Use of synchrotron- and plasma-based spectroscopic techniques to determine the uptake and biotransformation of chromium(iii) and chromium(vi) by Parkinsonia aculeata

Abstract

In this study, a combination of inductively coupled plasma optical emission spectroscopy and X-ray absorption spectroscopy (XAS) was used to study the uptake and speciation of chromium in Parkinsonia aculeata, commonly known as Mexican Palo Verde. Plants were treated for 14 days in a modified Hoagland solution containing chromium(III) or chromium(VI) at several concentrations. The results showed that plants treated with 70 mg Cr(III) L⁻¹ and 30 mg Cr(VI) L⁻¹ had similar Cr concentrations in leaves (∼200 mg kg⁻¹ dry weight, DW). The results also showed that neither Cr(III) nor Cr(VI) affected the uptake of phosphorus and sulfur. However, the concentration of calcium in the stems of plants treated with Cr(VI) at 40 mg L⁻¹ (about 6000 mg Ca kg⁻¹ DW) was significantly higher compared to the Ca concentration (about 3000 mg kg⁻¹ DW) found in the stems of plants treated with 150 mg Cr(III) L⁻¹. However, no differences were observed in potassium and magnesium concentrations. The iron concentration (about 1000 mg kg⁻¹ DW) in roots treated with 40 mg Cr(VI) L⁻¹ was similar to the iron concentration found in the roots of plants treated with 110 mg Cr(III) L⁻¹. The XAS data showed that Cr(VI) was reduced to Cr(III) in/on the plant roots and transported as Cr(III) to the stems and leaves. The XAS studies also showed that Cr(III) within plants was present as an octahedral complex.