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About pesticides and water monitoring

Pesticides are chemicals that are used to control pests (for example, insects, weeds, fungus, rodents, etc.). 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:

In general, people in Canada are concerned about pesticides and their transformation products in Canada's waters and how they may affect their health or the health of our ecosystems.

Health Canada’s Pest Management Regulatory Agency (PMRA) ensures that the use of pesticides is safe for both human health and the environment. As part of the evaluation process, PMRA scientists use a combination of computer modelling and real-world data to predict if there may be risks to human health and aquatic organisms from exposure to pesticides and their transformation products.

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How pesticides enter water

Pesticides and transformation products may enter Canada's waters in many ways. When pesticides are applied in agricultural, forestry and urban environments, they can travel by air (via spray drift) or by surface run-off and unintentionally enter surface water. They may also move through soil to enter groundwater. Pesticides can also enter surface water through rainfall or when attached to dry particles such as dust that fall onto water. Figure 1 shows how pesticides can enter waterbodies following application to a field. Although pesticides used indoors may enter surface water through wastewater discharge, the concentrations in water from these uses are expected to be much lower than those from agriculture, forestry and urban uses.

Figure 1. How pesticides can enter waterbodies following application to a field
Figure 1 - Text description

Cross-section of the surface of the Earth showing 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 five 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."

How Health Canada is improving the availability of water monitoring data for pesticides

Health Canada's Pest Management Regulatory Agency (PMRA) has established the Canadian Water Monitoring Program for Pesticides (CWMPP). This program will increase the amount of water monitoring data available for use by various groups who make decisions related to pesticides, including the PMRA. This program is supported by sampling partners across Canada.

To ensure enhanced consistency in data collection, a framework was developed to provide guidance on site selection and sampling frequency. To inform framework development, the PMRA engaged partners and stakeholders and completed a pilot sampling program.

Data from the CWMPP will help the PMRA make more informed regulatory decisions about pesticides. These data will also allow for the identification of areas where risks to human health and/or aquatic organisms may be present requiring further investigation. The results will also support the Government of Canada's commitment under Target 7 of the Kunming-Montreal Global Biodiversity Framework.

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Potential impact of pesticides on freshwater and drinking water in Canada

Drinking water for people in Canada is collected from both surface water and groundwater. Drinking water provided to people in Canada from community water systems is generally treated 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.

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.

Use of water monitoring data in pesticide risk assessment

For all pesticides risk assessments, computer models are used to estimate the concentration of a pesticides and transformation products in groundwater and surface water. The groundwater and surface water concentrations are used to provide an estimate of potential human exposure in drinking water. Only surface water estimates are considered for aquatic organisms. These estimations are based on the chemical and physical properties of the pesticide and how it is used based on the pesticide product label.

When reliable, relevant, and robust water monitoring data are available in Canada (and sometimes from other countries), they can be used to further inform risks to humans or aquatic organisms. In addition to data generated by the CWMPP, Health Canada is aware that other pesticide data are available in Canada. These data provide additional sites and pesticide concentrations that are considered in pesticide risk assessment along with data generated in the CWMPP.

Examples of other sources of pesticide water monitoring data in Canada include but are not limited to the following:

The ability to use the water monitoring data within a risk assessment is determined by scientists who analyze the data and other available information. This includes factors like sampling location, nearby crops, and weather during sample collection to assist with data interpretation.

If risks to human health or the environment are identified, PMRA will put in place measures to mitigate the risks. These measures may include such as spray drift buffer zones, vegetative filter strips or a reduction in the amount of pesticide applied. If the risks are deemed unacceptable, this could lead to withdrawal of the product from the market.

Contact us

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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