How safe levels are set for chemical residues in food

About chemical residues in food

Farmers and growers use agricultural compounds to help protect the food supply and to maximise the quantity and quality of the food they grow. Agricultural compounds include agricultural chemicals (such as herbicides and other pesticides) and veterinary medicines.

Using agricultural compounds helps to:

keep crops and animals healthy
manage outbreaks of pests and diseases
increase the reliability of food production, which reduces the cost of many foods (because the crops and animals can produce more when there are fewer pests and diseases).

Use of these compounds can leave residues in the food that’s harvested from treated crops and animals. The Ministry for Primary Industries (MPI) ensures that maximum residue levels are set well below what could harm somebody’s health.

Find out more about agricultural compound residues in food

Chemical residues and food safety

There are rules and limits for how much of an agricultural compound can be present in food. This ensures that:

good agricultural practice (GAP) is followed
food is safe to eat
trade is facilitated.

Maximum residue levels (MRLs) indicate the highest concentration of agricultural compound allowed in each New Zealand food after the use of a compound according to GAP. MPI sets MRLs after a technical assessment of the compound’s efficacy, safety, and residue data when used according to GAP.

MPI follows internationally agreed protocols to set MRLs at levels that are well below what could harm somebody's health. This is because we set MRLs to ensure GAP is being followed, rather than to the highest level allowed by food safety limits.

Infographic showing how MRLs relate to food safety

Long description of this infographic | Expand or collapse

The graphic has 3 coloured areas or boxes stacked on top of each other. Each coloured area has a heading and text with different information.

To the right of the boxes are 2 vertical arrows. A black arrow labelled "Level of agricultural compound residues" points up, and a blue arrow labelled "Level of food safety risk" points down. A brown bar appears under the box at the bottom. It is wider than the coloured boxes and also extends to sit under the arrows.

The top box is a light peach colour and its heading says "No Observed Adverse Effect Level (NOAEL)". Under the heading it says: "The NOAEL is the highest daily dose of an agricultural compound residue that does not cause any negative effects on health. It is based on assessment of New Zealand and international toxicological data. NOAELs are typically 100 to 1,000 times higher than the Health Based Guidance Value."

The middle box is a slightly darker shade of peach than the top box and its heading says "Health Based Guidance Value (HBGV)". Under the heading, it says, "The HBGV is based on the NOAEL and is the highest amount of a compound that a person can be safely exposed to every day over a long period of time."

The bottom box is a light brown colour and its heading says "Maximum Residue Levels (MRLs)". Under the heading, it says, "MRLs are generally set far below the HBGV."

The arrows to the right of the boxes are there to show that MRLs restrict agricultural compound residues to well below what could be a food safety risk.

[End of long description of the infographic]

MRLs are used to monitor whether an agricultural compound has been used as directed to control pests and diseases in food production.

Labels on agricultural compounds have instructions to ensure that the MRLs are met.

MRLs are not often exceeded, and when they are, this is rarely a food safety concern. This is because all MRLs are set well below both international and New Zealand safe exposure limits.

If a residue found in food is assessed to be a food safety risk to consumers, we will take appropriate action. Warranted officers will follow up with suppliers to determine what happened and which corrective actions are needed. If there is a food safety risk, food can be recalled, and food production can be suspended.

How we set maximum residue levels for agricultural compound residues in food

The first step in determining MRLs for an agricultural compound is establishing good agricultural practice (GAP). MPI does this by evaluating efficacy, animal health and safety, and crop safety for each use of a compound. Based on this, we find the use pattern that uses the least amount of compound to achieve a consistent effect.

Once a compound’s GAP has been established, MPI evaluates the residues resulting from GAP use. This information is then used to determine the MRLs in food commodities from treated crops and animals.

To ensure the MRLs will effectively manage the safety of residues in food, MPI uses New Zealand data to calculate the national estimated daily intake of a specific compound in all relevant foods. This calculation evaluates consumption risk and uses a robust scientific approach to set MRLs at well below both the international No Observed Adverse Effect Level (NOAEL) and the New Zealand Health Based Guidance Value (HBGV).

To evaluate trade risk, MPI reviews international MRLs for the relevant agricultural compound-food commodity combination and compares it to proposed New Zealand MRLs.

If MPI finds that an MRL being considered could pose a food safety or trade risk, the MRL is not progressed.

No Observed Adverse Effect Level

The No Observed Adverse Effect Level (NOAEL) is based on an assessment of New Zealand and international toxicological data. It is the highest daily dose of an agricultural compound residue that does not cause any negative effects on health.

For example, if an experiment or observation does not find an adverse effect at a dose of 10 mg/kg/day, but effects appear at higher than 10 mg/kg/day, then the NOAEL will be set at 10 mg/kg/day.

Health Based Guidance Value

MPI uses a Health Based Guidance Value (HBGV) to calculate the safety of residues in New Zealand food. The HBGV is based on the NOAEL and is the highest amount of a compound that a person can be safely exposed to every day over a long period of time.

The HBGV is usually established by the New Zealand Environmental Protection Authority.

There is usually at least a 100-fold safety factor built into the HBGV. This is to ensure food safety for the whole population, including vulnerable people such as those who are young, older, pregnant, or immunocompromised.

For example, the HBGV for a compound with a NOAEL of 10 mg/kg/day would be 0.1 mg/kg/day with a 100-fold safety factor applied.

If there's additional uncertainty, the HBGV can be set at 1,000 or 10,000 times lower than the highest safe dose.

HBGVs also apply to children

Residues in foods can potentially have a greater impact on very young children (less than 12 weeks) because:

their bodies are not fully developed
they eat more food (and any chemicals in the food) relative to their body size.

However, HBGVs are set based on the safe consumption of the food over an entire lifetime. The large safety margins help protect children and people sensitive to specific chemicals.

NZ diets are regularly checked against HBGVs

Every 5 to 7 years, MPI surveys foods sold in New Zealand that are commonly eaten in a typical diet. These foods are prepared as consumed (for example, bananas are peeled, and meat is cooked) before they are analysed for certain chemicals. We assess New Zealanders' dietary exposure to these chemicals and then estimate risks through comparison against HBGVs. These surveys also enable MPI to track trends in these chemical exposures over time.

Learn more about the New Zealand Total Diet Study

Who to contact

If you have questions about chemical residues in food, email info@mpi.govt.nz