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The increasing application of engineered nanomaterials (ENMs) unavoidably leads to environmental release and biological exposure. Understanding the potential hazards of ENMs on crops is essential for appropriate utilization and management. Herein, rice seedlings were hydroponically exposed to molybdenum sulfide (MoS 2 , a typical ENM) nanosheets at 5−20 mg/L for 7 days and then depurated for another 7 days in a fresh culture medium. Exposure to MoS 2 triggered irreversible reductions in root length (by 26.3%–69.9%) and tip number (by 22.2%–66.0%). Integration of biochemical assays, transcriptomic and metabolomics found that oxidative stress induced by MoS 2 in roots was persistent, whereas the activation of aquaporins, ionic transportation, and energy synthesis was normalized due to the recovery of nutrient uptake. The down-regulated levels of genes and metabolites associated with peroxidases, hemicellulose synthesis, expansins, and auxins caused persistent structural damages (sclerosis and rupture) of root cell walls. Approximately 64.5%–84.8% of internalized MoS 2 nanosheets were degraded, and the successive up-regulation of genes encoding cytochrome P450s and glutathione S -transferases reflected the biotransformation and detoxification of MoS 2 in the depuration period. These findings provide novel insights into the persistence and recovery of MoS 2 phytotoxicity, which will help advance the risk assessment of MoS 2 application on environment. [Display omitted] • MoS 2 exposure triggered irreversible reductions in root length and tip number. • Antioxidative genes were persistently down-regulated to adapt to the lowered ROS. • Activation of aquaporins, nutrient uptake, and energy synthesis was recoverable. • Inhibition on POD, hemicellulose, and expansins caused persistent cell wall damage. • Genes encoding CYP450 and GST were orderly activated for MoS 2 detoxification. [ABSTRACT FROM AUTHOR]

The transformation of silver ions (Ag+) mediated by engineered nanomaterials (ENMs) influences the biosafety of Ag-containing products in natural environments. Actually, modification of biomolecules to ENMs in aquatic ecosystems alters their interactions with Ag+. This study discovered that surface functionalization of glutathione (GSH, a sulfhydryl compound ubiquitous in natural waters) on molybdenum disulfide (MoS 2) nanoflakes suppressed the redox reaction between 1 T components and Ag+, inhibiting the MoS 2 -mediated reduction of Ag+ to Ag nanoparticles (AgNPs) in aqueous phase in the dark. However, AgNPs formation (from 2.32 ± 0.35–3.25 ± 0.29 mg/L per day, pH 7.0) and oxidation of MoS 2 were remarkably accelerated after GSH binding under light conditions. The dominant electron donator of MoS 2 to Ag+ was transformed from the electron-hole pairs to surface ligands driven by the introduction of chromophoric groups was authenticated as the cause for the elevated Ag+ reduction. These processes also occurred between Ag+ and MoS 2 at low levels (50 μg/L). Additionally, the joint algal toxicity of GSH-modified MoS 2 with Ag+ was weaker than that of pristine MoS 2 due to increased retention of free Ag+ and AgNPs formation. Our findings improve the understanding of the interaction between ENMs and Ag+ in aquatic ecosystems. [Display omitted] • The reduction of Ag+ to AgNPs by MoS 2 was prevented by GSH binding in the dark. • GSH stabilized 1 T phase of MoS 2 and inhibited redox reaction with Ag+ in the dark. • AgNPs formation on MoS 2 was quickened with GSH binding under light irradiation. • Light induced charge transfer from surface ligands of GSH-MoS 2 to adsorbed Ag+. • GSH adsorption significantly lowered the joint toxicity of MoS 2 and Ag+ to algae. [ABSTRACT FROM AUTHOR]

• Binding of hydrophilic compounds in EPS alter morphology and structure of MoS 2. • EPS binding enhanced the dispersity and colloidal stability of MoS 2 in water phase. • EPS retarded the catalytic activity of MoS 2 by inhibiting free radicals generation. • Initial oxidation and carbon grafting by EPS slowed down the dissolution of MoS 2. • Co-exposure of EPS decreased the risk of MoS 2 toward aquatic organisms. Molybdenum disulfide (MoS 2) poses great potential in water treatment as a popular transition metal dichalcogenide, arousing considerable concern regarding its fates and risk in aquatic environments. This study revealed that the interplay with extracellular polymeric substances (EPS) of freshwater algae significantly changed the properties and toxicity of MoS 2 to aquatic fish. The predominant binding of aromatic compounds, polysaccharides, and carboxyl-rich proteins in EPS on the 1T polymorph of MoS 2 via hydrophilic effects and the preferential adsorption of carboxylic groups contributed to morphological alterations, structural disorders (band gap and phase alterations), and the attenuated aggregation of MoS 2 in aqueous solutions. Electron charge transfer and n -π* interactions with EPS decreased the catalytic activity of MoS 2 by inhibiting its capability of generating reactive intermediates. The dissolution of MoS 2 slowed down after interacting with EPS (from 0.089 to 0.045 mg/L per day) owing to rapid initial oxidation (i.e., forming Mo-O bond) and carbon grafting. Notably, the morphological and structural alterations after EPS binding alleviated the toxicity (e.g., malformation and oxidative stress) of MoS 2 to infantile zebrafish. Our findings provide insights into the environmental fate and risk of MoS 2 by ubiquitous EPS in natural waters, serving as valuable information while developing water treatment processes accordingly. [Display omitted] [ABSTRACT FROM AUTHOR]

Sulfur vacancy (SV) defects have been engineered in two-dimensional (2D) transition metal dichalcogenides (TMDs) for high performance applications in various fields involving environmental protection. Understanding the influence of SVs on the environmental fate and toxicity of TMDs is critical for evaluating their risk. Our work discovered that SVs (with S/Mo ratios of 1.65 and 1.32) reduced the dispersibility and promoted aggregation of 2H phase molybdenum disulfide (2H-MoS 2 , a hot TMD) in aqueous solution. The generation capability of •O 2 - and •OH was increased and the dissolution of 2H-MoS 2 was significantly accelerated after SVs formation. Different with pristine form, S-vacant 2H-MoS 2 preferentially harvested proteins (i.e., forming protein corona) involved in antioxidation, photosynthetic electron transport, and the cytoskeleton structure of microalgae. These proteins contain a higher relative number of thiol groups, which exhibited stronger affinity to S-vacant than pristine 2H-MoS 2 , as elucidated by density functional theory calculations. Notably, SVs aggravated algal growth inhibition, oxidative damage, photosynthetic efficiency and cell membrane permeability reduction induced by 2H-MoS 2 due to increased free radical yield and the specific binding of functional proteins. Our findings provide insights into the roles of SVs on the risk of MoS 2 while highlighting the importance of rational design for TMDs application. [Display omitted] • S vacancies decreased the dispersibility and promoted the aggregation of 2H-MoS 2. • Free radicals yield and dissolution of S-vacant MoS 2 were faster than pristine form. • S-vacant MoS 2 specifically harvested proteins which are abundant in -SH group. • The -SH group exhibited higher affinity to S-vacant MoS 2 than -COOH and -NH 2 groups. • S vacancies obviously aggravated the adverse effects on algae induced by 2H-MoS 2. [ABSTRACT FROM AUTHOR]

The transformation of Ag+ is strongly correlated with its risks in aquatic environment. Considering the wide application of molybdenum disulfide (MoS 2) and the inevitable release into the environment, the effects of MoS 2 on Ag+ transformation and toxicity are of great concerns. This study revealed the pH-dependent reduction of Ag+ (0.5 mM) to Ag nanoparticles (AgNPs) by MoS 2 (50 mg/L) and solar irradiation obviously accelerates the AgNPs formation (2.638 mg/L per day, pH=7.0) compared with dark condition (0.637 mg/L per day), ascribing to the electrons capture from electron-hole pairs of MoS 2 by Ag+. Ionic strengths and natural organic matter decreased the AgNPs yield. Metallic 1 T phase of MoS 2 primarily participated in AgNPs formation and was oxidized to soluble ions (MoO 4 2−) due to the oxygen generation in valance band. The above processes also occurred between Ag+ and MoS 2 at environmentally relevant concentrations. Further, photoinduced transformation of Ag+ by MoS 2 (10–100 μg/L) significantly lowered its toxicity to freshwater algae. The AgNPs formation on MoS 2 reduced the bioavailability of Ag+ to algae, which was the mechanism for attenuated Ag+ toxicity. The provided data are helpful for better understanding the roles of MoS 2 on the environmental fates and risks of metal ions under natural conditions. [Display omitted] • Solar irradiation speeded up the pH-dependent reduction of Ag+ to Ag NPs by MoS 2. • Electron transfer from electron-hole pairs of MoS 2 to Ag+ drived Ag NPs formation. • Metallic phase of MoS 2 participated in Ag NPs formation and was oxidized to ions. • MoS 2 at environmentally relevant concentrations could also reduce Ag+ to Ag NPs. • Photoinduced reduction of Ag+ by MoS 2 attenuated its toxicity to freshwater algae. [ABSTRACT FROM AUTHOR]