ABSTRACT
Aquatic plant duckweed can enrich high concentration of arsenic, it is thus used as the representative of phytofiltration.The mechanism of arsenic tolerance in duckweeds has received much concern.In this study, synchrotron radiation X-ray fluorescence (SRXRF) and X-ray absorption near edge structure (XANES) techniques were used to study the micro-distribution and speciation of arsenic in natural As-rich duckweed from lead-zinc mine.Two monolithic duckweeds, FP1 and FP2, were analyzed by micro SRXRF, setting single point scan time and spot size were 5 s, 70 μm×80 μm and 2 s, 100 μm×100 μm respectively.Six points of FP2 were selected and analyzed by micro XANES in energy range of 11.81-11.96 keV.Pressed-pellet duckweed was analyzed by bulk XANES in energy range of 11.67-12.27 keV.The result showed that As(Ⅲ) was the major speciation of duckweed from bulk XANES and micro-XANES data.SRXRF micro analysis showed that arsenic had significant vein distribution in duckweed, and was not spread into the photosynthetic mesophyll within certain concentration, which may reduce the leaf toxicity triggered by arsenic.This vein distribution may play a role in arsenic tolerance in duckweed.
ABSTRACT
To investigate the mechanism of lead biosorption and biotransformation in lead-resistant bacteria in microcosmic scale, synchrotron radiation micro X-ray fluorescence (μ-SRXRF ) and X-ray absorption near edge structure ( XANES) was used to determine the element distribution characteristics and speciation of lead ( Pb) in lead-resistant bacteria strain isolated from farmland soil samples taken from a lead-zinc mine in Lanping county, Yunnan province in China. The isolated species was identified to be Arthrobacter sp. The concentration of Pb biosorpted in lead-resistant bacteria was directly determined byμ-SRXRF, and the results showed that the highest concentration was 5925μg/g and the bioaccumulate factor was 14 . 8 . Speciation of Pb in lead-resistant bacteria B2, LB ( Lysogeny Broth) medium and soil were also presented after using Pb LⅢXANES. Compared with Pb LⅢ XANES peak shape and peak position between standard samples, it was demonstrated that the Pb in lead-resistant bacteria was mainly formed by amorphous forms like PbS (58. 0%), (C17H35COO)2Pb (22. 2%), Pb5(PO4)3Cl (19. 8%) rather than organic Pb speciation which was exist in LB medium. Therefore, the isolated lead-resistant bacteria could biotransform Pb to sulfuric compounds. The biotransformation regular could be of great interest for other investigators as reference in study of bioavailability impact factor of heavy metals.
ABSTRACT
Synchrotron radiation X-ray fluorescence analysis technology (SRXRF) can effectively reduce the detection limit for the determination of heavy metal elements, especially suitable for in situ nondestructive analysis of biological samples with low contents. By corn seed germination test, and combining with SRXRF technology, the effects of Pb on corn seed germination and Pb micro-distribution in the corn seed were studied. X-ray absorption near edge structure (XANES ) technique was used to analyze the Pb chemical speciation in different parts of corn seed. The above experiment was taken to understand the absorption and transformation mechanism of Pb by corn seeds. Results showed that germination rate, bud length and root length decreased with increased Pb contents. The analysis of variance showed that P-value of the germination rate, bud length and root elongation of corn seeds which were exposed to different concentration of Pb were 2. 0×10-3, 1. 4×10-4 and 2. 39×10-8, which were all less than 0. 01, therefore there were highly significant differences during these three indicators and the content of Pb. In addition, the inhibition effect on root growth was greater. SRXRF analysis results showed that Pb was mainly enriched in episperm and embryo, which would inhibit embryonic develop into bud and root. The Pb-LⅢ(13035 eV) XANES spectra of all samples include of root, shoot and the different part of seed were the same, they were the same speciation. Linear combination fitting results indicated that the lead phosphate chloride and lead stearate accounted for 74 . 3 %and 24. 2 % respectively, which suggested that the main Pb speciation of corn was lead phosphate chloride which deposited inside of corn, and a few combined with carboxylic to form the organic lead.