Toxicity and hazard assessment of neonicotinoids on freshwater invertebrates and fish

Neonicotinoids (NNIs) are a class of systemic insecticides that have gained widespread use in industrial and agricultural applications since the 1980s, raising growing environmental concerns due to their persistence, high water solubility, and potent toxicity. These compounds readily leach into freshwater systems, where they exert detrimental effects on aquatic biota, particularly invertebrates and fish. Freshwater invertebrates, especially aquatic insects such as mayflies, caddisflies, and midges, exhibit heightened sensitivity to neonicotinoid exposure, often resulting in impaired development, altered behavior, and population declines. Similarly, freshwater fish are vulnerable to sublethal and chronic effects, including neurotoxicity, reproductive disruption, and oxidative stress. While fish are generally less sensitive to direct toxicity, they are negatively impacted by disruptions of the food web caused by the decline of their invertebrate food resources. A major limitation in current research is the focus on single-stressor lab studies, which fails to capture the real-world effects of multiple pollutants interacting with each other. Despite substantial research on the chemical properties and insecticidal mechanisms of NNIs, their ecological impacts on freshwater organisms remain inadequately understood. This review seeks to synthesize current knowledge on the toxicological effects of NNIs in freshwater invertebrates and vertebrates, assess the comparative toxicity across different compounds, and emphasize the need for regulatory action. Enhancing public awareness and fostering collaborative efforts among policymakers, scientists, and environmental organizations are essential to mitigate the risks posed by these emerging contaminants. • Neonicotinoids are widely used systemic insecticides with aquatic ecotoxicity. • Freshwater invertebrates are highly sensitive to neonicotinoid exposure. • Findings reveal mechanistic, biochemical, and bibliometric insights on NNIs.