Abstract The present work evaluated the ecological risk of glyphosate by its commercial formulation (Roundup Original®) used to control floating aquatic macrophytes. Exposure analysis and ecological effects were performed from microcosm studies. The risk characterization was performed based on the calculation of the risk quotient. The commercial formulation of glyphosate had high toxicity when it was assessed separately. On the other hand, ecotoxicological evaluation of water samples from microcosms did not present toxicity to any tested organisms, however, glyphosate application is recommended exclusively to water bodies that have the surface completely covered by macrophytes.

RESUMO A possibilidade do uso de herbicidas em ecossistema aquático para controle de macrófitas quando em condições de desequilíbrio levou à necessidade de estudos que avaliam a concentração de efeito que seja eficiente e ecologicamente equilibrada, sem causar maiores impactos aos organismos não alvo e ao ecossistema aquático. O glifosato é o princípio ativo de alguns herbicidas e é conhecido pela sua eficácia, amplo espectro de ação e baixa toxicidade. Neste trabalho foi investigada a menor concentração de efeito para controle da Eichhornia crassipes e da Salvinia sp em experimentos realizados em triplicata e observados pelo período de 20 dias após aplicações de glifosato nas concentrações de 6,25; 12,5; 25,0; 50,0 e 100 L.ha-1. Como resultado, verificou-se que apenas a concentração de 100 L.ha-1 apresentou diferença significativa de efeito comparada ao controle. O efeito ao final do vigésimo dia foi superior a 90%, tornando-se aparente a partir do décimo dia. Existiu uma pequena diferença na sensibilidade entre as espécies, no entanto, a concentração de efeito foi semelhante. A dose de 100 L.ha-1 impediu a ocorrência de rebrota, no prazo de 30 dias, e causou efeito residual pobre em espécies vegetais inseridas no ambiente após a aplicação do herbicida.

ABSTRACT The possibility of using herbicides in an aquatic ecosystem, to macrophytes control in unbalanced conditions, led to the need for studies that evaluate the concentration of effect that is effective and ecologically balanced, without causing major impacts to the non-target organisms in the aquatic ecosystem. The glyphosate is the active ingredient of some herbicides and it is known for its efficacy due its broad-spectrum and non-selectivity. This study investigated the minor concentration of effect to control Eichhornia crassipes and Salvinia sp., in experiments conducted in triplicate and observed during a period of 20 days after glyphosate application in the concentrations: 6.25, 12.5, 25.0, 50.0 e 100 L.ha-1. It was verified that only the concentration of 100 L.ha-1 had significant difference of effect when compared to the control. The effect at the end of the twentieth day it was superior to 90%, becoming apparent from the tenth day on. It was observed a small difference in sensibility between the evaluated species; however, the concentration of effect was similar. The dose of 100 L.ha-1 prevented the occurrence of regrowth during thirty days, and caused a residual effect in vegetal species inserted in the environment after the herbicide application.