Driving Role of Zinc Oxide Nanoparticles with Different Sizes and Hydrophobicity in Metabolic Response and Eco-Corona Formation in Sprouts (Vigna radiata).

Zinc oxide nanoparticles (ZnO NPs) cause biotoxicity and pose a potential ecological threat; however, their effects on plant metabolism and eco-corona evolution between NPs and organisms remain unclear. This study clarified the molecular mechanisms underlying physiological and metabolic responses induced by three different ZnO NPs with different sizes and hydrophobicity in sprouts (Vigna radiata) and explored the critical regulation of eco-corona formation in root-nano systems. Results indicated that smaller-sized ZnO inhibited root elongation by up to 37.14% and triggered oxidative burst and apoptosis. Metabolomics confirmed that physiological maintenance after n-ZnO exposure was mainly attributed to the effective stabilization of nitrogen fixation and defense systems by biotransformation of the flavonoid pathway. Larger-sized or hydrophobic group-modified ZnO exhibited low toxicity in sprouts, with 0.89-fold upregulation of citrate in central carbon metabolism. This contributed to providing energy for resistance to NP stress through amino acid and carbon/nitrogen metabolism, accompanied by changes in membrane properties. Notably, smaller-sized and hydrophobic NPs intensely stimulated the release of root metabolites, forming corona complexes with exudates. The hydrogen-bonded wrapping mechanism in protein secondary structure and hydrophobic interactions of heterogeneous functional groups drove eco-corona formation, along with the corona evolution intensity of n-ZnO > s-ZnO > b-ZnO based on higher (α-helix + 3-turn helix)/ß-sheet ratios. This study provides crucial insight into metabolic and eco-corona evolution in bionano fates.

Toxicity and tolerance mechanism of binary zinc oxide nanoparticles and tetrabromobisphenol A regulated by humic acid in Chlorella vulgaris.

Recent studies have reported that nanoparticles (NPs) released into the aquatic environment may interact with persistent organic pollutants such as brominated flame retardants, whereas the environmental processes and toxicological impacts induced by such binary NPs require further specification. This study investigated the ultrastructural damage of Chlorella vulgaris triggered by exposure to zinc oxide (ZnO) NPs, tetrabromobisphenol A (TBBPA), ZnO-TBBPA, and ZnO-TBBPA-humic acid (HA), clarified the uptake and distribution of ZnO NPs in cells, and explored the physiological toxicity and tolerance mechanism. The results demonstrated that ZnO NPs induced irregular morphology in algal cells, and the disruption of the cellular ultrastructure by binary ZnO-TBBPA was also extremely severe due to the excessive uptake of ZnO NPs, which resulted in strong oxidative stress responses. In particular, the accumulation of reactive oxygen species further exacerbated the reduction of total chlorophyll content and algal density. Moreover, the cluster heat map and correlation analysis revealed that superoxide dismutase activity played a critical role in alleviating lipid peroxidation damage and enhancing the tolerance of algal cells to the stress of binary ZnO NPs. More notably, the existence of HA intensified the dispersion stability of NP suspensions and significantly mitigated the synergistic toxicity of binary ZnO-TBBPA. This study provides new insights into the environmental behavior and biological impacts of binary NPs in the natural environment.

Physiological Toxicity and Antioxidant Mechanism of Photoaging Microplastics on Pisum sativum L. Seedlings.

Recent studies have confirmed that changes in the physical properties of microplastics (MPs) trigger toxicological effects and ecological risks. To explore the toxicity of different types of MPs on plants, and the influence of MP photoaging, this study investigated the toxicity mechanisms of pristine, 7 and 14 d photoaged polystyrene (PS), polyamide (PA), polyethylene (PE), and polyethylene terephthalate (PET) MPs on seed germination, root growth, nutrient fraction, oxidative stress, and antioxidant systems of Pisum sativum L. (pea) seedlings. The results showed that pristine PS and 14 d photoaged PET inhibited seed germination. Compared to the pristine MPs, photoaged MPs had negative effects on root elongation. Moreover, photoaged PA and PE impeded the nutrient transport of soluble sugars from roots to stems. Notably, the production of superoxide anion radicals (•O2-) and hydroxyl radicals (•OH) through the photoaging of MPs exacerbated oxidative stress and reactive oxygen species formation in roots. Antioxidant enzyme data revealed that the activities of superoxide dismutase and catalase were significantly activated in photoaged PS and PE, respectively, in order to scavenge •O2- and hydrogen peroxide (H2O2) accumulation and alleviate lipid peroxidation levels in cells. These findings provide a new research perspective on the phytotoxicity and ecological risk of photoaged MPs.

New insights into the decrease in Cd2+ bioavailability in sediments by microplastics: Role of geochemical properties.

Microplastics (MPs) are considered to influence the bioavailability of heavy metals through direct adsorption, but this neglects the distribution of heavy metal chemical speciation indirectly influenced by MPs by altering geochemical properties. The present study aims to explore the link between the fractionation distribution of cadmium (Cd2+) and changes in geochemical properties in sediments induced by polyethylene terephthalate microplastics (PET-MPs). The PET-MPs reduced the acid-soluble fraction of Cd2+ in sediments and increased its organically bound fraction. In addition, the concentration of bioavailable Cd2+ in the sediment decreased by 4.09-25.96 % with increasing PET-MPs doses and aging. Whereas the thermal aging of PET-MPs led to a decrease in the molar ratio of oxygen-containing functional groups and the BET surface area, which is not favorable for improving the adsorption capacity of PET-MPs. On the other hand, the correlation analysis demonstrated the key role of PET-MPs in increasing the content of sediment organic matter and its humification level, which indirectly led to a decrease in Cd2+ bioavailability. The microbial analysis demonstrated that PET-MPs increase the relative abundances of Chloroflexi, hexokinase, and 6-phosphofructose kinase in sediments, thereby increasing the humification level of sediment organic matter. The present study provides a new perspective for understanding the environmental risks of MPs-altered heavy metals.

Modulation mechanism of phytotoxicity on Ipomoea aquatica Forssk. by surface coating-modified copper oxide nanoparticles and its health risk assessment.

To evaluate the influence of surface coatings on nano-fertilizers uptake and their phytotoxicity to crops and its health risk to Chinese adults, trisodium citrate (TC) and polyethylene glycol (PEG) coatings were prepared on the surface of copper oxide nanoparticles (CuO NPs), respectively, with 100 and 500 mg/L of bare CuO NPs, TC-CuO NPs, and PEG-CuO NPs were exposed to soil-grown Ipomoea aquatica Forssk. Combined bio-transmission electron microscopy and micro-CT observed cellular migration of coated CuO NPs in symplastic and apoplastic pathways, as well as nanoparticles transported through vascular tissues to the above-ground parts. Since TC-CuO NPs had less inhibition on vascular phylogeny of I. aquatica roots which was determined by RT-qPCR, their migration in plants was more efficient, thus exhibiting greater phytotoxicity to shoots. Meanwhile, coatings significantly reduced the phytotoxicity of CuO NPs by stimulating plant antioxidant defense. The risk of CuO nano-fertilizers on human dietary safety was evaluated, the HQ > 1 in the 500 mg/L CuO NPs treatment indicated a potential health risk to Chinese adults, which was reduced by the coatings. This work explored for the first time the mechanism of coating effects on nanoparticles migration efficiency and phytotoxicity at the molecular level and demonstrated that the migration of nanoparticles between tissues could have an impact on phytotoxicity. It implied that coating can be tailored to target nanoparticles to specific regions of the plant. In addition, this study highlights the potential health risks associated with the consumption of I. aquatica fertilized with CuO NPs and provides valuable insights into the environmental applications of nano-fertilizers.

Phytotoxicity of binary nanoparticles and humic acid on Lactuca sativa L.

Nanoplastics and metal oxide nanoparticles are serious threats that inevitably enter the environment. Their similar particle properties likely lead to interaction and thus cause more unpredictable ecotoxicity to organisms. In this study, it was found that polystyrene nanoplastics (PS NPs) aggravate the toxic effect of iron oxide nanoparticles (Fe2O3 NPs) on Lactuca sativa L. by inducing severe oxidative stress and root deformation, and the expansion of damaged cells from the xylem to the epidermis was observed using confocal laser scanning. Exposure to PS NPs + Fe2O3 NPs correspondingly elevated iron accumulation in the roots and leaves by 1.39 and 1.17 times compared to the amount observed with Fe2O3 NPs individually. Examination of the physicochemical properties, iron ion release, and molecular interactions of the NPs indicated that PS NPs interact with Fe2O3 NPs to form heteroaggregates and facilitate leaching of iron ions, which resulted in aggravating the toxic effect. These were alleviated by the addition of humic acid (HA), which dispersed the heteroaggregates and reduced the release of iron ions. The findings in the present study provide new perspectives for the ecotoxicological risk of binary nano-pollution in the natural environment.