Mitigation Effects and Associated Mechanisms of Environmentally Relevant Thiols on the Phytotoxicity of Molybdenum Disulfide Nanosheets.

Thorough investigations of the environmental fate and risks are necessary for the safe application of engineered nanomaterials. Nevertheless, the current understanding of potential transformations of MoS (an intensively studied two-dimensional nanosheet) upon interactions with ubiquitous environmentally relevant thiols (ERTs) in water is limited. This study revealed that two ERTs, l-cysteine and mercaptoacetic acid, could modify MoS by covalently grafting thiol groups on S atoms of 1T phases, improving the colloidal persistence and chemical stability of MoS. Compared with the pristine form, MoS-thiols with higher dispersity exhibited significantly mitigated envelopment and ultrastructural damage to microalgae. MoS-triggered growth inhibition, upregulation of reactive oxygen species, photosynthetic injury, and metabolic perturbation in algae were remarkably attenuated by ERTs. The diminished capability for MoS to generate reactive intermediates and glutathione oxidation driven by ERTs caused the weakness of oxidative stress and negative effects. Additionally, molecular dynamics simulations demonstrated that ERTs altered the extent of the influence of MoS on the secondary structures and functions of adsorbed intracellular proteins, which also contributed to the lower phytotoxicity of MoS. Our findings provide evidence for the crucial role of specific organic ligands in the risk of MoS in aquatic environments.