A Comprehensive Ecotoxicity Study of Molybdenum Disulfide Nanosheets versus Bulk form in Soil Organisms

The increasing use of molybdenum disulfide (MoS₂) nanoparticles (NPs) raises concerns regarding their accumulation in soil ecosystems, with limited studies on their impact on soil organisms. Study aim: To unravel the effects of MoS₂ nanosheets (two-dimensional (2D) MoS₂ NPs) and bulk MoS₂ (156, 313, 625, 1250, 2500 mg/kg) on Enchytraeus crypticus and Folsomia candida. The organisms' survival and avoidance behavior remained unaffected by both forms, while reproduction and DNA integrity were impacted. For E. crypticus, the individual endpoint reproduction was more sensitive, increasing at lower concentrations of bulk MoS₂ and decreasing at higher ones and at 625 mg/kg of 2D MoS₂ NPs. For F. candida, the molecular endpoint DNA integrity was more impacted: 2500 mg/kg of bulk MoS₂ induced DNA damage after 2 days, with all concentrations inducing damage by day 7. 2D MoS₂ NPs induced DNA damage at 156 and 2500 mg/kg after 2 days, and at 1250 and 2500 mg/kg after 7 days. Despite affecting the same endpoints, bulk MoS₂ induced more effects than 2D MoS₂ NPs. Indeed, 2D MoS₂ NPs only inhibited E. crypticus reproduction at 625 mg/kg and induced fewer (F. candida) or no effects (E. crypticus) on DNA integrity. This study highlights the different responses of terrestrial organisms to 2D MoS₂ NPs versus bulk MoS₂, reinforcing the importance of risk assessment when considering both forms.