Applications of creosotebush in phytoremediation of copper(II) and chromium(VI) ions.

摘要

Larrea tridentata (creosotebush), a common, North American native desert shrub, shows the ability to take up copper(II) and chromium(VI) ions rapidly from solution. EPA method 200.3 was followed to digest the plant samples and flame atomic absorption spectroscopy (FAAS) was used to determine-the amount of copper and chromium taken up in different parts of the plant. The amount of copper found within the roots, stems, and leaves was 13.8 mg/g, 1.1 mg/g and 0.6 mg/g, respectively, after the creosote bush was exposed to a 63.5-ppm copper(II) solution for 48 hours. When the plant was exposed to a 635-ppm copper(II) solution, the roots, stems and leaves contained 35 mg/g, 10.5 and 3.8, respectively. The amount of chromium found within the roots, stems, and leaves was 57.4 mg/g, 14.2 mg/g and 19.3 mg/g, respectively, after the creosote bush was exposed to a 520-ppm chromium(VI) solution. In addition to FAAS analysis, X-ray microfluorescence (XRMF) analysis of the plant samples provided in situ documentation of copper and chromium absorption by the various plant parts. It was noticed with XRMF, a higher content of copper when the plant was exposed to a higher copper concentration. Also, higher amounts were detected on the roots, followed by the stems and the smallest amount was detected in the leaves. In the case of chromium, XRMF showed that the higher chromium content was present on the roots followed by the leaves and finally the lowest chromium content was observed on the stems. X-ray absorption spectroscopy (XAS) elucidated the oxidation state of the copper and chromium absorbed by the plants. The copper(II) absorbed from solution remained as copper(II) bound to oxygen-containing ligands within the plant samples. On the other hand, the chromium(VI) absorbed from solution was partially reduced to chromium(III) in the roots. Some chromium(VI) and the reduced chromium(III), were transported through the stems, and finally accumulated as chromium(III) in the leaves of the plant. Chromium was bound to oxygen-containing ligand within the plant samples. Another analytical technique used to detect the metal-compound ligands was Fourier Transform Infrared Spectroscopy (FT-IR). FT-IR corroborated the presence of the copper-oxygen bond, most likely from a carboxyl group. (Abstract shortened by UMI.)