Visualizing different uranium oxidation states during the surface alteration of uraninite and uranium tetrachloride

Low-temperature alteration reactions on uranium phases may lead to the mobilization of uranium and thereby poses a potential threat to humans living close to uranium-contaminated sites. In this study, the surface alteration of uraninite (UO₂) and uranium tetrachloride (UCl₄) in air atmosphere was studied by confocal laser scanning microscopy (CLSM) and laser-induced fluorescence spectroscopy using an excitation wavelength of 408 nm. It was found that within minutes the oxidation state on the surface of the uraninite and the uranium tetrachloride changed. During the surface alteration process U(IV) atoms on the uraninite and uranium tetrachloride surface became stepwise oxidized by a one-electron step at first to U(V) and then further to U(VI). These observed changes in the oxidation states of the uraninite surface were microscopically visualized and spectroscopically identified on the basis of their fluorescence emission signal. A fluorescence signal in the wavelength range of 415–475 nm was indicative for metastable uranium(V), and a fluorescence signal in the range of 480–560 nm was identified as uranium(VI). In addition, the oxidation process of tetravalent uranium in aqueous solution at pH 0.3 was visualized by CLSM and U(V) was fluorescence spectroscopically identified. The combination of microscopy and fluorescence spectroscopy provided a very convincing visualization of the brief presence of U(V) as a metastable reaction intermediate and of the simultaneous coexistence of the three states U(IV), U(V), and U(VI). These results have a significant importance for fundamental uranium redox chemistry and should contribute to a better understanding of the geochemical behavior of uranium in nature. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

FISH方法解析大辽河入海口沉积物中微生物的垂直分布特征

取大辽河人海口柱状沉积物,通过寡核苷酸荧光探针原位杂交(FISH)方法分析了沉积物中微生物数量及种群的垂直分布特征,并考察了沉积物理化特性对微生物丰度的影响.结果表明,用5-(4,6-二氯三嗪基)氨基荧光素(简称DTAF)染料染色及EUB338探针杂交检测出的微生物细胞总数及细菌数量随沉积物深度呈现相同变化趋势.在沉积物表层(0-5cm)和中间层(23.5-29.5 cm)数量相对较高.细胞总数为7.9×108-20.1×108cell·cm-3,细菌数量为5.1×108-14.4×108个·cm-3,细菌检出率平均值为75.4%.用ALF1b、BET42a和GAM42a探针检测出α-、β和γ-变形杆菌在柱状沉积物中的普遍存在,α-、β和γ-变形杆菌检出量占细胞总数的25.O%-65.6%,其中以γ-变形杆菌为优势菌,其检出率为9.8%-40.8%.用ARCH915探针检测出的古细菌数量占细胞总量的1.0%-11.8%.总体看来,沉积物中微生物数量与沉积物的粘土含量呈正相关,在一定程度上受总有机碳影响,但与汞含量关系不明显.     

不同来源的疏水性有机酸的光谱学研究

选取2个地表水体水样、2个城市污水处理厂二级处理出水水样和2个土样,从中提取出疏水性有机酸(HPO-A).采用紫外-可见光谱、红外光谱和荧光光谱技术,对不同来源的HPO-A的特性进行了比较和表征.结果表明,这6种HPO-A的吸光度均是随着波长的增加而下降.280nm处的吸收系数(A280)和600nm处的吸收系数(A600)均可排序为:土壤HPO-A地表水体HPO-A二级处理出水HPO-A.HPO-A的E253/E203(波长在253nm处的吸光度与波长在203nm处的吸光度的比值)与A600之间缺乏必然的联系.土壤HPO-A中不含有—CH3官能团.C=O官能团在地表水体HPO-A和土壤HPO-A中的含量较高,而脂族化合物在二级处理出水HPO-A中的含量较高.二级处理出水HPO-A中含有酰胺类化合物.类富里酸和类腐殖酸物质是HPO-A中主要的荧光物质.在地表水体HPO-A和二级处理出水HPO-A中,类富里酸荧光物质的相对含量较高.类溶解性微生物代谢产物荧光物质的存在与否与HPO-A的来源无关.     

原子荧光法测定大气PM_(2.5)中重金属的条件试验研究

对原子荧光法测定大气PM2.5中汞、砷、硒等重金属元素的条件进行了研究。研究得出最佳采样滤膜材质为石英纤维滤膜;样品在前处理完成后还原剂硫脲的加入使测定方法更准确;对电热板消解法、沸水浴法和微波消解法3种前处理方法进行比较试验,得出沸水浴法同时测定汞、砷、硒等5种重金属元素加标回收率最好,为94.5%~105.0%。该方法精密度较高,相对标准偏差在1.43%~4.70%,同时具有设备成本低的优点。     

基于多模态信息融合的心理负荷评估*

为了相对稳定地识别人员是否处于心理负荷状态,设计并实施含能材料起爆作业心理负荷诱导试验。首先对心理负荷诱导情况进行判断,然后分别采集27名被试在静息状态和实施含能材料撞击起爆作业状态下的眼动、心率变异性（HRV）和脑电信号（EEG）,通过正态性检验和假设检验获得心理负荷表征指标并进行统计功效分析,依据表征指标,采用支持向量机（SVM）和随机森林（RF）算法建立多模态信息融合的心理负荷评估模型,最后采用被试工作特征曲线（ROC曲线）分析各模态组合和分类器的心理负荷识别性能。研究结果表明:双模态（眼动+EEG）下SVM算法和3模态下RF算法评估性能和稳健性较高,多模态信息组合具有优异的识别效果。     

荧光技术在太湖蓝藻水华预警监测中的应用

湖库蓝藻水华发生日益频繁,加强湖库饮用水水源地藻类监测,已成为环保、水务部门和学术界共同关注的课题.应用荧光技术分析了蓝藻爆发期苏州太湖三个水源地蓝藻水华的基本特征.结果表明:(1)苏州地区太湖水源地蓝藻水牛的产生主要是受水体动力和气象条件的影响;(2)建基于荧光技术的蓝藻传感器能很好地反映蓝藻水华的变化趋势;(3)荧光技术以其快速测定、可比性强和可连续跟踪监测等优点在太湖蓝藻预警监测中发挥了重要作用.     

Effect of natural organic matter and green microalga on carboxyl-polyethylene glycol coated CdSe/ZnS quantum dots stability and transformations under freshwater conditions

The influence of pH, ionic strength, presence of humic or alginic acids, extracellular polymeric substances (EPS), or freshwater microalga Chlorella kesslerii on the stability and transformation of carboxyl-PEG-CdSe/ZnS core/shell quantum dots (QDs) in terms of number, hydrodynamic size and fluorescence of individual particles, was studied by fluorescence correlation spectroscopy. Obtained results demonstrated that QDs form stable dispersions at nanomolar concentrations under conditions typical for freshwaters. The presence of 5 or 15 mg C L⁻¹ of humic acid or 50 mg C L⁻¹ EPS did not significantly affect these parameters. In contrast, 5 or 50 mg C L⁻¹ alginate at ionic strength of 10 mM shifted the hydrodynamic radius toward larger values, suggesting a possible capture of QDs by the linear alginate chains. The addition of microalga to the QD dispersions resulted in a slight reduction of the number of QDs and a significant decline in the fluorescence of individual QDs.     

Interaction of latex colloids with mineral surfaces and Grimsel granodiorite

Bentonite clay is considered as possible backfill material for nuclear waste repositories in crystalline rock. The same material may also be a source of clay colloids, which may act as carriers for actinide ions possibly released from the repository. Depending on the geochemical parameters, these colloids may be retained by interaction with mineral surfaces of the host rock. In the present study interaction of carboxylated fluorescent latex colloids, used as a model for bentonite colloids, with natural Grimsel granodiorite and some of its component minerals is studied by fluorescence microscopy and SEM/EDX. The experiments are carried out by varying the pH from 2–10. Strong adsorption is observed at pH values close to or below the points of zero charge (pH_pzc) of the mineral surfaces. The influence of Eu(III), used as a chemical homologue for trivalent actinide ions, on colloid adsorption is investigated. Depending on mineral phase and pH, a significant increase of colloid adsorption is observed in the presence of Eu(III).     

Construction and comparison of fluorescence and bioluminescence bacterial biosensors for the detection of bioavailable toluene and related compounds

Environmental pollution with petroleum products such as benzene, toluene, ethylbenzene, and xylenes (BTEX) has garnered increasing awareness because of its serious consequences for human health and the environment. We have constructed toluene bacterial biosensors comprised of two reporter genes, gfp and luxCDABE, characterized by green fluorescence and luminescence, respectively, and compared their abilities to detect bioavailable toluene and related compounds. The bacterial luminescence biosensor allowed faster and more-sensitive detection of toluene; the fluorescence biosensor strain was much more stable and thus more applicable for long-term exposure. Both luminescence and fluorescence biosensors were field-tested to measure the relative bioavailability of BTEX in contaminated groundwater and soil samples. The estimated BTEX concentrations determined by the luminescence and fluorescence bacterial biosensors were closely comparable to each other. Our results demonstrate that both bacterial luminescence and fluorescence biosensors are useful in determining the presence and the bioavailable fractions of BTEX in the environment.