Water monitoring for pesticides

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Health Canada's Pest Management Regulatory Agency (PMRA) is working to establish a national water monitoring program for pesticides. This program will collect more water monitoring data and be supported by sampling partners across Canada. To ensure consistency in the data, a framework is being developed to establish guidance for items such as site selection and sampling frequency. To inform framework development a pilot sampling program is underway.

Data from this program will help the PMRA make more informed and timely regulatory decisions about pesticides. These data will also allow for the identification of areas where risks to human health and aquatic organisms may be present and further investigation is needed to inform regulatory action.

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How do pesticides enter water?

Pesticides are chemicals that are used to control pests. When pesticides enter the environment, various chemical reactions and biological processes break them down over time into other chemicals. Those chemicals are called transformation products. Pesticides and their transformation products can move through the environment:

Pesticides may enter Canada's waters many different ways. When pesticides are applied in agricultural and forestry environments, they can travel in the air (called spray drift) and unintentionally land in a body of water. After pesticides are applied, they may enter surface water through runoff or move through soil to groundwater. Pesticides can also enter surface water through rainfall and when they are attached to dry particles such as dust. See Figure 1 below. Pesticides used indoors may enter surface water through wastewater discharge.

Figure 1. Diagram that shows how pesticides can enter waterbodies following application to a field
Figure 1. Text version below.
Figure 1 - Text description

Cross-section of the surface of the Earth representing the major compartments of air, soil, surface water, and groundwater. The image shows the routes by which pesticides can enter into surface water and groundwater. There is a long, gold-coloured, rectangular box across the bottom of the image that is labeled "Soil" with six green plants on the surface of the ground on the left. Underneath the box representing soil, there is a thin blue strip on the left that reads, "Groundwater." The word "Transformation" is in the soil along with the word "Leaching" and a black downwards arrow pointing from the top of the soil towards the groundwater. On the right side of the image, there is a blue colour on top of the soil representing a cross-section through a lake. The blue colour is labeled, "Surface Water" and there is a black silhouette of a fish in the lake and the label "Transformation." A tractor is on top of the soil on the left side. The tractor is spraying a pesticide on the green plants. There is a grey arrow pointing from the pesticide spray to the lake and this arrow is labeled "Spray drift." There is also a grey arrow pointing from the soil where the pesticide is sprayed to the surface water and this arrow is labeled as "Surface runoff." Above the image, in the area representing the sky, is the word, "Precipitation" with a grey cloud and three rain drops falling from it in the middle of the image and a yellow image of the sun in the top right corner of the sky area. From the lake, there is a black arrow pointing upwards with the word "Volatilization." Between the sun and the lake are the words "Phototransformation in water and soil."

Why Canadians may be concerned about pesticides in water

Some Canadians are concerned about pesticides in Canada's waters and how they may affect their health and/or the health of our ecosystems.

Drinking water is collected from both surface water and groundwater and may be treated by communities to reduce contaminants such as bacteria, viruses, debris and chemicals. The level of treatment and methods used to treat drinking water can differ across Canada. For example:

Pesticides that enter freshwater environments, such as lakes and rivers, may cause effects to non-target organisms that live in and around these environments. The possible effect on non-target organisms depends on the amount and type of pesticide that may enter these environments and how long the organisms are exposed in the water.

How water monitoring data are used in pesticide risk assessment

The PMRA determines the possible risks to humans from pesticides that may be found in drinking water (surface water and groundwater) and the possible risks to aquatic non-target organisms (surface water).

PMRA's scientists use a combination of computer modelling and real-world data to predict if there may be risks to human health and aquatic organisms.

Computer models are used to estimate the concentration of a pesticide in groundwater and surface water. These estimations are based on the chemical and physical properties of the pesticide and how it is used based on the product label.

When water monitoring data is available from Canada (and sometimes other countries), it can be used to further investigate if there are risks to humans or aquatic organisms. If possible risks are identified, PMRA may put in place measures to manage the risk from that pesticide. These measures would appear on product labels and are legal requirements that must be followed to use the pesticide.

Measures to protect human health and the aquatic environment from pesticides can include spray drift buffer zones, vegetative filter strips or a reduction in the amount of pesticide applied.

Contact the water monitoring program

PMRA continues to welcome feedback from all stakeholders and partners about our pesticide water monitoring work at: pmra.water-eau.arla@hc-sc.gc.ca.

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