Few people would make an important purchase on trust alone. The same logic applies to pesticides.
Getting the best scientific information about the safety of pesticides can be challenging. There is almost always some uncertainty in the science, making it sometimes difficult to navigate the research on pesticides.
Workers spray pesticides on strawberry fields. Most of the studies that examine the effects of pesticides are funded by the chemical’s producer. (Shutterstock)
I have been researching environmental contaminants for 25 years, focusing on situations where chemical products are found at above-normal concentrations in the environment, and trying to determine when they pose a real environmental threat.
Unbiased study design
The design of a scientific experiment influences its results. The experiment can be engineered to demonstrate a chemical’s positive effects or its environmental impact, depending on the desired outcome.
Potatoes contaminated by insects. A poor risk analysis can have disastrous effects on a crop yield. Shutterstock
For example, if I did a small pilot study on a number of randomly selected farms, I could determine after my first season which sites showed the most (or the least) variation. The next year, when I do a more thorough study, if my sites are truly chosen at random, the results won’t be misleading.
But if I have selectively chosen certain types of sites to obtain a clearer result, and not mentioned it, I will have introduced a sampling bias that may be very difficult to detect when others evaluate the quality of my research. The results may appear valid, but they will in fact have been manipulated to promote the desired results.
When perusing the scientific literature on pesticides, it is difficult to screen out what has been designed objectively and what has been funded by industry with a potentially biased intent. The recent obligation of scientists to declare conflicts of interest has been essential to trust the results. Many of the available studies on pesticides are funded and designed by the companies that produce the chemicals. Companies that do a large number of studies may set aside the results of some studies, but widely distribute the results of others.
Pesticides being spread in a field. Most pesticide research is funded by the producers of the chemical products. Shutterstock
Worse still, some researchers working on the environmental impact of pesticides may face attacks by industry on their scientific credibility, ethics and even their personal lives. For example, Tyrone Hayes, a biologist at the University of California, Berkeley, experienced numerous setbacks. His work on the herbicide atrazine was challenged by Syngenta, the large agribusiness that makes the chemical and attempted to discredit him and invalidate his published work.
Pesticides are designed to be toxic and used to eliminate pests. Herbicides target weeds, insecticides control insects and rodenticides target harmful rodents.
Desert locusts wreak havoc on horticultural farms and create headaches for farmers. Shutterstock
Unfortunately, given their inherent toxicity, they are never fully selective —all pesticides have the potential to harm plants, fish, insects and birds. Some affect predators, such as marine mammals, eagles and polar bears, and many are persistent organic pollutants.
The challenge for regulators is to figure out how much of the chemical will have a significant deleterious impact on significant individuals or organisms. The scientist can determine the number of species that will be affected and to what extent, but the level of acceptable impact is often a societal decision.
Uncertainties in risk estimates
When a manufacturer markets a new pesticide, it must produce several risk assessment studies. Toxicological studies need to address a pesticide’s effects on humans; ecotoxicological research shows its interactions with the environment. These studies determine maximum doses and threshold criteria to preserve environmental quality in drinking water, soils or aquatic life.
This exercise determines the highest possible concentrations that can be allowed without adverse effects on human health and the environment, and it must be done on the basis of quality scientific studies free from conflicts of interest.
If there’s any doubt about the environmental or health risks associated with a chemical, regulatory agencies should use the precautionary principle to avoid causing irreparable damage. This approach, however, is often in conflict with the U.S. approach of not regulating a chemical until the damage is demonstrated and proven to prevent any legal challenge.
It’s also important to understand that as scientists do more studies and explore more situations, they are more likely to find a species that is particularly sensitive to the pesticide or identify conditions that aggravate its toxicity. The criteria to protect health and the environment almost always evolve over time and the regulations become tighter.
This is why we see pesticides introduced and then banned years later. For example, a century ago, lead arsenate was used to control insects. When DDT (dichlorodiphenyltrichloroethane) was introduced in the 1940s, scientists expected it would be more efficient and without the risks associated with arsenic.
By the 1970s, however, DDT was banned in the United States, based on its harmful effects on wildlife — it killed eagles and falcons — and affected human health. The agriculture industry then switched to organophosphate pesticides. These did not have the same risks as DDT, but were later found to have neurotoxic effects on children, even at low concentrations.
DDT is still being sprayed in villages in Thailand. The product kills mosquitoes responsible for malaria, encephalitis, dengue fever and Zika, but it has proven health risks. Shutterstock
Today, we use neonicotinoids and glyphosate, currently the most widely used herbicide in the world. More than one-third of food samples tested by the Canadian Food Inspection Agency between 2015 and 2018 contained glyphosate residues.
Beware of dogmas
We must also be careful not to fall into a dogmatic approach that rejects the use of all synthetic chemicals. A distinction must be made between cases in which moderate and minimized pesticide use can be beneficial without causing significant impact on human health or the environment.
We must also listen to alternative agronomic approaches that reduce pesticide dependence. Impartial information should be provided to agricultural producers.
We should not expect stakeholders whose livelihood depends on the sale of pesticides to be objective on the debate between conventional pesticide-based agronomic approaches and novel approaches that might be economical and efficient but would lower sales of pesticides and their revenues.
The Conversation Africa The Conversation Africa is an independent source of news and views from the academic and research community. Its aim is to promote better understanding of current affairs and complex issues, and allow for a better quality of public discourse and conversation. Go to: https://theconversation.com/africa
About the author
Sébastien Sauvé is a Professeur at the Université de Montréal.
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