Histopatologia de fígado para avaliação do efeito tóxico do 2,4-D (Ácido 2,4-Diclorofenoxiacético) em Rhamdia quelen (Teleostei, Pimelodidae)

Abstract

Technological advances in agriculture have led to increased productivity. Among these advances is the application of chemicals commonly called pesticides or herbicides, which allow the control of diseases and pests in crops. Their use has significantly increased in recent years in particular because of the development of transgenic cultivars resistant to agrochemicals that have led to a gradual increase in the amount of contaminants that reach aquatic environments through various forms of conveyance. Once in that environment pesticides can bio-accumulate and pass down the food chain until they reach the human body and/or trigger changes in organisms harming their integrity. The present study evaluated the toxic effect of the herbicide 2,4-D (2,4-dichlorophenoxyacetic acid) on fishes of the Rhamdia quelen (Teleostei, Pimelodidae) specie subject to acute exposure through water route. The fishes were submitted to realistic concentrations of the herbicide. The concentrations used were 0, 15, 30 and 60 μg/L with exposure times of 96 and 192 hours. After the exposition the fishes suffered euthanasia benzocaine hydrochloride (100 mg/L). Subsequently they were subjected to laparotomy and the liver was collected and fixed in ALFAC for 12 hours and then transferred to 70% alcohol. In order to analyze the histopathology, the samples were submitted to the standard histological procedure with dehydration, inclusion, triage, microtomy and staining with hematoxylin and eosin. After the preparation of the slides the qualitative and quantitative analyses of the tissues were carried out under light microscopy in order to evaluate the extent of damage through the Bernet Index. The histopathology findings were cytoplasmic vacuolization, macrophage infiltration, hepatic cord disorganization and presence of lipid vesicles. The results were compared with the mean values of the two-factor ANOVA, which found no significant difference between the concentrations tested and the exposure time. It was concluded that the herbicide 2,4-D had histopathological effect on the liver of the bioindicator Rhamdia quelen in the time tested, but it was not statistically significant for the concentrations allowed by the Brazilian legislation for class III fresh waters, according to CONAMA Resolution nº 357/2005.