Microplastics

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.

Tommy Cedervall, Lund University

4 990 389 SEK

Elena Gorokhova, Stockholm University

4 999 449 SEK

Brendan McKie, Swedish University of Agricultural Sciences

5 000 800 SEK

Martin Hassellöv, Gothenburg University

4 973 650 SEK