Selenium (Se) as one of the essential trace elements for human plays an important role in the oxidation reduction system. But the high toxicity of Se limits its application. In this case, the element Se with zero oxidation state (Se0) has captured our attention because of its low toxicity and excellent bioavailability. However, Se0 is very unstable and easily changes into the inactive form. By now many efforts have been done to protect its stability. And this work was conducted to explore the antioxidant capacities of the stable Se0 nanoparticles (SeNPs) stabilized using chitosan (CS) with different molecular weights (Mws) (CS-SeNPs). The different Mws CS-SeNPs could form uniform sphere particles with a size of about 103 nm after 30 days. The antioxidant tests of the DPPH, ABTS, and lipid peroxide models showed that these CS-SeNPs could scavenge free radicals at different levels. And the 1 month old SeNPs held the higher ABTS scavenging ability that the value could reach up to 87.45 ± 7.63% and 89.44 ± 5.03% of CS(l)-SeNPs and CS(h)-SeNPs, respectively. In the cell test using BABLC-3T3 or Caco-2, the production of the intracellular reactive oxygen species (ROS) could be inhibited in a Se concentration-dependent manner. The topical or oral administration of CS-SeNPs, particularly the Se nanoparticles stabilized with low molecular weight CS, CS(l)-SeNPs, and treated with a 30-day storage process, could efficiently protect glutathione peroxidase (GPx) activity and prevent the lipofusin formation induced by UV-radiation or d-galactose in mice, respectively. Such effects were more evident in viscera than in skin. The acute toxicity of CS(l)-SeNPs was tenfold lower than that of H2SeO3. Our work could demonstrate the CS-SeNPs hold a lower toxicity and a 30-day storage process could enhance the antioxidant capacities. All CS-SeNPs could penetrate the tissues and perform their antioxidant effects, especially the CS(l)-SeNPs in mice models. What’s more, the antioxidant capacities of CS-SeNPs were more evident in viscera than in skin.

In this study Granular Activated Carbon (GAC) used in drinking water treatment processes is evaluated for its capacity to adsorb and remove polystyrene (PS) nanoplastics. Batch experiments are conducted in ultrapure and surface water from Lake Geneva, currently used as drinking water resources. Equilibrium and kinetic studies are conducted to understand adsorption mechanisms and limiting factors. Our results show that in ultrapure water the adsorption and removal of PS nanoplastics are mainly due to electrostatic interactions between the positively charged nanoplastics and negatively charged GAC. It is found that the adsorption capacity increases with nanoplastic concentration with a maximum adsorption capacity of 2.20 mg/g. The adsorption kinetics follows a pseudo-second-order model and indicates that the intra-particle diffusion is not the only rate-controlling step. The Langmuir isotherm indicates that nanoplastics are adsorbed as a homogeneous monolayer onto the GAC surface with a maximum monolayer adsorption capacity of 2.15 mg/g in agreement with the experimental value. In Lake Geneva water the adsorption capacity and removal efficiency of PS nanoplastics are found three times higher than in ultrapure water and increase significantly with increasing PS nanoplastics concentration with a maximum adsorption capacity of 6.33 mg/g. This improvement in adsorption capacity is due to the presence of Dissolved Organic Matter (DOM), resulting in PS surface charge modification, presence of divalent ions making possible the adsorption of PS-DOM complexes, and, aggregation of PS nanoplastics. The kinetic pseudo-second-order and intra-particle diffusion provide a good correlation with the experimental data. In contrast, neither Langmuir nor Freundlich isotherms describe in a satisfactory way the adsorption of nanoplastics by GAC. This study reveals that GAC produced from renewable sources can be considered as a moderate adsorbent for the removal of PS nanoplastics in water treatment plants and that the presence of DOM and cationic species play a major role.

The presence and accumulation of micro- and nanoplastics in marine and fresh waters represent a huge environmental concern. Due to the complexity of nanoplastic surface chemistry and impact of the surrounding aquatic environment, the fate of nanoplastics is still difficult to evaluate. Our study aims to explore the effect of different water components such as natural organic matter and inorganic colloids as well as water composition on the stability of polystyrene nanoplastics. Heteroaggregation experiments are performed under contrasting conditions by considering mixtures of three components: nanoplastics, Fe₂O₃ and alginate and at different concentration ratios. It is found that the charge neutralization mechanism in most cases is responsible for the formation of large heteroaggregates. A shift in the optimal heteroaggregation concentration is observed in the presence of alginate indicating competitive effects between alginate and Fe₂O₃. The formation of primary heteroaggregates is found to be a requisite before the formation of large structures. The behavior of polystyrene nanoplastics is also studied here in natural water from the Rhône river. Nanoplastic particles are found to rapidly change their surface charge from positive to negative and form small heteroaggregates at low concentration. Increasing the nanoplastic particle concentration is found to result in the formation of large heteroaggregates when the isoelectric point is achieved indicating the importance of nanoplastic surface charge neutralization.

The contamination of aquatic environments by microplastics has been largely documented in the last years, especially in oceans, rivers, and lakes, but their occurrence in remote mountain lakes has been scarcely considered. This work aims to investigate the presence and abundance of microplastics and fibres in a remote, alpine, and uninhabited lake in Switzerland (Sassolo). In this study, the water column as well as the sediments were analysed. The isolation of microplastics and fibres from the samples of the sediment was achieved with a digestion process using H₂O₂ and a density separation technique with NaI. Classification of microparticles (from 5 mm to 125 μm) was first developed with an optical microscope. Infrared spectroscopy was then used to identify and characterize the chemical nature of the microplastics and fibres. On average, 2.6 microplastics and 4.4 fibres per litre were identified in the water column. On the other hand, the results of the sediment samples revealed significant fibre concentrations compared to plastic microparticles (514 fibres and 33 microplastics per kilogram). The most abundant types of microplastic identified in the samples were composed of polyethylene (PE) and polypropylene (PP). Microplastic and fibre sources were not determined, but it is likely that the number of human activities in this area as well as aerial deposition are contributing to contaminate this remote environment with microplastics and fibres.