微区X射线荧光光谱仪研制及元素生物地球化学动态分布过程研究

微区无损分析可提供物质组成元素的原位分布信息，以揭示物质形成条件、元素动态分布过程与相互作用机理、生物代谢作用等。文章报道了实验室型微区X射线荧光(μXRF)光谱仪的研发和元素生物地球化学动态分布过程研究结果。μXRF光谱仪采用15 μm光斑的聚束毛细管X射线透镜为激发源，选用分辨率为135 eV的硅漂移探测器(SDD)，样品和探测器间角度可调，使之可进行异型样品如地质样品的原位分析，利用五轴自控实现样品时空四维元素分布测定。利用该μXRF光谱仪测定了矿物-生物膜间的元素迁移和玉米种发芽过程中的元素分布，发现(1)生物膜可吸附、富集毒性元素铅，是重金属的重要汇集地，最大富集系数1.7。(2)生物膜是金属从固态矿物相经水相进入生态系统的重要途径。(3)在玉米种子中，可检测到K，Ca，Mn，Fe，Cu，Zn和Pb。Zn主要在胚乳中分布，胚中有少量Zn存在；在胚乳和胚中存在微量Fe；胚乳中存在微量Pb，胚中未观测到Pb。(4)经含Pb溶液浸泡发芽后，K在玉米种中胚和胚乳中部分富集，Fe分布在种皮和胚乳中，Cu和Zn主要在胚乳中分布；Pb主要在胚根、胚轴和胚芽中分布，且Pb在新生根中高度富集。研究表明，在种子萌发阶段，Pb等毒性元素可被植物滞留于根部，制约了其向地上部的转移，从而揭示了植物对毒性元素的耐受机制。

Development of Laboratory Microscopic X-Ray Fluorescence Spectrometer and the Study on Spatial Distribution of Elements in Biofilms and Maize Seeds

Microscopic X-ray florescence spectrometry (μX RF) can be used to obtain the information on distribution and correlation of the chemical elements in the biogeochemical samples.The information is useful in r evealing conditions of material formation,dynamic processes of elemental distri bution and correlation among them,as well as biological metabolism.A laborator y μXRF spectrometer was developed with combining a polycapillary microfocus Xray beam excitation with a rhodium anode (50 kV,1 mA),a silicon drift detector(SDD) and three-dimensional scanning capability.The angle between the sample stage and the SDD detector was designed to be adjustable so that an in situ dete rmination of a heterotypic sample,such as geological samples,can be made with the μXRF set.A rock-biofilm sample was taken from a field investigation,wher e there is a small mine and the rock in a shallow pool was covered by a green bi ofilm.The rock-biofilm sample was stored in a refrigerator for further μXRF m easurement.Maize seeds were from markets.Dry maize seeds and ones with Pb-soa ked were sliced before the μXRF measurements.Then,the developed laboratory μXR F spectrometer was applied to study the mobilization of lead in the rock-biofil ms,and location of K,Ca,Mn,Fe,Cu,Zn and Pb in germination of the maize see ds.We found that (1) Pb accumulated in biofilms with a bioaccumulation factor o f 1.7.(2) Pb increased gradually from rock to biofilm,and then decreased from biofilm to air.A peak occurred in the biofilm.(3) In maize seeds without Pbsoaked,K,Ca,Mn,Fe,Cu,Zn and Pb were detectable.Zn was mainly found in end osperm,a small amount of Zn in embryo;trace Fe was detected in endosperm and e mbryo;Trace Pb was detectable in endosperm,not in embryo.(4) In germination o f maize seeds soaked with dilute Pb solution,K was detected in both endosperm a nd embryo;Fe was distributed in seed coat and endosperm;Cu and Zn were in endo sperm;most of Pb occurred in embryo and especially accumulated in fresh roots,which implies that the accumulation of Pb in roots functions as tolerance of det oxification of toxic elements in seed germination.