The fate and impact of CoO nanoparticles in the soil environment: Observing the dose effect of nanoparticles on soybeans.

The widespread presence and distribution of metal-based nanoparticles (NPs) in soil is threatening crop growth and food security. However, little is known about the fate of CoO NPs in the soil-soybean system and their phytotoxicity. The study demonstrated the effects of CoO NPs on soybean growth and yield in soil after 60 days and 140 days, and compared them with the phytotoxic effects of Co. The results showed that CoO NPs (10-500 mg/kg) had no significant toxic effect on soybeans. Soil available Co content was significantly increased under 500 mg/kg CoO NPs treatment. Compared with Co, CoO NPs mainly accumulated in roots and had limited transport to the shoots, which was related to the particle size, surface charge and chemical stability of CoO NPs. The significant accumulation of CoO NPs in roots further led to a significant decrease in root antioxidant enzyme activity and changes in functional gene expression. CoO NPs reduced soybean yield after 140 days, but interestingly, at specific doses, it increased grain nutrients (Fe content increased by 17.38% at 100 mg/kg, soluble protein and vitamin E increased by 14.34% and 16.81% at 10 mg/kg). Target hazard quotient (THQ) assessment results showed that consuming soybean seeds exposed to CoO NPs (≥100 mg/kg) and Co (≥10 mg/kg) would pose potential health risks. Generally, CoO NPs could exist stably in the environment and had lower environmental risks than Co. These results help to better understand the environmental behavior and plant effect mechanisms of CoO NPs in soil-plant systems.