Impact of algal extracellular polymeric substances on the environmental fate and risk of molybdenum disulfide in aqueous media.

Molybdenum disulfide (MoS2) 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 MoS2 to aquatic fish. The predominant binding of aromatic compounds, polysaccharides, and carboxyl-rich proteins in EPS on the 1T polymorph of MoS2 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 MoS2 in aqueous solutions. Electron charge transfer and n-π* interactions with EPS decreased the catalytic activity of MoS2 by inhibiting its capability of generating reactive intermediates. The dissolution of MoS2 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 MoS2 to infantile zebrafish. Our findings provide insights into the environmental fate and risk of MoS2 by ubiquitous EPS in natural waters, serving as valuable information while developing water treatment processes accordingly.

Sulfur vacancies affect the environmental fate, corona formation, and microalgae toxicity of molybdenum disulfide nanoflakes.

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-MoS2, a hot TMD) in aqueous solution. The generation capability of •O2- and •OH was increased and the dissolution of 2H-MoS2 was significantly accelerated after SVs formation. Different with pristine form, S-vacant 2H-MoS2 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-MoS2, 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-MoS2 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 MoS2 while highlighting the importance of rational design for TMDs application.

Photolytic degradation elevated the toxicity of polylactic acid microplastics to developing zebrafish by triggering mitochondrial dysfunction and apoptosis.

Biodegradable plastics (BPs), as alternatives to conventional plastics, are increasingly consumed, but pose potential threats to aquatic ecosystems. In addition, the impact of natural aging on the toxicity of BPs is poorly understood. In this study, the photodegradation of polylactic acid (PLA, a typical BP) microplastics (MPs) under ultraviolet irradiation in water for 90 days was investigated, and the toxicities of virgin and degraded PLA to infantile zebrafish were compared. The results revealed that the size of MPs was reduced from ~25.56 to ~11.22 µm after degradation and nanoparticles were generated with a maximum yield of 7.13%. The formation of abundant oxygen-containing groups (i.e. CË­O and C-O-C) improved the hydrophilia and stability of MPs. Compared with pristine PLA, the efflux and detoxification of degraded PLA mediated by ABC transporters and P450 enzymes were slower, leading to higher bioaccumulation and skeletal development inhibition of zebrafish. Further, oxidative stress-triggered mitochondrial structural damage, depolarization, fission inhibition, and apoptosis were identified as crucial mechanisms underlying the elevated toxicity of PLA after degradation. These findings highlight the importance and necessity of considering natural degradation of BPs and related toxicity, which poses great implications for risk assessment and management of BPs.