Development of a technology to remove micro and nanoplastics from the ocean: proof of concept using mussel exposure tests

Since the discovery of petrochemicals in the 19th century, plastics have been developed for many commercial applications. Currently, the overproduction and mismanagement of plastics led to the accumulation of these materials in the environment, particularly in the marine ecosystem. Once in the environment, plastics break down and can acquire microscopic or even nanoscopic sizes. Given their sizes, microplastics (MPs) and nanoplastics (NPs) are hardly detected or removed from the aquatic environment, eventually interacting with the marine organisms. The main purpose of this thesis was to develop a technology for the aggregation of micro and nanoplastics (MNPs) to ease their removal from the marine environment. To this end, the size and stability of polystyrene (PS) MNPs were measured in synthetic seawater with the different components of the technology (ionic liquid and chitosan). The MPs were purchased in their plain form while the NPs displayed amines on their surface (PS NP-NH2). The results showed that this technology promoted a significant aggregation of the PS NP-NH2 whereas for the PS MPs no conclusive results were found, indicating that the surface charge plays an important role in the MNPs aggregation process. Moreover, to investigate the toxicological potential of MNPs, a mussel species (M. galloprovincialis) was exposed to different concentrations of MPs and NPs, separately, with and without technology. In this context, after 7, 14 and 21 days of exposure mussels were sampled, and the gills and digestive glands were collected for oxidative stress biomarkers analysis and histological observations. In general, results indicate that MNPs trigger the production of reactive oxygen species (ROS) in mussels and induce oxidative stress, being gills the most affected tissue. Yet, when the technology was applied in moderate concentrations, NPs showed less adverse effects in mussels. The histological analysis showed no evidence of MNPs presence within the gill’s tissues.