Why It Matters
Pesticide manufacturers may use dimethyl sulfoxide (DMSO) as a solvent or co-solvent in formulations applied to growing crops, animals, and food-contact surfaces without establishing a maximum residue level under a tolerance exemption that the Environmental Protection Agency finalized effective Oct. 30.
Before the rule, DMSO was not listed in the three federal tolerance-exemption tables covering those uses. The rule eliminates the need to set maximum permissible residue levels for DMSO when used under the new exemptions. It follows a petition filed by Spring Regulatory Sciences on behalf of Gaylord Chemical Company, L.L.C., whose notice of filing was published June 15. EPA received no relevant comments in response to that notice.
The Big Picture
The rule adds DMSO to three separate Code of Federal Regulations tables, each covering a distinct use category:
- 40 C.F.R. § 180.910 — Inert ingredients used before and after harvest on growing crops and raw agricultural commodities; DMSO is listed as "Solvent/Co-solvent" with a limit of "None."
- 40 C.F.R. § 180.930 — Inert ingredients applied to animals; the same designation and a limit of "None."
- 40 C.F.R. § 180.940(a) — Inert ingredients in antimicrobial formulations applied to food-contact surfaces in public eating places, dairy-processing equipment, and food-processing equipment and utensils; DMSO is listed as "Solvent/Co-solvent" without a numerical residue limit.
The exemptions impose no numerical residue limits, and EPA says no analytical enforcement method is required.
Potentially affected entities include agricultural producers, animal producers, food manufacturers and pesticide manufacturers. EPA notes that the list "is not intended to be exhaustive." The agency states that the rule imposes no enforceable duty on state, local, or tribal governments or the private sector and carries no information-collection burden.
EPA's Safety Rationale
EPA determined that DMSO "is of low acute, subchronic, and developmental toxicity," with systemic toxicity observed only at doses at or above 1,100 mg/kg/day. The agency also identified skin and eye irritation, skin sensitization, and changes to the eye lenses of laboratory animals at high doses. Because EPA identified no toxicological endpoints of concern for its risk assessment, it conducted a qualitative rather than quantitative assessment and concluded there is "a reasonable certainty that no harm will result from aggregate exposure to the pesticide chemical residue."
That finding that no threshold toxicological endpoints of concern were identified led EPA to forgo the default 10-fold Food Quality Protection Act safety factor for infants and children. The agency concluded it did not need an additional safety factor for its assessment of risks to those populations.
The Bottom Line
Anyone seeking to challenge the rule must file a written objection or request a hearing by Dec. 29 under 40 CFR Part 178. EPA states that failure to file an objection by the deadline waives the right to raise issues resolved by the final rule.
The Federal Register also provides a public comment option through Dec. 30 at regulations.gov, but submitting an ordinary docket comment does not replace the formal objection or hearing-request procedure.
Formal objections and hearing requests must identify Docket No. EPA-HQ-OPP-2026-0529 and be received by EPA's Hearing Clerk by Dec. 29. EPA encourages electronic filing through its administrative law judges' e-filing system. A nonconfidential copy should also be submitted to the public docket at Regulations.gov.
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