Abstract
The aims of this study were both the qualitative and quantitative analysis of chromium accumulation in the shoots of Callitriche cophocarpa. This globally distributed, submersed macrophyte exhibits outstanding Cr phytoremediation capacity in an aquatic environment. Cr was applied separately for 7 days at two stable forms as Cr(VI) and Cr(III), known from their diverse physicochemical properties and toxicities. The maps of Cr depositions in young leaves, mature leaves, and stems were obtained by micro X-ray fluorescence spectroscopy (μXRF). The detailed analysis of XRF maps was done based on Image-Pro PLUS (Media Cybernetics) software. Cr was accumulated either in trichomes or vascular bundles in respect to the element speciation and the plant organ. The concentration of Cr significantly increased in the following order: Cr(VI) mature leaves < Cr(VI) young leaves = Cr(VI) stems < Cr(III) young leaves ≤ Cr(III) mature leaves ≤ Cr(III) stems. The observed differences in distribution and accumulation of Cr were correlated with the different reduction potential of Cr(VI) by particular plant organs. The reduction of Cr(VI) is considered the main detoxification mechanism of the highly toxic Cr(VI) form. The unique L-band electron resonance spectrometer (L-band EPR) was applied to follow the reduction of Cr(VI) to Cr(III) in the studied material.
Highlights
Cr(III) and Cr(VI) are the two common and most stable forms of Cr in the environment
Cr was found solely in spot-like structures in all investigated samples, i.e., young leaves (Fig. 3a), mature leaves (Fig. 3c), and stems (Fig. 3e), when the shoots were exposed to trivalent chromium
It must be stressed that young leaves showed identical Cr localization regardless of the chromium speciation in the solution
Summary
Cr(III) and Cr(VI) are the two common and most stable forms of Cr in the environment. Cr(VI) is found mainly in the form of chromate (HCrO4−) or dichromate (CrO42−) anion in solutions It is an extremely strong oxidant, highly soluble within a wide range of pH, and it is bioavailable. When Cr(III) is present in higher concentrations, its harmful effects are associated with binding to functional groups of enzymes It can displace native ions in other biomolecules in a cell, resulting in changes in their structure and functions (Appenroth 2010; Codd et al 2001; Kotaś and Stasicka 2000; Saha et al 2011; Zayed and Terry 2003).
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