Characteristics of the toxic effect of imidacloprid on the state of Eisenia fetida (Annelida, Clitellata, Lumbricidae)

Imidacloprid became the most sold neonicotinoid insecticide in the world in the 21st century. Due to their constant use, neonicotinoids are stored in soils, bottom deposits, and surface waters. It is known that neonicotinoids reveal toxicity for non-target species: annelid worms, insects, fish, birds, and mammals. Neonicotinoids exhibit reproductive toxicity, neuro-, hepato-, and genotoxicity for mammals. Earthworms are useful modeling organisms that are proposed to carry out toxicity tests. Eisenia fetida is considered a convenient and adequate species in toxicological studies. Analysis of available data shows that even low concentrations of imidacloprid caused protrusion of a belt, blackening, leakage of a cellar fluid, narrowing areas of the body with edema in segments, and dark body pigmentation in E. fetida. There are also biochemical changes. Low concentrations of imidacloprid (<0.2 mg/L) suppress the activity of cellulase. Imidacloprid also causes damage to DNA, production of reactive oxygen species, and alterations in antioxidant enzymes activity in E. fetida: inhibition of catalase, but activation of superoxide dismutase and glutathione-S-transferase. Imidacloprid reduces reproductive success in E. fetida, causing significant deformation of sperm, reducing the average number and size of cocoons and the success of birth. At concentrations ≥10 mg/kg of imidacloprid, the high mortality of worms makes it impossible for vermiculture. At 5 mg/kg of imidacloprid in plants remains for vermicomposting in seven weeks, the mortality rate of 25% of E. fetida individuals is fixed. The stereotypical escape reflex behavior in the worms was observed in relation to imidacloprid at a concentration of 1.32 mg/kg. At the same time, molecular and cellular mechanisms of toxic effects of imidacloprid on E. fetida are almost not studied and needed special attention with further research.