17
Jul
Fungicide’s Nontarget Harm to Insect Confirms Deficiency in EPA’s Ecological Risk Assessment, Study Finds
(Beyond Pesticides, July 17, 2025) The widespread use of pesticides year-after-year, decade-after-decade, has been found to lead to unintended consequences not only for public health but also for broader ecosystem stability and biodiversity. These impacts include potential nontarget harm through adverse developmental and reproductive effects on the vinegar fly, Drosophila melanogaster, the subject of a peer-reviewed study in Royal Society Open Science. The authors, who studied the organochlorine fungicide chlorothalonil, conclude, “Chlorothalonil exposure decreases larval survival, extends developmental duration and reduces fecundity.”
“Even at the lowest tested concentration, chlorothalonil exposure resulted in reduced body weight, ovariole count and egg production compared with non-exposed individuals,” the researchers find. This study builds upon years of scientific research findings and critiques of existing federal pesticide law, as well as the U.S. Environmental Protection Agency’s (EPA) failure to fully assess the adverse impacts on biodiversity and ecosystem stability during the pesticide registration review process.
Methodology and Background
The goal of this study is to evaluate the health impacts on a nontarget insect species (Drosophila melanogaster) from chronic exposure to chlorothalonil. This specific fungicide was chosen for various reasons, including its wide use across cereals, vegetables, and fruits; evidence linked to adverse health effects on vertebrate and invertebrate species; and the fungicide’s “frequent detection in soil and water bodies near agricultural areas.”
The researchers simulated chronic exposure to reflect residue levels otherwise found on produce available in the market. The experimental design to evaluate adverse developmental and reproductive health impacts includes assays for larval survival, body weight, ovariole count, egg production (fecundity), iron content (ferrozine assay serving as a proxy for male fertility), and feeding. The control group of fruit flies was provided a diet without the fungicide, while the experimental group had the fungicide product (Surefire Chlortan 720 SC) dissolved in water and mixed into the standard diet.
The authors of this study include researchers at Australia-based Macquarie University and France-based PURPAN Engineering School. There are no competing interests declared by the authors. The only funding source for this study is linked to one of the author’s Master of Research scholarships through the International Macquarie University Research Excellence Scholarship (iMQRES MRES).
Results & Analysis
The authors identify numerous adverse health effects that chlorothalonil imposes on fruit fly developmental and reproductive health, including:
- Significant decline in larval survival as chlorothalonil concentration increases;
- Egg production dropped by 37 percent over the course of the study at the lowest tested dose (5mg/kg) and dropped by over 50% at a dosage of 120 mg/kg;
- Fewer ovarioles (egg-holding structures in the fruit fly body) were developed in exposed female fruit flies;
- Body weight was significantly reduced in exposed female fruit flies, with a positive correlation found between lower body weight and reproductive health;
- Iron content significantly dropped in exposed male fruit flies, with possible implications for male fertility; and
- No significant changes in food intake at the larval stages, suggesting that some reproductive and developmental effects are not directly attributed to reduced feeding.
“These findings emphasize the potential risks chlorothalonil poses to Drosophila and, more widely, insect populations, even at low doses, and underscore the importance of assessing non-target effects in broader ecological contexts, particularly for chemicals widely used in agriculture,” the authors write in the Discussion section of the study.
“We expected the effect to increase far more gradually with higher amounts. But we found that even a very small amount can have a strong negative effect,” Associate Professor Fleur Ponton, PhD, the supervising author of the study, told SciTechDaily.
Previous Research & Advocacy
Despite a growing body of scientific literature, complex ecosystem-wide effects of synthetic pesticides are not considered by EPA. To determine legal pesticide use patterns intended to protect ecosystems (the complex web of organisms in nature), EPA requires a set of tests to measure both acute and chronic effects. An ecological risk assessment (ERA) considers the lethal concentration at which 50% of a population of a given species will die (LC50), and the chronic impacts associated with environmental exposure. However, the ERA process has failed to account for sublethal and persistent exposures, as documented in the scientific literature.
A study published in Conservation Letters in 2024 exposes critical shortcomings in EPA’s ecological risk assessment process for modeling the risks that pesticides pose to bees and other pollinators. After reviewing 252 assays from 49 studies, the authors determined EPA’s reliance on honey bee data from lab studies focused on LD50 does not accurately capture the threats that pesticides pose in the real world to thousands of other bee species with diverse life histories, genetic compositions, and sensitivities to pesticides. Additionally, for both dietary and topical exposures to neonicotinoid insecticides, multiple non-Apis (wild) bee genera like Bombus, Megachile, Melipona, Nannotrigona, and Partamona exhibit significantly higher sensitivities and lower LD50 values compared to Apis (honey bees), in some cases up to six orders of magnitude more sensitive. Looking within just the Apis genus, LD50 values for the same neonicotinoid varied by up to seven orders of magnitude, likely due to factors like genetic diversity, temperature differences, nutrition levels, and other environmental parameters that were not adequately accounted for by the ERA process. The ECOTOX database—an EPA-hosted, publicly available resource with information on adverse effects of single chemical stressors to certain aquatic and terrestrial species—is overwhelmingly populated (79.4%) by acute lethality data from studies lasting just one to five days on the western honey bee. Compounding this issue of incomplete scientific data, the authors identify that chronic, longer-term studies on diverse bee species and real-world conditions are lacking. (See here for Daily News.)
On the issue of registering new active ingredients, EPA registered a new active ingredient in 2020 (Inpyrfluxam) without performing a thorough review of its impacts on biodiversity, as well as threatened and endangered species. After being sued by the Center for Biological Diversity for failure to comply with the Endangered Species Act (ESA), EPA committed to completing draft effects determinations by Fall 2022, but fell short with an incomplete assessment, given the failure to appropriately measure chronic toxicity or test for endocrine disruption. (See here for the Daily News.)
Call to Action
The structural issues in EPA’s ecological risk assessments are not a new phenomenon; Beyond Pesticides has continuously pointed out their deficiencies in evaluating numerous active ingredients and chemicals, including atrazine, fludioxonil, neonicotinoids, carbaryl and methomyl, indaziflam, pyrethroids, paraquat, glyphosate, and wood preservatives.
You can take action today by sending a message to EPA that, in order to meet its obligations under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and ESA, it must facilitate a transition to organic practices; you can also tell Congress to ensure that EPA meets its statutory obligations.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: Royal Society Open Science
