Fate of ZnO Nanoparticles in Soils and Cowpea (Vigna unguiculata)

Abstract

The increasing use of zinc oxide nanoparticles (ZnO-NPs) in various commercial products is prompting detailed investigation regarding the fate of these materials in the environment. There is, however, a lack of information comparing the transformation of ZnO-NPs with soluble Zn(2+) in both soils and plants. Synchrotron-based techniques were used to examine the uptake and transformation of Zn in various tissues of cowpea ( Vigna unguiculata (L.) Walp.) exposed to ZnO-NPs or ZnCl2 following growth in either solution or soil culture. In solution culture, soluble Zn (ZnCl2) was more toxic than the ZnO-NPs, although there was substantial accumulation of ZnO-NPs on the root surface. When grown in soil, however, there was no significant difference in plant growth and accumulation or speciation of Zn between soluble Zn and ZnO-NP treatments, indicating that the added ZnO-NPs underwent rapid dissolution following their entry into the soil. This was confirmed by an incubation experiment with two soils, in which ZnO-NPs could not be detected after incubation for 1 h. The speciation of Zn was similar in shoot tissues for both soluble Zn and ZnO-NPs treatments and no upward translocation of ZnO-NPs from roots to shoots was observed in either solution or soil culture. Under the current experimental conditions, the similarity in uptake and toxicity of Zn from ZnO-NPs and soluble Zn in soils indicates that the ZnO-NPs used in this study did not constitute nanospecific risks.

Bioavailability of Zn in ZnO nanoparticle-spiked soil and the implications to maize plants

“…ZnO NPs have smaller particle size than bulk ZnO NPs and may migrate further and dissolve more easily, and then they and their derivatives may exert adverse impacts on soil structure and properties, and seed germination and root elongation, as well as the seedling growth and mineral nutrient uptake. Under soil culture conditions, both ZnO NPs and Zn salt (ZnCl 2 ) (500 Zn mg/kg) had no phytotoxicity to Vigan unguiculata and produced similar biomass and tissues concentration (Wang et al 2013), while ZnO NPs induced more toxicity/stress compared to bulk ZnO for P. sativum plants (Mukherjee et al 2014). Our results seem to be partly consistent with the latter.…”

“…within 1 day of reaction (Scheckel et al 2010). In another study, ZnO NPs were found to dissolve rapidly following their entry into the soil, and could not be detected after incubation for 1 h in soil; the speciation of Zn was similar in shoot tissues of V. unguiculata for both ZnCl 2 and ZnO NPs, and no roots to shoots translocation of ZnO NPs was observed (Wang et al 2013). The free Zn ion (Zn 2? )…”

Barriers, pathways and processes for uptake, translocation and accumulation of nanomaterials in plants – Critical review

“…Keeping in mind that under environmental conditions, biovoids, mucilage and exudates from roots, hyphae and bacteria significantly alter soil porosity and transport (Oades, 1993;Zhao et al, 2012b), this low mobility of ENMs shows that (a) NPs can accumulate in the first few meters or centimeters of the soil, in close interaction with the rhizosphere (Gardea-Torresdey et al, 2014;Hawes et al, 2000;McNear, 2013;Walker et al, 2003) (i.e. the root system environment where mucilage and exudates act) and (b) the key process keeping plant-ENM accumulation low in soil is slow desorption kinetics or sequestration (Avanasi et al, 2014;Wang et al, 2013b;Zhao et al, 2012b;Zhao et al, 2014).…”

Quantifying the dissolution of nanomaterials at the nano-bio interface

“…Those techniques can not only provide the micro-regional distribution of NMs, but also roughly give the quantitative information of the speciation of NMs in situ [13]. Gilbert et al [47], who used XRF and STXM to determine the bio-distribution of ZnO NPs in BEAS-2B cells, revealed the chemical forms of ZnO, including the released ions, by μ-XANES.…”

“…Many metal (Ag [11]) and metal oxide (ZnO [12,13], CuO [14,15]) NMs, including quantum dots (QDs [16]), can release metal ions at the nano-bio interface. These metal ions contribute at least in part to the toxicity of NMs [17].…”