Efeito agudo do inseticida Fipronil em peixe Neotropical

Abstract

The use of fipronil as an agricultural insecticide has significantly increased, and its indiscriminate application has intensified the contamination of aquatic ecosystems, raising concerns about fish health. This study evaluated the acute toxicity of the insecticide fipronil in the neotropical fish Colossoma macropomum through integrated responses of multiple biomarkers. The animals were divided into three groups: Control (free from the contaminant); F40 (exposed to a concentration of 40 µg L-1); and F160 (exposed to 160 µg L-1), for 96 hours. After exposure, blood, liver, muscle, brain, and gill samples were collected for analysis of neurotoxic, physiological, cytogenetic, biochemical, and morphological biomarkers. The activity of acetylcholinesterase increased in the muscle of animals exposed to the F160 group compared to the control and F40, indicating a disturbance in the neuromuscular junction. Although there was no morphofunctional impairment (Iorg) of the brain tissue, there was an increase in the Individual Lesion Index (Ialt) for intracellular edema in F160, when compared to the control and F40, indicating neurotoxic action of the insecticide. There were no changes in gill morphology and ionocyte density among the exposed groups; however, plasma osmo- ion regulation was disrupted, evidenced by an increase in Na+ ion in the F160 group compared to the control, a concentration-dependent decrease in K+, and an increase in total osmolality in F40 when compared to the control. There were no changes in chloride ion after exposure. Hematological parameters, hematometric indices, and total leukocytes decreased in a concentration-dependent manner, indicating possible anemia and tissue infection, potentially leading to gas transport dysfunction. The frequency of micronucleated erythrocytes did not change after exposure; however, the cytogenotoxic potential of the contaminant was expressed through nuclear erythrocyte alterations. Although fipronil did not impair the functionality of the hepatic tissue, morphological alterations such as changes in hepatic architecture were observed in treated groups compared to the control, as well as cytoplasmic degeneration among treated groups. Plasma glucose and hepatosomatic index remained unchanged after exposure. Concentration-dependent reduction in hepatic glycogen levels indicated interference of the contaminant in fish metabolism, suggesting glycogen metabolism in cells to maintain normal blood glucose levels. The normalcy of the GSH-GST biotransformation system and hepatic damage biomarkers (alanine transaminase and bilirubins) demonstrated that hepatocyte integrity and biotransformation function were not affected by the action of the insecticide. The toxicity of fipronil in C. macropomum occurred at different concentrations, causing morphophysiological, neurotoxic, and physiological changes in the organism, while preserving the functionality of the analyzed organs.