Magnetic Nanoparticles as a Strategy in Microplastics Recovery from Waters

The term Plasticene Era is commonly associated to the massive production and use of plastic, a reality which is growing nowadays.Furthermore, it has been reported that plastic debris present in the environment can cause adverse effects on wildlife and ecosystems, especially aquatic ones, which play a vital role in the maintenance of biodiversity.Even more, several species have been found to be contaminated with such degraded plastics, either directly by ingestion or inhalation or incorporated by other routes.In the environment, they can bioaccumulate and potentially biomagnify between trophic chains.Micro-sized plastic particles, known as microplastics (MPs) can interact with other environment contaminants and microorganisms including pathogens, which represents a potential additional threat to biota and human health.Considering all this, it is utterly urgent to find new strategies to minimize the impact of MPs and nanoplastics (NPs).Among other strategies, magnetic nanoparticles have a great potential to separate recover MPs and NPs from water.Thus, superparamagnetic iron oxide nanoparticles (SPIONs), more precisely those of magnetite, were the starting point of the project.This type of SPIONs has verified biocompatibility and biodegradability, its synthesis is highly reproducible and cost effective, making of these nanostructures very promising for a direct application in the waters to be treated.For this proof of concept, the variables under analysis were carefully planned and assessed according to the following order: type of nanoparticles (formulation and coating), ratio ([SPIONs]/[MPs]) and saturation point.Different initial concentrations of MPs were tested (20.0, 3.6 and 1.0 g/L), as well as two types of MPs of similar medium size, namely fluorescent red MPs and polystyrene MPs.Even more, the effect of the water column in MPs removal was evaluated, in addition to the increase of the time contact.The different magnetic nanoparticles were characterized by Fourier-transform Infrared Spectroscopy (FT-IR) and Transmission Electron Microscopy (TEM) was used to assess the type of interaction between SPIONs and MPs.Hence, the SPIONs synthesized by the microwaveassisted co-precipitation technique, without coating, shown to be the type of nanoparticle most effective in removing the tested MPs.Even though the highest removal rate for such SPIONs has been 99.10% at 0.100 ratio, the 0.200 ratio also proved to be effective, reaching removal rates of 97.17% and 92.75% in 20.0 g of MPs/L and 3.6 g of MPs/L conditions, respectively.Thus, we achieved the validation of the removal of MPs and NPs by SPIONS in water samples, which constitutes the proof of concept that this approach can be used for mitigating microplastics.