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Pesticides: Impacts of Persistent Contamination



In collaboration with Valerie Degas, as part of the project «Diminuer les rejets toxiques dans l'eau: j'agis aujourd'hui»


Pour lire l'article en français, cliquez ici.


While Rachel Carson and her Silent Spring (the first book on the pesticide scandal, published in 1962) rang the alarm on pesticide pollution, research on the impacts of pesticides began long before and has continued since. While new pesticides are regularly put on the market, among others, to fight against crop "enemies", they inevitably end up in the environment with undesirable impacts on environmental health. Many scientists are evaluating their toxicity and monitoring them closely.


What is a pesticide?

According to the Quebec’s Ministère de l’environnement et de la lutte aux changements climatiques, a pesticide is "a product designed to destroy organisms considered undesirable or harmful" (MELCC, 2021).

At the federal level, the name that is most commonly used is pest control product, defined as a "product, substance or organism - including those resulting from biotechnology - consisting of an active ingredient as well as formulants and contaminants, and manufactured, presented, distributed or used as a means of direct or indirect control of pests by destruction, attraction or repulsion, or by mitigation or prevention of their harmful, injurious or troublesome effects."


What do pesticides contain?

Pesticides contain active ingredients, which are at the origin of the destruction action, and adjuvants, also called formulants or inert materials (which does not mean without effect). Among the active ingredients, we find for example glyphosate, atrazine, thiamethoxam, etc. Their names are usually put forth on the labels. The formulants, meanwhile, improve the physical properties of the pesticide. They allow, for example, to obtain a better dispersion or stability of the product. They include kerosene, petroleum kerosene oil, corn syrup, honey, caramel, etc. (PMRA, 2021). These compounds do not appear on the pesticide label.


Pesticides are used for a variety of purposes. They are mainly used in agriculture, especially in "conventional" agriculture, which is the most practiced agricultural system worldwide and remains the main way to produce fruits and vegetables. This agricultural production system relies on the use of chemical fertilizers and pesticides. Pesticides can also be used by municipalities for the maintenance of parks and lawns and on private lawns to prevent the presence of unwanted species such as rodents, lice, fleas and bedbugs.

There are several ways to classify pesticides. This is done according to their use (insecticide, fungicide, rodenticide, etc.), their composition (carbamates and organophosphates, organochlorines, pyrethroids, etc.), and their toxicity (carcinogenic, hepatotoxic, immunotoxic, etc.). To list them would be long and tedious in addition to being incomplete. It is difficult to know all the types of pesticides present in the environment as well as their concentrations and their degradation by-products, but we can consider 5 large families of pesticides:

  1. Organochlorines: They are used to control pests, but are persistent in soil, food, human and animal organisms.
  2. Organophosphates: They are derived from phosphoric acid. They alter the work of acetylcholine, involved in muscle contraction and relaxation, disrupting the passage of nerve impulses at the synapses. This can lead to tetany. Organochlorines can therefore be neurotoxic.
  3. Organometallics: This is a chemical compound with at least one bond between a carbon atom and a metal.
  4. Pyrethroids: These are synthetic compounds derived from pyrethrins, natural substances from pyrethrum or chrysanthemum flowers that act as insecticides. They do not always kill insects, but they can have adverse effects on their development.
  5. Neonicotinoids: This is the most widely used class of insecticides in the world. They are known to have side effects on bees (Bonmatin et al., 2015), butterflies (Gilburn et al., 2015) and birds (Stanton et al., 2018)


What are the effects on the environment?

These pesticides are widely spread on crops, in storage areas to limit the proliferation of pests, on our heads or on pets for the treatment of lice, etc. In the agricultural sector, whether these applications are made by drone, plane, tractor or by hand, pesticides are found almost everywhere in the air, soil and water. Figure 1 shows the fate of these compounds in our environment and through the water cycle. They can be transported by air currents and end up thousands of miles away from where they were first used. During these journeys, they also have a good chance of being brought back to the ground by precipitation. It is therefore understandable that all compartments of our planet are affected. Precipitation or irrigation water will carry into the soil the pesticides not stored in the plants or their targets (insects, rodents, "weeds", etc.). Studies have shown, for example, that 100% of some agricultural soils contain pesticides (Pelosi et al., 2021).



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The effect of pesticides on health, Pierre-Henri VILLARD Mediterranean Institute of Biodiversity and Ecology


Let's take the case of persistent organic pollutants (POPs), substances known as being a serious threat to ecosystems and human health. POPs, of which there are currently 30, are persistent in the environment, i.e. they resist natural biological degradation, degrade very slowly in the environment and bioaccumulate in organisms along the food chain. This increases their life span in the environment. Exposure to pesticides leads to:

  • Biodiversity Loss: In addition to killing targeted species, pesticides are ubiquitous in the environment, contaminate the food chain and affect other non-targeted species. Some natural enemies of crop pests are also affected, as are some bird, reptile and fish populations (Marlatt et al., 2022).
  • Decline of pollinators: Although essential to the production of fruits and vegetables, bees are strongly affected by pesticides.
  • Degradation of soil health: Pesticides weaken various organisms present in the soil such as bacteria, fungi, earthworms and insects. The weakening of this microflora affects the fertility of the soil.



Pesticides also contaminate surface and ground water

Surface water runoff can carry pesticides to rivers, ponds, streams and groundwater. The St. Lawrence River is sampled and studied, and although improvements can be seen in some areas, it remains a river with many pesticides and degradation by-products (Montiel et al., 2019). Thus, there are many emerging contaminants (see Emerging contaminants article) whose effects on fauna and flora are not yet known and whose cross-toxicity mechanisms with other contaminants in the environment are also unknown.


What dangers do they represent for human health?

Because of their presence all around us and in the water, which is essential to our survival, we are constantly exposed to these pesticides. From the moment we are conceived, we are in contact, in more or less strong doses, in a chronic way (repetitive in time) or acute (in a unique way) with a multitude of pesticides. For a long time, it was thought that "the dose makes the poison". We now know that things are more complex than that. A low exposure over a longer period can lead to harmful effects.

This is the case, for example, with Parkinson's disease. According to the brief submitted by Parkinson Québec (Rigal, 2019), chronic exposure can triple the risk of developing this neurodegenerative disease in the context of professional use or passive exposure for more than 10 days per year. This degenerative disease costs more than US$ 22,000 in direct medical costs per patient per year. This document synthesizes 8 meta-analyses between 2000 and 2019 and reminds us that some pesticides that have been banned elsewhere are still used in Canada. In the list of incriminated pesticides, some have not been used for a long time, but their high persistence means that they are still found in the environment. DDT is a sad example.

Among other pesticide-related health problems, endocrine disruption is an important one. It is estimated that of the 800 or so pesticides identified, 650 are endocrine disrupting pesticides (EDP) (Girard et al. 2020). These contain ingredients that have the particularity of resembling certain natural hormones, which can lead to an alteration of the endogenous mode of action of hormones and thus disrupt natural processes such as reproduction and metabolism. This can lead to reproductive disorders such as sex ratio imbalance, various forms of infertility and cancers (Plante et al., 2022). The article by Girard et al. highlights the effects of EDPs on breast cancer, especially with compounds such as DDT, lindane or chlordane that are still in use. Atrazine, a herbicide implicated in cases of reproductive disorders, is the subject of numerous studies. Huge quantities of atrazine and its derivatives have been detected in the waters of the St. Lawrence. Despite the passage of water through treatment plants (Montiel et al., 2019), it is also found in tap water, although at levels below the Canadian guideline of 5,000 ng/L. On the other hand, it should be noted that in 48% of samples the concentrations of atrazine exceeded the European guideline of 100 ng/L and that atrazine was present in 100% of samples. This raises the issue of uniformity of recommendations and authorizations, as well as the application of the precautionary principle. For example, atrazine has been banned in Europe since 2003, where the maximal concentration limit is much lower than the one set in Canada.

Endocrine disruptors can be related to toxic effects on the immune system, as in the case of cancers, but also lead to increased allergic reactions, immunosuppression with greater sensitivity to infections, etc. (Dhouib et al. 2016, Bannerjee et al. 1996). Nothing to get excited about...


How are they regulated?

A major step forward in the field of pesticide control was made following the 2001 UN Conference on the Environment better known as the Stockholm Convention. It allowed the 12 persistent organic pollutants (POPs) most toxic to humans and the environment to be identified. Following this convention, several signatory countries committed to eliminate, reduce and/or monitor and limit the production of toxic degradation by-products of these 12 POPs (Stockholm Convention, 2001). This convention is regularly updated according to new knowledge and more than 180 countries have ratified this convention, the latest one being Equatorial Guinea in 2021.

In Canada, pesticides must be authorized by the Pest Management Regulatory Agency (PMRA) for import, sale or use and must obtain a registration number. Restrictions on use, storage, and maximum residue levels in food are tied to its use authorizations (MELCC, 2021b). Pesticides can be searched by type of active compound, formulant or trade name for mechanism of action, use patterns, risks and precautions, and toxic effects (Health Canada, 2021).

In addition to registration, these pesticides are subject to various provincial regulations such as Quebec’s Pesticides Act. The objective of this law is to reduce the damage to the environment and human health by regulating the use of pesticides. It allows for the classification of pesticides, the establishment of use permits, and the determination of contraventions to the law[GCE1] . It reinforces the law on the quality of the environment, which requires thorough impact studies before aerial applications of pesticides, for instance. It also makes it possible to establish standards and controls for the quality of water intended for consumption and to regulate the management of waste containing pesticides (MELCC, 2021b).

Municipalities also have the ability to regulate the use of pesticides and do so primarily for home use (Gerbet, 2021).


What can we do?

The use of pesticides and their presence in the environment are increasingly contested and alternative approaches, such as organic agriculture, sustainable agriculture, and others, are increasingly popular. To reduce the use of pesticides and their impact on the environment and human health, several actions can be taken at different levels. In 2019, the Regroupement national des conseils régionaux de l'environnement has submitted many recommendations to the Committee on Agriculture, Fisheries, Energy and Natural Resources. These include:

  • "Urge the federal government to reform the registration process so that it adequately protects human health."
  • "Invest in studies of alternative products for the control of nuisances of lesser health impact, while encouraging a change in farming methods."
  • "Apply the polluter pays principle, via a tax on pesticides, combined with access to subsidies for biopesticides."
  • "Conduct independent research on exposure and risks to human and ecosystem health."
  • "Prohibit agronomists from being both advisors to farmers and employees of the pesticide industry."
  • "Provide more support, and for a period of three to five years, for organizations that want to develop new niches under organic management."

From a citizen's point of view, the solutions lie in responsible consumption. On private land, favour a diversified lawn. Several tricks will allow you to completely avoid the use of pesticides and chemical fertilizers: do not cut the grass too short, do grass-cycling and leaf-cycling and grow clover. When it comes to food, choose organic options and reduce your meat consumption (a large proportion of pesticides are used for corn and soybean fields that are used as livestock feed). And don't forget to express your desire to live in a pesticide-free city to your elected officials!


For more information, see the following resources:




Bonmatin et al. (2015). Environmental fate and exposure; neonicotinoids and fipronil. Environ Sci Pollut Res 22, 35–67  

Carson, R., Darling, L., & Darling, L. (1962). Silent spring. Houghton Mifflin

Dhouib I et al. (2016). From immunotoxicity to carcinogenicity: the effects of carbamate pesticides on the immune system. Environ Sci Pollut Res Int. 2016 May;23(10):9448-58. doi: 10.1007/s11356-016-6418-6. Epub

Gerbet, T. (2021) Montréal interdit la vente et l’usage de 36 pesticides, dont le glyphosate. Radio-Canada.

Gilburn AS et al. (2015). Are neonicotinoid insecticides driving declines of widespread butterflies?

Girard, L, Reix, N. Mathelin, C. (2020). Impact des pesticides perturbateurs endocriniens sur le cancer du sein, Gynécologie Obstétrique Fertilité & Sénologie ,Volume 48, Issue 2 : 187-195,

Gouvernement du Canada. (2021) Liste des produits de formulation de l'Agence de réglementation de la lutte antiparasitaire

Hassaan, M.A., El Nemr, A. (2020). Pesticides pollution: Classifications, human health impact, extraction and treatment techniques, The Egyptian Journal of Aquatic Research, Volume 46, Issue 3,

Klaassen, C. D. (2008). Casarett and doull's toxicology : the basic science of poisons (seventh, Ser. Mcgraw hill professional). McGraw-Hill Education

Langlois, V. et al. (2010). Low Levels of the Herbicide Atrazine Alter Sex Ratios and Reduce Metamorphic Success in Rana pipiens Tadpoles Raised in Outdoor Mesocosms. Environmental health perspectives.

Marlatt et al. (2022). Impacts of endocrine disrupting chemicals on reproduction in wildlife and humans

MELCC. (2021).  A propos des pesticides

MELCC. (2021b) Encadrement légal et réglementaire.

Montiel-León et al. (2019). Widespread occurrence and spatial distribution of glyphosate, atrazine, and neonicotinoids pesticides in the St. Lawrence and tributary rivers. Environmental Pollution,Vol. 25:p29-39

Pelosi et al. (2021) .Residues of currently used pesticides in soils and earthworms: A silent threat? Agriculture, Ecosystems & Environment, Volume 305 : 107-167.

Plante et al. (2022).  Killing two birds with one stone: Pregnancy is a sensitive window for endocrine effects on both the mother and the fetus 

Regroupement national des conseils régionaux de l’environnement . (2019). Impacts des pesticides sur la santé publique et l’environnement. Favoriser la transition vers un modèle plus durable.

Santé Canada. (2021) Sécurité des produits de consommation, recherche dans les étiquettes de pesticides.

Stanton, R.L, Morrissey, C.C, Clark, R.G. (2018). Analysis of trends and agricultural drivers of farmland bird declines in North America: A review, Agriculture, Ecosystems & Environment, Volume 254, 244-254,



 [GCE1]Pas certaine de la signification en français « déterminer quelles sont les contraventions à la loi. »