Pesticide assessments in Canada: Human health risk

On this page

• Purpose of a human health risk assessment
• Understanding risk
• Conducting a human health risk assessment
• Types of human health risk assessments

Purpose of a human health risk assessment

The purpose of a human health risk assessment is to study if pesticide exposure could negatively affect people's health. Health effects from pesticide exposure could include: cancer, birth defects, impacts on reproduction and development, damage to genetic material, and other health problems.

Certain groups of people may be at higher risk of harm from pesticides. High-risk groups include pregnant people, infants, children, and older adults. So, we pay special attention to protect these groups of people.

Understanding risk

A human health risk assessment considers:

• toxicity: potential for a pesticide to cause negative health effects
• exposure: when, where, and how much people could be exposed to a pesticide

Risk will depend on how harmful something is (toxicity) and how much a person comes into contact with it (exposure). A pesticide with low toxicity and high exposure could have similar risks as a pesticide with high toxicity and low exposure. This is why we tailor human health risk assessments to real-world situations.

Conducting a human health risk assessment

PMRA scientists use a four-step scientific risk assessment process to protect human health. The process is accepted by scientists and organizations across the world.

1. Hazard identification

A hazard is a possible source of danger or harm. When we identify hazards, we look for possible negative health effects that could happen after exposure to a pesticide.

We review a broad range of animal toxicity studies. These are experiments done on animals to determine if a pesticide could have negative effects on humans. We review studies on cancer, birth defects, reproduction and development, damage to genetic material, and other health effects.

For more information on animal toxicity studies for pesticides, visit Guidance for Developing Datasets for Conventional Pest Control Product Applications: Data Codes for Parts 1, 2, 3, 4, 5, 6, 7 and 10.

2. Dose-response assessment

The dose-response assessment studies the relationship between different levels of pesticide exposure (dose) and health effects (response).

It determines:

• how much pesticide a person can be exposed to without harm
• the level of pesticide exposure that may cause health effects
• potential health effects from a single exposure to a pesticide
• potential health effects from pesticide exposure over a person's entire life

3. Exposure assessment

The exposure assessment checks when, where, and how much a person may be exposed to a pesticide. A person can be exposed to a pesticide in many ways. For example, through what they eat and drink (considered in the Dietary assessment) or where they live or work (considered in the Occupational, residential and bystander assessment).

People can be exposed to a pesticide through:

• the food and water they consume
• breathing in residues in the air
• direct skin contact
• activities that lead to contact with pesticide residues on surfaces

People can be exposed to different amounts of pesticide based on factors like age, sex, and lifestyles. We consider these factors when conducting the exposure assessment. We make decisions about the pesticide to protect the most high-risk population.

4. Risk characterization

The risk characterization estimates how likely it is for people to have negative health effects after exposure to a pesticide. It brings together information from the:

• hazard identification
• dose-response assessment
• exposure assessment

PMRA scientists use the information to describe the overall risk from a pesticide, including the likelihood and severity of health effects. We use the risk characterization to decide whether the pesticide can be used in Canada safely, and if so, under what conditions.

Types of human health risk assessments

A human health risk assessment evaluates how pesticides could affect people's health through different activities in their daily lives — from what they eat and drink to where they live and work. Each type of human health risk assessment follows the steps in Conducting a human health risk assessment.

Dietary risk assessment

Dietary assessments check for potential risk from exposure to pesticides in food and drinking water.

We check the different types and amounts of food that people eat based on:

• age
• sex
• ethnicity
• geographic areas
• seasonal eating habits (including imported and domestic food)

We also consider how much residue from a specific pesticide is on the food that a person may eat in one day and over a lifetime.

If a dietary risk assessment shows that there is no health concern from exposure to the pesticide-treated food, then we set a maximum residue limit (MRL). We set MRLs for each combination of pesticide and food. An MRL is the highest amount of pesticide residue that may stay on or in food when a pesticide is used according to label directions. We use MRLs to check if pesticides are used properly. The amount of pesticide residue on food grown in or imported to Canada must be low enough to not harm people's health.

For more information on maximum residue limits, visit Maximum residue limits, human health, and food safety.

Occupational, residential and bystander risk assessments

These assessments check the potential risk from pesticide exposure based on where people live and work:

• Pesticide exposure at work: Occupational exposure assessments estimate how much a person who works with pesticides could be exposed to them. The assessment considers people who handle or apply pesticides. It also considers people who work in areas that are treated with pesticides.
• Pesticide exposure at home: Residential exposure assessments estimate how much pesticide a person could be exposed to in and around their home. The assessment considers how people are exposed to pesticides through uses like personal insect repellents, flea and tick products for pets, pesticides for household insects, and products used in lawns, gardens and pools. This assessment also considers pesticide uses in institutions such as schools and hospitals, public areas such as parks and other recreational areas.
• Bystander exposure to pesticides: Bystander exposure assessments estimate how much pesticide a person could be indirectly exposed to near an area where a pesticide is used.

For information occupational, residential and bystander risk assessments, visit Science Policy Note SPN2014-01: General Exposure Factor Inputs for Dietary, Occupational, and Residential Exposure Assessments.

Cancer risk assessment

If scientific studies show that a pesticide could cause cancer, we do a cancer risk assessment. The cancer risk assessment follows the steps in Conducting a human health risk assessment. We evaluate how carcinogenic (cancer-causing) a pesticide is, and how people may be exposed to it.

The assessment is based on evidence from cancer studies in animals and other resources, including information about:

• how likely it is that being exposed to a pesticide could increase the chance of getting cancer (carcinogenic potential)
• the way a pesticide could cause cancer (mode of action)
• effects after short- and long-term exposure to a pesticide
• effects to the genetic content of a cell (genotoxic effects)

Aggregate risk assessment

This assessment considers how much combined non-occupational exposure a person may have to one pesticide. We consider how a person may be exposed to a pesticide through:

Different pathways, like:

• food
• drinking water
• household uses

And different routes, like:

• breathing it in
• skin contact
• ingestion

Then, we study the possible health effects of the combined exposure across all pathways and routes.

For more information on aggregate risk assessments, visit Science Policy Note: General Principles for Performing Aggregate Exposure and Risk Assessments.

Cumulative risk assessment

This assessment considers how much non-occupational exposure a person may have to two or more pesticides that work in similar ways or have the same mode of action. Then, we study the possible health effects of the various exposures.

For more information on cumulative risk assessments for human health, visit Science Policy Note SPN2018-02, Cumulative Health Risk Assessment Framework

More information

For more information on human health risk assessments, visit:

• Video: Pesticides – Health Canada assesses health risks
• Infographic: Pesticides and Human Health
• Infographic: Consideration of Sex and Gender in Pesticide Risk Assessment