Environmental impact of nanoplastics from fragmentized consumer plastic.

Published on November 10, 2023

The smallest microplastics are called nanoplastics. Due to the small size, they are difficult to find and study, but have different biological impact then larger pieces of plastics. The project has used model polystyrene nanoplastics to fill knowledge gaps about life-time toxicity to filtrating zooplankton D. magna and to identify what proteins from the gut of D. magna bind to toxic and non-toxic nanoplastics. Nanoplastics in nature will come from break-down of larger plastics. The project has mechanically mimicked this process and produced nanoplastics from 8 different plastics and rubbers using 14 different daily used products.

The nanoplastics are irregular in shape and highly oxidized compared to the starting material. Nanoplastics from HDPE and PLA are not toxic to D. magna. On the contrary D. magna exhibit increased lifetime probably due to that the nanoplastics can support bacterial growth which can be used as food by D. magna. UV-irradiation further degraded polystyrene nanoplastics. This, together with the bacterial growth, may imply faster plastic degradation in nature than believed today.

The project has been funded by the Swedish EPA’s environmental research grant, which aims to fund research in support of the Swedish EPA and the Swedish Marine and Water Authority’s knowledge needs.

Misplaced plastics is an ongoing environmental problem. The breakdown of plastics into smaller pieces, microplastics, likely cause additional environmental burdens as they affect animals and plants at the beginning of the food chain. This may be even more true for the smallest of microplastics: the nanoplastics as they will behave differently in nature and interact in new ways with organisms and potentially be taken up by the organisms and affect internal organs. The small size of nanoplastics and their chemical resemblance with the surrounding environment makes them difficult to find, isolate and study. Most of what is known about nanoplastics behaviour in nature and their effect on nature derives from studies using commercially available polystyrene nanoparticles. These are probably different in many ways, such as structure, surface chemistry, and size distribution, compared to nanoplastics broken down in nature from plastic debris. Despite this, we have used polystyrene nanoparticles to study knowledge gaps. The toxicity to zooplankton Daphnia magna (D. magna) of small positively charged amine-modified polystyrene nanoparticles is not affected by protein-induced aggregation. All tested polystyrene nanoparticles were toxic to D. magna regardless of their toxicity in acute tests. Proteins bound to polystyrene nanoparticles after filtration by D. magna were different on acutely and non-acutely toxic particles which may imply different mechanisms behind the toxicity. In order to study the effect of nanoplastics that resemble what can be expected in nature we have mechanically broken down 8 different plastics and rubbers from 14 different consumer products and isolated the nanoplastics. Careful characterization shows that the nanoplastics are irregular in shape, have a slightly negative surface charge, and often have a strongly oxidized surface compared to the starting material. The nanosized fractions are not toxic to D. magna in the used concentrations. In contrary, for at least two plastics High Density Polyethylene (HDPE) and Polylactic acid (PLA) the nanoplastics increase the lifetime of the D. magna probably because the nanoplastics can be utilized by bacteria which in turn serve as additional food for the zooplankton. However, leached additives and/or smaller polymers from HDPE are toxic to D. magna. We have also seen that UV irradiation further degrade polystyrene nanoparticles. The bacterial growth and the UV breakdown may imply that the nanoplastics break down faster than believed in nature and that they with time may disappear.