Why abandon pesticides?
Chemical control of harmful organisms has been known for millennia. The application of sulfur, lead, or arsenic was already practiced in ancient Greece. Closer to our time, the insecticidal properties of tobacco (nicotine) were known as early as the 17th century. In the 19th century, chemistry made major advances, and new copper sulfate–based compounds made it possible to control fungal diseases of grapevines. In the 20th century, mercury salts began to be used for seed treatment. Because of their toxicity, these substances were quickly banned.
The generic term “pesticide”, derived from the Latin meaning “to kill a contagious disease”, covers various substances (insecticides, fungicides, herbicides, and parasiticides) whose purpose is to eliminate organisms considered harmful. Pesticides therefore act against pest insects, fungi, “weeds”, and parasites. They include numerous molecules for domestic use (ant sprays, lice powders, mothballs, flea collars), for animal health applications (e.g. wood treatments against decay), and above all for plant protection or phytopharmaceutical use in agriculture, forestry, and horticulture.
The first synthetic pesticide was the well-known DDT (dichlorodiphenyltrichloroethane), created in 1874 but used as an insecticide from the Second World War onwards. It made it possible to combat vectors of serious diseases such as malaria, epidemic typhus, and bubonic plague. Because of its significant environmental impact, major health side effects, and high persistence—traces are still found in soils today—it was banned in most countries from 1970 onwards.
From the early 1980s, new insecticidal molecules appeared on the lucrative pesticide market. These synthetic products are thousands of times more potent than the original DDT.
They have worrying properties:
They are hydrophilic, meaning that rainfall disperses them into surface waters (rivers, lakes, seas) and groundwater (aquifers from which drinking water is extracted). It should be recalled that when pesticides are applied by spraying, up to 90% of the product does not reach the target organism but ends up directly in soils or in the air due to spray pressure, with well-known consequences in inhabited areas.
They are designed to coat seeds and diffuse throughout all plant structures, from roots to stamens that produce pollen. This problematic property is known as “systemic” and allows uncontrolled exposure of pollinators.
They do not target only harmful organisms but also affect many beneficial or ecologically essential species, particularly pollinators. Moreover, they are transferred to higher organisms through the food chain (e.g. contaminated insects or pesticide-laden earthworms eaten by birds; contaminated fish consumed by mammals, which in turn enter the human diet).
Finally, they have an extremely long persistence, lasting several years. In agriculture, they are not applied to treat a specific disease but are administered preventively against any potential pest threat, throughout the year. Treatments are therefore often unnecessary, while mixtures of multiple molecules amplify harmful effects on non-target organisms.
The class of neonicotinoids is even more insidious. This term refers to molecules that act on the insect nervous system, causing, among other effects, disorientation by interfering with chemical signal transmission between nerve cells. Like nicotine, these substances are addictive, causing insects to repeatedly return to treated plants and ultimately accumulate lethal doses. Other effects are also documented: reduced fertility in male and female insects and decreased overall survival.
Pesticides act not only on invertebrates but, through ecosystem diffusion and the food chain, ultimately reach humans. They are suspected of affecting the brain (neurodegenerative diseases, impaired embryonic brain development), the immune system (neoplasms), and the reproductive system (male infertility).
Numerous studies have shown that pesticides are responsible for the disappearance of three quarters of insect biomass since 1980 in Western Europe. A study published in PLOS One shows that “the American agricultural landscape is now 48 times more toxic to bees than it was 25 years ago”. A US study published in September 2018 also demonstrates the harmful effects of glyphosate on bees: this herbicide alters their gut microbiota, a barrier against many pathogens. The agrochemical industry continues to deny the results of these independent scientific studies and claims that pollinator collapse remains a mystery. Pressure from major agribusiness groups on legislative systems prevents reasonable decisions to abandon pesticides. When bans are adopted in producing countries, exports of these toxic substances to developing countries often remain authorised. This represents a peak of economic cynicism.
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