MRLs, human health, and food safety: How MRLs are set
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Food and crop terminology
When regulating pesticides in Canada, the term “food” may refer to:
- crops, sometimes called “raw agricultural commodities”
- processed foods made from crops treated with pesticide
- dairy or meat products from livestock animals that have eaten crops treated with pesticide
To be used in Canada, a pesticide must undergo a highly regulated, science-based risk assessment to ensure that it meets Health Canada’s human health and environment protection requirements. Setting a maximum residue level (MRL) is one component of the rigorous pesticide risk assessment process. Health Canada scientists may set an MRL at the time of registration of the pesticide or after receiving an application for a different use for that pesticide.
As part of the risk assessment, there are 4 main steps our scientists go through before setting an MRL:
1. Determining the acceptable daily intake (ADI) and acute reference dose (ARfD)
Health Canada scientists evaluate scientific studies to identify the toxicity of a pesticide. From these studies, scientists determine the No Observed Adverse Effect Level (NOAEL). This level is the amount of pesticide at which no observable health effects are found in these studies. As a protective measure, scientists include a large safety margin when setting the following values:
- acute reference dose (ARfD): the amount of a specific pesticide residue that a person could eat in one day without any negative health effects
- acceptable daily intake (ADI): the amount of a specific pesticide residue a person could eat every day over their entire life without any negative health effects
Health Canada scientists consider all vulnerable populations when setting these levels, such as:
- pregnant people
This large safety margin ensures that there are no health risks for the public.
2. Estimating the potential daily intake (PDI)
The potential daily intake is the amount of a specific pesticide that a person may eat based on their diet. When scientists determine this intake, they consider:
- a variety of diets
- the amount and type of food someone in Canada could eat
Certain pesticides may be used on several different foods, so it’s important to account for both domestic and import uses when determining a person’s PDI of a pesticide.
3. Determining the maximum residue limit (MRL) for each food
Scientists determine the amount of pesticide residue left on food when the pesticide has been used according to label directions. This is done by collecting pesticide residue data for the food after it has been treated in a field study. Field studies may differ from each other because of different environments or weather, so scientists typically review multiple studies from different locations.
Once the residue data is collected, scientists use it and an internationally standardized calculator to determine what the MRL will be. The calculator harmonizes the way MRLs are determined across countries belonging to the Organisation for Economic Co-operation and Development (OECD).
4. Comparing the potential daily intake (PDI) to the acceptable daily intake (ADI) and the acute reference dose (ARfD)
Finally, scientists compare the potential daily intake (PDI) to the acceptable daily intake (ADI) and the acute reference dose (ARfD). The potential daily intake must be lower than both of these for Health Canada to approve the proposed MRL.
Health Canada will not approve the pesticide for its proposed use if the PDI is higher than the ADI or the ARfD. The pesticide would need to be used differently for Health Canada to approve it, such as:
- a reduction in the amount applied
- changing the timing of the application
This change in use would then go through the entire scientific review process again to ensure the requirements set by Health Canada are met before the MRL is set.
Health Canada scientists can set MRLs for crop groups as well as for individual crops. A crop group is a group of plants or crops categorized based on similar features, such as:
- function, like whether a plant produces fruit
- plant structure
- how the crop is grown or harvested
- botanical and taxonomic criteria
For example, apple, crabapple, pear, loquat, and quince are all crops in Crop Group 11-09: Pome Fruit because they share similar growing and harvesting methods.
Within a crop group, a representative crop (or crops) is identified. This representative crop often:
- is the biggest or most important crop produced or eaten
- has residue levels that will generally be representative of the crops within the crop group
For example, the representative crops of Crop Group 11-09: Pome Fruit are apple and pear.
Processed food products
Typically, an MRL applies to a crop and any processed foods made from that crop. For example, apples are a crop and apple juice is a processed food. However, if a processed food is found to have higher potential pesticide residues than the crop, Health Canada sets a separate MRL for the processed food.
When no specific limit is set, pesticide residues must not exceed 0.1 ppm. This is commonly known as the general or default MRL and is set out in subsection B.15.002(1) of the Food and Drug Regulations.
Consulting the public on MRLs
After scientists determine that the PDI is lower than the ADI and ARfD, Health Canada consults on the proposed MRL. The consultation process involves:
- publishing a proposed MRL (PMRL)
- consulting the public
- addressing comments and, if appropriate, adjusting the:
- MRL value
- final decision
Once the decision is made on the MRL value, there are two more important steps:
- legally setting the MRL in a database
- using the MRL to monitor and protect Canada’s food supply, in collaboration with the Canadian Food Inspection Agency (CFIA)
Health Canada repeats the whole evaluation and consultation process if an established MRL needs adjustment. The proposed maximum residue limit document (PMRL) is published on the pesticides consultations page. The types of PMRL include:
- MRLs for new imported foods
- amendments to existing MRLs
- MRLs for new pesticide active ingredients
- MRLs for new food uses of a pesticide registered in Canada
A consultation document outlines:
- the major findings of the evaluation
- the proposed MRLs
- how long the consultation is open to the public
Health Canada considers all comments from the public consultation before making a final science-based decision. Comments received are addressed in a document linked to the published proposed MRL.
The established MRL will be legally in effect as of the date it is entered into the MRL database.
After setting an MRL, it is used to monitor Canada’s food supply to make sure it complies with food safety laws.
Every year, the Canadian Food Inspection Agency (CFIA) tests more than 15,000 samples of a wide variety of foods for the presence of pesticide residues. Each sample can include monitoring for more than 450 different pesticide residues, generating more than 6 million pesticide residue monitoring results.
The CFIA uses a number of monitoring activities to conduct compliance testing. These activities include:
Testing in 2019-2020 shows that 94% of imported fresh fruits and vegetables and 99% of fresh fruits and vegetables produced in Canada meet the established or default MRL. If the CFIA finds a food with residues greater than the MRL or the default limit, it takes the appropriate regulatory action.
Learn more about:
- Food and Drug Regulations
- Maximum residue limits database
- Pesticides and pest management consultations
- National Chemical Residue Monitoring Program and Chemistry Food Safety Oversight Program Annual Report 2019-2020
An MRL can change if an application is received and the scientists at Health Canada re-assess the risk of the pesticide under the Pest Control Products Act. They make sure the new MRL will continue to meet the requirements to protect human health.
If these requirements are not met, the requested change will not be supported, or the pesticide product won’t be allowed for sale, use, or import into Canada.
MRLs may change by being increased or decreased as agricultural practices change in Canada and internationally. If an MRL increases, it doesn’t mean that human health protection decreases.
MRLs are a function of how a pesticide is used and not a measurement of pesticide toxicity or safety.
When growers or food producers use a pesticide in a different way, the highest amount of residue that could remain on that food may change.
Different ways could include applying:
- more of a pesticide to deal with a new pest
- a pesticide at different points in the growing season
- a pesticide differently because of changing climatic conditions
Sometimes a change to an MRL is needed because a pesticide is being used differently on an imported food. This could happen when a country that imports food to Canada has to increase the amount of pesticide used to manage a new pest. Changing the MRL for an imported food does not change how the same pesticide will be used in Canada. Growers and food producers in Canada are still legally required to follow the use directions on Canadian registered labels.
This means that when an MRL is changed based on an imported food application there is:
- No change to the Canadian registered labels for the pesticide.
- No change to how the pesticide is used in Canada.
- No increase to the amount of pesticide residues on the food grown in Canada.
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