Nanotoxicity of 2D Molybdenum Disulfide, MoS2, Nanosheets on Beneficial Soil Bacteria, Bacillus cereus and Pseudomonas aeruginosa

Abstract

Concerns arising from accidental and occasional releases of novel industrial nanomaterials to the environment and waterbodies are rapidly increasing as the production and utilization levels of nanomaterials increase every day. In particular, two-dimensional nanosheets are one of the most significant emerging classes of nanomaterials used or considered for use in numerous applications and devices. This study deals with the interactions between 2D molybdenum disulfide (MoS₂) nanosheets and beneficial soil bacteria. It was found that the log-reduction in the survival of Gram-positive Bacillus cereus was 2.8 (99.83%) and 4.9 (99.9988%) upon exposure to 16.0 mg/mL bulk MoS₂ (macroscale) and 2D MoS₂ nanosheets (nanoscale), respectively. For the case of Gram-negative Pseudomonas aeruginosa, the log-reduction values in bacterial survival were 1.9 (98.60%) and 5.4 (99.9996%) for the same concentration of bulk MoS₂ and MoS₂ nanosheets, respectively. Based on these findings, it is important to consider the potential toxicity of MoS₂ nanosheets on beneficial soil bacteria responsible for nitrate reduction and nitrogen fixation, soil formation, decomposition of dead and decayed natural materials, and transformation of toxic compounds into nontoxic compounds to adequately assess the environmental impact of 2D nanosheets and nanomaterials.

Keywords: 2D nanosheets; MoS2 nanomaterials; nanotoxicity; soil bacteria.

Figure 1

Scanning electron microscopy images of (a) B. cereus and (b) P. aeruginosa, and (c) zeta-potential of these microorganisms.

Figure 2

(a) Scanning electron microscopy image of bulk MoS₂, (b) atomic force microscopy image of 2D MoS₂ nanosheets, and (c) zeta potential of bulk and exfoliated MoS₂.

Figure 3

Normalized (with respect to initial concentration) survival of B. cereus in peptone water and MoS₂ suspension inoculated with (a) bulk MoS₂ and (b) exfoliated MoS₂. The error bars represent the standard error of the mean.

Figure 4

Normalized (with respect to initial concentration) survival of P. aeruginosa in peptone water and MoS₂ suspension inoculated with (a) bulk MoS₂ and (b) exfoliated MoS₂. The error bars represent the standard error of the mean.

Figure 5

Dose–response curve of (a) B. cereus and (b) P. aeruginosa against bulk and exfoliated MoS₂. The error bars represent the standard error of the mean.

Figure 6

SEM micrographs showing interactions between soil bacteria and MoS₂ particles at a concentration of 4.0 mg/mL for an inoculation time of 12 h. (a) B. cereus inoculated with bulk MoS₂, (b) B. cereus inoculated with exfoliated MoS₂, (c) P. aeruginosa inoculated with bulk MoS₂, and (d) P. aeruginosa inoculated with exfoliated MoS₂. Additional SEM images are shown in Figures S5 and S6, in the Supplementary Materials.