Abstract
The evaluation of nanoparticle bioavailability or the bioavailability of dissolved elements by direct measurement through plant uptake is a strenuous process. Several multi-step sequential extraction procedures, including the BCR sequential extraction procedure, have been created to provide potential accessibility of elements, where real soil-plant transfer can be problematic to implement. However, these have limitations of their own based on the used extractants. For the purposes of our research, we enriched two soils: an untilted forest soil with naturally acidic pH and a tilted agricultural soil with alkaline pH by three Zn forms—ionic Zn in the form of ZnSO4, ZnO nanoparticles (ZnO NP) and larger particles of ZnO (ZnO B)—by batch sorption. We then extracted the retained Zn in the soils by BCR sequential extraction procedure to extract three fractions: ion exchangeable, reducible, and oxidizable. The results were compared among the soils and a comparison between the different forms was made. Regardless of the difference in soil pH and other soil properties, ZnO NP, ZnO B, and ionic Zn showed little to no difference in the relative distribution between the observed soil fractions in both forest soil and agricultural soil. Since ionic Zn is more available for plant uptake, BCR sequential extraction procedure may overestimate the easily available Zn when amendment with ionic Zn is compared to particulate Zn. The absence of a first extraction step with mild extractant, such as deionized water, oversimplifies the processes the particulate Zn undergoes in soils.
Highlights
The mobility of Zn in soils is strongly affected by its physicochemical forms and by the types of bonds formed with soil constituents
The two soils were contaminated by batch sorption with three forms of Zn, ionic Zn added as ZnSO4, ZnO nanoparticles (ZnO NP), and ZnO B
Zn forms were primarily immobilized in ion exchangeable soil fraction, which is accessible for plants and microorganisms as well
Summary
The mobility of Zn in soils is strongly affected by its physicochemical forms and by the types of bonds formed with soil constituents. Its bioavailability and toxicity are tied to the Zn forms that are the most mobile rather than to the total Zn concentration in soils [1] Taking this knowledge into consideration, studies on the speciation of trace elements were conducted for many environmental partitions to evaluate their effects on the environment. Nanofertilizers offer new avenues of application to plants with the potential to increase growth yield while at the same time reducing the volume of the used fertilizer; this may result in economic and environmental benefits. Their direct application into soils is very likely in the near future [9]. Even though ZnO NP enhance plant growth at the right concentrations [10,11,12], their repeated use may result in toxic effects on soil organisms and plants when
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