Aflatoxins in Nuts, Peanut Butter and Grains: What the 20 ppb Action Level Actually Covers

Last updated: September 21, 2026

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The short version

Aflatoxins are produced by molds that grow on crops in the field and in storage, and they are one of the few food contaminants with a clear federal number attached. The FDA action level for total aflatoxins in food is 20 parts per billion. For aflatoxin M1 in milk, which arrives through dairy cattle eating contaminated feed, it is 0.5 ppb.

The crops most affected are peanuts, corn, tree nuts — Brazil nuts and pistachios in particular — and some small grains including rice.

The part that surprises people: organic certification does nothing about this. Aflatoxin is a mold question, not a pesticide question. It is governed by how the crop was dried, sorted and stored, and those are processing decisions that the organic standard does not address.

The number that governs it

What aflatoxins are, and where they come from

Aflatoxins are toxins produced by Aspergillus molds. They are not added to food, not a residue of farming chemicals, and not a manufacturing byproduct. They are what certain molds make when they grow on certain crops, and the conditions that favor them are heat, humidity, drought stress in the field, and damp storage afterwards.

That origin explains most of what follows:

• It is a climate and handling problem. A hot, humid growing season followed by slow drying produces more of it than a dry season with rapid drying, on the same farm with the same practices.
• It concentrates in individual nuts or kernels. Contamination is patchy rather than uniform, which is why sorting matters so much and why testing is a sampling problem.
• It survives normal cooking. Roasting reduces levels somewhat but does not eliminate them, so the control has to happen before the food reaches you.

The FDA’s position is that “the foods most susceptible to aflatoxins include peanuts, corn, tree nuts such as Brazil nuts and pistachios, and some small grains such as rice”, that modern agricultural and processing techniques reduce the possibility of contamination, and that the agency regularly tests foods for them.

The action levels, and what an action level means

An action level is an enforcement threshold, not a safety line. It is the point at which the FDA may consider a food adulterated and act against it. It is set with the agency’s analytical capability and the practical aim of limiting exposure in mind, which is a different exercise from identifying a dose below which nothing happens.

The milk figure is the one worth pausing on. At 0.5 ppb it is forty times stricter than the general food level, because aflatoxin M1 appears in milk when dairy cattle eat contaminated feed, and milk is consumed daily by young children. Animal feed has its own separate action levels for the same reason — which is also why aflatoxin shows up periodically in pet food recalls, a category where a contaminated corn lot can reach a great many animals eating the same product every day.

Why nut butters are a distinct case

Whole nuts and ground nut butters behave differently, and both directions are worth understanding.

Grinding disperses. A jar of peanut butter contains a great many nuts, so one badly contaminated nut is spread through the whole jar rather than eaten whole by one person. That lowers the peak exposure from a single bad nut and raises the floor slightly across the batch.

Sorting is the main defense, and it happens before grinding. Modern processors use optical sorters that reject discolored, shriveled and damaged kernels — exactly the ones most likely to carry mold damage. A processor’s sorting capability matters more to the outcome than almost anything printed on the jar.

Visual inspection is lost. With whole nuts you can see and discard a shriveled or discolored one. With butter, flour or a paste you are relying entirely on the processor. That is the honest argument for buying from larger, better-equipped producers in this specific category, even when the brand story is less appealing.

Our guides to organic peanut butter, almond butter, almond flour and organic nuts record what each listing says about sourcing, processing and testing, which in this category is usually very little.

Brazil nuts and pistachios: why they are named specifically

The FDA’s own list of susceptible foods calls out Brazil nuts and pistachios, and both have structural reasons for it.

Brazil nuts are gathered from wild trees in the Amazon rather than cultivated in managed orchards. Collection, transport and drying happen in a hot, humid environment with long supply chains, which is precisely the condition set that favors mold growth. Brazil nuts are also the food most people buy for a single nutrient — selenium — and eaten in small daily quantities, which makes sourcing worth attention. Our Brazil nuts guide goes through what the listings state about origin and handling.

Pistachios split their shells on the tree, which is the characteristic that makes them pleasant to eat and also creates an opening for mold before harvest. Early splitting is associated with higher contamination risk, which is why sorting and moisture control in pistachio processing are so developed.

Neither fact is a reason to avoid either nut. Both are reasons to buy from suppliers whose handling you have some confidence in, and to store them properly once they are yours.

Why organic certification does not address this

This is the part that matters most for readers of this site, and it deserves to be stated flatly.

Organic certification governs inputs: which substances may be applied to a crop, and what processing aids may be used. Aflatoxin is not an input. It is produced by a mold that arrives on its own, and the controls that prevent it — rapid drying after harvest, moisture control in storage, aggressive sorting, testing of incoming lots — sit outside what the organic standard evaluates.

A certified organic peanut butter and a conventional one face the same aflatoxin question, and the answer depends on the processor rather than the certification. This is the same structure we describe in our explainer on heavy metals in organic food: the seal answers a real question, and it is not this one.

There is one indirect connection worth mentioning honestly. Some fungicides used in conventional production do suppress mold growth in the field, and organic production cannot use them. Whether that translates into measurably different aflatoxin levels in finished retail products is not something we can demonstrate from the sources available to us, so we are not going to claim it in either direction. What we can say is that certification is not designed to answer the question, and that published testing is.

What a careful producer actually does

Knowing the control points makes it possible to ask a brand a question it can answer concretely.

1. Drying speed after harvest. Getting moisture down quickly is the single biggest lever, and it happens within hours and days of picking.
2. Storage humidity and temperature. Mold grows in storage, not only in the field, so silo and warehouse conditions matter for as long as the crop is held.
3. Optical and manual sorting. Removing damaged, shriveled and discolored kernels removes most of the risk, because contamination is concentrated in those.
4. Lot testing. Because contamination is patchy, sampling plans matter: a larger, well-distributed sample finds what a token sample misses.
5. Supplier controls. Under food safety preventive controls rules, a facility’s hazard analysis is expected to consider known or reasonably foreseeable chemical hazards, and for these commodities aflatoxin is exactly that.

The question worth asking a brand is therefore not “is your product aflatoxin free”, which nobody can promise, but “do you test incoming lots for aflatoxin, and what is your acceptance limit?” A processor with a program answers with a number and a method. That is the same three-part standard — method, limit, result — we set out in our explainer on third-party testing.

What you can do at home

Storage is the part within your control, and it is more consequential for nuts than for most foods because you typically keep them for months.

• Keep nuts cool, dry and sealed. Refrigeration or freezing is genuinely worthwhile for anything you will not finish quickly, and it also slows the rancidity that ruins the flavor of nuts and their oils.
• Discard shriveled, discolored or moldy-looking nuts rather than eating around them. Visual defects correlate with the damage that allows mold in.
• Be cautious with bulk bins in humid conditions, where product may sit open and warm for long periods.
• Do not try to rescue visibly moldy food. Cutting off the visible part does not remove toxins that have diffused into the rest.
• Vary your sources and your foods. The same argument that applies to rice, cocoa and spices applies here: rotation limits how much of any single contaminated lot you consume.

For nuts and seeds you buy regularly, our pumpkin seeds, chia seeds, ground flaxseed and dried fruit guides cover the storage and freshness questions that sit alongside this one, and our organic rice and popcorn guides cover two of the grains on the FDA’s susceptible list.

Why testing for aflatoxin is harder than it sounds

Most contaminant testing assumes the contaminant is spread fairly evenly through a batch. Aflatoxin is not, and that single fact shapes the entire control system.

Contamination clusters in individual kernels. A truckload of peanuts can average well under the action level while containing a handful of nuts with very high concentrations. Take a small sample from the wrong part of the load and you find nothing; take it from the wrong part twice and you certify a lot that should have been rejected.

The consequences run in both directions, and they explain why serious processors talk about sampling plans rather than tests:

• Sample size and distribution matter more than laboratory precision. A large, well-distributed composite sample, finely ground before sub-sampling, gives a far more reliable answer than a more sensitive test run on a token handful.
• A single clean certificate proves less than a program. One result describes one sample from one lot. A supplier that tests every incoming lot to a defined acceptance limit is describing a system.
• This is why sorting is the real defense. Removing the damaged kernels removes the extreme values, and it does so physically rather than statistically.

The practical translation for a shopper: when a brand tells you its product “tested below the limit”, the useful follow-up is how often it tests and against what acceptance limit, not what the single number was. That is the same method-limit-result standard we set out for supplements, and the same reason our almond butter and peanut butter guides note which brands mention testing at all.

The other mycotoxins, briefly

Aflatoxins are the most regulated of the mycotoxins, and they are not the only ones. Knowing the names and where each tends to appear makes food safety reporting easier to read.

The FDA maintains levels for several of these in its contaminant database alongside aflatoxin, and the levels differ by commodity and by whether they are framed as action, advisory or guidance levels. We have not reproduced the individual figures here because we verify every number we print at its source, and the database’s commodity definitions matter for reading them correctly — the tool linked in our sources is the place to check a specific one.

Patulin is the one most likely to come up in ordinary shopping, because it is the reason pressing practice matters in apple juice. Juice made from windfall or bruised fruit carries more of it, which is covered in our organic apple juice guide and in our explainer on what juice labels mean.

A buying and storing checklist

Everything above reduces to a handful of habits, none of which requires paying more.

1. Buy nuts from sellers with high turnover. Fresh stock has spent less time in warm storage, whether that is a busy supermarket or a specialist with rapid throughput.
2. Prefer sealed packaging over open bulk bins in warm or humid conditions, where product sits exposed for long periods.
3. Move nuts to the fridge or freezer at home if they will not be eaten within a few weeks. This addresses mold growth and rancidity together.
4. Look at what you are eating. Discard shriveled, discolored or unusually dark kernels rather than eating around them.
5. Do not salvage moldy food. Trimming the visible growth does not remove what has diffused into the rest.
6. Vary sources and foods so that no single contaminated lot becomes a large share of what you eat.
7. Ask about lot testing for products you buy repeatedly, especially nut butters and flours, where you cannot inspect the raw material yourself. Our almond flour and granola guides note where listings are silent.

For pets, the equivalent habit is watching recall notices rather than reading bags, since aflatoxin incidents in pet food have historically been identified through recalls rather than labeling. Our organic dog food and cat food guides cover what the listings state about ingredients and sourcing.

Corn, and the category most people forget

Nuts get the attention, and corn is the crop where aflatoxin has the widest reach, because so much of it travels onward into other products rather than being eaten as corn.

Corn appears in cornmeal and grits, in tortillas and chips, in popcorn, in cereals, in starches and sweeteners used across processed food, and in animal feed. A contaminated corn lot therefore has many more routes into a diet than a contaminated bag of pistachios, and its route into milk runs through dairy cattle, which is the reason the milk action level exists at all.

Two habits follow, and neither is dramatic. Buy corn products with reasonable turnover rather than from the back of a pantry shelf, and store cornmeal and flours cool and sealed rather than in a warm cupboard for a year. Whole kernels keep better than milled products, for the same reason whole spices keep better than ground ones: less surface area, less exposure. Our organic popcorn guide covers the whole-kernel end of that, and our breakfast cereal and granola guides cover the processed end.

If you eat a lot of one thing

Almost every contaminant page on this site ends in the same place, and it is worth saying explicitly here because nut butters and daily nut habits are so common.

The exposure that matters is not one meal. It is the same food, from the same producer, eaten most days for years. A child eating peanut butter daily, an adult eating a fixed handful of the same brand of nuts every afternoon, a household getting most of its grain from one bulk purchase — those are the patterns where a single supplier’s controls stop being an abstraction.

If that describes you, three adjustments cost nothing:

1. Rotate brands every few purchases, so no single producer’s practices dominate your intake.
2. Rotate foods. Alternate peanut with almond or sunflower seed butter; alternate rice with other grains, as the FDA advises for arsenic in our heavy metals explainer.
3. Buy smaller packs more often rather than the large economy size that spends months open in a warm kitchen.

None of this is about fear. It is the same principle a diversified portfolio runs on, applied to a pantry: variety limits how much any single failure can cost you.

Keeping it in proportion

Two things are true at once, and leaving out either one distorts the picture.

Aflatoxins are a serious contaminant class. They are why the action levels exist, why testing programs exist, and why the milk limit is forty times stricter than the food limit.

And the US food supply is among the more tightly monitored for them. The FDA tests, importers test, and the commodity industries most affected have developed sorting technology specifically for this problem. The realistic risk from ordinary retail nuts and nut butters in a varied diet is low.

The sensible posture is the one we recommend throughout this site: buy from producers who can describe their controls, store what you buy properly, vary what you eat, and treat a product’s silence about testing as information rather than reassurance.

How the risk compares with the rest of your shopping

Context is what turns a contaminant number into a decision, so it is worth placing this one beside the others we cover.

Two of the four rows say no, which is not an argument against organic certification. It is an argument for knowing what you are buying with it. Our explainers on heavy metals, glyphosate and what organic certification covers work through each row in turn.

The pattern worth internalizing: certification answers questions about inputs. Contaminants that arrive from the environment or from handling need a different kind of evidence, which is testing — and testing is published far less often than seals are printed.

What we would like to see on a label

Since this site exists to read listings, it is worth being concrete about what a genuinely informative nut or nut butter listing would say. None of this is required, and very little of it appears.

• Country and region of origin, not merely “packed in” a location. Growing conditions drive the risk.
• Harvest or production date, since time in storage is a variable that matters here as much as it does for coffee.
• Whether incoming lots are tested for aflatoxin, at what frequency, and against what acceptance limit.
• Whether optical sorting is used, which is the single most effective physical control.
• Storage guidance on the pack that reflects reality — refrigerate after opening, rather than “store in a cool dry place” printed on a jar destined for a warm cupboard.

A brand doing three of those five is unusual. A brand doing none of them is normal, and that is the state of the category rather than a mark against any individual product. It is also why, in this one instance, we are comfortable saying that scale and equipment count for more than provenance storytelling: optical sorters are expensive, and they work.

Common questions about aflatoxins

What is the legal limit for aflatoxins in food?

The FDA action level for total aflatoxins in human food is 20 parts per billion, which applies to peanuts and peanut products, pistachios, Brazil nuts and foods generally. Aflatoxin M1 in milk has a much lower action level of 0.5 ppb. Action levels are enforcement thresholds rather than safety guarantees.

Which foods are most affected?

The FDA names peanuts, corn, tree nuts such as Brazil nuts and pistachios, and some small grains including rice as the most susceptible. Dried fruit, spices and animal feed can also be affected.

Does organic peanut butter have less aflatoxin?

Not by virtue of being organic. Aflatoxin comes from mold growth governed by drying, storage and sorting, which the organic standard does not address. The processor’s controls and testing determine the outcome, not the certification.

Does roasting destroy aflatoxins?

Roasting can reduce levels but does not eliminate them, because aflatoxins are heat stable in the range used for normal cooking. Control has to happen through sorting and storage before the food is processed.

Can I see or taste aflatoxin?

No. The toxin itself is invisible and tasteless, although the mold damage associated with it often shows as shriveling or discoloration. That is why discarding visually poor nuts is worthwhile even though it is not a complete safeguard.

Why is the limit for milk so much lower?

Aflatoxin M1 reaches milk when dairy cattle eat contaminated feed, and milk is consumed daily and in quantity by young children. The action level of 0.5 ppb reflects that exposure pattern rather than a different toxicity.

Are Brazil nuts especially risky?

They are on the FDA’s named list, largely because they are wild-gathered in a hot, humid environment with long handling chains. That is a reason to buy from suppliers who describe their sourcing and to store them cold, not a reason to avoid them.

Does refrigerating nuts help?

Yes, for two reasons. Cool, dry storage slows mold growth, and it also slows the oxidation that turns nut oils rancid. For anything kept longer than a few weeks, the freezer is better still.

Should I worry about aflatoxin in pet food?

It is a real category risk, which is why animal feed has its own action levels and why aflatoxin appears periodically in pet food recalls. Corn-heavy formulas are the usual vector. Checking recall notices is more useful here than reading the bag.

How do I know if a brand tests?

Ask directly: do you test incoming lots for aflatoxin, and what is the acceptance limit? A producer with a program will answer with a method and a number. Almost no retail listing states any of this, which is itself worth knowing.

Sources

• FDA: Mycotoxins
• FDA: Chemical Contaminants Transparency Tool, contaminant levels
• FDA: Action Levels for Poisonous or Deleterious Substances in Human Food and Animal Feed

Related reading

• Organic Food and Pantry hub
• Heavy metals in organic food, explained
• Best Organic Peanut Butter
• Best Organic Nuts
• Organic Product Database — compare brands across every guide

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