Geostatistical analysis to identify hydrogeochemical processes in complex aquifers: a case study (Aguadulce unit, Almeria, SE Spain)

The Aguadulce aquifer unit in southeastern Spain is a complex hydrogeological system because of the varied lithology of the aquifer strata and the variability of the processes that can take place within the unit. Factorial analysis of the data allowed the number of variables to be reduced to 3 factors, which were found to be related to such physico-chemical processes as marine intrusion and leaching of saline deposits. Variographic analysis was applied to these factors, culminating in a study of spatial distribution using ordinary kriging. Mapping of the factors allowed rapid differentiation of some of the processes that affect the waters of the Gador carbonate aquifer within the Aguadulce unit, without the need to recur to purely hydrogeochemical techniques. The results indicate the existence of several factors related to salinity: marine intrusion, paleowaters, and/or leaching of marls and evaporitic deposits. The techniques employed are effective, and the results conform to those obtained using hydrogeochemical methods (vertical records of conductivity and temperature, ion ratios, and others). The findings of this study confirm that the application of such analytical methods can provide a useful assessment of factors affecting groundwater composition.     

Evaluation of Cu-PPHs as active catalysts for the SCR process to control NOx emissions from heavy duty diesel vehicles

Copper based catalysts supported on mesoporous materials, which were in turn based on a surfactant expanded zirconium phosphate for the formation of silica galleries in the interlayer space, were prepared by the impregnation method. They were then characterised and tested in the selective catalytic reduction of NO with ammonia as active catalysts for the control of the NOx emissions from heavy duty vehicles. Copper catalysts displayed a high catalytic performance, even in the presence of 14% (v/v) of H2O and 100 ppm of SO2. They also displayed improved catalytic behaviour when compared to a CuZSM5 catalyst.     

A new hybrid system of QSAR models for predicting bioconcentration factors (BCF)

The aim was to develop a reliable and practical quantitative structure-activity relationship (QSAR) model validated by strict conditions for predicting bioconcentration factors (BCF). We built up several QSAR models starting from a large data set of 473 heterogeneous chemicals, based on multiple linear regression (MLR), radial basis function neural network (RBFNN) and support vector machine (SVM) methods. To improve the results, we also applied a hybrid model, which gave better prediction than single models. All models were statistically analysed using strict criteria, including an external test set. The outliers were also examined to understand better in which cases large errors were to be expected and to improve the predictive models. The models offer more robust tools for regulatory purposes, on the basis of the statistical results and the quality check on the input data.     

Natural attenuation of diesel aliphatic hydrocarbons in contaminated agricultural soil

A diesel fuel spill at a concentration of 1 L m(-2) soil was simulated on a 12 m(2) plot of agricultural land, and natural attenuation of aliphatic hydrocarbons was monitored over a period of 400 days following the spill after which the aliphatic hydrocarbon concentrations were found to be below the legal contamination threshold for soil. The main fraction of these compounds (95%) remained at the surface layer (0-10 cm). Shortly after the spill (viz. between days 0 and 18), evaporation was the main origin of the dramatic decrease in pollutant concentrations in the soil. Thereafter, soil microorganisms used aliphatic hydrocarbons as sources of carbon and energy, as confirmed by the degradation ratios found. Soil quality indicators, soil microbial biomass and dehydrogenase activity, regained their original levels about 200 days after the spill.     

Spectroscopic and conformational properties of size-fractions separated from a lignite humic acid

A lignite humic acid (HA) was fractionated by preparative high performance size-exclusion chromatography (HPSEC) in seven different size-fractions. The size-fractions were characterized by cross polarization (CP) magic angle spinning (MAS) (13)C NMR spectroscopy and a further analytical HPSEC elution under UV and fluorescence detection. The alkyl hydrophobic components mainly distributed in the largest molecular-size-fraction, whereas the amount of oxidized carbons increased with decreasing size of fractions. Cross polarization time (T(CH)) and proton spin-lattice relaxation time in the rotating frame (T(1rho)(H)) were measured from variable contact time (VCT) experiments. The bulk HA was characterized by the shortest T(CH) values and the longest T(1rho)(H) values which suggested, respectively, one. an aggregation of components in a large conformation that favored a fast H-C cross polarization, and, two. consequent steric hindrances that prevented fast local molecular motions and decreased proton relaxation rates. Conversely, the separated size-fractions showed longer T(CH) values and shorter T(1rho)(H) values than the bulk HA, thereby indicating that they were constituted by a larger number of mobile molecular conformations. The UV and fluorescence absorptions were both low in the large size-fractions that mainly contained alkyl carbons, whereas they increased in the olephinic- and aromatic-rich fractions with intermediate molecular-size, and decreased again in the smaller fractions which were predominantly composed by oxidized carbons. These results support the supramolecular structure of humic substances and indicate that the observed variation in conformational distribution in humic association may be used to explain environmental processes with additional precision.     

Total and inorganic arsenic in Antarctic macroalgae

The Antarctic region offers unparalleled possibilities of investigating the natural distribution of metals and metalloids, such as arsenic. Total and inorganic As were analysed in nine species of Antarctic macroalgae collected during the 2002 summer season in the Potter Cove area at Jubany-Dallmann Station (South Shetland Islands, Argentinian Base). Total As was determined by inductively coupled plasma-optical emission spectrometry after microwave-assisted acid digestion. Inorganic As was determined by acid digestion, solvent extraction, flow injection-hydride generation-atomic absorption spectrometry. Total As ranged from 5.8 microg g(-1) dry weight (dw) (Myriogramme sp.) to 152 microg g(-1)dw (Himantothallus grandifolius). Total As concentrations were higher in Phaeophytes (mean+/-SD: 71+/-44 microg g(-1)dw) than in Rhodophytes (mean+/-SD: 15+/-11 microg g(-1)dw). Inorganic As ranged from 0.12 microg g(-1) (Myriogramme sp.) to 0.84 microg g(-1)dw (Phaeurus antarcticus). The percentage of inorganic As with respect to total As was 0.7 for Phaeophytes, but almost 4 times higher for Rhodophytes (2.6). The work discusses possible causes for the presence of As in marine organisms in that pristine environment.