Alterações histológicas no fígado dos girinos de Rhinella marina (Linnaeus, 1758) (Anura: Bufonidae) expostos ao glifosato

Abstract

In the last decades, amphibian declines have been extensively discussed and how pesticides may be negatively impacting these populations. Most ecotoxicological studies with amphibian anurans were conducted with North American species and they tested the acute and chronic exposure of tadpoles to a particular pesticide, there are a very few studies investigating Brazilian species and the effects of these chemicals at a histological level. The objective of this study was to analyze the effect of the herbicide glyphosate (in sub-lethal concentrations of 25%, 50% and 75%) on the liver of tadpoles on Gosner stage 40 of the toad Rhinella marina collected in northern Mato Grosso, Brazil. Liver samples were taken from tadpoles from the control (no pesticide) and treatment with glyphosate. Liver samples were embedded in plastic resin, sequentially cut in 3µm thickness, stained with toluidine blue, viewed and photographed under light microscopy. The number of melanomacrophages (immune cells resident in the liver), measurement of area occupied by edema and hemorrhage and the hepatossomatic index were determined. The liver of the control group showed hepatocytes arranged in collar-like with the nuclei in central position and the presence of melanomacrophages. Changes in hepatocytes showing loss of cytoplasm, cell degeneration and lateralization of the nuclei, swelling and bleeding were observed in individuals exposed to glyphosate. However, these variations in both the amount of melanomacrophages as well as the area occupied by edema and hemorrhage and the reason of hepatossomatic index showed no statistically significant variations among control and different treatments with glyphosate. Other studies have reported differential responses of amphibians to different formulations and times of exposure to pesticides, among them the glyphosate, suggesting a wide spectrum of reactions that vary both with species and tested formulations, as well as the exposure time. It is imperative to continue to monitoring and to analyzing histologically the amphibian anuran species to determine the impact that pesticides may be having on the decline of this taxonomic group.