06
Aug
Pesticide Contamination of Waterway Impairs Development of Freshwater Fish, a Keystone Species
(Beyond Pesticides, August 6, 2025) A study published in Science of The Total Environment finds that “chronic pesticide exposure alters metabolism and impairs fish growth and health.”
With increasing concern about the long-term consequences of pesticide persistence in ecosystems, the scientific literature continues to expand the body of research findings on adverse effects, including impacts on marine or aquatic ecosystems and organisms. Given the known and growing risks, there is an ongoing movement to move beyond petrochemical-based chemicals for agriculture and land management by adopting policies and programs that advance organic criteria and principles, as outlined in national organic law and practiced by tens of thousands of certified farmers and land managers across the country, and even more at the international level.
Background and Methodology
“The objective of this study was to assess the physiological responses of juvenile P. lineatus exposed to environmentally relevant pesticide mixtures by integrating multiple biological endpoints across sub-individual and organismal levels,” the authors write.
The study was conducted at two sites in the Tibagi River watershed located in Paraná, a southern region in Brazil. There was a reference site (RFS) and an agricultural site (AGS), the former having minimal pesticide contamination and the latter having been managed with pesticides. The test organism for this study was the six-month-old Prochilodus lineatus (a native Neotropical freshwater fish), which is a keystone species known for its contribution “to nutrient cycling, energy flow, and sediment bioturbation [mixing of soil materials by living organisms].” The fish were exposed for 120 days, with sampling conducted at days 5, 15, 30, 60, 90, and 120.
The authors gathered biomarkers on hematological, metabolic, neurological, and histopathological data at the sub-individual level, as well as organism-level endpoints, including growth rates (absolute and specific), somatic indexes on overall nutritional health (Fulton’s Condition and Liver Somatic Index), and behavior (Swimming Endurance Index). More information can be found in the methodology section of the study. The researchers analyzed 22 organochlorine (legacy) and 33 current-use pesticides in the water samples. While the paper does not include a full list of the 55 pesticides in the study, the fungicide carbendazim, the insecticide fipronil, and the insecticide breakdown product endosulfan sulfate are specifically mentioned in terms of significant findings. The data was analyzed through three tools: Two-Way analyses of variance (Two-Way Anova) to test for significance, Principal Component Analysis (PCA), and Integrated Biomarker Response (IBR) index. PCA is used to better understand patterns among the various biomarkers over the course of the experiment, and the IBR index is used to combine and summarize biomarker responses into one number.
The authors are researchers at the State University of Londrina in Brazil, based in the Physiological Sciences Department. The authors declare “no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.” The authors acknowledge the financial support of the Brazilian Council for Scientific and Technological Development and funding from the Coordination for the Improvement of Higher Education Personnel in support of one of the PhD student co-authors on the study.
Results
The authors successfully answered their hypothesis that “chronic pesticide exposure elicits compensatory and adaptive responses in fish, increasing energetic demands and ultimately compromising growth and swimming performance.”
More specifically, AGS (agricultural site) fish exhibit various metabolic and hematological disruptions, including increased blood glucose, elevated hematocrit (percentage of red blood cells compared to blood volume), and high hemoglobin levels early in the exposure period, which the authors believe is indicative of an acute stress response. AGS fish were found to face transient inhibition of acetylcholinesterase (AChE) activity in the muscle and brain, which the authors suggest could be attributed to neurotoxic pesticide exposure, such as organophosphates.
As mentioned earlier, the authors mention carbendazim, fipronil, and endosulfan sulfate specifically, given that these compounds were detected at higher concentrations at the AGS site than at the RFS (reference or control) site. These active ingredients are linked to altered energy metabolism and growth suppression, with fipronil specifically linked to the inhibition of acetylcholinesterase, an enzyme necessary for nervous system functioning.
In terms of data analysis, IBR scores were higher at the AGS site, which the authors indicate as having greater overall stress and biological disruption. Additionally, the PCA analysis (found in Figures 8 and 9) finds that pesticide exposure was a primary driver for these physiological changes in demonstrating site- and time-dependent clustering of various biomarker responses.
Previous Research
Freshwater organisms and ecosystems are at serious risk of collapse given the cumulative exposure to pesticides, microplastics, and other toxic substances, as documented in the literature. One of the most recent studies to demonstrate this, published in Ecotoxicology, focuses on the impacts of MPs and chlorpyrifos (CPF), a widely used organophosphate insecticide, on cladocerans, a group of microcrustaceans. Chronic exposure shows reduced survival and reproductive output in both cladoceran species in this study. (See Daily News here.) A 2025 study, published in Environmental Pollutants and Bioavailability, assesses the impacts on Nile tilapia (Oreochromis niloticus), with subacute and chronic exposure to thiamethoxam, a neonicotinoid insecticide, and finds genotoxicity, oxidative stress (imbalances affecting the body’s detoxification abilities that lead to cell and tissue damage), and changes in tissue structure, among other threats to organ function and overall fish health. (See Daily News here.)
Another study published in Ecotoxicology earlier this year finds that Nile tilapia exposure to the herbicide florpyrauxifen-benzyl (FPX) elicits oxidative stress, with specific genotoxic (damage to genetic material) and hepatotoxic (damage to the liver) effects on nontarget species. (See Daily News here.) At the ecosystem level, a 2025 study in Ecology Letters finds “severe degradation of ecosystem functioning in the form of loss of organic matter consumption and dramatic shifts in primary productivity,” after performing an experiment with “36 naturally established freshwater ecosystems exposed to increasing field-realistic concentrations of the neonicotinoid thiacloprid.” (See Daily News here.)
Communities near agricultural fields are also known to experience elevated exposure to wastewater contaminants, per a recent study published in Journal of Environmental Chemical Engineering. (See Daily News here.) In analyzing nonagricultural streams in Germany in a 2025 study published in Water Research, researchers find that pesticide contamination, while lower than levels found in streams directly next to agricultural land, can occur through various routes and threatens biodiversity in essential ecosystems. (See Daily News here.)
Pesticide exposure also induces critical effects on non-freshwater ecosystems. A study in Environmental Science and Technology Letters, funded by the National Oceanic and Atmospheric Administration, is the first to find halogenated organic compounds (HOCs) in deep ocean sediment and biota off the coast of California. The test area, known as the Southern California Bight (SCB), is home to historic offshore DDT waste dumping, with part of the SCB designated as a U.S. Environmental Protection Agency (EPA) Superfund site. A total of 49 HOCs were detected in the sediment and biota, many of which are DDT-related and not previously screened for. (See Daily News here.) Pesticide exposure has also been detected in the atmosphere of deep ocean ecosystems (see Daily News here) and found to impact coral reef health. (See Daily News here.)
With the climate crisis leading to increased likelihood and severity of extreme weather events such as flooding, research published through the American Chemical Society finds that frequently flooded sites have higher levels of pesticides present due to the pesticides in surface waters contaminating the soil. The study results show that the plant vegetation in the contaminated soil then takes up the pesticides, which bioaccumulate and lead to higher contamination that can further cascade throughout the ecosystem and affect terrestrial food webs. (See Daily News here.)
For further Daily News coverage on the latest peer-reviewed science, consider reviewing the sections dedicated to water, water regulation, and aquatic organisms.
Call to Action
Beyond Pesticides continues to advocate for solutions that address the root causes of the existential threats to biodiversity, public health, and climate change. If we do not move beyond siloed approach to environmental, public health, and climate policies, there is risk of advancing piecemeal solutions that fail to meet this moment of cascading and intersecting crises.
Take action: Tell state legislators to focus on ecosystem protection, not just individual pesticides. You can also tell Congress to ensure that federal agencies affirm U.S. commitment to restoring and maintaining the chemical, physical, and biological integrity of all the nation’s protected water resources.
Featured Image Credit: dariocrosa from iNaturalist, CC0 1.0 Universal Public Domain Dedication, via Wikimedia Commons.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: Science of The Total Environment
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