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Chemical Contaminants

Contemporary Pesticides

Pesticides are substances used to prevent or terminate pests. Pests include a variety of living things, each capable of causing damage to human activities, such as crop farming. 

The most widely used classes of pesticides in Canada are herbicides, insecticides and fungicides for the control of weeds, insects and funguses, respectively. Pesticides have been used for hundreds of years all over the world, though the active ingredients have changed over time due to improved understanding of environmental pollution, including unintended toxicity to living things that are not the target pest. 

Herbicides, such as 2,4-D, can be applied through spraying operations over agricultural areas. But the herbicide can drift through the atmosphere to other areas, including nearby aquatic ecosystems (rivers and lakes).

Urban centres also contribute pollution from lawns and golf courses that use pesticides, and from the leaching of products such as paint and construction material which use fungicides for protection from mildew. Human pharm​aceuticals and personal care products can also contain pesticides in the form of antimicrobials (anti-dandruff shampoo, for example) and these can enter the municipal waste stream through household drains (the shower). The contaminants aren’t necessarily removed during waste treatment and are then released into aquatic ecosystems through the effluent.

In 2009, the Cosmetic Pesticides Ban took effect in Ontario and prohibits the sale and use of specific pesticides for cosmetic (appearance) purposes on lawns, gardens, parks and schoolyards. Societies require effective pest management strategies (which could include natural remedies) that are also safe for the environment.  The search for sustainable solutions presents a continuous challenge to agricultural, chemical and scientific communities.

A program for monitoring pesticides from an agricultural area in the Lake Simcoe watershed began in 2018 and has indicated the presence of some herbicides and insecticides.​

What are contemporary pesticides?​

A pesticide, sometimes referred to as a biocide, is a general term to describe substances used for preventing, destroying, repelling, or mitigating any biological pest. The most widely used types of pesticides in Canada include herbicides for weed control, insecticides for insect control and fungicides for fungi control. There are many other types of pesticides such as rodenticides to control rodents, or antimicrobials and disinfectants to control bacteria and viruses. Ideally, a pesticide should be harmful to the pests of interest only and not to other, non-target organisms.

Pesticides have provided incredible advantages to societies in many ways, for example, by increasing crop yields and therefore bolstering food availability and the economy. Unfortunately, their use can have negative impacts as well. The agricultural, pesticide-producing and scientific communities are continually challenged to find sustainable solutions. This is a very difficult goal to achieve, especially when adverse effects to the environment from the chemicals used are not always known.   

This page discusses contemporary pesticides which are used currently or have recently come under restriction in Ontario. Pesticides that were used more historically such as DDT, often referred to as legacy contaminants because they can remain in the environment long after they were used. Some pesticides are also classed as flame retardants​ (including Mirex). There are many other contemporary pesticides than those described on this pesticides page; the specific pesticides summarized here were chosen because of their widespread use in Canada and globally, their potential for environmental damage, recent regulations pertaining to them and simply to use as examples amongst the many other existing pesticides.


One of the most commonly used of all pesticides is 2,4-D (2,4-dichlorophenoxyacetic acid), used as a herbicide to control weeds. Being commercially available since 1945, 2,4-D is one of the oldest and most widely used herbicides in the world. It kills most broadleaf weeds including dandelions, but does not affect grasses such as cereals and lawn grass. It can be used in home gardening, agriculture (crops and orchards), forestry applications, to control aquatic plants and other uses, though its use is restricted in some parts of Canada (see section below, “Action to Reduce Pesticides in the Environment”). In Canada, there are 143 registered products that contain 2,4-D, with about 10% of these being registered for domestic use (though their availability for domestic purposes would depend on provincial restrictions). An example of a product containing 2,4-D has the trade name Ortho Killex®. 


Glyphosate is an organophosphate compound that was first registered for use as a pesticide in Canada in 1976. It is now the most widely used herbicide in Canada (and the U.S.), especially in the agricultural sector, but it is also used in forestry, industrially, commercially, for home gardening and for aquatic plant control. According to a recent label search, there were 176 products listed with glyphosate as an active ingredient registered in Canada (Health Canada, 2016) with about 20% of these registered for domestic use. An example of a product that contains glysophate is the trade name Round-Up®. Like 2,4-D, products containing glyphosate are banned for certain purposes in some provinces including Ontario (see section below, “Action to Reduce Pesticides in the Environment”). 


Neonicotinoids are a relatively new class of insecticide made up of nicotine-based systemic chemicals. The first neonicotinoid, Imidacloprid, was developed in a research center in 1985 and launched as an insecticide in the early 1990s. It was the most used insecticide globally by the late 1990s (Yamamoto, 1999), including widespread use in Canada. Several other neonicotinoids have entered the market since then. They are used for crops in Ontario, especially corn and soybean (by coating the seeds with the insecticide before planting) and in horticulture, nurseries and urban forestry and have the ability to control beetles, fleas, some wood-boring pests, flies, cockroaches and others. When neonicotinoid coated seeds sprout, the insecticide is translocated to the leaves, stems and roots of the plant, protecting the plant from targeted pests, but also potentially harming non-target org​anisms.​​

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Mobility and fate of contemporary pesticides in the environment​​

Many contemporary pesticides can be highly persistent and mobile in the environment, toxic to non-target organisms and can negatively affect ecological integrity.

Herbicides, such as 2,4-D, can be applied by spraying operations and can volatilize and drift through the atmosphere to unintended target areas, including aquatic systems. Herbicides have the potential to travel through the atmosphere for hundreds of kilometres from the original source and be deposited in distant and possibly pristine aquatic systems (Metcalfe et al., 2016; Thurman and Cromwell, 2000).

Agriculture is not the only source of contemporary pesticides to surface waters. Urban centres can contribute these contaminants from water pollution control plant (WPCP) discharges, lawn runoff, manicured green spaces such as golf courses and from leaching of products such as paint and construction material. Human pharmaceuticals and personal care products can also contain pesticides such as antimicrobials (anti-dandruff shampoo, for example) and fungicides which can enter aquatic systems through the municipal waste stream (Metcalfe et al., 2016). WPCPs are typically not designed to remove pesticides, however Kahle et al. (2008) noted that one fungicide used as a pharmaceutical was unintentionally removed during treatment of other wastes.


The herbicide, 2,4-D, is moderately persistent in the environment, lasting a week in most soil types depending on conditions (aerobic versus anaerobic conditions, for example) and several weeks or months in surface waters, but only lasting about a day in the atmosphere (World Health Organization (WHO), 2003). Microbial metabolism is the primary mechanism of degradation though the rate depends on environmental conditions (soil moisture, for example; Tu et al., 2001). It does not typically accumulate in bottom sediments and, except for some algae, it does not bioaccumulate in organisms or biomagnify in the food chain (Health Canada, 1993). There is potential that ground water systems could become contaminated, especially where spraying occurs often.


Glyphosate binds readily to soil and can persist for up to six months before it is degraded by microbes in the soil. It is extremely soluble in water but also strongly adsorbs to sediment, reducing its movement in runoff during rain events (Byer et al., 2008), though this would be dependent on how much erosion occurs in a given system. Byer et al. (2008) found measurable quantities of glyphosate in surface water throughout southern Ontario from both urban and agriculture areas, but they were always below the Canadian Water Quality Guideline (CWQG) for the protection of aquatic life (Canadian Council of Ministers of the Environment (CCME), 1999 and 2012). The increasing use of ethanol in gasoline has led to a greater demand for corn production resulting in additional pesticide use (i.e., glyphosate). With these increases of glyphosate use, Byer et al. (2008) suggested that monitoring of surface waters should continue.


Neonicotinoid compounds are highly persistent and mobile in the environment. They are stable in soil and also soluble in water having the potential to move into watercourses through runoff. Nicotinoid-containing dust from treated seeds can be dispersed into the atmosphere during planting. Pollinating insects such as bumblebees, a non-target species, can come in contact with these insecticides on parts of the treated plant when they are consuming and collecting pollen. They can also track the residues back to their hives. Neonicotinoids can be directly toxic to honey bees and their colonies, causing death, or can cause behavioral issues including navigation (returning to their hives) and reproduction problems.


Environmental impacts​


Generally, 2,4-D is considered to have moderate toxicity to birds and mammals and is slightly toxic to fish and aquatic invertebrate, but evidence suggests that it is not toxic to honeybees [United States Environmental Protection Agency (USEPA), 2018] or other beneficial insects. Some ch​emical forms of 2,4-D used in  pesticide formulations are more toxic than others, though the most toxic chemical form, esters, can degrade to a less toxic form once they are in the environment (USEPA, 2016).


Reports have found that glyphosate is relatively non-toxic to fish species. Invertebrates, freshwater plants and algae studied did not exhibit particular sensitivity to short-term glyphosate toxicity. For long-term exposures, freshwater algae and aquatic plants were generally more sensitive than invertebrates and fish. But glyphosate seems to be directly toxic to some species of amphibians. See summarization of several studies by CCME (2012) for more information regarding the above toxicity results. Glyphosate can also alter ecosystem functioning by changing vegetation structure (e.g., plant species diversity; Rodríguez et al., 2017) and microbial populations (Druille et al., 2015). The effects of glyphosate on the environment are a concern and of importance to researchers, who are trying to understand any harmful effects more fully. 


There is increasing evidence that some neonicotinoid compounds are very toxic to honey bees and other beneficial insects.  Once in watercourses, they may also harm aquatic insects. Reports of declining bee populations, including from bee farmers, have been documented since the late 1990s. Honey bees not only produce honey but they are important pollinators of agricultural crops and natural vegetation. Seeds treated with neonicotinoids can be toxic to birds that ingest them and insect-eating birds could otherwise be affected when invertebrate populations decline from neonicotinoid toxicity.  

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Pesticides in the Lake Simcoe watershed

As part of the Provincial Water Quality Monitoring Network (PWQMN), monitoring of pesticides commenced in 2018 at the outlet of the Holland Marsh vegetable polder (collaborators include LSRCA, Ontario Ministry of the Environment, Conservation and Parks (MECP) and Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). Over 500 pesticides (both contemporary and legacy/historically used pesticides) are being screened, including neonicotinoid insecticides and herbicides such as glysophate.

So far, samples have been collected on four occasions in the early part of 2018 (January to April) and data show that several neonicotinoid compounds were present, including Imidacloprid at levels below the interim CWQG (CCME, 2007). Glyphosate was not present but several other herbicides including 2,4-D were observed. There were also sev​eral fungicides and insecticides. In total, there were 28 different pesticide chemicals observed (including legacy pesticides such as DDT and its metabolites) with 17 of these occurring only at levels below the Method Detection and Quantification Limits (MDLs and MQLs; benchmarks of the lowest concentration values that can be reliably detected or quantified, respectively, in the laboratory procedures). Many of the pesticides are listed as Class 9 pesticides, banned under the Pesticides Act (MECP, 2018c). Observations of some pesticides at this location may represent previous use rather than current use, due to their persistent nature. Sampling will continue and more detailed results will be available in future. 

Additional Ontario Studies and Resources

Metcalf et al. (2016) reported that 2,4-D was detected in samples from three out of six Lake Ontario urban river sites with levels recorded below the CWQG for the protection of aquatic life in freshwater ecosystems. The Ministry of Environment and Climate Change (MOECC; in collaboration with ECCC and Conservation Ontario) observed that levels of three herbicides in Ontario streams, including 2,4-D, decreased significantly in correspondence with the Cosmetics Pesticides Ban, both in its pending and enacted period (Todd and Struger, 2014; MECP, 2018a).

There has been widespread use of neonicotinoids in Ontario, where up to 100% of corn seed and 60% of soybean seed sold in Ontario were treated (MECP, 2018b), in the peak of their use. These insecticides were often used preventatively, in places where there were no signs of pest issues. The MOECC initiated a monitoring study in 2015 to observe neonicotinoid levels in the surface waters, soils and benthic invertebrates of watersheds with substantial amounts of corn and soybean crops. These and several other studies by MECP (neonicotinoid concentrations in pollen, for example) are being carried-out in order to better understand effects that this class of insecticides and use-reductions may have on pollinator populations. Additional monitoring in future years will track changes from the initial 2015 study (MOECC, 2017).

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Action to reduce contemporary pesticides in the environment

Under Ontario’s legislation including the Ontario Pesticides Act and Ontario Regulation 63/09, the Cosmetic Pesticides Ban that took effect in 2009 prohibits the sale and use of specific pesticides for cosmetic purposes on lawns, gardens, parks and schoolyards (MECP, 2018a). More than 250 pesticide products are banned for sale and over 95 pesticide ingredients are banned for cosmetic uses, including products with glysophate, 2,4-D and some neonicotinoids. Consumers would have to use lower risk pesticides, biological controls (natural predators, for example) or other alternatives outside of the banned products. There are exceptions for various uses such as public health and safety (e.g., poisonous plants), on golf courses and for the protection of Natural Resources (e.g., invasive species) (MOE, 2009).

On July 1, 2015, the sale and use of neonicotinoid-treated seeds in Ontario became regulated. The requirements support the objective of reducing the number of acres planted with neonicotinoid-treated corn and soybean seed by 80 % by 2017 (MECP, 2018b). Neonicotinoid-treated corn and soybean seeds can only be used where there is a valid pest problem. The reduction of neonicotinoid use for these two crops should substantially decrease pollinator exposure to this pesticide.

The reductions of neonicotinoid use will undoubtedly impact conventional farming practices, with changes in equipment and labour required to uphold the regulations. For farmers already engaged in organic methods, practices that work with the natural environment are already in place to assist in the prevention of damage to crops from pests and to preserve yields.

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Byer JD, Struger J, Klawunn P, Todd A, Sverko E. 2008. Low cost monitoring of glyphosate in surface waters using the ELISA method: An evaluation. Environ. Sci. Technol. 42: 6052–6057.

Canadian Council of Ministers of the Environment (CCME). 1999. Canadian water quality guidelines for the protection of aquatic life. In: Canadian environmental quality guidelines. Winnipeg, Manitoba: CCME.

CCME. 2007. Canadian water quality guidelines for the protection of aquatic life, imidacloprid. In: Canadian environmental quality guidelines. Winnipeg, Manitoba: CCME.

CCME. 2012. Canadian water quality guidelines for the protection of aquatic life, glyphosate. In: Canadian environmental quality guidelines. Winnipeg, Manitoba: CCME.

Druille M, Cabello M, García Parisi P, Golluscio R, Omacini M. 2015. Glyphosate vulnerability explains changes in root-symbionts propagules viability in Pampean grasslands. Agric. Ecosyst. Environ. 202: 48–55.

Health Canada. 1993. 2,4-Dichlorophenoxyacetic acid. In: Guidelines for Canadian drinking water quality. Ottawa, Ontario: Health Canada.

Health Canada. 2016, October 4. Pest Management Regulatory Agency (PMRA)’s pesticide label search.

Kahle M, Buerge IJ, Hauser A, Muller MD and Poiger T. 2008. Azole fungicides: occurrence and fate in wastewater and surface waters. Environ. Sci. Technol. 42: 7193–7200.

Metcalfe CD, Sultana T, Li H and Helm PA. 2016. Current-use pesticides in urban watersheds and receiving waters of western Lake Ontario measured using polar organic chemical integrative samplers (POCIS). J. Great Lakes Res. 42: 1432-1442.

Ministry of the Environment (MOE). 2009, March 4. Newsroom (archived backgrounder): Ontario’s Cosmetic Pesticides Ban. Retrieved from:

Ministry of the Environment and Climate Change (MOECC). 2017, June 6. Pollinator health. Retrieved from:

Ministry of the Environment, Conservation and Parks (MECP). 2018a, July 17. Water quality in Ontario report, 2014. Retrieved from:

MECP. 2018b, August 31. Neonicotinoid regulations. Retrieved from:

MECP, 2018c. July 30. Class 9 pesticides. Retrieved from:

Rodriguez AM, Jacobo EJ and Golluscio RS. 2017. Glyphosate alters aboveground net primary production, soil organic carbon, and nutrients in Pampean grasslands (Argentina). Rangeland Ecol. Manage. 71: 119-125.

Thurman EM and Cromwell AE. 2000. Atmospheric transport, deposition, and fate of triazine herbicides and their metabolites in pristine areas at Isle Royale National Park. Environ. Sci. Technol. 34: 3079–3085.

Todd A and Struger J. 2014. Changes in acid herbicide concentrations in urban streams after a cosmetic pesticides ban. Challenges 5: 138-151.

Tu M, Hurd C and Randall JM. 2001. Weed control methods handbook: Tools & techniques for use in natural areas. The Nature Conservancy.

United States Environmental Protection Agency (USEPA). 2018, February 21. 2,4-D. Retrieved from:

USEPA. 2016, February 20. Pesticides: Reregistration, 2,4-D RED facts. Retrieved from:

World Health Organization (WHO). 2003. 2,4-D in drinking-water: Background document for development of WHO guidelines for drinking-water quality. Geneva, Switzerland: WHO.

Yamamoto I. 1999. “Nicotine to nicotinoids: 1962 to 1997”. In: I Yamamoto and J Casida (Eds.), Nicotinoid insecticides and the nicotinic acetylcholine receptor. Tokyo, Japan: Springer-Verlag. ​

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Chemical Contaminants in Lake Simcoe and its Tributaries

in 2015, a study was undertaken to investigate levels of chemical contaminants in the surface water and sediments of Lake Simcoe and its tributaries. The contaminants included in this study were chosen based on historical use within the watershed, previous research undertaken (such as the LSRCA 2004 study), and literature from similar areas in the Great Lakes Region. 

Read Chemical Contaminants in Lake Simcoe and its Tributaries

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