Adsorption behavior of lead on aquatic sediments contaminated with cerium dioxide nanoparticles

Aquatic sediments serve as an important sink for engineered nanomaterials (ENMs), such as metal oxide nanoparticles (MeO NPs) and carbon nanotubes (CNTs). Owing to their remarkable properties, ENMs demonstrate significant potential to disturb the adsorption behavior of other contaminants in aquatic sediments, thereby altering the bioavailability and toxicity of these contaminants. Thus far, most studies have investigated the effect of CNTs on the adsorption of other contaminants on sediments. Cerium dioxide nanoparticles (CeO₂ NPs), as one of the important MeO NPs, are also inevitably discharged into aquatic sediments because of their widespread use. In this study, we investigated the adsorption behavior of Pb²⁺ on sediments spiked with CeO₂ NPs at a weight ratio of 5.0%. The results showed that the adsorption rates at three stages occurring during adsorption clearly increase for sediments contaminated with CeO₂ NPs. Moreover, the results obtained from the adsorption isotherms indicated that the Langmuir isotherm model best fits the isotherm data for both sediments and those contaminated with CeO₂ NPs. After spiking the sediments with CeO₂ NPs, the theoretical maximum monolayer adsorption capacity (Q_max) for Pb²⁺ increased from 4.433 to 4.995 mg/g and the Langmuir isotherm coefficient (K_L) decreased from 8.813 to 7.730 L/g. The effects of CeO₂ NPs on the surface charge and pore surface properties of sediments were also studied as these properties affect the adsorption of several chemicals in sediments. The results showed that pH_zpc, S_BET, S_ext, and average pore size of sediments clearly decrease for sediments contaminated with CeO₂ NPs. Hence, the strong adsorption capacity of CeO₂ NPs and the changes of sediment surface charge and pore surface properties caused by CeO₂ NPs are important factors affecting the adsorption behavior of Pb²⁺. The potential risk of Pb²⁺ in aquatic environment may increase with CeO₂ NPs buried in sediments.