16
May
Study Identifies Developmental Effects from Neonicotinoid Insecticides that Harm Biodiversity
(Beyond Pesticides, May 16, 2024) In a recent study at the Institute of Biochemistry and Molecular Biology at Ulm University in Germany, published in Current Research in Toxicology, scientists exposed embryos of South African clawed frogs (Xenopus laevis) to three neonicotinoids (NEOs), which led to developmental effects down to a molecular level. These frogs are a well-established model species often used in ecotoxicology studies as bioindicators for overall environmental and ecosystem health. When amphibian species like Xenopus laevis are exposed to contaminants in the water, it leads to negative impacts in the food chain and harms biodiversity. The study concludes that exposure to NEOs directly or through contaminated water leaves entire ecosystems vulnerable. Â Â
The NEOs that the embryos were subjected to include imidacloprid (IMD), thiamethoxam (TMX), and its metabolite clothianidin (CLO). NEOs are a class of insecticides that target the central nervous system of insects and lead to death. These insecticides pose a potential hazard to nontarget organisms, such as animals and humans, since they are persistent in the environment and “are found in natural waters as well as in tap water and human urine in regions where NEOs are widely used,†this study states. The authors continue by saying, “Pesticide residues can enter natural waters through leaching, run-off, or “worst-case†scenarios (e.g., incorrect handling or improper disposal), which brings amphibians into contact with the pesticides.†Previous studies have shown impacts on amphibians to NEOs throughout multiple life stages, but this study focused on early developmental effects to determine impacts on survival. Â
To ascertain if NEO exposure was harmful during embryogenesis, the frog embryos were incubated in five milliliters of the three different NEO solutions and analyzed over two weeks for changes in “embryonic morphology and mobility as well as development of cranial cartilage, cranial nerves and cardiac structure and function including the heart rate. In addition, tissue-specific gene expression was investigated to compare possible effects of the three NEOs at the molecular level.†Looking at key organs like the heart and brain, as well as motor skills, helps to assess the fitness (ability to live and reproduce) needed for the survival of the species.Â
Fertilized eggs, created from 310 female frogs and 49 male frogs, were incubated in single pesticide solutions for a maximum of 14 days in concentrations of 0.1, 1, 10, 50 to 100 mg/L. “The exposure of embryos to 0.1 and 1 mg/L of each NEO reflects environmentally relevant concentrations, with 10, 50 and 100 mg/L NEO representing ‘worst-case’ scenarios (e.g., incorrect handling or improper disposal),†the authors say.Â
Throughout the incubation period, measurements and observations were made using cameras, imaging software, RNA probes, and microscopes before processing all data using a rank sum test through GraphPad Prism 9 software to determine significance. The results that the scientists found, “included a reduced body length, a smaller orbital space, impaired cranial cartilage and nerves, and an altered heart structure and function. At the molecular level, NEO exposure partially resulted in an altered expression of tissue-specific factors, which are involved in eye, cranial placode, and heart development.â€Â
NEO exposure caused delays in the growth and development of the organisms’ bodies and the organs within. Decreased embryonic mobility was noted, and “all three NEOs altered the heart rate. Imidacloprid (as of 50 mg/L) and TMX (as of 10 mg/L) significantly increased the heart rate, while CLO (100 mg/L) reduced the heart rate.†A significant reduction in eye development was observed for all three NEOs at every concentration, and visible cranial cartilage deformations were also seen for all three insecticides. Nerves in the brain were found to have significant shortening and structural differences, and all three NEOs impacted cardiac parameters as well. “Contact with the NEOs affected the structure of the heart. Some isolated hearts had wider atria and ventricles,” the study states. The most significant structural differences were seen with IMD: “An exposure to IMD resulted in abnormal hearts in 78.00% (50 mg/L) and 86.36% (100 mg/L) of the embryos examined.â€Â
Several negative effects, such as external appearance, swimming mobility, and neural/cardiac embryonic development, were seen with exposure to each of the three NEOs studied. Some effects occurred upon exposure to as little as 0.1 mg/L of these insecticides. Overall, the most concerning of the three types is IMD. The scientists found “that IMD has the strongest effect on X. laevis embryogenesis, because an exposure to IMD leads to negative effects in all organs and tissues studied (eyes, cranial cartilage, cranial nerves, and heart). Most importantly, IMD leads to a drastic reduction in mobility up to complete immobility, which is a major problem in nature in terms of foraging and escape from predators.â€Â
NEOs became one of the leading insecticide classes in the early 2000s by offering targeted pest control. More recently, however, there have been concerns for their safety and the impacts on nontarget organisms. After numerous studies, these three NEOs were banned in the European Union based on the environmental risks, especially with bees. With NEOs “occur[ing] in high concentrations in some areas of the world in natural waters… [they bring] a variety of non-target organisms into contact with NEOs… Amphibians are especially threatened by biodiversity loss, with various causes such as habitat loss, climate change, infectious diseases, or contaminants being responsible for the amphibian extinction,†say the authors of this study.Â
Contamination in ecosystems from pesticides is an ongoing concern. Not only are there effects on soil and water but biodiversity loss has reached unprecedented levels. There is a long history of the effects on human health, essential pollinators (even at extremely low doses), and aquatic organisms from NEOs, which harm biodiversity and jeopardize ecosystem health. Current environmental laws do not adequately protect biodiversity, which furthers the urgency to advance organic practices and preserve biodiversity. Â
Learn about Managing Pests Safely Without Neonicotinoids and visit Tools for Change to learn how to organize your community against pesticide use. Sign up to get Beyond Pesticides’ Action of the Week and Weekly News Updates delivered right to your inbox, and stay informed on the health and environmental hazards of pesticides, pesticide regulation and policy, pesticide alternatives, and cutting-edge science with the Daily News. Â
All unattributed positions and opinions in this piece are those of Beyond Pesticides. Â
Source:Â
Flach, H. et al. (2024) Comparing the effects of three neonicotinoids on embryogenesis of the South African clawed frog xenopus laevis, Current Research in Toxicology. Available at: https://www.sciencedirect.com/science/article/pii/S2666027X24000227?via%3Dihub.Â
