| dc.description.abstract | CCerium oxide nanoparticles (CeO2NPs) have received much attention recently
because of their popular uses in industrial and commercial products. The accumulation of CeO2NPs in the environment, especially in natural soils, becomes a potential risk to terrestrial plants. Although below-ground vegetables are most likely to accumulate the highest concentrations of CeO2NPs, little work has been done to investigate the interactions between this plant group and CeO2NPs. In this dissertation, the uptake and accumulation of CeO2NPs by Raphanus sativus L. (radish) were evaluated in hydroponic and soil systems.
In the hydroponic system, the accumulation patterns and the effect of Ce on plant growth and physiological processes varied with the characteristics of Ce. While active transport appeared to be the primary pathway for ionic Ce accumulation in plant tissues, adsorption and diffusion of particulate Ce along the radial direction govern the accumulation of bulk CeO2 and CeO2NPs accumulation in radish storage roots. The intact CeO2NPs could be taken up by the radish fine roots, but the upward transport was limited. Ce detected in radish shoots through root exposure is predominantly in the dissolved form. Importantly, the transformation of CeO2NPs to ionic Ce on the radish fine root surface was first confirmed and the enhanced transformation was attributed to the organic acids with low molecular weight (e.g. malic acid) in the roots exudates of radish.
In the soil system, many soil properties, including the soil texture, mineral content, and organic matter content, affect the fractionation of CeO2NPs in soil and their bioavailability to radish. Aging of CeO2NPs in soil led to higher availability of dissolved Ce in the rhizosphere soil and greater accumulation of Ce in radish shoots. Efforts were also made to understand the interactions of CeO2NPs with two major soil components (sand and clay). Experimental results and mathematical modeling results indicated that adsorption to sand and kaolin (a typical clay) particles had strong impact on the mobility of CeO2NPs in soil. The surface properties of CeO2NPs play a crucial role in these interactions. | en |
