Efeitos histopatológicos dos agrotóxicos deltametrina, imidacloprido, glifosato e diuron nas brânquias de quatro espécies de peixes amazônicos

Abstract

Agricultural activity in the Amazon has been intensified to meet food demand in the region. This intensification has led to heavy and widespread pesticide use. In addition to the direct risks to human health, it is possible that fish are being contaminated by pesticides that reach aquatic environments. Histological analysis has been shown to be an important tool in understanding and identifying the sublethal effects of water pollutants. Here we evaluated how sub-lethal exposure to the principal agrochemicals sold in Manaus (deltamethrin, imidacloprid, glyphosate and diuron) alter the gill morphology of four species of Amazonian fish. Methods: The species Carnegiella strigata, Paracheirodon axelrodi, Rhodostomus hemigrammus and Colossoma macropomum were exposed to sub-lethal concentrations of deltamethrin, imidacloprid, glyphosate and diuron for 96 h. Histopathological semi-quantitative analyses, by optical microscopy (OM), and qualitative analyses, as scanning electron microscopy were performed (SEM) and transmission (TEM), were performed. The Kruskal-Wallis test was used to identify whether there were differences in the injury indexes between treated and control groups for each species, Dunn’s test was used to identify which groups differed from the control. Results and discussion: In general, the observed lesions were common in all treatments and species. Through MO, we observed epithelium lifting, hypertrophy, hyperplasia, and lamellar fusion. Loss of microridges in the filaments and lamellar fusion were observed by SEM. The presence of epithelium lifting, dilation of intercellular spaces, hyperplasia on mitochondria rich cells and intracellular vacuolization. These injuries were observed in all four studied species. They can act as barriers to avoid the entry of pesticides as a compensatory mechanism intnding to restore gill function, but may compromise fish health. Previous studies have reported similar histopathologic effects by glyphosate and deltamethrin in other fish species. The gill lesion index was significantly higher in H. rhodostomus after imidacloprid and glyphosate exposure and in C. macropomum exposed to imidacloprid, deltamethrin and diuron (p <0.05). P. axelrodi and C. strigata showed suggestive effects after exposure to glyphosate and C. strigata after exposure to deltamethrin (0.05 <p <0.1). C. macropomum presented injuries following exposure to three of the four pesticides tested and is thus considered the most of the sensitive species investigated here. The higher vulnerability of C. macropomum may be related to the life stage, since they were fingerlings, whereas the other fish species were adults. P. axelrodi was the most resistant species to the tested pesticides. Previous studies have shown that this genus has physiological and behavioural characteristics that may help to be resistant to the exposure to pesticides. The most toxic of the tested pesticides was Glyphosate, causing injury in three of the four species evaluated. Conclusion: Glyphosate was the most toxic of the agrochemicals tested here. P. axelrodi was most resistant and C. macropomum most sensitive to the tested pesticides. The gill lesions we observed were mild to moderate and could potential recover in the absence of pesticides.