Concentration-dependent photoredox conversion of As(III)/As(V) on illuminated titanium dioxide electrodes

The photoconversion of As(III) (arsenite) and As(V) (arsenate) over a mesoporous TiO(2) electrode was investigated in a photoelectrochemical (PEC) cell for a wide range of concentrations (μM-mM), under nonbiased (open-circuit potential measurements) and biased (short-circuit current measurements) conditions. Not only As(III) can be oxidized, but also As(V) can be reduced in the anoxic condition under UV irradiation. However, the reversible nature of As(III)/As(V) photoconversion was not observed in the normal air-equilibrated condition because the dissolved O(2) is far more efficient as an electron acceptor than As(V). Although As(III) should be oxidized by holes, its presence did not increase the photooxidation current in a monotonous way: the photocurrent was reduced by the presence of As(III) in the micromolar range but enhanced in the millimolar range. This abnormal concentration-dependent behavior is related with the fate of the intermediate As(IV) species which can be either oxidized or reduced depending on the experimental conditions, combined with surface deactivation for the water photooxidation process. The lowering of the photooxidation current in the presence of micromolar As(III) is ascribed to the role of As(IV) as a charge recombination center. Being an electron acceptor, the addition of As(V) consistently lowers the photocurrent in the entire concentration range. A global concentration-dependent mechanism is proposed accounting for all the PEC results and its relation with the photocatalytic oxidation mechanism is discussed.     

Analysis of pesticides in water by liquid chromatography-tandem mass spectrometric techniques

Pesticide residues continue to be the focus of many environmental studies, and the number of articles describing the development of more advanced, multiresidue analytical methodologies does not decline. The use of liquid chromatography-mass spectrometry based on single quadrupole or ion trap analyzers is consolidated for this purpose. The implementation, in the near future, of more sophisticated mass analyzers, such as triple quadrupole and hybrid quadrupole-time-of-flight is anticipated for routine analysis. This article reviews the various works published so far in the literature for the determination of pesticides and transformation products (TPs) in water by means of liquid chromatography (LC) coupled to tandem mass spectrometry. It discusses the various ionization sources and analyzers used for this purpose, as well as the extraction procedures employed for previous sample preconcentration. Because of the widespread use of triple quadrupole analyzers for the generation of pesticides levels in water using tandem mass spectrometry, a table compiling the transitions monitored for ca. 70 compounds is also included.     

Priority pesticides and their degradation products in river sediments from Portugal

A multiresidue gas chromatography-mass spectrometry method was developed to determine 28 priority pesticides of different chemical families (organochlorine, organophosphorus, triazines, anilides) together with some of their transformation products in river sediment. Ultrasonic, Soxhlet and pressurized liquid extraction (PLE) methods were compared in spiking experiments using acetone:hexane (1:1) followed by alumina solid phase extraction cartridges or in-cell alumina clean-up for PLE. All extraction techniques produced acceptable recoveries for the pesticides under study, although Soxhlet extraction produced the lowest recoveries for 2,4-DDE, trifluralin, lindane, and hexachlorobenzene (<50%) whereas ultrasonic extraction resulted in low recoveries for hexachlorobenzene and lindane (<50%). However, PLE using in-cell alumina clean-up produced an overestimation of more apolar compounds, given the amount of coextracted compounds. Limits of detection at the low microg L(-1)-ng L(-1) levels were obtained with Soxhlet and ultrasonic extraction, while PLE produced higher variability due to the lack of exhaustive clean-up. Given the simplicity of ultrasonic extraction, this method was further employed to determine target compounds in river sediments collected in Portugal. Lindane was detected in practically all samples, followed by trace levels of the pesticides simazine, diazinon, fenitrothion, and parathion-methyl.     

Adsorption of heavy metals by pirymidine-derivated mesoporous hybrid material

This paper describes the synthesis of pyrimidine-derivated hybrid mesoporous material via chemical bonding. This has been done by modifying the silanol groups of the support with a synthesised pyrimidine propyl triethoxysilane. The hybrid material has been characterized by X-ray diffraction, nitrogen adsorption techniques, FT-IR, ²⁹Si and ¹³C MAS NMR. The potential of the material of removing heavy metal as copper, nickel and cobalt from water has been tested. Effects of pH, velocity of adsorption, selectivity, maximum adsorption capacity and preconcentration capacity have been determined.     

Dynamics of Fatty Acids,Tocopherols and Phenolic Compounds Biogenesis During Olive (Olea europaea L.) Fruit Ontogeny

Fatty acids, tocopherols, and phenolic compounds biogenesis from two major Spanish olive cultivars (Arbequina and Manzanilla) were analyzed for the function of the thermal regime during the fruit ontogeny in a non‐Mediterranean environment. Bilinear models characterized the dynamics of fatty acid biogenesis. Regressions between the accumulated thermal time (TT) and the levels of both oleic and linoleic acids showed different responses to temperature of each olive cultivar. After reaching similar absolute maximum oleic acid contents at similar TT, the levels of this fatty acid decreased markedly in cv. Arbequina and its final concentration was 10 % lower than that found in cv. Manzanilla. In both cultivars, concentrations of all tocopherol isoforms were negatively associated with the TT accumulated over the entire oil accumulation period. Dynamics of phenolic compounds biogenesis showed no clear tendencies with TT. Nevertheless, and whatever the stage of fruit development, secoiridoids were the major phenolic components. Results suggest greater sensitivity of fatty acid metabolism to temperature in cv. Arbequina. This fact points out the necessity of appropriate evaluation of the ambient thermal characteristics before introducing this cultivar into new growing environments.     

2-Mercaptothiazoline modified mesoporous silica for mercury removal from aqueous media

Mesoporous silicas (SBA-15 and MCM-41) have been functionalized by two different methods. Using the heterogeneous route the silylating agent, 3-chloropropyltriethoxysilane, was initially immobilized onto the mesoporous silica surface to give the chlorinated mesoporous silica Cl-SBA-15 or Cl-MCM-41. In a second step a multifunctionalized N, S donor compound (2-mercaptothiazoline, MTZ) was incorporated to obtain the functionalized silicas denoted as MTZ-SBA-15-Het or MTZ-MCM-41-Het. Using the homogeneous route, the functionalization was achieved via the one step reaction of the mesoporous silica with an organic ligand containing the chelating functions, to give the modified mesoporous silicas denoted as MTZ-SBA-15-Hom or MTZ-MCM-41-Hom. The functionalized mesoporous silicas were employed as adsorbents for the regeneration of aqueous solutions contaminated with Hg (II) at room temperature. SBA-15 and MCM-41 functionalized with MTZ by the homogeneous method present good mercury adsorption values (1.10 and 0.7mmolHg (II)/g of silica, respectively). This fact suggests a better applicability of such mesoporous silica supports to extract Hg (II) from aqueous solutions. In addition, it was observed the existence of a correlation between mercury adsorption with pore size and volume since, SBA-15 with lower areas and higher pore sizes functionalized with sterically demanding ligands, show better adsorption capacities than functionalized MCM-41.     

Uncertainty Management in Context-Aware Applications: Increasing Usability and User Trust

Uncertainty in context-aware computing is mainly a consequence of the complexity of context acquisition mechanisms and context processing. The presence of uncertainty may harm the users’ confidence in the application, rendering it useless. This paper describes a three-phase strategy to manage uncertainty by identifying its possible sources, representing uncertain information, and determining how to proceed, once uncertain context is detected. We conducted an experiment to assess the impact and utility of uncertainty management in a location-aware museum guide that incorporated the approach proposed. The impact was measured by comparing the number of erroneous location estimations and the number of interactions performed by users. A survey was used to measure user friendliness, the utility of the application and user trust among 118 museum visitors who participated in the experiment. Results suggest that uncertainty management helps improve the accuracy of context estimates and the user’s perception on the reliability of the application.     

Factors affecting linear alkylbenzene sulfonates removal in subsurface flow constructed wetlands

The behavior of linear alkylbenzene sulfonate (LAS) and sulfophenyl carboxylate (SPC) biointermediates in a pilot subsurface flow constructed wetland (SFCW) is reported for the first time. The effects of wetland configuration and operation on their treatment efficiency were investigated. The pilot SFCW constituted by eight beds of 55 m2 with different aspect ratios (1 x 1; 1.5 x 1; 2 x 1; 2.5 x 1), two water depths (i.e., 0.47 and 0.27 cm) at 5 cm below surface and two medium sizes (i.e., D60 = 10 mm and 3.5 mm) planted with Phragmites sp. That SFCW pilottreats urban wastewater (i.e., 200 inhabitants) and was operated at four hydraulic loading rates (HLRs) (20, 27, 36, and 45 mm d(-1)). Influent and effluent sampling was carried out from May 2001 to January 2002 with a weekly pattern. Main results were as follows: (i) water depth has a major influence on the performance of SFCW for the LAS removal, and HLR shows significant effect on SPC evolution; (ii) water temperature has a significant effect on the LAS evolution; (iii) biodegradation of LAS and SPC can occur under sulfate-reducing environment and mixed conditions (i.e., sulfate-reducing and denitrification), but aerobic respiration cannot be excluded; and (iv) C13 LAS homologues were generally removed in higher extent than the shorter alkyl chain counterparts. In the most appropriate conditions, LAS and SPC can be biodegraded up to 71% and 11%, respectively, in the pilot SFCW evaluated.