Session: Applications & Implications of Nanomaterials in the Environment:

In this paper, we report the dissolution, aggregation and stability of four metal oxide nanoparticles (NPs) based on Ce, Cu, Mn and Mo, in root exudates (RE), soil leachate and water as control. Characterization indicated that all four NPs has a primary size from 8 nm to 60 nm in diameter. Surface analysis indicated binding energy mainly at regions Ce-3d, Mn-2p, Cu-2p and Mo-3d. Our findings indicated the aggregation of nano-Cu(OH)₂and nano-MoO₃ exposed to RE over time, while nano-CeO₂ and nano-Mn₃O₄ formed smaller aggregates in same medium with time. In soil leachate, all nanomaterials disaggregate with time (5 days) and presented negative charge in the particle surface. These smaller aggregates can promote the apoplastic transport to xylem in roots of some plants. Mobility of nanoparticles has been also related to organic ligands, such as organic acids. The availability of organic acids such as fumaric, gallic and malic acids in soil leachate, as well as malic, ascorbic, ferulic, glutaric, and salicylic acids in RE promoted lower dissolution of nano-Cu(OH)₂and nano-Mn₃O₄, and higher stability over time for all NPs. The size distribution of all NPs obtained via single particle ICP-MS during the early 6 h in contact with RE indicated the main changes in size distribution of all four NPS occurred in this period. The ions released from NPs in root exudates after 6 days were 38%, 1.2%, 0.5% and <0.1% of the elemental content of Mo, Cu, Mn and Ce in the respective NPs. Since nanoparticles based in these metals are considered nano-enabled agricultural products, the delivery system via roots-soil interface need to consider the type and content of organic ligands, time of exposure, as well as the physicochemical properties of the media in order to enhance the effectiveness of their application.

Arturo Keller

University of California, Santa Barbara

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