Efeitos de micropartículas de prata, em diferentes dorfologias, isoladas e em misturas, sobre organismos planctônicos dulcícolas de dois diferentes níveis tróficos

Abstract

Currently, particles with silver in their composition have drawn attention for their wide applicability. In particular, the silver tungstate (α-Ag2WO4), which has microbicidal, fungicidal and antitumor activities, is used in photocatalysis processes, sensors, among others. Furthermore, the material can be a source of release of silver ions, whose toxicity to aquatic organisms is widely known. Thus, the objective of this research was to evaluate the effects and toxic mechanisms, via multiple endpoints, of α-Ag2WO4, in different morphologies (cubic - C - and rod - R) on two freshwater planktonic species, the microalgae Raphidocelis subcapitata and the cladoceran Ceriodaphnia silvestrii. For this, acute and chronic toxicity tests were performed with the isolated composites for both species and toxicity tests of mixtures with the cladoceran. The results of ecotoxicity tests with the microalgae indicated that α-Ag2WO4 affected population parameters, such as cell growth; morphological, such as cell complexity; biochemical, such as total carbohydrate composition and chlorophyll a content; and physiological, such as the production of reactive oxygen species (ROS) and changes in parameters measured by Phyto-PAM, such as maximum yield and oxygen evolution complex (OEC). For the species C. silvestrii significant negative effects were observed only in the acute toxicity tests, where both morphologies caused immobility in the organisms when exposed to the composites isolated and in mixture. Regarding the combined exposure of α-Ag2WO4 - C and α-Ag2WO4 - R the reference model of Independent Action (IA) with dose-level dependent (DL) deviation was the best fit to the data, indicating synergism at low concentrations and antagonism at high doses. The negative effects on organisms were probably caused by the availability of silver ions, which are highly toxic. Unlike acute exposure, chronic exposure of α-Ag2WO4 - C and α-Ag2WO4 - R alone did not cause significant reproductive damage to cladocerans. Comparing the toxicity of microcrystals on the two species of organisms tested, it was possible to identify that the cladoceran has a higher sensitivity, to the different morphologies of α-Ag2WO4 (EC50-48h= 0.64 μg L-1 para α-Ag2WO4 – C e EC50-48h= 0.81 μg L-1 para α-Ag2WO4 –R) compared to the microalgae (IC50-96h= 23.47 μg L-1 para α-Ag2WO4 – C e IC50-96h= 13.72 μg L-1 para α-Ag2WO4 – R), which highlights the importance in evaluating more than one trophic level in ecotoxicological studies.