Ensaios ecotoxicológicos como subsídio para a avaliação do impacto ambiental de uma formulação de glifosato em Eisenia andrei Bouché

Abstract

Considered a low toxicity herbicide by current Brazilian laws, glyphosate is the target of this study, as its constant use ends up reaching the soil and can cause damage to micro and macro organisms and the environment. Earthworms maintain the organic matter and physical structure of the soil, promoting its aeration, thus favoring the production of crops, and its preservation is recommended as a strategy to keep the soil healthy. Therefore, the aim of this study is to provide subsidies for understanding the impacts on soil biota of one of the main glyphosate formulations, widely used in family farming, through ecotoxicological tests with an emphasis on histological assessments of the earthworm Eisenia andrei Bouché. For this purpose, doses of 0 (control) were used; 0.96; 1.92; 3.84; 7.68 and 15.68mg e.a Kg-1 of the pesticide Roundup Transorb R® (product containing 588g L-1 i.a and 480g L-1 e.a). 24 experimental units were prepared containing 400g of test substrate. The substrate was moistened until reaching 60% humidity with the treatments. Fifteen adult earthworms were inserted into each experimental unit. This chronic test lasted 35 days and aimed to weekly assess the biomass of adult individuals, the mortality of earthworms and the number of juveniles at 56 days of experiment in the doses tested. Weekly, two earthworms were removed from the experimental units for histological analysis of tissue morphometry: intestinal epithelial, chloragogen and tiflosol region. Under the conditions in which the experiment was carried out, it was not possible to verify the statistical effect of glyphosate on the mortality and reproduction of earthworms. As for biomass, in relative terms, there was also no evidence of the effect of treatments on earthworms. Nevertheless, the analysis of the absolute values of the individual average mass indicates a significant tendency of reduction of this parameter with the increase of the glyphosate concentration. There was no statistical difference for the thickness of the intestinal epithelial tissues, chloragogen and the tiflosol region in the different treatments. However, there is a clear tendency for these variables to present higher values in the absence of glyphosate. Likewise, morphological changes in the body of earthworms, such as loss of segments and necrosis, were only observed in individuals exposed to glyphosate. Such findings must be considered for new and essential studies on the potential environmental impact of the use of glyphosate.