In SituSynchrotron X-ray Fluorescence Mapping and Speciation of CeO₂and ZnO Nanoparticles in Soil Cultivated Soybean (Glycine max)

Abstract

With the increased use of engineered nanomaterials such as ZnO and CeO₂ nanoparticles (NPs), these materials will inevitably be released into the environment, with unknown consequences. In addition, the potential storage of these NPs or their biotransformed products in edible/reproductive organs of crop plants can cause them to enter into the food chain and the next plant generation. Few reports thus far have addressed the entire life cycle of plants grown in NP-contaminated soil. Soybean ( Glycine max ) seeds were germinated and grown to full maturity in organic farm soil amended with either ZnO NPs at 500 mg/kg or CeO₂ NPs at 1000 mg/kg. At harvest, synchrotron μ-XRF and μ-XANES analyses were performed on soybean tissues, including pods, to determine the forms of Ce and Zn in NP-treated plants. The X-ray absorption spectroscopy studies showed no presence of ZnO NPs within tissues. However, μ-XANES data showed O-bound Zn, in a form resembling Zn-citrate, which could be an important Zn complex in the soybean grains. On the other hand, the synchrotron μ-XANES results showed that Ce remained mostly as CeO₂ NPs within the plant. The data also showed that a small percentage of Ce(IV), the oxidation state of Ce in CeO₂ NPs, was biotransformed to Ce(III). To our knowledge, this is the first report on the presence of CeO₂ and Zn compounds in the reproductive/edible portion of the soybean plant grown in farm soil with CeO₂ and ZnO NPs.

Environmental release, fate and ecotoxicological effects of manufactured ceria nanomaterials

“…Nodule content of ceria approached 11 mg/kg in some instances and electron microscopy confirmed the complete absence of symbiotic bacteria. Similarly, HernandezViezcas et al 67 used synchrotron µXRF and µXANES to observe nanoceria within soybean root nodules and pods, although up to 20% had been transformed from Ce(IV) to Ce(III).…”

Interaction of colloidal nanoparticles with their local environment: the (ionic) nanoenvironment around nanoparticles is different from bulk and determines the physico-chemical properties of the nanoparticles

“…fertilizers [2][3][4], antimicrobial agents [5][6][7], removal of contaminants [8][9][10] and clinical use [11][12][13][14][15]), as well as unintended exposure (e.g. contamination [16] and general uptake by all types of organisms [17][18][19][20]) has been analysed in a large body of work. These studies clearly point out that in fact NPs have an impact on the environment, whether intended or unintended.…”

Interactions between engineered nanomaterials and agricultural crops: implications for food safety

“…While all Au remained as particles in plant shoots and 79% of Ce maintained the original CeO 2 coordination, CuO ENMs accumulation by Triticum aestivum (wheat) shoot were in particulate ((64±10)%) and complexed forms (Cu(I)-sulfur complexes ((36±10)%)). ZnO ENMs-exposed plants (Triticum aestivum, Glycine max) have Zn as Zn(II)-phosphate or Zn-citrate complexes; no elemental particles were observed (Lopez-Moreno et al, 2010a;Judy et al, 2011;Dimkpa et al, 2012;Hernandez-Viezcas et al, 2013). This cursory review of the literature clearly suggests that observed phytotoxicity likely result from a combination of ion-driven and sizedependent effects.…”

“…Synchrotron-based microfocused X-rayfluorescence (μ-SXRF) with microX-ray absorption near-edge structure (μ-XANES) or microXray diffraction (μ-XRD) are currently the most powerful set of techniques used for a complete characterization of biological samples. Among the set of techniques, μ-SXRF is very useful, allowing in situ mapping of nanoparticles with high sensitivity, negligible sample damage, and enable tuning of the incident energy as desired (Ma et al, 2011;Majumdar et al, 2012;Hernandez-Viezcas et al, 2013;Hummer and Rompel, 2013). Other promising advances include single particle inductively coupled plasma-mass spectrometry (spICP-MS), solid sampling highresolution-continuum source atomic absorption spectrometry (HR-CS AAS) and two-photon excitation microscopy (TPEM) (Wild and Jones, 2009;Feichtmeier and Leopold, 2013;Gray et al, 2013).…”