In the last decade, plastic waste has become one of the main threats to marine ecosystems and their biodiversity due to its abundance and increased persistence. Microplastics can be classified as either primary, i.e., fabricated for commercial use, or secondary, i.e., resulting from the fragmentation/weathering processes of larger plastic pieces in the environment. In general, microplastics are detected in a number of aquatic organisms (e.g., fish, bivalves, mollusks, etc.) with alarming effects on their health. Therefore, the present work focuses on the detection and identification of microplastics in fish species (Dicentrarchus labrax, Sparus aurata) and mussels (Mytilus galloprovincialis) from aquaculture systems since these aquatic organisms are largely commercially available for consumption. In addition, seawater was also screened for the types of polymers present as well as their aging. The experimental protocol for biota samples contains a digestion step using Fenton’s reagent (0.05 M FeSO₄⋅7H₂O with 30% H₂O₂ at a volume ratio of 1:1) to remove organic material followed by filtration and a density separation step where the sample material was mixed with a saturated ZnCl₂ solution to separate microplastic particles from heavier material. For seawater samples (sampled by a microplastic net sampler), only sieving on stainless steel sieves followed by filtration on silica filters was applied. Detection of microplastics and identification of their polymeric composition was achieved through the combined use of micro-Raman analysis, Attenuated Total Reflectance–Fourier Transform Infrared spectroscopy, and Scanning Electron Microscopy in tandem with Energy Dispersive X-ray spectroscopy. Microplastic abundance was 16 ± 1.7 items/individual in mussels and 22 ± 2.1 items/individual in sea bass, and 40 ± 3.9 items/individual in sea bream, with polyethylene (74.4%) being the most detected polymer type, while polyethylene-co-vinyl acetate (65%), polyvinyl-butyral (36.8%), polyvinyl alcohol (20%), and polybutyl methacrylate (15.8%) were also detected to a lesser extent. The microplastics isolated from seawater samples were films (30%), fragments (30%), and fibers (20%), while some of them were derived from foams (20%). Also, in most of these seawater-recovered microplastics, a relatively high degree of oxidation (carbonyl index > 0.31) was observed, which was further confirmed by the results of Energy Dispersive X-ray spectroscopy. Finally, the Scanning Electron Microscopy images showed various morphological characteristics (cracks, cavities, and burrs) on the surfaces of the microplastics, which were attributed to environmental exposure.

The valorization of food industry byproducts has become a significant issue worldwide because of the drive towards a circular economy. The “zero waste target” in human activities seems to be a dominant objective in the design of future products by enterprises. In this work, food waste from the crayfish processing industry was converted into useful products (quantum dots), as nowadays, biowaste-derived materials tend to be more attractive than conventionally produced materials with a similar structure due to their lower production costs and environmentally friendly development processes. More specifically, shell waste from the crayfish industry was treated hydrothermally and, after a freeze-drying process, was transformed to useful quantum dots. Instrumental and chemical techniques, such as XRD, SEM-EDS, AFM, XPS, elemental analysis, fluorescence spectroscopy, TG, Microtox bioassay, and DPPH antioxidant activity, were employed to characterize the final product. The results indicated the existence of thermally stable spherical particles, with a diameter of 5–8 nm, which were mainly composed of carbon, oxygen, nitrogen, calcium, and sulfur. Their external surface was rough and rich with various functional groups that further contributed to their overall optical properties. The final product presented low ecotoxicity, as studied by the Microtox assay. The superior antioxidant activity of this product compared to other similar materials reported elsewhere renders it a potential material for, e.g., food packaging applications. In addition, for the first time, N/S-Carbon QDs were applied as an antioxidant/antibacterial agent for strawberry preservation, showing promising results as the coated strawberries maintained their color and weight for three consecutive days with no mold growth observed on their surface.

Photocatalysis is a prominent alternative wastewater treatment technique that has the potential to completely degrade pesticides as well as other persistent organic pollutants, leading to detoxification of wastewater and thus paving the way for its efficient reuse. In addition to the more conventional photocatalysts (e.g., TiO₂, ZnO, etc.) that utilize only UV light for activation, the interest of the scientific community has recently focused on the development and application of visible light-activated photocatalysts like g-C₃N₄. However, some disadvantages of g-C₃N₄, such as the high recombination rate of photogenerated charges, limit its utility. In this light, the present study focuses on the synthesis of WO₃ fibers/g-C₃N₄ Z-scheme heterojunctions to improve the efficiency of g-C₃N₄ towards the photocatalytic removal of the widely used insecticide clothianidin. The effect of two different g-C₃N₄ precursors (urea and thiourea) and of WO₃ fiber content on the properties of the synthesized composite materials was also investigated. All aforementioned materials were characterized by a number of techniques (XRD, SEM-EDS, ATR-FTIR, Raman spectroscopy, DRS, etc.). According to the results, mixing 6.5% ^W/_W WO₃ fibers with either urea or thiourea derived g-C₃N₄ significantly increased the photocatalytic activity of the resulting composites compared to the precursor materials. In order to further elucidate the effect of the most efficient composite photocatalyst in the degradation of clothianidin, the generated transformation products were tentatively identified through UHPLC tandem high-resolution mass spectroscopy. Finally, the detoxification effect of the most efficient process was also assessed by combining the results of an in-vitro methodology and the predictions of two in-silico tools.