Can photocatalytic and magnetic nanoparticles be a threat to aquatic detrital food webs?

Synthesis of zinc oxide nanoparticles using Trichoderma harzianum and its bio-efficacy on Alternaria brassicae

Increasing concerns about chemical fungicides require sustainable alternatives for crop protection. Microbe-mediated synthesis of metal nanoparticles offers a sustainable, eco-friendly and highly effective strategy for plant disease management. This study investigates the mycosynthesis of zinc oxide nanoparticles (ZnO NPs) using the culture filtrate of Trichoderma harzianum and their antifungal activity against Alternaria brassicae. Nanoparticles were synthesized under optimized conditions of cell-free culture filtrate (CFCF) concentration, substrate concentration, pH and temperature. Ultraviolet-visible (UV-Vis) spectroscopy confirmed an absorption peak between 200 and 400 nm, while X-ray diffraction (XRD) confirms the hexagonal crystal structure with an average size of 29 nm. Dynamic light scattering (DLS) and zeta potential analysis revealed a hydrodynamic size of 50.79 nm and a surface charge of -17.49 mV, indicating good stability. Fourier transform infrared (FTIR) spectroscopy analysis identified functional groups (C=O, N-O, and O-H) that are crucial for nanoparticles stabilization. Scanning electron microscopy (SEM) and High-resolution transmission electron microscopy (HR-TEM) analysis revealed spherical, rod-shaped and hexagonal nanoparticles with sizes between 12 and 41 nm. Mycogenic-zinc oxide nanoparticles (M-ZnO NPs) significantly inhibited the mycelial growth of A. brassicae by 91.48% at 200 μg/mL, compared to chemically synthesized ZnO NPs at 200 μg/mL (79.62%) and mancozeb 0.2% (82.96%). SEM-EDX analysis revealed deformations and absorption of M-ZnO NPs in fungal hyphae, while confocal laser scanning microscopy (CLSM) showed increased reactive oxygen species (ROS) formation and impaired membrane integrity in treated fungal cells. Stress enzyme analysis confirmed increased superoxide dismutase (SOD) and catalase (CAT) activity by 44.2 U/mol and 39.6 U/mol at 200 μg/mL M-ZnO NPs. Our studies suggest that the M-ZnO NPs synthesized with T. harzianum culture filtrate have increased antifungal activity even at lower doses and can be used as an alternative to traditional fungicides without affecting environment.

Microplastics and silver nanoparticles compromise detrital food chains in streams through effects on microbial decomposers and invertebrate detritivores

Abundance of microplastics (MPs) in freshwater ecosystems has become an emerging concern due to their persistence, toxicity and potential interactions with other contaminants. Silver nanoparticles (Ag-NPs), which share common sources with MPs (e.g., personal care products), are also a subject of concern. Thus, the high probability of co-occurrence of both contaminants raises additional apprehensions. This study assessed, for the first time, the impacts of MPs and Ag-NPs, alone or in mixtures, on stream detritus food webs. Physiological and ecological responses of aquatic fungal communities, invertebrate shredders (Allogamus sp.) and collectors (Chironomus riparius) were examined. Additionally, antioxidant enzymatic responses of microbes and shredders were analyzed to unravel the mechanisms of toxicity; also, neuronal stress responses of Allogamus sp. were assessed based on the activities of cholinesterases. Organisms were exposed to environmentally realistic concentrations of polyethylene MPs, extracted from a personal care product (0.1, 0.5 and 10 mg L-1), for 7 days, in the absence or presence of Ag-NPs (0.1 mg L-1 and 1 mg L-1). The exposure to both contaminants reduced the growth rates of all tested organisms. MPs, Ag-NPs, and their mixtures led to a decrease in leaf litter decomposition by fungi and shredders. The availability of fine particulate organic matter, released by the shredders, increased when exposed to these contaminants. The negative effects of these contaminants were further strengthened by the responses of antioxidant enzymes that revealed high level of oxidative stress in both fungi and Allogamus sp. Moreover, the activities of cholinesterases showed that Allogamus sp. were under neuronal stress upon exposure to both contaminants. The impacts in mixtures were stronger than those of individual contaminants suggesting interactive effects. Overall, our study showed adverse effects of MPs and Ag-NPs across trophic levels and indicated that they may compromise key processes, such as organic matter decomposition in streams.

Large-scale aqueous synthesis of Cu(In,Ga)Se2 nanoparticles for photocatalytic degradation of ciprofloxacin

Environmentally friendly synthesis of Cu(In,Ga)Se₂ (CIGS) nanoparticles (NPs) is pivotal for producing sustainable photocatalytic compounds to be applied in the remediation of contaminants of emerging concern from water. To this end, we herein report an aqueous synthesis of CIGS NPs, followed by annealing, to give access to phase-pure CIGS crystals with chalcopyrite structure and no signs of secondary phases. Morphological and compositional characterization revealed NPs with an average size of 10-35 nm and uniform distribution of Cu, In, Ga, and Se elements. In addition, the first aqueous large-scale synthesis of CIGS NPs is developed by up-scaling the synthesis procedure, resulting in 5 g of highly crystalline nanoparticles exhibiting an ideal optical band gap of 1.14 eV. The as-synthesized NPs proved the ability to remove 71 and 83% of a contaminant of emerging concern, ciprofloxacin (CIP), under ultraviolet (UV) and visible (Vis) radiations, respectively.

Reusable Ag@TiO2-Based Photocatalytic Nanocomposite Membranes for Solar Degradation of Contaminants of Emerging Concern

Two significant limitations of using TiO2 nanoparticles for water treatment applications are reduced photocatalytic activity under visible radiation and difficulty recovering the particles after use. In this study, round-shaped Ag@TiO2 nanocomposites with a ≈21 nm diameter and a bandgap energy of 2.8 eV were synthesised by a deposition-precipitation method. These nanocomposites were immobilised into a porous poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) matrix and well-distributed within the pores. The photocatalytic activity of Ag@TiO2/PVDF-HFP against metronidazole (MNZ) under solar radiation was evaluated. Further, an adaptive neuro-fuzzy inference system (ANFIS) was applied to predict the effect of four independent variables, including initial pollutant concentration, pH, light irradiation intensity, and reaction time, on the photocatalytic performance of the composite membrane on MNZ degradation. The 10% Ag@TiO2/PVDF-HFP composite membrane showed a maximum removal efficiency of 100% after 5 h under solar radiation. After three use cycles, this efficiency remained practically constant, demonstrating the membranes' reusability and suitability for water remediation applications.