Half a Part per Billion: The Number at the Center of the FDA Food-Additive Fight

In August the FDA proposed to end the practice that critics have long called the GRAS loophole: companies deciding for themselves, without telling the agency, that a new food ingredient is “generally recognized as safe”. On Saturday 10 October 2026 The Guardian published an analysis of a different part of the same 48-page proposal. Buried in it is an expansion of a much older exemption, the threshold of regulation, which has let trace substances from packaging skip food additive review since 1995. Under the proposal it would cover substances added to food directly.

The whole argument turns on one number: half a part per billion. That is a chemistry question before it is a policy question, so this article starts with what the rule text actually says, then works out how small 0.5 ppb is, sets out what critics and the agency each say about it, and ends with what the proposal leaves alone. That last part covers the old, plain food acids most buyers handle every day.

We take no side on whether the rule should be adopted. Every rule quotation below comes from the Federal Register text or the Code of Federal Regulations. Every critic is quoted from published reporting, and every calculation is shown so you can check it. All sources are listed at the end.

What the proposed rule actually changes

Direct answer: it widens who can use a low-exposure exemption, keeps the same safety level in a new unit, and lets that exemption stand in for the new mandatory GRAS notice.

The threshold of regulation, or TOR, has been in the regulations since July 1995. In the proposal’s own words, it covers a substance in food packaging or processing equipment “that migrates or, that may be expected to migrate, into food”, if the substance “has not been shown to be a carcinogen and data supporting the resultant dietary concentration will be below 0.5 parts per billion.” The FDA describes what it asks for: “TOR submissions to FDA only require minimal data (e.g., identity, dietary exposure) to demonstrate the safe use of a substance. A full safety narrative is not required for a TOR submission.”

The proposal would change four things:

Two things do not change. An exemption is still something a company has to request. And the FDA keeps the power to refuse one: the proposed text says the agency “may decline to grant an exemption in those cases in which available information establishes that the proposed use may pose a public health risk.” The proposal also adds a second route. A substance already approved for direct addition to food can be exempted for a new use if that use adds no more than 1% of its acceptable daily intake.

The FDA states its scientific basis plainly: “The scientific basis for the TOR is FDA’s determination that very low dietary exposure presents no meaningful safety concern.” Whether that holds for every substance that is not a carcinogen is the argument in the rest of this article.

How small is half a part per billion?

Direct answer: 0.5 ppb means half a gram in every thousand metric tons. For a typical day’s food and drink, that is 1.5 millionths of a gram.

The 1995 rule did the first conversion itself. It assumes a person eats 1,500 grams of solid food and drinks 1,500 grams of liquid a day, 3,000 grams in all. At 0.5 parts per billion, 3,000 grams contains 0.0000015 grams, or 1.5 micrograms. The rest of the table uses the same arithmetic:

For a sense of the daily figure: a grain of table salt about 0.3 mm on a side has a volume of 0.027 cubic millimetres. At salt’s density of 2.17 milligrams per cubic millimetre, it weighs about 59 micrograms. That one grain is about forty times the 1.5 micrograms the threshold allows across a whole day of eating.

The proposed new unit changes the number differently for different people. The FDA says moving from a concentration in food to a dose per kilogram of body weight “normalizes exposure across subpopulations, ensuring an equivalent level of safety for all subpopulations.” Here is what 0.025 micrograms per kilogram per day works out to:

So the change is not a loosening on paper. At 60 kg the two definitions match exactly. A lighter person, including a child, gets a lower allowance, and a heavier person a higher one. Critics are not arguing about the conversion. They are arguing about which substances can use the threshold at all, and whether any single threshold makes sense for every substance that is not a carcinogen.

Why critics say small is not the same as safe

Direct answer: some substances that are not classed as carcinogens are reported to act on the body at very low doses. Critics also say small doses of many substances add up, and that consumers cannot tell when a product contains one.

The Guardian’s analysis, by Tom Perkins, quoted two scientists. Maricel Maffini, an independent food consultant who has worked on TOR issues, said: “The FDA and industry have this position that if there’s only a little bit of something in the diet, then it’s not going to be problematic, but that isn’t supported by science of any kind.” Maria Doa, a scientist with the Environmental Defense Fund, said: “They’re widening another loophole, but trying to say they made our food safer.”

The critics’ case, as that reporting sets it out, has three parts:

Critics have one real-world example: perchlorate, which has been used as an antistatic agent in the plastic of bulk bags for dry food. The FDA’s own perchlorate page says that since 4 May 2017, perchlorate may be used only “as a component of antistatic agents used in certain containers and food processing equipment in contact with only certain dry foods”, at no more than 1.2 percent by weight of the finished polymer. That use goes back to a 2005 threshold of regulation exemption. The Guardian reported that FDA data published in 2017 showed more samples of children’s cereal containing perchlorate after the 2005 exemption. The FDA’s exposure assessments found that estimated average perchlorate intakes for the US populations studied, counting all sources, were below the EPA reference dose of 0.7 micrograms per kilogram per day. The two sides do not agree on which measure matters. This article does not settle that, but both positions are on the record.

For scale, the proposed threshold of 0.025 micrograms per kilogram per day is one twenty-eighth of that perchlorate reference dose: 0.7 divided by 0.025 is 28. Critics would answer that a reference dose for one well-studied chemical tells you nothing about a substance with far less data behind it. That is exactly what a TOR submission skips, because it does not require a full safety narrative.

What the proposal leaves alone: the old food acids

Direct answer: substances already listed or affirmed as GRAS in 21 CFR parts 182, 184 or 186 need no new notice, for their listed uses.

Much of the coverage has merged two separate things: the new, self-affirmed ingredients the August rule targets, and the familiar food chemicals that have been on the FDA’s own lists for decades. The proposed rule keeps them apart. Its new section 170.205 makes GRAS notices mandatory, then lists seven situations where “A GRAS notice is not required”. The second reads: “The substance is listed or affirmed as GRAS under the conditions of its intended use in parts 182, 184, or 186 of this chapter”.

Part 182 is the original GRAS list from the years after the 1958 Food Additives Amendment. Part 184 holds substances the FDA affirmed directly, many of them after the systematic review of GRAS substances it began in 1969. Several of the most common acids, glycols and humectants in food manufacturing are in one or the other:

None of these needs a GRAS notice under the proposal for its listed uses, and none needs the threshold exemption. They are permitted at the level “reasonably required” to do their job, which is typically far above any trace level. The fight over 0.5 ppb is about other substances.

There is a catch, and it is one buyers often miss. A GRAS listing covers the substance used the right way, not every drum that carries its name. 21 CFR 182.1 makes good manufacturing practice part of the listing, and one of its conditions is that the substance “is of appropriate food grade and is prepared and handled as a food ingredient.” Citric acid is GRAS. Technical-grade citric acid bought to clean scale out of a boiler is not a food ingredient just because the molecule is on the list. The listing is about the chemical, and suitability for food is about the grade and how it was handled.

What this means on a specification

The proposal is not final, and nothing in it changes the grade a food or beverage job needs today. Our guide to chemical grades explains the difference between technical, USP, FCC and ACS specifications in full.

A word on what this article does not say. It reports what the proposed rule says, what critics and the FDA have said about it, and the arithmetic behind the threshold. It makes no claim about ours: it does not say how any product we list was made or handled beyond what the product page and its certificate state, and it gives no regulatory advice for any one ingredient. Anyone with a stake in the threshold change can comment on docket FDA-2025-N-3262 until 9 December 2026.

This is a federal story. For how individual states have been setting their own food-chemical rules, see our earlier piece on states moving ahead of the FDA.

Common questions

What is the FDA threshold of regulation?

It is an exemption in 21 CFR 170.39, in place since 1995. It lets a substance from food packaging or processing equipment that migrates into food skip food additive review, if the substance has not been shown to cause cancer and the resulting dietary concentration stays at or below 0.5 parts per billion, about 1.5 micrograms per person per day. A request needs only minimal data, such as identity and dietary exposure, not a full safety narrative.

What would the August 2026 proposal change about it?

The FDA’s GRAS proposal, published 11 August 2026, would extend the exemption to any substance used in food, both directly or indirectly added to food. It would restate the limit as 0.025 micrograms per kilogram of body weight per day, tighten the wording on carcinogenic impurities, and let an exemption take the place of the new mandatory GRAS notice. The FDA could still refuse an exemption where a use may pose a public health risk.

How small is half a part per billion?

It is half a gram in a thousand metric tons, about 1.25 grams in an Olympic swimming pool, or one second in about 63 years. Across a day’s 3,000 grams of food and drink it comes to 1.5 micrograms, roughly a fortieth of a single grain of table salt.

Why do critics object to the threshold?

Scientists quoted by The Guardian on 10 October 2026 say some substances that are not carcinogens, especially hormone-active ones, act at doses below 0.5 parts per billion. They also say small doses of many substances add up, and that consumers cannot tell when a product contains an exempted substance. They point to perchlorate in bulk food bags, exempted under the threshold in 2005, as an example.

Does the rule affect citric acid, phosphoric acid or vinegar?

Not for their listed uses. Proposed 21 CFR 170.205(b)(2) says no GRAS notice is required for a substance listed or affirmed as GRAS in parts 182, 184 or 186. Citric acid (184.1033), acetic acid (184.1005), phosphoric acid (182.1073), glycerin (182.1320) and propylene glycol (184.1666) are all on those lists. The listing still assumes good manufacturing practice and a grade suited to food use.

Is the rule final, and can the public comment?

No, it is a proposed rule. Comments on docket FDA-2025-N-3262 are open until 9 December 2026. The FDA would then review them before deciding on a final rule, which may differ from the proposal.

References & Authoritative Sources

Rule language is quoted from the Federal Register text of the proposed rule and from the Code of Federal Regulations. Critics are quoted from The Guardian’s reporting. Perchlorate facts are from the FDA. All arithmetic is shown in the article.

1. Substances Generally Recognized as Safe (proposed rule) — Food and Drug Administration, Federal Register, 11 August 2026, 91 FR 51834, docket FDA-2025-N-3262. Every quotation of the proposal, including proposed sections 170.39 and 170.205.
2. 21 CFR 170.39, Threshold of regulation for substances used in food-contact articles — Electronic Code of Federal Regulations. The rule as it stands today.
3. 21 CFR 182.1, Substances that are generally recognized as safe — Electronic Code of Federal Regulations. Good manufacturing practice and “appropriate food grade”.
4. FDA may allow some toxic chemicals to be added to food without safety review. Experts are alarmed — Tom Perkins, The Guardian, 10 October 2026. The quotations from Maricel Maffini and Maria Doa, and the critics’ perchlorate account.
5. Perchlorate Questions and Answers — US Food and Drug Administration. The permitted antistatic use since 4 May 2017, the 1.2 percent limit, and estimated intakes against the EPA reference dose.
6. Generally Recognized as Safe (GRAS) — US Food and Drug Administration. The agency’s overview of the GRAS program and the August 2026 proposal.
7. Docket FDA-2025-N-3262 — Regulations.gov. Where comments on the proposal are filed until 9 December 2026.
8. Understanding Chemical Grades: Technical, ACS, USP, FCC and Water Treatment — Alliance Chemical. What each grade specification means.

The food-use acids and glycols we stock