Hematological and systemic pathological disorders in Danio rerio induced by sublethal concentrations of imidacloprid

Introduction. The neuroactive insecticide imidacloprid, a member of the neonicotinoid class, is widely used worldwide to control various insect pests. Its high solubility leads to its entry into surface and groundwater, posing a significant risk to aquatic life.

The aim of this study was to evaluate the acute and subchronic toxicity of imidacloprid on Danio rerio, including determining the LC₅₀ and investigating the effects of varying insecticide concentrations on hematological parameters, genotoxicity, and histopathology of the gills, liver, trunk kidney, and middle intestine.

Material and methods. The study used standard methods for determining the sublethal concentration in aquatic toxicology, as well as examining the leukocyte formula, genotoxicity, and histological preparations of D. rerio.

Results. The 96-hour LC₅₀ (LC₅₀⁹⁶) was determined to be 85.3 mg/L, with a 95% confidence interval (CI) of 76.16-96.98 mg/L. Hematological and histopathological changes were investigated for subchronic toxicity across a concentration range of 4 to 76 mg/L. Imidacloprid exposure resulted in a concentration-dependent decrease in erythrocyte counts, an increase in leukocyte counts, lymphopenia, and elevated numbers of monocytes, neutrophils, and basophils. An increased number of erythrocytes with nuclear abnormalities (deformed nuclei, 2.77‰; and fragmented nuclei, 2.85‰) was observed at concentrations of 38 and 76 mg/L. Histological changes were observed in the gills (basal epithelial atrophy and respiratory epithelial detachment), liver (sinusoidal capillary dilation and hepatocyte vacuolization), and kidneys (capillary dilation and tubular epithelial necrosis). The most prevalent histopathological finding was impaired circulation. In the middle intestine, an increased number of goblet cells and intraepithelial lymphocytes was observed.

Limitations. The toxic effect of imidacloprid was assessed within the acute experiment. Additional experiments with longer duration and on other laboratory species would allow to reveal in more detail the mechanisms of toxic effect and related histopathological in disorders.

Conclusion. The findings demonstrate the systemic toxicity of imidacloprid at concentrations exceeding 19 mg/L in Danio rerio organs and tissues.

Compliance with ethical standards. The study was approved by the Commission on Bioethics of K.G. Razumovsky Moscow State University of Technology and Management, carried out in accordance with the European Convention for the Protection of Vertebrate Animals used for Experimental or other Scientific Purposes (ETS No. 123), Directive of the European Parliament and the Council of the European Union 2010/63/EU of September 22, 2010 on the protection of animals used for scientific purposes.

Authors’ contribution. All co-authors made an equal contribution to the research and preparation of the article for publication.

Conflict of interests. The authors declare no apparent and potential conflicts of interest in relation to the publication of this article.

Funding. This work was supported by the Russian Science Foundation (project No. 23-16-00123).

Received: March 1, 2025 / Revised: April 30, 2025 / Accepted: November 25, 2025 / Published: January 15, 2026

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