Histopathological Changes in Tissues of Danio rerio Exposed to Sub Lethal Concentration of Combination Pesticide

Abstract

The objective of this study is to investigate in detail the histopathological changes in gill, liver, brain, spinal cord, ovary and kidney of zebra fish exposed to combination pesticide. Twenty one days semi static exposure to sublethal concentration of 8.4 and 4.2 μg/L of Chloropyrifos 50% + Cypermethrin 5% EC was conducted and it was followed with a reversal period of 7 days without pesticide in the exposure water. Three fish were collected from control and treatment group periodically. Whole body fixation of zebra fish as per OECD guidance document 123 was adopted for obtaining the histopathology sections. Structural damages of gill observed were of inflammatory cell infiltration, minimal congestion in primary lamellae, fusion of secondary lamellae, diffused epithelial hyperplasia and multifoci mucus cell hyperplasia. In liver, moderate, diffused to severe cytoplasmic vacuolation, diffused minimal to mild sinusoidal congestion, steatosis, pyknotic, karyorrhectic nuclei with complete dissolution of necrotic hepatocytes was observed. Minimal focal tubular degeneration was observed in kidney. Minimal to mild multifocal follicular atresia was observed in the ovary. In spinal cord neuronal cell degeneration, cytoplasmic vacuolation and enlargement of neuronal body was observed. In brain, mild to moderate demyelination in the neurophil and mild necrotic changes observed in the cerebrum. Some of the lesions were less pronounced after recuperation period. Pesticide in exposure water was analyzed using Agilent QQQ GC-MS/MS equipped with Election Impact Ionization mode. Limit of detection and quantification was 1 μg/L with a Correlation Co-efficient (CC) of 0.999. The recovery of active content of Chlorpyrifos for 4.2 and 8.4 μg/L at 0 hour was 88.1%, 90.3% and at 48 hour was 83.48%, 85.70%, respectively. Similarly, Cypermethrin active content recovered at 0 hour for 4.2 and 8.4 μg/L was 78.74%, 86.24% and at 48 hour was 57.85%, 62.09%, respectively. Further, this is the first study to report pathological findings in Zebrafish exposed to a combination pesticide formulation. The histopathological finding of this investigation reveals the potential toxic hazard from exposure to sub lethal level of the combination pesticide. Few literatures have reported on the mixture toxicity of pesticides and this research work throws light on histopathological lesions of Zebrafish. Further, this is the first study to report spinal lesions in fish due to pesticide exposure. Pesticides usage in pest management or in agriculture practice should be applied safely to prevent pollution and contamination.