By Efstathia Robakis
Synthetic pesticides can be a hot-button issue–they may be important in maximizing crop yields for an ever-growing global population, but they have also been implicated in the ongoing decline in biodiversity, despite their perception as being highly regulated. This disconnect, between seemingly-tight regulations and the environmental reality we are facing, might be an indication that we need to be doing a better job of understanding the risks and effects of these chemicals.
In a new article in Science1, Dr. Christopher John Topping and colleagues suggest that the current underestimation of the link between pesticides and biodiversity loss comes down to the questions we’re asking when they are evaluated for risk. The authors argue that the assumptions and methodologies underlying Environmental Risk Assessment (ERA) today are insufficient–leading to an incomplete picture of what’s going on in our farmlands and ecosystems–and they propose a new solution.
A central problem in ERA is that we take a “single product, single crop” approach. Pesticides are tested by applying one formulation to one crop, which is in stark contrast to the way pesticides are actually used. Farmers usually apply more than one, and often a group of pesticides, to a crop. Additionally, there are also many animals that are wide-ranging enough to encounter several different pesticides as they move between fields. The idea that plants or animals are exposed to a single pesticide at a time simply doesn’t reflect reality.
Another potential concern is that the amount of land over which a pesticide is likely to be used is not taken into account during risk assessment. When pesticides affect non-target animals (in other words, animals like bees that live in the area but don’t threaten plant growth), experiments must be done to determine whether those populations can bounce back. However, population recovery happens largely because new animals move into the depleted region from elsewhere–something that is increasingly unlikely as the area over which these pesticides are applied grows. As animal populations decline, they become less and less resilient, creating a self-reinforcing cycle that makes it difficult, if not impossible, for them to rebound.
Other problems include the indirect effects on soil health that aren’t assessed, and the fact that only a small number of animals are involved in testing. Unhealthy soil can hinder growth in non-target plants and, as a result, the animals that rely on them. For example, a pesticide may leave a spider vulnerable to predators by harming the growth of a non-target weed it depends on for shelter.
During toxicity testing, only a small number of “surrogate species” are used as stand-ins for a host of “similar animals.” To imagine how dangerous this could be, consider that small primates known as bamboo lemurs are specially adapted to eat an amount of cyanide each day that would kill a similarly-sized human twelve times over. If we were testing cyanide toxicity and used bamboo lemurs as a surrogate species for mammals in general, we would be in for a terrible surprise.
Right now, it is likely that the scope of potential problems with pesticides is underestimated. We have developed a system where negative effects of pesticides are often only identified after they occur, because we’re looking at the wrong things on the front end.
Pathways of pesticide movement in the hydrologic cycle (modified from Barbash and Resek, 1996)
To fix this, the authors of the paper call for a holistic analysis of pesticides that would reflect actual use and realistic ecological interactions. They propose using more complicated computer models to better understand how pesticides affect animals and the environment–simulations that incorporate a variety of data, such as landscape information and what happens when multiple pesticides are used on a crop.
The authors acknowledge that change at the administrative level can be slow, and argue that giving more autonomy to assessors would allow for a collaborative, nuanced approach to risk assessment. With this new method, farms, landscapes, pesticides, and farmers themselves are seen as all being part of a dynamic system. Assessors would be given the freedom to work with farmers on multi-pronged approaches to monitor risks, benefits, and outcomes. Pesticides would be grouped and scheduled to minimize potential damage to ecosystems, and other important factors–such as non-target animal population health–would be monitored. In the meantime, government bodies would work on improving ERA regulations overall.
This approach would allow farmers, assessors, and scientists to use as much data as possible to minimize risks and arrive at best practices, and will hopefully work to address a very real problem in pesticide risk assessment and biodiversity today.
1 Topping, C. J., Aldrich, A., & Berny, P. (2020). Overhaul environmental risk assessment for pesticides. Science, 367, 360-363.
More Reading. . .
Information on the USA’s Environmental Protection Agency Pesticide ERA: www.epa.gov.pesticide-science-and-assessing-pesticide-risks.factsheet-ecological-risk-assessment-pesticides
Biodiversity Decline as a Consequence of Inappropriate Environmental Risk Assessment of Pesticides: www.frontiersin.org.articles.10.3389.fenvs.2019.00177.full
Pesticides Spark Broad Biodiversity Loss: www.nature.com/news/pesticides-spark-broad-biodiversity-loss-1.13214