Interactions between CeO2 Nanoparticles and the Desert Plant Mesquite: A Spectroscopy Approach

Exploring the effects of ecosystem exposure to unusual concentrations of engineered nanoparticles (ENP) is a critical issue in current environmental research. Nanotoxicological studies on plants have focused on model and crop plants, leaving plants from desert ecosystems virtually ignored. This research was designed to explore the interactions between CeO2 ENP and the desert plant mesquite (Prosopis juliflora velutina). Mesquite plantlets were grown for 15 days in a hydroponic CeO2 ENP-nutrient suspension at concentrations ranging from 500 to 4000 mg L-1. Biochemical assays showed that ascorbateperoxidase activity in roots increased when exposed to 2000 and 4000 mg CeO2 L-1; whereas in leaves, catalase presented an increasing trend associated with the external concentration of the ENP. However, mesquite plants exhibited no visible signs of stress. At all CeO2 ENP treatments, the accumulation of Ce in root tissue was much higher (>= 79%) than in the aerial part of the plant (<= 21%). X-ray absorption near edge structure (XANES) and micro X-ray fluorescence (mu-XRF) showed that most of the Ce was adsorbed in the mesquite root's epidermis and cortex suggesting passive uptake of the Ce. Lastly, it was determined that Ce in the root remained in the +4 oxidation state and it mostly remained coordinated as CeO2.