Determination and interpretation of environmental water samples contaminated by uranium mining activities

Interpretation of environmental behavior of uranium is based on several steps of data analysis and statistical inference. First step is sampling and analyzing of uranium in field samples by routine laboratory methods. Such methods have to fulfill multiple requirements like robustness, efficiency, low detection limit and precision. A comparison of different approaches in assigning uncertainty to experimentally obtained analytical data shows that classical error estimation is not significantly inferior to more sophisticated modern techniques like inverse regression or orthogonal regression. A second step is the correlation of analytical data with current state of insight into environmental behavior of uranium. Such a correlation furthers the choice of adequate geochemical models and quality of geochemical data base for subsequent detailed analysis, e.g. by geochemical modeling. An appraisal of the individual steps in this complex analysis is given on the basis of statistical procedures for calibration and an E_H-pH diagram of uranium for atmospheric conditions. Received: 30 July 1998 / Revised: 18 November 1998 / Accepted: 26 November 1998     

Photon activation analysis of iodine, thallium and uranium in environmental materials

Iodine, thallium and uranium were determined by photon activation analysis. Two electron linear accelerators were used for the analysis of several kinds of environmental, biological and geochemical reference materials under different irradiation conditions. Both analytical results for iodine were in good agreement with each other but not with literature values in the case of environmental samples. The results of thallium and uranium agreed well with their reference values. The detectable concentration levels of iodine, thallium and uranium were almost 0.3μg/g.     

Resolution of the two phases of limestones with respect to their trace element contents

The carbonate and the non-carbonate fractions of marine limestones from Southern Germany have been resolved with respect to their trace element contents. The analytical steps involved (1) instrumental neutron activation analysis on the whole rock sample (2) plotting regression lines for the element concentration (ppm) versus corresponding predetermined insoluble residue content (wt%) and (3) reading out the regression functions. Such a regression analysis is simple to perform, less tedious and time consuming and more reliable as compared to the separate analysis of the carbonate and the non-carbonate components of the rock. Judging from the regression functions the elements analysed have been grouped into (a) those associated with clastic material (Sc, Cr, Hf, Zr etc.) (b) those with pronounced diagenetic history (Sr, U) and (c) those which were partly associated with authigenic material (rare earth elements). The geochemical significance of group (c), with particular reference to their coprecipitation with CaCO₃ precipitated from sea water, has been discussed.     

Separation of uranium from iron in ground water samples using ion exchange resins

Uranium determination in environmental samples is faced with problems due to presence of iron and other major elements. Iron is also used many a times for pre-concentration of uranium and actinides. Separation of milligram quantity of Fe from microgram quantity of uranium becomes essential during the estimation step. A simple two step procedure has been standardized for separating uranium and iron using anion exchange in 0.025 M H₂SO₄. Quantitative recovery of uranium was obtained as well as good separation from iron. This method was applied for estimation of uranium in water samples.     

Use of the Eurachem guide on method validation for determination of uranium in environmental samples

Three analytical methods for determination of uranium in environmental samples by a fluorescence technique have been validated and compared in accordance with the Eurachem Guide on method validation. The first method depends on uranium separation from iron using the mercury anode technique; in the other two methods uranium is separated from iron on an anion exchange column by use of either a solution of hydrochloric acid containing ascorbic acid and hydrazine hydrate or a dilute sulfuric acid solution. Detection limits, repeatability, reproducibility, and recovery coefficient were the main validation characteristics. The results showed that better statistical values can be achieved by using the third method. Control charts for in-house control samples and international intercomparison samples have also shown that the third method is more statistically stable with time. In addition, uncertainties of measurement were estimated and compared for the three methods. It was found that the Eurachem Guide and comparison of quality statistical validation data can be good tools for selection of the appropriate method for an application.     

River Pollution Data Interpreted by Means of Chemometric Methods

Environmental data, including river pollution data, are characterized by high variability. Much information is lost by using only univariate graphical or statistical methods for data evaluation and interpretation. Chemometric methods, in particular methods of multivariate data analysis, help to extract the latent information in such data. The combination of cluster analysis as the first step and multivariate analysis of variance and discriminant analysis as the second step enables identification of similar locations in a river. Pollution sources and dischargers can be detected by means of factor analysis. The deposition–remobilization behavior of metals in a river can be described using partial least squares regression. Summarizing, it can be stated that methods of multivariate data analysis are powerful tools for the evaluation and interpretation of river pollution data.     

Robust regression techniques A useful alternative for the detection of outlier data in chemical analysis

The validation of an analytical procedure means the evaluation of some performance criteria such as accuracy, sensitivity, linear range, capability of detection, selectivity, calibration curve, etc. This implies the use of different statistical methodologies, some of them related with statistical regression techniques, which may be robust or not. The presence of outlier data has a significant effect on the determination of sensitivity, linear range or capability of detection amongst others, when these figures of merit are evaluated with non-robust methodologies.In this paper some of the robust methods used for calibration in analytical chemistry are reviewed: the Huber M-estimator; the Andrews, Tukey and Welsh GM-estimators; the fuzzy estimators; the constrained M-estimators, CM; the least trimmed squares, LTS. The paper also shows that the mathematical properties of the least median squares (LMS) regression can be of great interest in the detection of outlier data in chemical analysis. A comparative analysis is made of the results obtained by applying these regression methods to synthetic and real data. There is also a review of some applications where this robust regression works in a suitable and simple way that proves very useful to secure an objective detection of outliers. The use of a robust regression is recommended in ISO 5725-5.     

Methodology for uranium compounds characterization applied to biomedical monitoring

Chronic exposure to uranium compounds led to the development of a methodology in order to characterize those compounds. This methodology, based on the recommendation of the I.C.R.P,¹ involves three main steps: the measurement of the uranium concentration and the particle size distribution at workstations; the characterization of the industrial compound, i.e. its physico-chemical properties; and the study of in-vitro solubility using chemical and cellular tests. Different methods for uranium analysis are presented. Results and comments on UF₄, UO₃, U₃O₈, UO₂ and U+UO₂ are given.     

Improved spectrophotometric vitellogenin determination via alkali-labile phosphate in fish plasma–a cost effective approach for assessment of endocrine disruption

Vitellogenin (VTG) is a well known protein biomarker for exposure to environmental estrogens and possible endocrine disruption in fish. VTG is very dominant in plasma after the onset of vitellogenesis and the protein is heavily phosphorylated. This enables indirect quantification through measurement of alkali-labile protein bound phosphate (ALP) as an alternative to the more expensive enzyme linked immunosorbent assay. Good correlation has previously been shown between ALP and actual VTG levels but little effort has been made to investigate the method in an analytical way e.g., to assure the origin of the measured phosphate. During this method development care has been taken to rule out non-VTG sources of phosphate such as phospholipids and free phosphate in the blood plasma. Sample preparation has been simplified and unnecessary steps have been omitted. The common spectrophotometric measurement for ALP involves measurement at two wavelengths and calculation of corrected absorbance values. With a quick phase separation step the spectrophotometric phosphate determination using molybdic acid and ascorbic acid has been improved and all matrix interference has been eliminated. The final ALP method presented here has a detection limit of 3.2 µg PO₄ ^3?/ml plasma which is six times lower than similar methods and it also has less variability. A high sample throughput in comparison to previous ALP methods is possible after scaling down sample and reagent volumes to fit in a 96 well microtiter plate. The cost for buying all chemicals and plastic consumer goods for setting up the indirect protocol for the analysis of 1000 samples is only circa 350 euro. This is only 1% of the material cost for buying commercially available test kit for direct quantification of VTG in the same number of samples. The ALP method should thus be of interest also for applied scientists outside advanced research laboratories.     

Estimation of Performance Characteristics of an Analytical Method Using the Data Set Of The Calibration Experiment

Abstract

A model to calculate the analytical sensitivity, limit of detection, limit of determination and precision of a method of instrumental analysis through a data set obtained by calibration experiment using the statistical analysis of linear regression, is proposed. This model has been applied to spectrophotometric, spectrofluorimetric and chromatographic methods. The values obtained are independent of the instrument used and can be applied as a criterion of comparison between different methods proposed for the same analyte. Also, these characteristics have been calculated using the IUPAC suggested model and both results have been compared.     

Comparability of thermodynamic data – a metrological point of view

In order to compare and to interpret chemical measurements, compliance with general rules of metrology is compulsory. Such rules are the more important the more the chemical measurements are applied under circumstances where material assets and goods or immaterial values like health may be affected. Metrology of chemical measurements attempts to define rules for achieving comparability and for guaranteeing quality of analytical data. Thermodynamic data are commonly derived from a set of analytical measurements. Comparability among thermodynamic data is an important issue especially for those data to be applied in politically sensitive issues of environmental prognosis, long-term safety assessment of nuclear waste repositories in deep geological formations and assessment of environmental impact of technical intervention in the geosphere. Taking the data evaluation step in the traceability chain of thermodynamic data as an example, the existing thermodynamic data is shown to be affected by deficiencies in comparability and quality that may severely limit its dependability in environmental prognosis. The need for a metrologically acceptable approach is demonstrated. Statistical concepts improving a reliable assignment of meaningful measurement uncertainty to a thermodynamic datum are presented. Unresolved issues, i.e. measurement uncertainty of a pH measurement, hampering the construction of a traceability chain are outlined.     

Comparability of thermodynamic data--a metrological point of view

In order to compare and to interpret chemical measurements, compliance with general rules of metrology is compulsory. Such rules are the more important the more the chemical measurements are applied under circumstances where material assets and goods or immaterial values like health may be affected. Metrology of chemical measurements attempts to define rules for achieving comparability and for guaranteeing quality of analytical data. Thermodynamic data are commonly derived from a set of analytical measurements. Comparability among thermodynamic data is an important issue especially for those data to be applied in politically sensitive issues of environmental prognosis, long-term safety assessment of nuclear waste repositories in deep geological formations and assessment of environmental impact of technical intervention in the geosphere. Taking the data evaluation step in the traceability chain of thermodynamic data as an example, the existing thermodynamic data is shown to be affected by deficiencies in comparability and quality that may severely limit its dependability in environmental prognosis. The need for a metrologically acceptable approach is demonstrated. Statistical concepts improving a reliable assignment of meaningful measurement uncertainty to a thermodynamic datum are presented. Unresolved issues, i.e. measurement uncertainty of a pH measurement, hampering the construction of a traceability chain are outlined.     

Uranium determination in seawater by total reflection X-ray fluorescence spectrometry

A study regarding uranium determination in seawater by total reflection X-ray fluorescence (TXRF) spectrometry is reported. Uranium, present in seawater in concentration of about 3.3 ng/mL, was selectively extracted in diethyl ether and determined by TXRF after its preconcentration by evaporation and subsequent dissolution in a small volume of 1.5% suprapure HNO₃. Yttrium was used as an internal standard. Before using diethyl ether for selective extraction of uranium from seawater, its extraction behavior for different elements was studied using a multielement standard solution having elemental concentrations in 5 ng/mL levels. It was observed that the extraction efficiency of diethyl ether for uranium was about 100% whereas for other elements it was negligible. The detection limit of TXRF method for uranium in seawater samples after pre-concentration step approaches to 67 pg/mL. The concentrations of uranium in seawater samples determined by TXRF are in good agreement with the values reported in the literature. The method shows a precision within 5% (1σ). The study reveals that TXRF can be used as a fast analytical technique for the determination of uranium in seawater.     

A simple method for the determination of natural uranium and226Ra in waters and soils

A procedure for the determination of natural uranium and²²⁶Ra in waters and soils has been carried out and applied to the analysis of samples for environmental radiological monitoring.²²⁶Ra determination consists of co-precipitation with BaSO₄,²²²Rn emanation in toluene and finally liquid scintillation counting. Natural uranium is then determined by a fluorometric technique. This paper describes the method and the conditions that were tested to optimize it. The technique was found to be suitable for the analysis of surface and ground waters, samples from rivers, streams and lakes and soil samples, because of its few steps, short processing time, high recovery percentages and suitable detection limits.     

State-of-the-art of gas chromatography-based methods for analysis of anthropogenic volatile organic compounds in estuarine waters,illustrated with the river Scheldt as an example

This review focuses on a number of key procedural steps in the analysis of volatile organic compounds (VOCs) in estuarine waters. The most critical step, from an analytical point of view, is sample preparation. So far, only purge-and-trap and, to some extent, membrane inlet mass spectrometry have successfully been applied in estuarine monitoring of VOCs. The advantages and disadvantages of both techniques are discussed and novel developments are reviewed. Other key elements in VOC analysis and assessment include quality assurance (QA), quality control (QC) and statistical data analysis. This paper gives a brief overview of QA/QC measures of interest in the estuarine monitoring exercise, and provides guidelines for adequate statistical treatment of environmental data. Finally, field measurements of VOCs in estuarine waters are reviewed. Concentrations are reported, and distribution patterns, sources and time-trends are discussed. In addition to literature data, results of a 3-year monitoring survey (May 1998–November 2000) in the Scheldt estuary are presented.     

The synthesis of flower shaped microstructures of Co3O4 by solvothermal approach and investigation of its catalytic activity

A unique flower like microstructures of cobalt oxide (Co₃O₄) are prepared by solvothermal method in two steps: In first step the Co(OH)₂ micro particles are generated and in second step Co₃O₄ flower like microstructures are obtained after annealing for 2 h. The final product of Co₃O₄ is subjected to different instrumental analysis to investigate its morphology and other properties. It is clear from the Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) that the product is flower like in shape with a size of approximately 10–15 μm from sideway view. It is also observed that these structures are composed of nanosheets, which are further organized into layer by layer pattern to form a specific flower like morphology. The experimental data proved that the solvent and temperature played a significant role in the formation of such flowers like morphology under provided reaction conditions. These microstructures have shown remarkable catalytic activity for thermal decomposition of ammonium perchlorate (AP).     

Extraction of thorium,uranium and cerium from fresh water using manganese dioxide coprecipitation

A manganese dioxide coprecipitation procedure is utilized to replace a time-consuming evaporation step for the extraction of thorium, uranium and cerium from freshwater samples. The average recovery for 20-liter samples is greater than 95% for²³⁴Th and¹⁴⁴Ce. The data indicate that the manganese dioxide coprecipitation process does not affect the recovery of thorium and uranium during our routine analytical procedure.     

Global test for metabolic pathway differences between conditions

In many metabolomics applications there is a need to compare metabolite levels between different conditions, e.g., case versus control. There exist many statistical methods to perform such comparisons but only few of these explicitly take into account the fact that metabolites are connected in pathways or modules. Such a priori information on pathway structure can alleviate problems in, e.g., testing on individual metabolite level. In gene-expression analysis, Goeman's global test is used to this extent to determine whether a group of genes has a different expression pattern under changed conditions. We examined if this test can be generalized to metabolomics data. The goal is to determine if the behavior of a group of metabolites, belonging to the same pathway, is significantly related to a particular outcome of interest, e.g., case/control or environmental conditions. The results show that the global test can indeed be used in such situations. This is illustrated with extensive intracellular metabolomics data from Escherichia coli and Saccharomyces cerevisiae under different environmental conditions.     

Solid-phase microextraction in biomedical analysis

Chromatographic methods are preferred in the analysis of organic molecules with lower molecular mass (<500 g/mol) in body fluids, i.e., the assay of drugs, metabolites, endogenous substances and poisons as well as of environmental exposure by gas chromatography (GC) and liquid chromatography (LC), for example. Sample preparation in biomedical analysis is mainly performed by liquid-liquid extraction and solid-phase extraction. However, new methods are investigated with the aim to increase the sample throughput and to improve the quality of analytical methods. Solid-phase microextraction (SPME) was introduced about a decade ago and it was mainly applied to environmental and food analysis. All steps of sample preparation, i.e., extraction, concentration, derivatization and transfer to the chromatograph, are integrated in one step and in one device. This is accomplished by the intelligent combination of an immobilized extraction solvent (a polymer) with a special geometry (a fiber within a syringe). It was a challenge to test this novel principle in biomedical analysis. Thus, an introduction is provided to the theory of SPME in the present paper. A critical review of the first applications to biomedical analyses is presented in the main paragraph. The optimization of SPME as well as advantages and disadvantages are discussed. It is concluded that, because of some unique characteristics, SPME can be introduced with benefit into several areas of biomedical analysis. In particular, the application of headspace SPME-GC-MS in forensic toxicology and environmental medicine appears to be promising. However, it seems that SPME will not become a universal method. Thus, on-line SPE-LC coupling with column-switching technique may be a good alternative if an analytical problem cannot be sufficiently dealt with by SPME.     

Wide-scope screening of polar contaminants of concern in water: A critical review of liquid chromatography-high resolution mass spectrometry-based strategies

The number of chemicals with potential to reach the environment is still largely unknown, which poses great challenges for both environmental scientists and analytical chemists. Liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) is currently the instrumentation of choice for identification of wide-scope polar chemicals of concern (CECs) in water. This review critically evaluates all steps involved in screening for polar CECs in water, including sampling and extraction, analysis by LC-HRMS, data (pre-)treatment, evaluation and reporting. Passive samplers and direct injection, in combination with LC-HRMS, provide new opportunities compared with conventional grab water sampling, as do instrumental advances such as ion-mobility spectrometry coupled to HRMS (IM-HRMS). In this paper, we argue that target, suspect and non-target screening should not be viewed as three separate principles, but rather as conceptual approaches to general data treatment strategies that can be linked together. Due to the large amount of data generated, smart prioritisation strategies are needed, in particular for non-target screening, to reduce complexity and focus on data of high interest. We critically evaluate existing strategies and consider that each prioritisation step will result in data loss (as any other step in a screening study), requiring compromises depending on the research question to be tackled. Many different data treatment strategies have been developed in recent years, but structure elucidation remains a challenging and time-consuming task. We discuss current and potential future trends, e.g. effect-based methods that can be used as future prioritisation tools, technological advances like IM-HRMS and improved software solutions that can enable new data treatment strategies.