Luis Fernández

TEMPORAL EVOLUTION OF GROUNDWATER COMPOSITION IN AN ALLUVIAL AQUIFER (PISUERGA RIVER, SPAIN) BY PRINCIPAL COMPONENT ANALYSIS

Abstract A set of quantitative analytical data from the alluvial aquifer of the Pisuerga river, located at the north-east of Valladolid (Spain), has been processed by multivariate statistical techniques in order to investigate the evolution of the groundwater composition between two surveys. The original matrix consisted of 16 physico-chemical variables, determined in 32 groundwater samples collected in 32 sampling sites of the aquifer. The surveys were carried out in October 1994, at the end of the irrigation and low water period just before autumn rains, and in April–May 1995 at the beginning of the irrigation and high water period and after the recharge of aquifer. The experimental 64×16 matrix was analysed by Principal Component Analysis (PCA), and the resulting Principal Components (PCs) and Varimax rotated PCs (VFs) analysed by means of box and bivariate plots. The exploration of the correlation matrix allowed to uncover strong associations between some variables (sulphate, chloride, hydrogencarbonate, sodium, potassium, magnesium, calcium and electrical conductivity) as well as a lack of association between the others (pH, nitrate, and trace metals). PCA showed the existence of up to five significant PCs which account for 71.39% of the variance. Two of them can be initially assigned to ‘mineralization’ whereas the other PCs are built from variables indicative of pollution. Box and bivariate plots of the two first PCs showed that ‘mineralization’ is maintained through surveys and that trace elements increase from the first to the second survey in all zones, as a possible consequence of soil leaching caused by the rise of the groundwater level. Varimax rotation allowed to ‘break up’ the ‘mineralization’ PC into two VFs, assigned respectively to ‘natural’ mineralization and to ‘saline’ man-made contamination (sodium and chloride). Box and bivariate plots of VFs confirmed the existence of a differential ‘natural’ mineralization pattern, now ascribed exclusively to dissolution of geological materials, as well as the presence of a zone with unusually high levels of ‘saline’ contamination attributed to leakages from sanitary systems. The plot of VFs also allowed to visualise seasonal variations, identifying a process of dilution of the ‘natural’ mineralization during the recharge of the aquifer, and an increase of the ‘saline’ contamination, assigned to a variety of non-natural causes.

Comparison of accelerated solvent extraction with microwave-assisted extraction and Soxhlet for the extraction of chlorinated biphenyls in soil samples

Abstract The extraction and determination of chlorinated biphenyls (CBs) in soils and solid wastes is an ongoing subject of study. This is an overview article that compares the microwave-assisted extraction (MAE) and accelerated solvent extraction (ASE) techniques. The extraction of CBs by ASE has been optimised taking into account the variation of pressure, temperature and extraction time by means of experimental design and the Simplex approach. The recoveries obtained under the optimum conditions are compared and discussed with those obtained from MAE and Soxhlet extractions.

Green copper pigments biodegradation in cultural heritage: from malachite to moolooite, thermodynamic modeling, X-ray fluorescence, and Raman evidence.

Moolooite (copper oxalate), a very rare compound, was found as a degradation product from the decay of malachite in several specimens of Cultural Heritage studied. Computer simulations, based on heterogeneous chemical equilibria, support the transformation of malachite to moolooite through the intermediate copper basic sulfates or copper basic chlorides, depending on the presence of available free sulfate or chloride anions in the chemical system. Raman and X-ray fluorescence spectral evidence found during the analysis of the three case studies investigated supported the model predictions. According to the study, the presence of lichens and other microorganisms might be responsible for the decay phenomena. This work tries to highlight the importance of biological attack on specimens belonging to Cultural Heritage and to demonstrate the consequences of oxalic acid, excreted by some of these microorganisms, on the conservation and preservation of artwork.

A Case of Hydrochemical Characterization of an Alluvial Aquifer Influenced by Human Activities

Abstract21 physico-chemical parameters have been determined in 47 groundwater samples collected in October 1994 from the alluvial aquifer of the Pisuerga river, located at the north-east of Valladolid (north-western Spain). Conventional hydrochemical methods and multivariate statistical analysis have been used to discriminate natural phenomena and pollution processes in the area. It has been demonstrated the existence of a heterogeneity in groundwater mineral contents related to anthropic actions such as irrigation, source of irrigation water and location of polluting sources. This study demonstrates the existence of two sub-units in the alluvial aquifer (left and right river banks) with different hydrochemical characteristics, and identifies three different singular areas in the left bank. Groundwater from this bank showed higher levels of dissolved ions caused by concentration processes derived from the predominant use of groundwater for crop irrigation, whilst in the right bank of the aquifer less saline water from canals is used. Degradation of groundwater quality has been observed in some areas of the left aquifer sub-unit (north, Santovenia and south-central sites) where anomalous high concentrations of sulphate, sodium, chloride and nitrate were measured, and can be related to the presence of potentially polluting sources such as leachates from industrial waste disposals, sewage effluents and use of organic and inorganic fertilizers.

Development of a Modified Bromley's Methodology (MBM) for the estimation of ionic media effects on solution equilibria. Part 2. Correlation of the molar and molal interaction parameters with the charge and crystal radii of the ions

Abstract The interaction parameters of strong electrolytes obtained for both the molar and molal scales using the Modified Bromleys Methodology (MBM) have been correlated with the ionic charge and individual crystal radius of each ion. The correlation function for each ion with opposite counterions is a straight line centered in the water radius value (1.39 × 10−10m). These correlations allow the prediction of values of unknown interaction parameters of a cation with several anions even if only one interaction parameter of the cation with a given anion is known.

Optimisation and comparison of microwave-assisted extraction and Soxhlet extraction for the determination of polychlorinated biphenyls in soil samples using an experimental design approach

Optimisation of microwave-assisted extraction (MAE) for the extraction of polychlorinated biphenyls (PCBs) from soil samples has been accomplished using an experimental design approach. Variables studied have been: percentage of acetone (v/v) in an acetone:n-hexane mixture, solvent volume, extraction time, microwave power and pressure inside the extraction vessel. Five samples of a certified soil (CRM 481) have been extracted under the optimum conditions of the developed method and the results have been compared to those obtained by Soxhlet extraction. Good recoveries (>95%) have been obtained for all the PCBs studied. All extracts have been analysed by gas chromatography/mass spectrometry (GC/MS) and an optimum determination method for the electron impact mass spectrometric (EIMS) has also been developed.

Focused ultrasound solid–liquid extraction for the determination of perfluorinated compounds in fish, vegetables and amended soil

In the present work a method was developed for the determination of different perfluorinated compounds (PFCs), including three perfluorinated sulfonic acids (PFSAs), seven perfluorocarboxylic acids (PFCAs), three perfluorophosphonic acids (PFPAs) and perfluorooctanesulfonamide (PFOSA) in fish, vegetables and amended soil samples based on focused ultrasound solid-liquid extraction (FUSLE) followed by solid-phase extraction (SPE) clean-up and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Different variables affecting the chromatographic separation (column type and pH of the mobile phase), the electrospray ionization (capillary voltage, nebulizer pressure and drying gas flow) and mass spectrometric detection (fragmentor voltage and collision energy) were optimized in order to improve the sensitivity of the separation and detection steps. In the case of FUSLE variables such as the solvent type, the solvent volume, the extraction temperature, the sonication and extraction time and the percentage of applied irradiation power were studied. Under optimized conditions, sonication of 2.5min with pulse times on of 0.8s and pulse times off of 0.2s in 7mL of (9:1) acetonitrile (ACN): water mixture in duplicate guaranteed exhaustive extraction of the matrices analyzed. Due to the non-selective extraction using FUSLE, different SPE cartridges (200-mg Waters Oasis-HLB, 150-mg Waters Oasis-WAX and 150-mg Waters Oasis-MAX) were tested in terms of extraction efficiency and matrix effect both in the extraction and detection steps. Mix mode SPE using Waters Oasis-WAX provided the best extraction efficiencies with the lowest matrix effect. The final method was validated in terms of recovery at two fortification levels (in the 80-120% for most of the analytes and matrices), precision (relative standard deviation in the 2-15% range) and method detection limits (MDLs, 0.3-12.4ng/g for vegetables, 0.2-12.5ng/g for fish and 1-22ng/g for amended soil). Finally the method was applied for the determination of the 14 PFCs in different vegetables and fish samples from a local supermarket and in a soil amended with a compost from a local wastewater treatment plant (WWTP).

Application of the electrical conductivity of concentrated electrolyte solutions to industrial process control and design: from experimental measurement towards prediction through modelling

Different aspects of the conductivity of concentrated electrolyte solutions and their application to design and control of chemical processes are discussed and reviewed, with particular focus on the work of our research group during the last few years. An automated system based on the electrodeless conductivity technique for the measurement of the electrical conductivity of solutions as the basis of a titration strategy is described. The inadequacy of classical calibration methods when high conductivities are to be measured is highlighted and an alternative methodology is proposed. Our measurements on specific concentrated systems of interest in industrial applications and the development of general methodologies to treat experimental conductivity data at constant or varying temperature in order to get comprehensive inter- and extrapolation mathematical models are summarised. Theoretical approaches to explain the variability of conductivity data of electrolyte solutions with the solute concentration as well as the deviations from ideality found at higher concentrations are reviewed and critically evaluated. Solutions of mixed electrolytes are treated in a similar fashion.

Emerging needs for sustained production of laboratory reference materials

Many different analytes are determined on a daily basis in many different matrices and the quality control (QC) for these determinations requires the use of reference materials (RMs), not only certified RMs (CRMs) but also laboratory RMs (LRMs) for routine purposes (e.g. control charting). In some cases, such materials are not available and the possibility of producing them in-house has to be considered. This article provides two examples showing that LRMs can be prepared by following a systematic approach without a very complex infrastructure: fly ash from cement manufacture; and, contaminated estuarine sediment.

MultiSimplex optimisation and comparison of different purge-and-trap extractions of volatile organic compounds in soil samples

Abstract Two different purge-and-trap (PT) extraction methods have been optimised for nine volatile organic compounds (VOCs) (benzene, toluene, chlorobenzene, ethylbenzene, m-xylene, o-xylene, 1,3-dichlorobenzene, 1,4-dichlorobenzene and 1,2-dichlorbenzene) making use of the simplex method implemented in the MultiSimplex program. In both cases, the determination of the VOCs was performed by a coupled GC–FID system. In the first extraction method the soil sample was sonicated with methanol and 100xa0ml of the extract were analysed as an aqueous sample. Variables considered were heating temperature, heating time, purge time and concentration of sodium chloride and the optimum conditions were 4.3xa0min purge after a sample heating at 46°C for 7.5xa0min and a sodium chloride solution of 4.3xa0molxa0l−1. In the second method, the soil sample was directly introduced in the test tube for soils, heated and purged. Except for the concentration of sodium chloride, the previous variables were also considered and the optimum conditions were 51.1xa0min purge after 42.6xa0min heating at 61°C. These two methods are compared with a previously optimised method where soils samples were mixed with an aqueous phase and the VOCs were directly determined by the PT–GC–FID system.