Environmental implications of MoS₂ nanosheets on rice and associated soil microbial communities

Molybdenum disulfide (MoS₂) is a transition metal dichalcogenides (TMDCs) material that is seeing rapidly increasing use. The wide range of applications will result in significant environmental release. Here, the impact of MoS₂ nanosheets on rice and associated soil microbial communities was evaluated. Rice plants were grown for 4 weeks in a natural paddy soil amended with either 1T or 2H phase MoS₂ nanosheets at 10 and 100 mg kg^-1. The 1T MoS₂ nanosheets have a significantly greater dissolution rate (58.9%) compared to 2H MoS₂ (4.4%), indicating the instability of 1T MoS₂ in environment. High dissolution rate resulted in a high Mo bioaccumulation in rice leaves (272 and 189 mg kg^-1 under 1T and 2H exposure at 100 mg kg^-1). However, this did not induce overt phytotoxicity, as indicated by a range of phenotypic or biochemical based determine endpoints, e.g., biomass, photosynthetic pigments, and malondialdehyde (MDA) content. Additionally, rice P uptake was significantly increased upon exposure to 1T and 2H MoS₂ (10 mg kg^-1). Gas chromatography-mass spectrometry (GC-MS) reveals that both phases of MoS₂ in soil systematically enhanced the carbon and nitrogen related metabolic pathways in exposed plants. Soil 16S rRNA gene sequencing data show that soil microbial community structure was unchanged upon MoS₂ exposure. However, both phases of MoS₂ remarkably increased the relative abundance of N₂-fixation cyanobacteria, and 2H MoS₂ exposure increased a plant growth-promoting rhizobacteria-Bacillus. Overall, our results suggest that MoS₂ nanosheets at tested doses did not exert negative impacts on rice plant and the associated soil microbial community.