27
Mar
New Herbicide that Mimics Hormones Threatens Nontarget Aquatic Species and Biodiversity, Study Finds
(Beyond Pesticides, March 27, 2025) In Ecotoxicology, results of a study on Nile tilapia (Oreochromis niloticus) exposed to florpyrauxifen-benzyl (FPX) suggest the new herbicide causes oxidative stress (imbalances affecting the body’s detoxification abilities that lead to cell and tissue damage), with specific genotoxic (damage to genetic material) and hepatotoxic (damage to the liver) effects on nontarget species. The authors state: “According to the available literature, no data exist on the toxicity of FPX in fish. Therefore, this study aims to investigate, for the first time, the potential toxicity and associated mechanistic effects of the pyridine-carboxylic acid herbicide (FPX) on the non-target species, Nile tilapia.â€
According to the Wisconsin Department of Natural Resources, “Florpyrauxifen-benzyl is a systemic herbicide (i.e., it moves throughout the plant tissue). It is a WSSA Group 4 herbicide, meaning that the mechanism of action is by mimicking the plant growth hormone auxin and causing excessive elongation of plant cells, ultimately killing the plant.â€
The researchers, from Menoufia University, the Agricultural Research Center, and Cairo University in Egypt, focus on FPX as it is the active ingredient in Divixton 2.5% EC, a newly released herbicide used in rice fields and applied directly to freshwater aquatic bodies for emergent aquatic vegetation. Studying the effects in Nile tilapia is crucial for the area, as the species “accounts for about 80% of Egyptian fish production,†the authors share, and “can be used as an environmental indicator of xenobiotic biotransformation and biomarker response, making it a valuable model for various monitoring programs,†they continue.
As has been extensively documented, the excessive use of pesticides and other agricultural chemicals poses a significant threat to both terrestrial and aquatic environments. (See Daily News coverage here.) The researchers note that, “Water-borne derivatives of herbicides strongly affect the well-being of aquatic animals, their productivity, and safety of aquatic organisms for human consumption.†Water contamination occurs through various sources such as runoff, soil leaching, and aerial drift. When chemicals reach bodies of water, “they may interact with other pollutants, increasing their toxicity to aquatic organisms†and cause, even in very low concentrations, “morphological, histological, and biochemical changes in their tissues,†the authors state.
The active ingredient FPX was unconditionally registered by the U.S. Environmental Protection Agency (EPA) in 2017 and is a selective herbicide used to kill post-emergent weeds. In studying this herbicide in a nontarget aquatic species, the researchers highlight disrupted hepatic (liver) functions and antioxidant responses of Nile tilapia that represent the threat to other aquatic species and biodiversity. Hepatotoxic implications can leave organisms susceptible to further health impacts, as the liver is “responsible for the detoxification of xenobiotics and other pollutants†and is “a histologically extraordinarily sensitive organ that is used to evaluate the toxic effects of different contaminants on fish, as it is the major site for pesticide’s storage, biotransformation, and excretion,†the researchers note.
Through blood samples, dissections, and analyses performed on 400 fish after exposure periods of 7 and 15 days to sublethal concentrations of FPX, the results identify oxidative, genotoxic, and hepatic changes within the organisms. The researchers find that at both durations of exposure to FPX, levels of malondialdehyde (MDA) were elevated. MDA is a biomarker associated with lipid peroxidation and oxidative stress (leading to cell damage), and elevated levels of MDA in the liver are associated with liver damage and fibrosis. The authors also report: “Concentrations of FPX induced oxidative stress in fish by altering activities of antioxidant enzymes and their transcripts. The genotoxic effect of FPX was evidenced by a significant increase in micronuclei (MNs) and ENA [erythrocytic nuclear abnormalities] frequencies.â€Â
The researchers attribute these results to FPX causing changes to hematopoiesis (the process of producing blood cells) in the fish. They report that the “oxidative stress caused vigorous damage in the mitochondrial DNA of hepatocytes resulting in the rupture of blood sinusoids and pushing of blood in the liver which resulted in the hepatopathological [liver tissue] changes.†These findings, while very complex, highlight the intricacies of health effects from pesticide exposure that are often overlooked or dismissed during pesticide regulation processes. (See more on regulatory deficiencies of EPA here.)
Additional results of the study suggest FPX toxicity may alter cell wall elasticity and gene expression, cause the enlargement of the gallbladder, encourage degeneration of the pancreatic area, alter blood vessels, cause hemorrhaging, and lead to necrosis (death of body tissue). While this is a novel study for FPX, previous research supports herbicides inducing oxidative stress in Nile tilapia and causing alterations in antioxidant activity and mRNA expression. (See studies here, here, here, here, and here.)
Of note is another study from 2024 in mice, published in the Journal of Experimental Zoology Part A: Ecological and Integrative Physiology, which found similarly that FPX exposure “exhibited apoptosis [cell death], oxidative stress, immunosuppression, and inflammatory response in a dose-dependent manner, leading to spleen tissue damage and immunotoxicity.â€
As Beyond Pesticides previously reported, pesticide contamination inflicts devastating effects on the food web and overall biodiversity. The health of aquatic ecosystems is at risk with indirect effects on nontarget species from pesticides in the environment. This includes impacts on species of fish, invertebrates, microbial communities, and marine mammals. There is an overwhelming body of science that shows the negative implications associated with pesticide exposure on the environment, including in soil, water, and air, as well as detrimental effects on human health.
Alternatives, such as organic agriculture, offer a path forward that eliminates these threats and also mitigates the current climate change crisis. Beyond Pesticides’ mission is to lead the transition to a world free of toxic pesticides. To join in this holistic solution, you can start by buying organic products and making The Safer Choice to avoid hazardous home, garden, community, and food use pesticides. Stay informed with the Daily News Blog and take action to create meaningful change with Action of the Week.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Nabet, N. et al. (2025) The induced hepatotoxicity and genotoxicity in Oreochromis niloticus exposed to a newly released florpyrauxifen-benzyl herbicide, Ecotoxicology. Available at: https://link.springer.com/article/10.1007/s10646-025-02864-1.
