant contributors to unreasonable risk of injury to human health for workers due to inhalation exposure. For COUs with unreasonable risks to workers, these determinations do not reflect the use of personal protective equipment (PPE); however, PPE may reduce exposures and mitigate risk.

COUs Significantly Contributing to Unreasonable Risk:

Industrial Use:
- Manufacturing - domestic manufacturing
- Manufacturing - importing
- Processing as a reactant - intermediate in various industries such as adhesive manufacturing and synthetic rubber manufacturing
- Processing as a reactant - monomer used in polymerization process in synthetic rubber, plastic material, and resin manufacturing
- Processing - incorporation into formulation, mixture, or reaction product - monomers in plastic, resin, and synthetic rubber manufacturing
- Processing - incorporation into formulation, mixture, or reaction product - plasticizer in asphalt paving, roofing, and coating materials manufacturing
- Processing - incorporation into article - monomer in rubber product manufacturing
- Processing - use-non-incorporative activities - fuel in petroleum refineries
- Processing - repackaging in wholesale and retail trade involving synthetic rubber and petrochemical manufacturing
- Processing - recycling
- Disposal

Changes from Draft to Final

28 COUs were evaluated in the draft RE compared to the 30 COUs that were evaluated in the final RE due to changes in the Chemical Data Reporting (CDR) .
- 4 COUs were added as a result of the latest CDR and 2 COUs were removed due to stakeholder feedback regarding the use (or lack) of 1,3 butadiene in industrial production, and CDR , indicating use is no longer active.
In total, 13 COUs were updated based on additional information from stakeholder feedback clarifying activities under the COU and/or updated CDR (see Appendix D - Updates to the 1,3-Butadiene Conditions of Use Tables for details).
For workers, 11 COUs contributed to the unreasonable risk.
8 COUs were unchanged
3 new COUs not in the draft risk evaluation were included in the final risk evaluation as a result of updated CDR and were determined to contribute to the unreasonable risk
- This change was due to updates based on new CDR. The CDR rule, under TSCA, requires manufacturers (including importers) to provide EPA with information on the production and use of chemicals in commerce when production volumes for a chemical are 25,000 pounds or greater. This reporting occurs on 4-year cycles and assures that EPA and (for non-confidential data) the public have access to up-to-date information on chemicals.
2 COUs in the draft risk evaluation were either reclassified or removed
- This change was due to updates based on CDR that the use was no longer active and public comment providing clarification of activities under the COU.
  - One COU (commercial use-laboratory chemicals) changed from unreasonable risk to no unreasonable risk.
    - This change was due to changes based on information; EPA refined this analysis and determined that the full-shift assumption used for the draft risk evaluation was overly conservative. EPA estimates that there are 10 workers for this COU.
  - For occupational non-users (ONUs), 2 COUs changed from unreasonable risk to no unreasonable risk. EPA is still finding that 1 COU contributes to the unreasonable risk for ONUs .
    - In the draft risk evaluation, EPA preliminarily determined that Manufacturing-import, Processing-repackaging, and Processing as a reactant-monomer used in polymerization process contributed to unreasonable risk for ONUs.
In the final risk evaluation, EPA determined that Processing-repackaging contributed to the unreasonable risk for ONUs.
This change is based on information submitted on 1,3-butadiene industrial hygiene data. EPA refined the analysis and determined that the shift-length assumptions used for the draft risk evaluations were overly conservative.
For the general population, 3 COUs were changed from unreasonable risk to no unreasonable risk. In the final risk evaluation, EPA determined that no COU contributed to the unreasonable risk for the general population.
This change is due to refinements in the general population evaluation, including the use of an updated IUR and use of NEI data in the HEM analysis.
- Instead of using basic facility information (TRI), EPA switched to a more detailed database (NEI) that includes specific details including stack height, what angle they release emissions at, and emission temperatures. This allowed our evaluation to move away from defaults to more accurate, facility-specific conditions. The database also provided exact coordinates of where emissions are released, rather than just general facility locations. This geographic precision gives a more accurate picture of actual exposure risks.
EPA also considered other risk-based factors, such as the size of population at increased risk, maximum risk, and uncertainty measures for making the unreasonable risk determination, based on learnings from the Office of Air and Radiation.

Risk Evaluation and Supporting Documents

Draft Risk Evaluation and Supporting Documents

In December 2024, EPA released the draft risk evaluation for 1,3-butadiene public comment and peer review. In March 2025, EPA released a supplement to the risk evaluation describing a preliminary refinement of cancer risk estimates from exposure to 1,3-butadiene in air from releasing facilities. These refined facility specific risk estimates provide important updated estimates for incorporation into the risk evaluation.

For more information, please visit the draft risk evaluation webpage.