Behavior of cerium dioxide nanoparticles in chernozem soils at different exposure scenarios

Nowadays, widespread application of engineered nanoparticles (ENPs) inevitably leads to their release into the environment. Soils are regarded as the ultimate sink for ENPs. The study on mobility of ENPs in soils is important in the assessment of potential risks related to their toxicity. The behavior of ENPs is dependent not only on parameters of soil but also on exposure scenarios, namely, the amount of ENPs trapped in soil. In the present work, the mobility of cerium dioxide nanoparticles (nCeO₂) in soils at different exposure scenarios has been studied. The relationship between mobility of nCeO₂ and their concentration in soil in the range from 1 to 1000 μg g^-1 is evaluated. It is shown that the mobility of nCeO₂ decreases with decreasing their concentration in soil and attains the minimum value at the concentration of nCeO₂ below 10 μg g^-1. In relative terms, only about 0.1-0.2% of nCeO₂ at their concentration in soil 10-1000 μg g^-1 are mobile and can migrate in soil profile under saturated conditions. The major portion of nCeO₂ (about 99.8%) remains immobile in soil. Evidently, the vertical transport of nCeO₂ in soil profile should depend on volume of released suspensions. In the case of small or moderate wet deposition, nanoparticles will accumulate in upper soil horizons, where biological activity is highest, and affect the soil inhabitants (plant roots, earthworms, insects, microorganisms, etc.).