In Vitro Evidence of Thiamethoxam Toxicity in Tubifex tubifex: Implications for Aquatic Risk Assessment

Thiamethoxam (TMX) is a widely used neonicotinoid insecticide (NNI) in agriculture, causing worries about how it affects marine life. TMX, the second-generation NNI, is widely used for vegetable crops, forage, fruits, and nonagricultural purposes, including seed protection, residential dwellings and food handling. On the other hand, Tubifex tubifex, which is an important link in the aquatic food chain, generally inhabits the sediment interface. Tubificid worms are important aquatic fauna that are extremely susceptible to aquatic and sediment toxicity. Acute toxicity testing revealed LC₅₀ values of 44.43, 31.8, 17.68 and 11.63 mg/L at 24, 48, 72 and 96 h, respectively (****p < 0.0001). The study assessed the impact of TMX on the tubificid worm, including nitrosative stress, oxidative stress, DNA fragmentation, oxidation of lipid and observed on sublethal exposure. The decreased total antioxidant capacity (TAC) was determined through 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric-reducing antioxidant assay (***p < 0.001) in the 96-h toxicological endpoint. The cell viability or mitochondrial dysfunction, as well as lysosomal membrane stability, decreases significantly in chronic exposure. Increased activity of catalases (CATs), superoxide dismutase (SOD) and peroxidases significantly increases the capability for antioxidant defence (***p < 0.001) during a toxicological period. Glutathione peroxidases (GPx) and glutathione reductases (GRs) are significantly altered, indicating a disruption in the glutathione system (GSH/GSSG). Myeloperoxidases (MPOs) showed increased activity, and acetylcholinesterase (AChE) showed decreased activity, indicating changes in the tubificid worm's neurotoxicity and inflammation. The increased glutathione-transferases (GST) brought on by TMX's exposure to tubificid suggest an improvement in detoxification processes as well (***p < 0.001), a toxicological endpoint. Changes in the activity of LDH, HK, G6Pases and G6PD are indicative of both oxidative and metabolic stress (***p < 0.001), a toxicological endpoint. The aquatic ecosystem's exposure to TMX causes bioaccumulation and biomagnification in the upper trophic level, which negatively impacts human health. This study aims to design and evaluate the sublethal impact of TMX on the aquatic benthic tubificid worm.