Avaliação da toxicidade de nanopartículas de prata para o microcrustáceo Daphnia magna - um estudo de múltiplas gerações

Abstract

Nanotechnology seeks to develop new methodologies for the production of nanoscale products, helping to solve global problems. However, with the huge range of products currently using nanoparticles (NPs), the amount released into aquatic ecosystems is considerable. As an example of NP we have silver, which is the most toxic metal found in water bodies, and can cause serious damage to humans and the environment. Thus, the present study aimed to evaluate the acute and chronic toxicity of silver nanoparticles (AgNPs) suspensions, in addition to evaluating multigenerational effects and the postexposure effects to the toxic agent, using the crustacean Daphnia magna as a test organism. The AgNPs synthesis and characterization consisted of the traditional chemical synthesis methodology using PVA as a stabilizing agent. The NPs characterization showed that the AgNPs suspension was not in a state of agglomeration, and the spherical shape, characteristic of the AgNPs, was confirmed through a wavelength of 401 nm and an average diameter of 4.6 nm. Acute toxicity tests indicated mean EC50,48h values of 0.13 µg·L-1 . Based on this result, chronic tests were performed for the F0 generation, where significant effects were verified for the longevity parameter, with the observed effect concentration (OEC) of 0.065 µg. L-1 and fertility with an increase in the average number of babies/posture and OEC of 0.055 µg. L-1 . Unlike F0, in the post-exposure chronic toxicity tests (F0PE), exposed only in M4 medium, significant effects on longevity were observed with a reduction in the number of organisms in the lowest concentrations, however in the largest there was a reduction of practically 50% of the organisms. Thus, 0.025 µg. L-1 was obtained as OEC. In terms of fertility and the average number of postures, the organisms managed to recover the number of babies, being able to understand this increase as an effect of the organism recovery. The chronic toxicity tests for multiple generations were defined as F1 the first generation of neonates of the generation F0, and F4 the fourth generation. Both generations became more resistant to the toxic agent than the F0 generation, due to the longer exposure time of mothers. As for fertility, the organisms suffered stressful effects, which caused an increase in reproduction in order to perpetuate the species. In the post-exposure tests of the multigeneration, generation F1PE and F4PE, the organisms had greater sensitivity to the toxic agent since small doses, and the survival rate was lower than the descendants, given the longer exposure time in the test medium, in addition to toxic effects in the average number of postures. Thus, based on this study, it was concluded that the results reflect multi-generational and post-exposure effects, since the generations have consequences in their life cycle.