Influence of Size and Phase on the Biodegradation, Excretion, and Phytotoxicity Persistence of Single-Layer Molybdenum Disulfide

Abstract

The increasing applications of single-layer molybdenum disulfide (SLMoS2) pose great potential risks associated with environmental exposure. This study found that metallic-phase SLMoS2 with nanoscale (N-1T-SLMoS2, ∼400 nm) and microscale (M-1T-SLMoS2, ∼3.6 μm) diameters at 10–25 mg/L induced significant algal growth inhibition (maximum 72.7 and 74.6%, respectively), plasmolysis, and oxidative damage, but these alterations were recoverable. Nevertheless, membrane permeability, chloroplast damage, and chlorophyll biosynthesis reduction were persistent. By contrast, the growth inhibition (maximum 55.3%) and adverse effects of nano-sized semiconductive-phase SLMoS2 (N-2H-SLMoS2, ∼400 nm) were weak and easily alleviated after 96 h of recovery. N-1T-SLMoS2 (0.011 μg/h) and N-2H-SLMoS2 (0.008 μg/h) were quickly biodegraded to soluble Mo compared with M-1T-SLMoS2 (0.004 μg/h) and excreted by algae. Incomplete biodegradation of SLMoS2 (26.8–43.9%) did not significantly mitigate its toxicity. Proteomics and metabolomics indicated that the downregulation of proteins (50.7–99.2%) related to antioxidants and photosynthesis and inhibition of carbon fixation and carbohydrate metabolism contributed to the persistent phytotoxicity. These findings highlight the roles and mechanisms of the size and phase in the persistent phytotoxicity of SLMoS2, which has potential implications for risk assessment and environmental applications of nanomaterials.

Persistence and Recovery of ZIF-8 and ZIF-67 Phytotoxicity

“…For example, ZIF-67 increased the synthesis of chlorophyll a by 14.41% at 72 h. However, ZIF-67 and ZIF-8 decreased the synthesis of chlorophyll a by 15.97–22.28 and 7.80–30.58%, respectively, at 120 h. After recovery for 120 h, the chlorophyll a contents were similar in all groups. The biosynthesis of chlorophyll a did not recover upon exposure to graphene and single-layer MoS 2 , compared with the two tested ZIFs, at the same concentrations and over the same time periods. , However, the ZIFs caused physical damage to the chloroplasts and potentially affected chlorophyll synthesis for a long time, which was consistent with the TEM image below.…”

“…The algal densities in the exposure period and the recovery period are shown in Figure S4a,b. The recovery of algal growth was observed for graphene oxide and single-layer MoS 2 . , , However, the synthesis of chlorophyll a in Figure b was not completely consistent with the algal growth in Figure a. Inconsistent results were observed for organic pollutants .…”

Recent Advances in Two-Dimensional MoS2 Nanosheets for Environmental Application

“…The environmental transformation and ecotoxicity of MoS 2based composites remains largely unknown. 249,250 Thereby, the tremendous efforts and further explorations should be made in the future: (1) the scalable and controllable production of various MoS 2 -based composites with large surface area, small particle size, and high stability, using low cost and easy operation method; and (2) the massive investigations concerning the transformation, fate, and ecotoxicity of MoS 2based composites in actual environments.…”

“…The overlapping and coalescing of MoS 2 nanosheets reduced the specific surface area and the interlayer distance of MoS 2 nanosheets due to the interaction of S–Mo–S layer, which decreased exposure toward active sites. How does one increase stability of MoS 2 under special conditions? For instance, MoS 2 under extreme pH and high E h conditions might release extra ions (e.g., MoO 4 2– , SO 4 2– ), which is harmful for the application of MoS 2 in environmental remediation; How does one synthesize various functionalized MoS 2 -based composites using low-cost and simplified manufacturing processes? How are the biological compatibility and actual feasibility evaluated? The environmental transformation and ecotoxicity of MoS 2 -based composites remains largely unknown. , Thereby, the tremendous efforts and further explorations should be made in the future: (1) the scalable and controllable production of various MoS 2 -based composites with large surface area, small particle size, and high stability, using low cost and easy operation method; and (2) the massive investigations concerning the transformation, fate, and ecotoxicity of MoS 2 -based composites in actual environments.…”

Transcriptomics and Metabolomics Revealed the Biological Response of Chlorella pyrenoidesa to Single and Repeated Exposures of AgNPs at Different Concentrations

“…In recent years, toxicity studies of engineered nanoparticles (ENPs) to algae have been conducted, as ENPs represent a potential threat to aquatic environments. − Microalgae are vital producers in aquatic ecosystems and widely used to evaluate the nanotoxicity of ENPs as model organism. − According to previous reports, ENPs were able to enter algae through particle penetration, endocytosis, transport carrier proteins, or ion channels, inducing oxidative stress by excessive production of intracellular reactive oxygen species (ROS) . But due to the variety of ENPs characteristics and variations in exposure concentrations, ENPs might facilitate the algal growth .…”