What MRL, ADI, and ARfD mean for pesticide residues in food

A maximum residue level, or MRL, is one of the most misread numbers in food safety. A test finds a residue above the MRL, a headline calls the food unsafe, and the two things get treated as the same. They are not. An MRL indicates whether a pesticide was used as intended on the farm. Whether a residue is safe to eat is decided by two separate toxicology figures, the acceptable daily intake and the acute reference dose.

These three numbers are set by the Joint FAO/WHO Meeting on Pesticide Residues (JMPR), an expert body that evaluates pesticide active substances and recommends limits that the Codex Alimentarius Commission then adopts as international standards. In its 2025 round, JMPR evaluated around 38 active substances, including widely used compounds such as azoxystrobin, difenoconazole, bifenthrin, malathion, spinetoram, and the neonicotinoids clothianidin and thiamethoxam. This article explains what each figure means, how they are derived, and why they so often get confused.

What a maximum residue level really measures

A maximum residue level is the highest concentration of a pesticide residue legally permitted in or on a food, expressed in milligrams per kilogram, when the pesticide has been used in accordance with good agricultural practice. Good agricultural practice covers the approved use pattern: the maximum dose, the number of applications, the intervals between them, and the pre-harvest interval, which is the minimum time that must pass between the last spray and harvest.

The key point is what the MRL is for. Its purpose is to verify that a pesticide was applied correctly, not to mark the boundary of safe consumption. An MRL is set based on residue data, not on toxicology. It reflects how much residue realistically remains when the product is used as approved, which is why a residue above the MRL is, first and foremost, a sign that the use pattern may not have been followed, for example, through too high a dose, too many applications, or harvesting too soon after spraying. It is a flag for an agricultural and trade problem before it is a health question.

How an MRL is derived from field trials

MRLs come from supervised field trials. The crop is treated under the most demanding approved use pattern, the critical good agricultural practice, meaning the highest registered dose applied the maximum number of times with the shortest pre-harvest interval. Residues are then measured in the harvested crop, typically across a series of trials.

From those measurements, JMPR derives two values that feed into both the MRL and the later safety check. The supervised trials median residue (STMR) is the median residue level found across the trials, used to represent a typical residue for long-term exposure estimates. The highest residue (HR) is the largest single residue measured, used for short-term exposure estimates. The recommended MRL is set to cover the residues expected under correct use, so that compliant produce sits below it and produce treated outside the rules tends to exceed it.

How the ADI sets the long-term limit

The acceptable daily intake (ADI) is the amount of a pesticide that a person can consume every day over a lifetime without appreciable health risk, expressed in milligrams per kilogram of body weight per day. It is the figure that protects against chronic, long-term exposure.

The ADI is derived from toxicology studies, usually in animals, that identify the highest dose at which no adverse effect is observed. That no-effect level is then divided by safety factors, commonly a total of 100, to allow for differences between test animals and humans and for variation between individual people. The result is a conservative daily ceiling with a wide margin built in.

To check long-term safety, JMPR estimates how much of a pesticide people eat across their whole diet, using the median residue figures and national food consumption data, and expresses that estimated daily intake as a percentage of the ADI. As long as the estimate stays below the ADI, long-term dietary exposure is considered acceptable.

How the ARfD sets the short-term limit

The acute reference dose (ARfD) is the amount of a pesticide that can be consumed in a single meal or over a single day without appreciable health risk, again in milligrams per kilogram of body weight. It exists because some pesticides can cause effects from one high exposure, not only from long-term accumulation, so a separate short-term ceiling is needed.

Not every pesticide needs an ARfD. It is set only for substances that can produce effects after a single or one-day exposure. Where it applies, JMPR assesses short-term safety by estimating intake from a single large portion of a food with a high residue, using the highest residue figure, and comparing it with the ARfD. This short-term estimate is most likely to flag a concern for a specific food, and JMPR clearly notes any case where it could exceed the ARfD.

Why a residue above the MRL usually does not mean unsafe food

The confusion comes from treating the MRL as a health threshold, which it is not. Because MRLs are set to the residue level expected under correct use, and because ADIs and ARfDs are built with safety factors that put them well above realistic dietary exposure, a residue can sit above the MRL while still being far below the level that would approach the ADI or ARfD.

A result above the MRL means the produce should be investigated, because the pesticide may not have been used as approved, and it may not be legally tradable. It does not, on its own, mean the food is dangerous to eat. The actual safety judgment requires comparing realistic dietary exposure against the ADI for long-term risk and the ARfD for short-term risk. This is why regulators respond to an MRL exceedance with a compliance assessment rather than an automatic safety alarm, and why the two questions, was it used correctly and is it safe to eat, have to be answered with different numbers.

This distinction also explains why residue limits differ between countries and why import rules can tighten without any new safety finding. A jurisdiction can lower or remove an MRL for policy or precautionary reasons, as the European Union and individual member states have done for several substances, thereby changing what is tradable without necessarily reflecting a change in the underlying toxicology.

What this means for growers

For anyone applying pesticides, the practical message sits in good agricultural practice. The MRL is effectively a check on whether label instructions were followed, so the reliable way to stay within it is to apply the approved dose, respect the number and timing of applications, and observe the pre-harvest interval. Harvesting too soon after the final application is one of the most common reasons residues exceed the MRL.

Reducing reliance on chemical applications in the first place lowers residue risk at the source, a practical benefit of integrated pest management. And because residue definitions, MRLs, and the underlying ADI and ARfD values are reviewed and updated, growers producing for export benefit from checking the current Codex limits and the destination market's rules for each pesticide-crop combination rather than relying on older figures.

Frequently asked questions

Does a residue above the MRL mean the food is unsafe? Usually not. An MRL marks whether a pesticide was used according to good agricultural practice. Safety is judged separately by comparing dietary exposure against the ADI and ARfD, which carry large safety margins, so a residue can exceed the MRL while remaining well below the level of health concern.

What is the difference between ADI and ARfD? The ADI is the amount safe to consume every day over a lifetime, protecting against long-term exposure. The ARfD is the amount safe to consume in a single day or meal, protecting against effects from one high exposure. Not all pesticides need an ARfD.

Who sets these limits? The Joint FAO/WHO Meeting on Pesticide Residues (JMPR) evaluates pesticides and recommends ADIs, ARfDs, and MRLs. The Codex Alimentarius Commission then adopts MRLs as international reference standards, which countries may apply or adjust.

Why do residue limits differ between countries? MRLs can be set or changed for policy and precautionary reasons, not only toxicology, so a country can lower or remove a limit, which changes what is legally tradable without necessarily reflecting a new safety finding.

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