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 poly-ethylene microplastics (MPs) and the resulting photocatalytic properties. This effort was supported by ecotoxi-cological 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 ho-mogeneous 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

Exploring the impacts of microplastics and associated chemicals in the terrestrial environment – Exposure of soil invertebrates to tire particles

Highlights • Negative impacts of tire particles on soil invertebrates are possible at roadsides. • Tire particles slightly decreased reproduction and survival of springtail F. candida. • Tire particles decreased AChE activity of isopod P. scaber. • No dose-dependent effects of tire particles on enchytraeid E. crypticus observed. • Tire particles contained a variety of potentially harmful substances.Abrasion of tire wear is one of the largest sources of microplastics to the environment. Although most tire particles settle into soils, studies on their ecotoxicological impacts on the terrestrial environment are scarce. Here, the effects of tire particles (<180 μm) on three ecologically relevant soil invertebrate species, the enchytraeid worm Enchytraeus crypticus, the springtail Folsomia candida and the woodlouse Porcellio scaber, were studied. These species were exposed to tire particles spiked in soil or in food at concentrations of 0.02%, 0.06%, 0.17%, 0.5% and 1.5% (w/w). Tire particles contained a variety of potentially harmful substances. Zinc (21 900 mg kg−1) was the dominant trace element, whilst the highest concentrations of the measured organic compounds were detected for benzothiazole (89.2 mg kg−1), pyrene (4.85 mg kg−1), chlorpyrifos (0.351 mg kg−1), HCB (0.134 mg kg−1), methoxychlor (0.116 mg kg−1) and BDE 28 (0.100 mg kg−1). At the highest test concentration in soil (1.5%), the tire particles decreased F. candida reproduction by 38% and survival by 24%, and acetylcholinesterase (AChE) activity of P. scaber by 65%, whilst the slight decrease in the reproduction of E. crypticus was not dose-dependent. In food, the highest test concentration of tire particles reduced F. candida survival by 38%. These results suggest that micro-sized tire particles can affect soil invertebrates at concentrations found at roadsides, whilst short-term impacts at concentrations found further from the roadsides are unlikely

Synthesis of nanostructured TiO2_2 microparticles with high surface area

Hydrothermal reactions represent a simple and efficient method for the preparation of nanostructured TiO$_2$ particles that could be of interest as photocatalysts or catalytic supports. Although the particle size is in the range of 2–5 µm, the nanostructures composing the particles ensure a large specific surface area with values above 100 m$^2$/g. The effects of the different synthesis parameters on the morphology, photocatalytic activity, and stability of the prepared material were studied. The surface morphology of the prepared TiO$_2$ powders was studied by scanning electron microscopy (SEM). To further characterize the samples, the specific surface area for different morphologies was measured and the photocatalytic activity of the prepared powders was tested by degrading model pollutants under UV irradiation. The results show that the initial morphology had little effect on the photocatalytic properties. On the other hand, the final calcination temperature significantly increased the degradation rates, making it comparable to that of P25 TiO$_2$ (particle size 20–30 nm)

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

Interactions between titanium dioxide nanoparticles and polyethylene microplastics

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

An extensive characterization of various environmentally relevant microplastics – material properties, leaching and ecotoxicity testing

Microplastics in the environment occur in different sizes and shapes and are made of various polymers. Therefore, they also considerably differ in their properties and ecotoxicity. However, the majority of microplastics research uses pre-made spherical microplastics, which practically do not exist in the environment. Our work focused on a comprehensive study of six different types of microplastic that were prepared to simulate common microplastics found in the environment. All types of microplastics where chemically and physically characterized using Fourier-transform infrared spectroscopy, thermal analysis, field-emission scanning electron microscopy, optical microscopy and laser diffraction analysis. The specific surface area was determined using the BET method. Furthermore, effects of microplastics and microplastic leachates on a common duckweed (Lemna minor) were evaluated. All tested microplastics did not affect specific growth rate and chlorophyll a content in duckweed, while microplastics with a rough surface and sharp edges caused a significant reduction of duckweed root length. Microplastics made of Bakelite also showed an intensive leaching, which increased their ecotoxicity potential. Natural particles used as a control did not have any negative effect on duckweed. Overall, microplastic particles have significantly different ecotoxicity profiles depending on their physico-chemical properties. Therefore, the testing of environmentally relevant particles and their proper characterization, as well as the testing of microplastic leaching properties, is crucial for understanding of microplastics ecotoxicological potential

Exploring the impacts of plastics in soil - The effects of polyester textile fibers on soil invertebrates

Polyester fiber is one of the most abundant types of microplastics in the environment. A major proportion of the fibers entering wastewater treatment plants end up in sewage sludge, which is used as a soil fertilizer in many countries. As their impacts in the terrestrial environment are still poorly understood, we studied the effects of polyester fibers on enchytraeids (Enchytraeus crypticus), springtails (Folsomia candida), isopods (Porcellio scaber) and oribatid mites (Oppia nitens), all playing an important role in soil decomposer food webs. We exposed these invertebrates in the laboratory to short (12 µm–2.87 mm) and long (4–24 mm) polyester fibers, spiked in soil or in food at five concentrations ranging from 0.02% to 1.5% (w/w) and using five replicates. Overall the effects of polyester fibers on the soil invertebrates were slight. Energy reserves of the isopods were slightly affected by both fiber types, and enchytraeid reproduction decreased up to 30% with increasing fiber concentration, but only for long fibers in soil. The low ingestion of long fibers by the enchytraeids suggests that this negative impact arose from a physical harm outside the organism, or from indirect effects resulting from changes in environmental conditions. The short fibers were clearly ingested by enchytraeids and isopods, with the rate of ingestion positively related to fiber concentration in the soil. This study shows that polyester fibers are not very harmful to soil invertebrates upon short-term exposure. However, longer lasting, multigeneration studies with functional endpoints are needed to reveal the possible long-term effects on soil invertebrates and their role in the decomposition process. This study also shows that polyester fibers can enter terrestrial food web via ingestion of fibers by soil invertebrates

Exploring the impacts of plastics in soil – The effects of polyester textile fibers on soil invertebrates

Polyester fiber is one of the most abundant types of microplastics in the environment. A major proportion of the fibers entering wastewater treatment plants end up in sewage sludge, which is used as a soil fertilizer in many countries. As their impacts in the terrestrial environment are still poorly understood, we studied the effects of polyester fibers on enchytraeids (Enchytraeus crypticus), springtails (Folsomia candida), isopods (Porcellio scaber) and oribatid mites (Oppia nitens), all playing an important role in soil decomposer food webs. We exposed these invertebrates in the laboratory to short (12 µm–2.87 mm) and long (4–24 mm) polyester fibers, spiked in soil or in food at five concentrations ranging from 0.02% to 1.5% (w/w) and using five replicates. Overall the effects of polyester fibers on the soil invertebrates were slight. Energy reserves of the isopods were slightly affected by both fiber types, and enchytraeid reproduction decreased up to 30% with increasing fiber concentration, but only for long fibers in soil. The low ingestion of long fibers by the enchytraeids suggests that this negative impact arose from a physical harm outside the organism, or from indirect effects resulting from changes in environmental conditions. The short fibers were clearly ingested by enchytraeids and isopods, with the rate of ingestion positively related to fiber concentration in the soil. This study shows that polyester fibers are not very harmful to soil invertebrates upon short-term exposure. However, longer lasting, multigeneration studies with functional endpoints are needed to reveal the possible long-term effects on soil invertebrates and their role in the decomposition process. This study also shows that polyester fibers can enter terrestrial food web via ingestion of fibers by soil invertebrates.publishedVersio

Exploring the impacts of microplastics and associated chemicals in the terrestrial environment

Abrasion of tire wear is one of the largest sources of microplastics to the environment. Although most tire particles settle into soils, studies on their ecotoxicological impacts on the terrestrial environment are scarce. Here, the effects of tire particles (<180 μm) on three ecologically relevant soil invertebrate species, the enchytraeid worm Enchytraeus crypticus, the springtail Folsomia candida and the woodlouse Porcellio scaber, were studied. These species were exposed to tire particles spiked in soil or in food at concentrations of 0.02%, 0.06%, 0.17%, 0.5% and 1.5% (w/w). Tire particles contained a variety of potentially harmful substances. Zinc (21 900 mg kg−1) was the dominant trace element, whilst the highest concentrations of the measured organic compounds were detected for benzothiazole (89.2 mg kg−1), pyrene (4.85 mg kg−1), chlorpyrifos (0.351 mg kg−1), HCB (0.134 mg kg−1), methoxychlor (0.116 mg kg−1) and BDE 28 (0.100 mg kg−1). At the highest test concentration in soil (1.5%), the tire particles decreased F. candida reproduction by 38% and survival by 24%, and acetylcholinesterase (AChE) activity of P. scaber by 65%, whilst the slight decrease in the reproduction of E. crypticus was not dose-dependent. In food, the highest test concentration of tire particles reduced F. candida survival by 38%. These results suggest that micro-sized tire particles can affect soil invertebrates at concentrations found at roadsides, whilst short-term impacts at concentrations found further from the roadsides are unlikely