Toxicity of α-AgWO Microcrystals to Freshwater Microalga Raphidocelis Subcapitata at Cellular and Population Levels

Silver-based materials have microbicidal action, photocatalytic activity and electronic properties. The increase in manufacturing and consumption of these compounds, given their wide functionality and application, is a source of contamination to freshwater ecosystems and causes toxicity to aquatic biota. Therefore, for the first time, we evaluated the toxicity of the silver tungstate (α-AgWO), in different morphologies (cube and rod), for the microalga Raphidocelis subcapitata. To investigate the toxicity, we evaluated the growth rate, cell complexity and size, reactive oxygen species (ROS) production and chlorophyll a (Chl a) fluorescence. The α-AgWO - R (rod) was 1.7 times more toxic than α-AgWO-C (cube), with IC and IC values of, respectively, 8.68 ± 0.91 μg L and 13.72 ± 1.48 μg L for α-AgWO - R and 18.60 ± 1.61 μg L and 23.47 ± 1.16 μg L for α-AgWO-C. The release of silver ions was quantified and indicated that the silver ions dissolution from the α-AgWO - R ranged from 34 to 71%, while the Ag ions from the α-AgWO-C varied from 35 to 97%. The α-AgWO-C induced, after 24 h exposure, the increase of ROS at the lowest concentrations (8.81 and 19.32 μg L), whereas the α-AgWO - R significantly induced ROS production at 96 h at the highest concentration (31.76 μg L). Both microcrystal shapes significantly altered the cellular complexity and decreased the Chl a fluorescence at all tested concentrations. We conclude that the different morphologies of α-AgWO negatively affect the microalga and are important sources of silver ions leading to harmful consequences to the aquatic ecosystem.