The Effect of ZnO Nanoparticles Morphology on the Toxicity Towards Microalgae Pseudokirchneriella subcapitata.

Zinc oxide nanoparticles (ZnO NPs) have been widely employed in technological applications due to their appealing properties for catalytic, optoelectronic and antimicrobial applications. Moreover, ZnO NPs can also be employed in fertilizers as a source of zinc micronutrient, which is a primary element for enzymes and proteins synthesis in plants, allowing their regular growth and improving crop productivity. However, the extensive use of nanoparticles as a source of fertilizers in agricultural activities also raises concerns once nanoparticle features including surface charge, chemical fucntionalittes, size and shape can alter the toxicity of NPs. In this scenario, the toxicity of distinct ZnO NPs towards microalgae Pseudokirchneriella subcapitata, which is the base microorganism for the aquatic food chain, was evaluated and compared. ZnO NPs employed here were obtained by co-precipitation method and co-precipitation followed by hydrothermal method using different times. After characterizing the physical-chemical properties of ZnO NPs, they were employed in toxicity biossays in order to evaluate their ability to inhibit algal growth as well as to induce changes in algae morphology. Our results indicate that ZnO NPs concentrations below 10 mg L-1 presented low toxicity towards P. subcapitata microalgae. Higher concentrations of ZnO NPs, however, presented significant toxic effects, and revealed changes in morphology of the algae cells, and therefore, should be avoided for agri-related applications.

Investigation of nanotoxicological effects of nanostructured hydroxyapatite to microalgae Pseudokirchneriella subcapitata.

The advance of nanotechnology has enabled the development of materials with optimized properties for applications in agriculture and environment. For instance, nanotechnology-based fertilizers, such as the candidate hydroxyapatite (HAp) nanoparticles (Ca10(PO4)6(OH)2), can potentially increase the food production by rationally supplying phosphorous to crops, although with inferior mobility in the environment (when compared to the soluble counterparts), avoiding eutrophication. Nonetheless, the widespread consumption of nanofertilizers also raises concern about feasible deleterious effects caused by their release in the environment, which ultimately imposes risks to aquatic biota and human health. Nanoparticles characteristics such as size, shape, surface charge and chemical functionality strongly alter how they interact with the surrounding environment, leading to distinct levels of toxicity. This investigation aimed to compare the toxicity of different HAp nanoparticles, obtained by two distinct chemical routes, against algae Pseudokirchneriella subcapitata, which composes the base of the aquatic trophic chain. The as synthesized HAp nanoparticles obtained by co-precipitation and co-precipitation followed by hydrothermal method were fully characterized regarding structure and morphology. Toxicity tests against the microalgae were carried out to evaluate the growth inhibition and the morphological changes experienced by the exposition to HAp nanoparticles. The results showed that high concentrations of coprecipitated HAp samples significantly decreased cell density and caused morphological changes on the algal cells surface when compared to HAp obtained by hydrothermal method. HAp nanoparticles obtained with dispersing agent ammonium polymethacrylate (APMA) indicated negligible toxic effects for algae, due to the higher dispersion of HAp in the culture medium as well as a reduced shading effect. Therefore, HAp nanoparticles obtained by the latter route can be considered a potential source of phosphorous for agricultural crops in addition to reduce eutrophication.