Sequential extractions of selenium soils from Stewart Lake: total selenium and speciation measurements with ICP-MS detection

Different techniques have been employed in order to evaluate the most efficient procedure for the extraction of selenium from soil as required for speciation. Selenium contaminated sediments from Stewart Lake Wetland, California were used. A strong acid mineralization of the samples gives quantitative total selenium, which is then used to estimate recoveries for the milder extraction methods. The different extraction methodologies involve the sequential use of water, buffer (phosphate, pH 7) and either acid solution (e.g. HNO3 or HCl) or basic solutions (e.g. ammonium acetate, NaOH or TMAH). Pyrophosphate extraction was also evaluated and showed that selenium was not associated with humic acids. The extractants were subsequently analyzed by size exclusion chromatography (SEC) with UV (254 and 400 nm) and on-line ICP-MS detection; anion exchange chromatography, and ion-pair reversed phase chromatography with ICP-MS detection. For sequential extractions the extraction efficiencies showed that the basic extractions were more efficient than the acidic. The difference between the acidic and the basic extraction efficiency is carried to the sulfite extraction, suggesting that whatever is not extracted by the acid is subsequently extracted by the sulfite. The species identified with the different chromatographies were selenate, selenite, elemental selenium and some organic selenium.     

Effect of cooking on arsenic concentration in rice

Environmental Science and Pollution Research - This study assessed the effect of rinsing and boiling on total content of As (tAs) and of its inorganic and organic forms in different types of rice...     

Assays with Daphnia magna and Danio rerio as alert systems in aquatic toxicology

For the evaluation and monitoring of the water quality, a series of methodologies, which have as basis an ample variety of bioindicators, may be applied. The aim of this research was to evaluate the use of ecotoxicity assays with Daphnia magna and Danio rerio as alert systems in water contaminated with toxic substances. Using two toxicity databases, the sensibility of those aquatic organisms to a wide variety of chemical products and elements and to some chemical categories was investigated. The relation between the reference dose for human oral chronic exposure (RfD) of all chemical products and the acute toxicity values for both bioindicators was also studied. Acute toxicity tests with D. magna respond to a larger variety of chemicals with a higher sensitivity than those with D. rerio. Although mammals, crustaceans and fish have different routes of exposure, target organs and toxic mechanisms, acute toxicity essays with fish and Daphnia may be used as an initial screening before mammal models are used.     

Evaluation of the sensitivity spectrum of a video tracking system with zebrafish (<Emphasis Type="Italic">Danio rerio</Emphasis>) exposed to five different toxicants

The aim of this study was to develop a biological early warning system for the detection of aquatic toxicity and test it with five toxicants with distinct chemical nature. This was done in order to verify the spectrum of sensitivities of the proposed system, as well as the potential identification capability of the tested contaminants, using only the analysis of zebrafish’s behavior. Six experimental conditions were tested: negative control and five toxicants (bleach, lindane, tributyltin, mercury, and formaldehyde). The exposure time was 45 min, and the concentrations used corresponded to 9% of LC₅₀’s-96 h for the tested compounds, to ensure ecologically relevant results. A total of 108 fish were used, with each individual experimental condition being tested 18 times. A statistical model of diagnosis was used, combining self-organizing map and correspondence analysis. The values of sensitivity, specificity, accuracy, false positive, false negative, positive predictive value (PPV), and negative predictive value (NPV) were calculated. The objectives of the work were accomplished and the system showed a good overall diagnostic performance with 79% in accuracy, 77% in sensitivity, and 88% in specificity. The lowest result of the predictive values was 78% (lindane and mercury), in the case of the NPV, and 86% (bleach and lindane), in the case of the PPV. The best result of the predictive values was 100% (bleach and tributyltin), for the NPV, and 89% (tributyltin), for the PPV. Regarding the five tested toxicants, the system was able to correctly identify the agent responsible for the contamination in 40% of the positive diagnoses.     

Degradation of paracetamol by advance oxidation processes using modified reticulated vitreous carbon electrodes with TiO2 and CuO/TiO2/Al2O3

The degradation of paracetamol in aqueous solutions in the presence of hydrogen peroxide was carried out by photochemistry, electrolysis and photoelectrolysis using modified 100 pores per inch reticulated vitreous carbon electrodes. The electrodes were coated with catalysts such as TiO₂ and CuO/TiO₂/Al₂O₃ by electrophoresis followed by heat treatment. The results of the electrolysis with bare reticulated vitreous carbon electrodes show that 90% paracetamol degradation occurs in 4 h at 1.3 V vs. SCE, forming intermediates such as benzoquinone and carboxylic acids followed by their complete mineralisation. When the electrolysis was carried out with the modified electrodes such as TiO₂/RVC, 90% degradation was achieved in 2 h while with CuO/TiO₂/Al₂O₃/RVC, 98% degradation took only 1 h. The degradation was also carried out in the presence of UV reaching 95% degradation with TiO₂/RVC/UV and 99% with CuO/TiO₂/Al₂O₃/RVC/UV in 1 h. The reactions were followed by spectroscopy UV-Vis, HPLC and total organic carbon analysis. These studies show that the degradation of paracetamol follows a pseudo-first order reaction kinetics.     

Validation of an analytical method for the quantification of pyrethrins on lemons and apricots using high-performance liquid chromatography/mass spectrometry

An analytical procedure has been developed for the determination of natural pyrethrins (pyrethrin I, pyrethrin II, jasmolin I, jasmolin II, cinerin I and cinerin II) in lemon and apricot. The QuEChERS method, which stands for quick, easy, cheap, effective, rugged and safe was used for extraction. Analysis of the extract was performed by liquid-chromatography-electrospray ionisation-tandem mass spectrometry. The ions prominent in the ESI spectra were [M+H]+ for the six compounds. A Zorbax SB-C18 column was used with a programmed gradient mobile phase consisting of (A) water containing 0.1% formic acid and 5 mM ammonium formate and (B) ACN. The method was linear within the investigated concentration range, displaying a calibration curve correlation factor of 0.99. The coefficients of variation obtained (RSD) were below 20% and the recoveries were in the 70-110% range.     

Determination of sixteen pesticides in peppers using high-performance liquid chromatography/mass spectrometry

A method for the detection and quantification of 16 pesticides: flufenoxuron, fenoxycarb, dimethomorph, acetamiprid, imidacloprid, lufenuron, thiacloprid, thiabendazole, thiophanate-methyl, spinosad, fenbutatin oxide, methoxyfenozide, oxamyl, clothianidin, thiamethoxam and carbendazim has been developed based on high-performance liquid chromatography-mass spectrometry. Pesticide residues were extracted from the samples according to the QuEChERS method which stands for quick, essay, cheap, effective, rugged and safe. Homogenised analytical portions (10 g ± 0.1) of samples of peppers were spiked at two levels (10 and 100 μg kg?1) with a small volume of an appropriate standard mixture solution containing each pesticide. Analyses were performed using electrospray ionization (ESI) and a MSD trap system. Chromatography separation was achieved using a ZORBAX SB-C18 3.5 μm particle size analytical column, 2.1 × 50 mm from Agilent, with gradient elution at a flow-rate of 0.4 mL/min with mobile phases: waters-0.1 % HCOOH-5 mM HCOONH? and MeOH-5 mM HCOONH?. The method has been validated based on the SANCO European Guidelines. Under the optimized conditions the recoveries (n = 7) were in the range 70-110 % with satisfactory precision (CV ≤ 20 %). A linear dynamic range was obtained over a range of concentrations from 10 to 100 μg kg?1 for each of the analytes, with correlation coefficients >0.997.     

WATER YIELD AUGMENTATION THROUGH FOREST AND RANGE MANAGEMENT - ISSUES FOR THE FUTURE1

The demand for more water is increasing throughout the country. Research on upland watersheds clearly demonstrates that water yield can be increased using forest and range management practices. Based on the experience of the past several decades and a review of six papers in a recent AWRA series on water yield augmentation through vegetation management, the following issues and concerns are discussed: predicting increased yields from large basins; economic evaluation of additional flows; court acceptance and need for system models; the legal question of ownership and transferability of increased yields; and management emphasis on private and federal lands. The immediate potential for water yield augmentation is on carefully selected watersheds that have the bio-physical potential to produce high value water under environmentally acceptable multiple use management. We predict water yield management on a broader scale will result from increased pressures to solve the legal and economic issues involved.     

Global weapons' fallout 137Cs in soils and transfer to vegetation in south-central Chile

The contamination and depth distribution of 137Cs in soil due to the fallout from atmospheric weapons' tests were measured at 29 sites in the 9th and 10th administrative regions in Chile located in the 40 degrees latitude in the southern hemisphere. The depth distribution in most of the sites follows no systematic pattern in the upper few centimetres, but below this depth an exponential decline could be deduced. The calculated relaxation depth appears to be a good indicator for estimating the long-term 137Cs distribution in these soil profiles. It ranges from 4.4 +/- 1.9 cm in Palehumults to 8.4 +/- 4.4 and 9.7 +/- 5.1 cm in Hapludands and Psamments, respectively. For these soil types the value for the relaxation depth tends to increase with decreasing clay content and increasing volume of coarse pores. 137Cs activity densities at the selected sites ranged from 450 to 5410 Bq m(-2) and correlate significantly (r = 0.791) with the mean annual rainfall rate of the sampling sites. 137Cs concentration ratios of prairie plants/soil were found to be in the range 0.008-2.3 and could be related to relaxation depths in undisturbed soils.