The Environmental Protection Agency (EPA) announced on August 10, 2026, the availability of and is actively seeking public comment on its draft risk evaluations for o-dichlorobenzene (CASRN 95-50-1) and p-dichlorobenzene (CASRN 106-46-7) under the Toxic Substances Control Act (TSCA). This action marks a significant step in the federal government's ongoing effort to assess and mitigate risks posed by chemical substances in commerce. The agency's preliminary findings suggest that both chemicals pose an "unreasonable risk of injury to health" under specific conditions of use, prompting a 60-day public comment period ending October 9, 2026. This period allows stakeholders and the general public to provide crucial input that will help shape the final risk determinations and potential regulatory responses.
Understanding the Chemicals: o-Dichlorobenzene and p-Dichlorobenzene
o-Dichlorobenzene is a clear to pale yellow liquid with an aromatic odor, used extensively across various industrial and commercial sectors. Its applications include serving as a solvent in dyes and pigments, a component in lubricant and degreaser products, and an ingredient in inks and paint strippers. Consumer products also utilize o-dichlorobenzene, notably in air care items and cleaning solutions for ceramics glazing. Exposure pathways primarily involve inhalation of vapors and dermal contact, with the atmosphere being the predominant environmental route of exposure due to its volatility.
p-Dichlorobenzene, in contrast, is a colorless to white crystalline solid characterized by a strong, pungent odor. It exhibits poor solubility in water but readily mixes with most organic solvents. A key characteristic is its sublimation at ambient temperatures, transitioning directly from solid to vapor. Industrially, it is used in the manufacture of thermoplastics and as a solvent in various formulations. Consumer uses are widespread, particularly in air care products such as continuous-action air fresheners, as well as in lubricants, greases, and building materials. Similar to its isomer, exposure mainly occurs via inhalation of vapors and dermal contact, with air identified as the primary environmental exposure pathway.
The TSCA Risk Evaluation Framework
These risk evaluations are mandated by TSCA section 6, which requires EPA to determine whether a chemical substance presents an unreasonable risk to health or the environment under its conditions of use. A crucial aspect of this mandate is that these evaluations must be conducted without considering costs or non-risk factors, focusing solely on the scientific evidence regarding risk. The process also necessitates identifying and considering risks to "potentially exposed or susceptible subpopulations."
The current action builds upon a series of prior steps. Both o-dichlorobenzene and p-dichlorobenzene were designated as high-priority substances for risk evaluation in December 2019. This was followed by the publication of draft scopes in April 2020 and final scopes in September 2020. More recently, in April 2026, EPA released draft hazard assessments for both chemicals, which underwent public comment and external peer review by the Science Advisory Committee on Chemicals (SACC) in June 2026. The current release of the draft risk evaluations integrates these hazard assessments with exposure assessments to provide a comprehensive view of the risks. The methodologies underpinning these draft risk evaluations have been previously peer-reviewed by the SACC in the context of other chemical evaluations, including 1,1-dichloroethane, 1,3-butadiene, and phthalates, and in broader screening level approaches for fenceline communities.
EPA's Preliminary Findings and Call for Specific Input
In its draft evaluations, EPA has preliminarily determined, based on the weight of scientific evidence, that both o-dichlorobenzene and p-dichlorobenzene "present unreasonable risk to human health driven primarily by certain conditions of use." This finding underscores the potential for regulatory actions aimed at managing these risks.
The agency is particularly interested in receiving detailed feedback on several specific areas. For o-dichlorobenzene, EPA seeks information regarding: process descriptions, worker activities, and prevalence related to domestic manufacture, processing as a reactant, use in ink/toner/colorant products, use as a cleaning product in dry cleaning or furnishing care, and consumer/commercial use as a cleaner for septic and cesspool tanks. Additionally, EPA is requesting data on consumer septic tank cleaner products containing o-dichlorobenzene, including product availability, ingredients, composition, and use instructions. Input on the current use of exposure controls and personal protective equipment (PPE) during the manufacture, processing, and use of o-dichlorobenzene across various conditions of use is also critical. The agency also welcomes comments on the application of the Industrial Use of Solvents Occupational Exposure Scenario (OES) to specific conditions of use, the approach for deriving and utilizing 15-minute exposure values, and the modeling approach used for inhalation exposure from paints and coatings OES.
Implications and the Path Forward
The preliminary determination of unreasonable risk by EPA signals that some current uses of o-dichlorobenzene and p-dichlorobenzene may be unsustainable without further risk mitigation. The public comment period is a vital stage where industry, environmental groups, academics, and individuals can provide data, perspectives, and alternative solutions that will inform the EPA's final risk determinations. This feedback is essential for the agency to refine its understanding of real-world exposure scenarios, the effectiveness of existing controls, and the practical implications of potential regulatory actions.
Following the close of the comment period, EPA will review all submitted information to finalize the risk evaluations. A final determination of unreasonable risk for specific conditions of use would then trigger a risk management phase, where EPA would propose and implement measures to reduce or eliminate the identified risks. These measures could range from labeling requirements and worker protections to restrictions or outright bans on certain uses. The rigorous, science-based process outlined by TSCA aims to balance industrial needs with the protection of human health and the environment, and public engagement is a cornerstone of this delicate balance.
