Hepatic and morphological impairments induced by subchronic exposure to fipronil chlorination byproducts in adult zebrafish ( Danio rerio )

Fipronil is a phenylpyrazole pesticide extensively used in the domestic environment and in agriculture for insect control. Due to its relative stability in water, fipronil and its degradation byproducts, formed by the disinfection process of water with chlorine, have been detected in water sources used for human consumption. However, little is known about the toxicity of the byproducts formed by the chlorination of fipronil in higher organisms. Therefore, this work aimed to assess the subchronic toxicity (adult fish) of the byproducts formed from the chlorination of the pesticide fipronil in the zebrafish (Danio rerio) test organism. For this purpose, the animals were exposed to solutions containing standard fipronil (50 µg/L), standard fipronil degraded by chlorination (50 µg/L), commercial fipronil (50 µg/L), and commercial fipronil degraded by chlorination at concentrations of 10, 50, and 100 µg/L. In the subchronic test (28-60 days), macroscopic body alterations and liver histopathology were investigated. The results demonstrated a high degree of toxicity of the fipronil chlorination byproducts compared to the parent compound. Macroscopically, drastic alterations were observed in the spinal column of adult animals treated with these solutions. Microscopically, the main liver alterations observed were the presence of pyknosis and steatosis, both of which are early indicators of cell death. Fipronil chlorination byproducts demonstrate substantial toxicity in adult zebrafish, causing early liver lesions that highlight potential ecological and health risks associated with contaminated water.