Insights into the shape-dependent effects of polyethylene microplastics on interactions with organisms, environmental aging, and adsorption properties.

The shape-dependent effects of microplastics have been studied in the context of ingestion but have not been considered in other environmental processes. Therefore, we investigated how the shape of polyethylene microplastics (spheres, fragments, and films) affects interactions with plants, aging, and their adsorption properties. The shape had no effect on the growth rate and chlorophyll content of duckweed Lemna minor, but the fragments strongly adhered to the plant biomass and reduced the root length. The adsorption process of the model organic compound (methylene blue dye) was described by the same kinetic model for all shapes-the experimental data best fit the pseudo-second order model. However, twice as much methylene blue was adsorbed on films as on fragments and spheres. During environmental aging, most biofilm developed on films. The biofilm on spheres contained significantly less photosynthetic microorganisms, but twice as much extracellular polymeric substances (EPS) as on fragments and films. This suggests that the attachment of microorganisms to spherical particles is limited and therefore more intensive production of EPS is required for stable biofilm formation. From the results of this study, it is evident that the shape of microplastics significantly affects not only ecotoxicity but also other environmentally relevant processes.

A study of the adsorption of titanium dioxide and zinc oxide nanoparticles on polyethylene microplastics and their desorption in aquatic media.

In this study, we investigated the interactions between titanium dioxide (nTiO2) and zinc oxide (nZnO) nanoparticles and polyethylene microplastics (MPs) with respect to their adsorption and subsequent desorption in aquatic media. Adsorption kinetic models revealed rapid adsorption of nZnO compared to nTiO2, while nTiO2 was adsorbed to a greater extent - four times more nTiO2 (67%) was adsorbed on MPs than nZnO (16%). The low adsorption of nZnO can be explained by the partial dissolution of zinc from nZnO in the form of Zn(II) and/or Zn(II) aqua-hydroxo complexes (e.g. [Zn(OH)]+, [Zn(OH)3]-, [Zn(OH)4]2-), which were not adsorbed on MPs. Adsorption isotherm models indicated that the adsorption process is controlled by physisorption for both nTiO2 and nZnO. The desorption of nTiO2 was low (up to 27%) and not pH dependent, and only nanoparticles were desorbed from the MPs surface. On the other hand, the desorption of nZnO was pH dependent; at a slightly acidic pH (pH = 6), 89% of the adsorbed zinc was desorbed from the MPs surface and the majority were in the form of nanoparticles; at a slightly alkaline pH (pH = 8.3), 72% of the zinc was desorbed, but the majority were in the soluble form of Zn(II) and/or Zn(II) aqua-hydroxo complexes. These results demonstrated the complexity and variability of interactions between MPs and metal engineered nanoparticles and contribute to a better understanding of their fate in the aquatic environment.

Interactions between titanium dioxide nanoparticles and polyethylene microplastics: Adsorption kinetics, photocatalytic properties, and ecotoxicity.

The present study investigated the adsorption mechanism of titanium dioxide nanoparticles (nTiO2) on polyethylene microplastics (MPs) and the resulting photocatalytic properties. This effort was supported by ecotoxicological assessments of MPs with adsorbed nTiO2 on the immobility and behaviour of Daphnia magna in presence and absence of UV irradiation. The results showed that nTiO2 were rapidly adsorbed on the surface of MPs (72% of nTiO2 in 9 h). The experimental data fit well with the pseudo-second order kinetic model. Both suspended nTiO2 and nTiO2 immobilized on MPs exhibited comparable photocatalytic properties, with the latter showing a lower effect on Daphnia mobility. A likely explanation is that the suspended nTiO2 acted as a homogeneous catalyst under UV irradiation and generated hydroxyl radicals throughout the test vessel, whereas the nTiO2 adsorbed on MPs acted as a heterogeneous catalyst and generated hydroxyl radicals only locally and thus near the air-water interface. Consequently, Daphnia, which were hiding at the bottom of the test vessel, actively avoided exposure to hydroxyl radicals. These results suggest that the presence of MPs can modulate the phototoxicity of nTiO2 - at least the location at which it is active - under the studied conditions.

The first plastic produced, but the latest studied in microplastics research: The assessment of leaching, ecotoxicity and bioadhesion of Bakelite microplastics.

Bakelite, the first synthetic plastic, is a rather unexplored material in the field of ecotoxicology, despite its long production and use. The aim of this study was to investigate the ecotoxicity of Bakelite microplastics (before and after leaching) and its leachates on four aquatic organisms: the crustacean Daphnia magna, the plant Lemna minor, the bacterium Allivibrio fischeri and the alga Pseudokirchneriella subcapitata. Bakelite microplastics before and after leaching and leachates affected all organisms, but to varying degrees. Leachates showed increased ecotoxicity to Daphnia magna, while Pseudokirchneriella subcapitata was more affected by particles. For Lemna minor and Allivibrio fischeri, the effects of particles before leaching and leachate were comparable, while the negative effect of particles after leaching was minimal or not present. All leachates were analysed, and phenol and phenol-like compounds were the predominant organics found. In addition, bioadhesion of Bakelite microplastics to the surface of Daphnia magna and Lemna minor was confirmed, but the particles were mainly weakly adhered. Results of this study suggest that, in addition to the recently studied microplastics from consumer products (e.g. from polyethylene and polystyrene), microplastics from industrial plastics such as Bakelite may be of increasing concern, primarily due to leaching of toxic chemicals.