Identificação dos efeitos toxicológicos da coexposição de nanopartículas de prata e glifosato para o microcrustáceo Daphnia magna

Abstract

Glyphosate (Gly) and metallic nanoparticles are coexisting in the environment due to their demand and use in agriculture and industry. However, the effects of these combinations on the environment and biota are not fully understood. This work aims to identify the possible toxicological effects at acute levels, as well as at chronic multigenerational levels of the binary mixture (MR) of silver nanoparticles (AgNP) with glyphosate (Gly) in D. magna. We used Abbott's method to analyze possible acute interactions. The oxidative stress induced by the AgNP/Gly binary mixture, regarding the Toxic Unit (TU), it was evaluated for the level of Reactive Oxygen Species (ROS) and MDA. We also evaluated the activity of the antioxidant enzymes named Catalase (CAT), Superoxide Dismutase (SOD) and Glutathione (GSH) at 0, 1.5, 1 and 1.75 UT. In the chronic tests, we evaluated, after 21 days, the parameters of survival, growth, reproduction and age of the first brood for parental individuals, and exposed (F1E) and unexposed (recovery) (F1NE). For individuals fed with MR, the contaminants tested individually were used in their highest and lowest concentrations of the individual chronic ones. The binary AgNP/Gly mixture, at an acute level, presented an antagonistic effect in 1, 1.5 and 1.75 TU and an additive effect in 0.25, 0.50 and 2 TU, results possibly associated to the complexation of AgNP by Gly. There was deregulation of the biochemical biomarkers related to the antioxidant defense system in D. magna exposed to treatments, whose antioxidant enzymes evaluated CAT, SOD and GSH were not able to modulate the production of ROS, resulting in oxidative stress and damage by lipid peroxidation. We observed the chronic multigenerational effects related to the parameters of reproduction and age of the first brood in the descendants of the individual compounds, with no recovery for F1E and F1NE. There was a relevant change in the age of the first litter in organisms exposed to MR, with delay in all treatments for F1E and F1NE. There was a significant change (p <0.05) in the reproduction parameter, with a strong reduction for the parental F1E and F1NE, which indicates more toxicity than the compounds alone, being cumulative and harmful to the environmental balance over time. Although the results in the acute tests did not provide clear evidence about the interaction between AgNP and Gly, chronic multigenerational tests with MR resulted in unexpected combined toxicity compared to individual treatments. This raises a concern for this coexposure in other settings. Therefore, although exposure time and dose are variables to be considered, the action mode of mixtures in organisms still needs answers. However, this study brings relevant results for future researches.