Characterization of PLA Nanoplastics, and Their Effects on Daphnia magna

Sammanfattning: As plastic pollution in aquatic environments keeps happening it has become more and more important to learn more about nanoparticles. Bio-based and biologically degradable plastics, such as polylactic acid (PLA), are gaining popularity and it is therefore important to determine whether they break down into nanoplastics or not. Should this be the case, it is of interest to characterize their size, morphology, surface charge, chemical composition, and determine if they are toxic to aquatic organisms. The approach was to break down five different consumer PLA plastic products in Milli-Q water with an immersion blender. These products were a soup cup lid, coffee cup lid, plastic cup, plastic bag and 3D printer filament. The soup cup lid and coffee cup lid were also exposed to UV-C to see if that made any difference when characterizing them. Manufactured PLA nanoparticles were also purchased and studied. They were then characterized by using tools such as NTA, DLS, FTIR and TEM. To determine the toxicity of the particles, the zooplankton Daphnia magna was exposed to them. The results showed that nanoplastics were formed, with an average size 145 - 230 nm in diameter depending on the product. The particles seemed to have different shapes, there were particles with sharp edges, and particles with round edges. The surface charge differed between the different products, all values indicated they should be unstable in Milli-Q water. However, when the stability was studied with the NTA, they seemed stable. The chemical composition of the soup cup lid, plastic cup and 3D printer filament matched that of pure PLA, while the coffee cup lid and the plastic bag seemed to be made of polystyrene and polyester, terephtalic acid (PET), respectively. The toxicity was tested with the soup cup lid, the UV-C treated soup lid, the plastic bag and the manufactured nanoparticles in a short-term test where the plankton were not fed. They showed no sign of being toxic. On the contrary, the plankton seemed to live longer when exposed to breakdown PLA nanoplastics in the water. When exposed to the manufactured PLA, there was a toxic effect on the plankton.