Comparative toxicity of Cd, Mo, and W sulphide nanomaterials toward E. coli under UV irradiation

In this study, the phototoxicity of cadmium sulfide (CdS), molybdenum disulfide (MoS₂), and tungsten disulfide (WS₂) nanoparticles (NPs) toward Escherichia coli (E. coli) under UV irradiation (365 nm) was investigated. At the same mass concentration of NPs, the toxicity of three NPs decreased in the order of CdS > MoS₂ > WS₂. For example, the death rates of E. coli exposed to 50 mg/L CdS, MoS₂, and WS₂ were 96.7%, 38.5%, and 31.2%, respectively. Transmission electron microscope and laser scanning confocal microscope images of E. coli exposed to three NPs showed the damage of cell walls and release of intracellular components. The CdS-treated cell wall was more extensively damaged than those of MoS₂-treated and WS₂-treated bacteria. WS₂ and MoS₂ generated superoxide radical (O₂^-), singlet oxygen (¹O₂), and hydroxyl radical under UV irradiation, CdS produced only O₂^- and ¹O₂. CdS and WS₂ released ions under UV irradiation, while MoS₂ did not. Reactive oxygen species (ROS) generation and toxic ion release jointly resulted in the antibacterial activities of CdS and WS₂. ROS generation was the dominant toxic mechanism of MoS₂ toward the bacteria. This study highlighted the importance of considering the hazardous effect of sulfide NPs after their release into natural waters under light irradiation condition.