Acute toxicity of zinc oxide nanoparticles on blood cell morphology, haematology and histopathology of Heterobranchus longifilis

Abstract

This study investigated the toxicity effect of lethal concentrations of zinc oxide nanoparticles (ZnO-NPs) on the blood morphology, haematology and histopathology of Heterobranchus longifilis. The fish were assessed in a semi-static bioassay for 96 hours in five different concentrations (0.00, 60.00, 80.00, 100.00, 120.00 and 140.00 mg/l) of ZnO-NPs. The 96-hour LC₅₀ was estimated as 100 mg/l. At the end of the experiment, blood samples were collected for morphological and haematological assays, while the fish was sacrificed to remove the gill and liver for histological bioassay. Results showed that the levels of haematological parameters such as red blood cell (RBC), haemoglobin (HB) and packed cell volume (PCV) decreased significantly (p<0.05) compared to the control. The levels of white blood cell (WBC) and platelets increased significantly (p<0.05) compared to the control. Various pathological alterations such as oedema, epithelial lifting, necrosis, hyperplasia, lamellar disorganization and lamellar fusion were apparent in the gill of ZnO-NPs-exposed fish, while fatty degeneration, increased sinusoidal space, cytoplasmic degeneration, necrosis, and focal fibrosis were observed in the liver compared to the control. Different morphological alterations such as abnormal elliptical shape, irregular boundary with more than one lobopodial projections, shrinkage of erythrocytes, hole-like depression and spherocyte with double projections occurred in the erythrocytes of ZnO-NPs-exposed fish compared to the control. The results of this study revealed that lethal concentration of ZnO-NPs is harmful to Heterobranchus longifilis. Hence, the discharge of ZnO-NPs into water bodies should be regulated to guide against environmental hazards that may arise.

Keywords: Zinc Oxide Nanoparticles, Blood morphology, Haematology, Histology, Lethality, Heterobranchus longifilis