Dissolution and Retention Process of CeO2 Nanoparticles in Soil with Dynamic Redox Conditions

In situ characterization of silver nanoparticles sulfidation processes in aquatic solution by hollow fiber flow-field flow fractionation coupled with ICP-QQQ

The sulfidation is considered as one of the most important environmental transformation processes of silver nanoparticles (AgNPs), which affects their transport, uptake and toxicity. Herein, based on the hollow fiber flow-field flow fractionation coupled with triple quadrupole inductively coupled plasma mass spectrometry (HF5-ICP-QQQ), we developed an efficient approach to accurately characterize the sulfidation process of AgNPs in aquatic solutions. HF5 could efficiently remove interferential ions and separate nanoparticles with different sizes online, and ICP-QQQ could accurately detect S element through monitoring 32S16O+ in mass shift mode. By the proposed method, two kinds of AgNPs, citrate-coated AgNPs and PVP-coated AgNPs, were selected as models to trace their transfer behaviors during the sulfidation. The results showed once AgNPs were exposed to Na2S solution, the overlapping fractograms of 32S16O+ and 107Ag+ were rapidly detected by HF5-ICP-QQQ to indicate the co-presence of Ag and S, and thus confirming the production of Ag2S and AgNPs underwent a rapid sulfidation process. There were substantial differences in the influence of the two coated agents on the stability of the particles under the conditions examined. In the presence of sulfide, PVP-coated AgNPs could maintain initial size distribution with higher stability, while the size distribution of citrate-coated AgNPs changed considerably. The developed HF5-ICP-QQQ method provides a reliable tool to identify and characterize the transformation process of AgNPs in aquatic solution, which contributed to a deeper understanding of the environmental fate and behavior of AgNPs with different coating.

Synergistic Effects of Organic Ligands and Visible Light on the Reductive Dissolution of CeO2 Nanoparticles: Mechanisms and Implications for the Transformation in Plant Surroundings

Cerium oxide (CeO2) nanoparticles are one of the most important engineered nanomaterials with demonstrated applications in industry. Although numerous studies have reported the plant uptake of CeO2, its fate and transformation pathways and mechanisms in plant-related conditions are still not well understood. This study investigated the stability of CeO2 in the presence of organic ligands (maleic and citric acid) and light irradiation. For the first time, we found that organic ligands and visible light had a synergistic effect on the reductive dissolution of CeO2 with up to 30% Ce releases after 3 days, which is the highest release reported so far under environmental conditions. Moreover, the photoinduced dissolution of CeO2 in the presence of citrate was much higher than that in maleate, which are adsorbed on the surface of CeO2 through inner-sphere and outer-sphere complexation, respectively. A novel ligand-dependent photodissolution mechanism was proposed and highlighted: upon electron-hole separation under light irradiation, the inner-sphere complexed citrate is more capable of consuming the hole, prolonging the life of electrons for the reduction of Ce(IV) to Ce(III). Finally, reoxidation of Ce(III) by oxygen was observed and discussed. This comprehensive work advances our knowledge of the fate and transformation of CeO2 in plant surroundings.

Determination of the Particle Number Concentration, Size Distribution, and Species of Dominant Silver-Containing Nanoparticles in Soils by Single-Particle ICP-MS

The potential risk of various silver-containing nanoparticles (AgCNPs) in soils is related to the concentration, size, and speciation, but their determination remains a great challenge. Herein, we developed an effective method for determining the particle number, size, and species of dominant AgCNPs in soils, including nanoparticles of silver (Ag NPs), silver chloride (AgCl NPs), and silver sulfide (Ag₂S NPs). By ultrasonication wand-assisted tetrasodium pyrophosphate extraction, these AgCNPs were extracted efficiently from soils. Then, multistep selective dissolution of Ag NPs, AgCl NPs, and whole Ag NPs/AgCl NPs/Ag₂S NPs was achieved by 1% (v/v) H₂O₂, 5% (v/v) NH₃·H₂O, and 10 mM thiourea in 2% (v/v) acetic acid, respectively. Finally, the particle number concentration and size distribution of AgCNPs in the extracts and the remaining AgCNP particle number concentration after each dissolution were determined by single-particle inductively coupled plasma mass spectroscopy for speciation of the dominant AgCNPs. AgCNPs were detected in all five soil samples with the concentrations of 0.23-8.00 × 10⁷ particles/g and sizes of 16-110 nm. Ag₂S NPs were the main form of AgCNPs in the examined soils with the percentage range of 53.98-69.19%, followed by AgCl NPs (11.42-23.31%) and Ag NPs (7.78-16.19%). Our method offers a new approach for evaluating the occurrence and potential risk of AgCNPs in environmental soils.

Effects of CeO2 Nanoparticles on Nutritional Quality of Two Crop Plants, Corn (Zea mays L.) and Soybean (Glycine max L.)

With the widespread applications of manufactured nanoparticles (NPs), there are increasing concerns about their potential adverse effects on the environment and living systems. Many studies demonstrated that NPs could significantly affect the growth and development of crop plants. However, knowledge regarding the impacts of NPs on crop quality is rather limited. In this study, the effects of CeO₂ NPs (25, 75, and 225 mg Ce/kg) and CeCl₃ (25 mg Ce/kg) on the nutritional components of soil-cultivated corn and soybean plants were evaluated. Both treatments tended to decrease the dry weight of grain per plant, while only 225 mg/kg CeO₂ NPs on soybean and CeCl₃ on corn showed statistical significance compared with the respective control. CeO₂ NPs at 225 mg/kg significantly decreased the content of starch in the corn kernels by 18.2% but increased total phenols in soybean seeds by 18.4%. Neither CeO₂ NPs nor CeCl₃ significantly affected the contents of minerals in corn kernels except for Zn. However, in the case of soybean, the two treatments tended to decrease the contents of P, Zn, Mn, and Mo but increase the content of S. Overall, the results suggest that CeO₂ NPs and Ce³⁺ ions showed similar but not identical effects on corn and soybean plants. CeO₂ NPs affect the nutritional quality of crop plants in a species-dependent manner.

In Situ Tracking of Crystal-Surface-Dependent Cu2O Nanoparticle Dissolution in an Aqueous Environment

Metal-oxide-based nanoparticles (MONPs) such as Cu₂O NPs have attracted growing attention, but the potential discharges of MONPs have raised considerable concern of their environmental fate including their dissolution behavior. The impacts of morphology on MONP dissolution are largely uncertain due to the lack of in situ tracking techniques. In this study, we combined a series of in situ technologies including liquid-cell transmission electron microscopy and fluorescence probes to reveal the in situ dissolution process of Cu₂O NPs in freshwater. Our results suggest that cubic Cu₂O NPs exhibit a higher dissolution quantity compared with spherical NPs of the same surface area. The difference was mainly related to the crystal surface, while other factors such as particle size or aggregation status showed minor effects. Importantly, we demonstrated the simultaneous growth of new small NPs and the dissolution of pristine Cu₂O NPs during the dissolution of Cu₂O NPs. Cubic Cu₂O NPs became much less soluble under O₂-limited conditions, suggesting that O₂ concentration largely affected the dependence of dissolution on the NP morphology. Our findings highlight the potential application of in situ techniques to track the environmental fates of MONPs, which would provide important information for assessing the ecological risks of engineered NPs.