Of the flags EPA publishes on the TSCA Inventory, S is the one that can put you in violation while every other field on the record looks fine.
A substance carrying S is on the Inventory. It is an existing chemical. In 1,294 of the 2,010 cases in the July 2026 release it is also designated active, so a straightforward inventory check returns exactly the answer you were hoping for. And a Significant New Use Rule can still require you to notify EPA ninety days before you do the thing you were planning to do.
The flag means a rule exists. It does not tell you what the rule covers. That distinction is the whole subject of this article, and getting it backward in either direction is expensive.
What the flag actually marks
S indicates a substance identified in a final Significant New Use Rule. SP indicates one in a proposed SNUR. The July 2026 release carries 2,010 with S and 178 with SP. Twenty-six carry both, which is what a proposed amendment to an existing rule looks like on the record.
SNURs are made under TSCA section 5(a)(2), and the substance-by-substance rules live in subpart E of 40 CFR part 721. Each section in subpart E names one substance and designates the uses EPA considers significant and new for it. The flag on the Inventory is a pointer to such a section. It carries none of that section's content.
Where SNURs come from
The company a SNUR-flagged substance keeps explains most of them. Of the 2,010 substances with a final SNUR, 1,306 also carry the PMN flag and 494 carry 5E, which marks a substance subject to a TSCA section 5(e) order.
That is the ordinary life cycle. A new chemical goes through premanufacture review. EPA reaches an order under section 5(e) limiting how it may be made or used. The substance then enters commerce and joins the Inventory, and EPA issues a SNUR so that anyone else who wants to use it outside those limits has to come and say so first. The SNUR generalizes a restriction that originally applied to one company.
This is why SNUR substances are disproportionately newer chemicals rather than long-established commodities, and why the designated new uses are frequently about routes of exposure, protective equipment or release to water rather than about the product category.
The ninety days is real, and it is a review period
Section 721.25(a) requires the significant new use notice at least 90 calendar days before manufacture or processing for the significant new use begins. The notice goes on EPA Form 7710-25 and has to carry the information and test data specified in TSCA section 5(d)(1).
This is worth contrasting with the Notice of Activity Form B that an inactive substance requires. That form has no review clock, and its 90 days is a limit on how early you may file. A SNUN is the opposite. The 90 days is a genuine waiting period during which EPA evaluates, and the agency can extend it. Treating the two filings as comparable paperwork is a scheduling error with a quarter of a year in it.
Three obligations people miss
Most discussion of SNURs covers the case where you want to perform the designated new use yourself. Part 721 reaches considerably further than that.
Distributing the substance can require a notice. Under 721.5(a)(2), a person who manufactures or processes a subpart E substance and intends to distribute it in commerce must submit a SNUN, unless they can document one of three things about each recipient: that they notified the recipient in writing of the specific subpart E section identifying the substance and its designated new uses, that the recipient already knows of that section, or that the recipient cannot undertake any of the designated uses. In practice the first option is the one companies rely on, which makes written customer notification a live compliance task rather than a courtesy.
Knowing what your customer intends creates a duty. Section 721.5(b) requires a notice from a distributor who has knowledge, at the time of commercial distribution, that a recipient intends to engage in a designated significant new use without filing one themselves.
Export triggers a separate notification. Section 721.20 subjects anyone intending to export a subpart E substance to the export notification provisions of TSCA section 12(b), implemented at 40 CFR part 707. Read that sentence carefully, because it also covers a substance named "in any proposed rule which would amend subpart E." A proposed SNUR carries no notice obligation under 721.25 yet, and it already carries the export one. Those 178 SP-flagged substances are not waiting quietly for a final rule.
There is a trap worth naming where two of these meet. Section 721.45(g) exempts a person who manufactures or processes the substance solely for export and labels it under TSCA section 12(a)(1)(B). That exemption is from the SNUN requirement in 721.25. Section 721.20 still applies. Exporting can relieve you of one notice and leave the other in place.
What does not require a notice
Section 721.45 lists the exemptions, and they are narrower than they first appear. They cover a granted test marketing exemption under section 5(h)(1), small quantities solely for research and development, a granted 5(h)(5) exemption, manufacture or processing of the substance only as an impurity, and import or processing of the substance as part of an article.
The byproduct exemption at 721.45(e) is the one most often misread. It applies where the byproduct is used only by organizations that burn it as fuel, dispose of it as waste, or extract component substances from it. A byproduct that goes on to any other commercial use is outside the exemption.
Section 721.5(c) adds a limited defense for processors, and it requires documenting both halves: that the person does not know the specific chemical identity of what they are processing, and that they are processing it without knowledge that the substance appears in subpart E. Once a supplier sends the written notification described above, neither half remains available.
The thing the flag cannot tell you
An S flag establishes that a section of subpart E names the substance. It establishes nothing whatever about whether your use is one of the designated significant new uses.
This matters for how a lookup tool should behave, ours included. Three FEMA GRAS flavor substances carry a final SNUR in the July 2026 release, and 38 substances in our curated food and flavor catalog do. For every one of them, the honest statement is that a SNUR exists and the designated uses are set out in a specific section of subpart E that has to be read. The designated use in a SNUR written after a section 5(e) order is typically about industrial handling and exposure, and frequently has nothing to do with the food application at all. Any tool that turns the flag into a restriction on your use is inventing the restriction, and any tool that treats the flag as noise because the substance is active and listed is hiding a real obligation.
Report the flag, cite the part, and send the reader to the section. Nothing more can be said responsibly from the Inventory record alone.
How to check a substance
EPA publishes the non-confidential Inventory with the flags in each record, roughly every six months. Finding the subpart E section for a flagged substance means searching 40 CFR part 721 by CAS number or by chemical name.
Two limits apply to any search of the published data, ours included. EPA maintains a confidential portion of the Inventory that it does not publish, so a substance absent from the public file is not thereby unflagged or unregulated. And the flags arrive from EPA as one semicolon-separated field, so a substance with several of them reads as text like "PMN; S" rather than as separate values. A tool that stores that string whole cannot count or filter by flag at all, which is why published counts of SNUR substances vary.
Ambrose holds the July 2026 release, 70,774 substances with their flags split and searchable, and every lookup in our regulatory compliance platform reports which EPA release the answer came from.