Electrochemical screening procedure for arsenic contaminated soils

Voltammetry of immobilized microparticles was used to find arsenic and heavy metals in contaminated soils from areas with long history of industrial development. Traditional sample dissolution and extraction procedures are time consuming and might distort the chemical equilibrium of the sample causing a change in the original physicochemical forms of distribution. A minute amount of sample was physically attached to the carbon paste working electrode surface and an anodic differential pulse voltammogram was obtained without disturbing the original equilibria. The position of the peaks revealed the presence of Pb and Cu and As(V) and As(III) for the most contaminated soils. As(III) was detected when its percentage in soil was more than 0.001% (expressed as As₂O₃). The limit of detectability was strongly dependent on the presence of iron(III) which increased the signal 10 times.     

Use of pollution indices and ecological risk in the assessment of contamination from chemical elements in soils and sediments – Practical aspects

This paper presents a discussion involving practical aspects of applying contamination indices and ecological risk factors derived from chemical elements in the environmental assessment of soils and sediments. The single and integrated indices: Geoaccumulation index (I_geo), Enrichment factor (EF), Contamination factor (CF), Pollution Index (PI), Ecological risk factor (E_ir), Pollution Load Index (PLI), Degree of contamination (C_deg), Modified Contamination Factor (mC_deg), and potential ecological risk index (PERI) were discussed, and some applications were presented didactically. The analytical care needed to obtain reliable indices with the studied ecosystem is also evidenced. In addition, the advantages and limitations of the use of these indices are presented.     

The Determination of Manganese by Means of Tetrazolium Violet

Abstract

The optimum conditions for extraction of manganese (VII) as an ion-association complex with Tetrazolium Violet (TV) has been determined. The ratio MnO₄ ^?: TV⁺ is 1:1. Beer's law is obeyed in the range of 0.05 - 0.6 μg ml^?1 manganese (VII). The molar absorptivity of the ion-pair is (6.67 ± 0.05) × 10⁴ L mol^?1cm^?1, extraction constant K_ex = 3.1 × 10⁴, distribution constant K_D = 56.5 and association constant β = 5.59 × 10². A sensitive and selective method for determination of microquantities of manganese (VII) in soils has been developed.     

Hollow-fiber liquid-phase microextraction for the determination of pesticides and metabolites in soils and water samples using HPLC and fluorescence detection

A new and simple method has been developed for the determination of a group of four benzimidazole pesticides (carbendazim/benomyl, thiabendazole, and fuberidazole), a carbamate (carbaryl), and an organophosphate (triazophos), together with two of their main metabolites (2-aminobenzimidazole, metabolite of carbendazim/benomyl, and 1-naphthol, metabolite of carbaryl) in soils. First, an ultrasound-assisted extraction (UAE) was performed, followed by evaporation and reconstitution in water. Then, extraction and preconcentration of the analytes was accomplished by two-phase hollow-fiber liquid-phase microextraction (HF-LPME) using 1-octanol as extraction solvent. Parameters that affect the extraction efficiency in HF-LPME technique (organic solvent, pH of the sample, extraction time, stirring speed, temperature, and ionic strength) were deeply investigated. Optimum HF-LPME conditions involved the use of a 2.0 cm polypropylene fiber filled with 1-octanol to extract 10 mL of an aqueous soil extract at pH 9.0 containing 20% (v/v) of NaCl for 30 min at 1440 rpm. Separation and quantification was achieved by HPLC with fluorescence detection (FD). The proposed optimum UAE-HF-LPME-HPLC-FD methodology provided good calibration, precision, and accuracy results for two soils of different physicochemical properties. LODs were in the range 0.001-6.94 ng/g (S/N = 3). With the aim of extending the validation, the HF-LPME method was also applied to different types of waters (Milli-Q, mineral and run-off), obtaining LODs in the range 0.0002-0.57 μg/L.     

pHstatvs. single extraction tests to evaluate heavy metals and arsenic leachability in environmental samples

Here we compared the pH_stat test, which examines the leachability of major elements (Ca, Mg, Al, Fe, and Mn), dissolved organic carbon, and trace elements (Cd, Zn, Cu, Pb, and As) in a wide pH range, with single extraction tests based on the use of mild extractants (calcium chloride, acetic acid or EDTA). For this purpose, we examined samples from a variety of environmental conditions (sludges, mineral soils, organic soils, and soils with particulate and/or soluble contamination). Extraction yields obtained with CaCl₂ (0.01 mol L⁻¹) and CH₃COOH (0.43 mol L⁻¹) correlated well with those from the pH_stat at the same pH (r = 0.98 and 0.95, respectively), while the use of EDTA (0.05 mol L⁻¹) led to systematically higher extraction yields than those quantified with the pH_stat at the same pH. However, the pH_stat test had three distinct advantages: (1) it revealed the relationship between the solubility of the main soil phases and pH; (2) it showed the variation in pollutant leachability due to changes in pH; and (3) it better predicted the maximum contaminant availability. Thus we propose that the pH_stat is the best laboratory tests to evaluate the contaminant leachability over a wide range of sample types (soil, sludge, and sediment).     

Comparison of action of mixed permanent chemical modifiers for cadmium and lead determination in sediments and soils by slurry sampling graphite furnace atomic absorption spectrometry

Slurry sampling atomic absorption spectrometry with electrothermal atomization was used to the determination of cadmium (Cd) and lead (Pb) in soils and sediments using permanent modifiers. Comparison of action of mixed permanent modifiers niobium (Nb)/iridium (Ir) and tungsten (W)/iridium (Ir) were studied in detail. The effect of amount of Ir, W and Nb on analytical signals of Cd and Pb was examined. The optimal amounts of modifiers for Cd and Pb determination were stated. Niobium carbide formation on graphite surface was studied for different pyrolysis temperatures. Finally for Cd determination in sediments and soils 200 μg of Nb mixed with 5 μg of Ir was used as permanent modifiers and 15 μg of Nb mixed with 200 μg of Ir for Pb determination. Suspensions were prepared in 5% HNO₃. The analytical procedure was optimized carefully basing on data from pyrolysis and atomization curves studies. Ammonium dihydrogen phosphate was used additionally as matrix modifier during Cd determination in samples in order to prevent interferences coming from matrix components. The analysis of CRMs confirmed the reliability of the proposed approach. The precision and accuracy of Cd and Pb determination by the described method for soils and sediments were acceptable.     

Determination of pentachlorophenol in wastewater irrigated soils and incubated earthworms

The analyses of low pentachlorophenol (PCP) in soils and earthworms require a sensitive and reliable analytical method. In this paper, several derivatization methods and extraction solvents were compared systematically. The derivatization reagents included acetic anhydride, 2,3,4,5,6-pentafluorobenzyl bromide (PFBBr) and diazomethane. Hexane, acetone, hexane–acetone (1:1), dichloromethane and methanol were used as the extraction solvents. PFBBr derivatization showed the highest sensitivity. The derivatization parameters of PFBBr including the amount of PFBBr, the power and irradiation time of microwave were optimized. As a result, 200 μl of PFBBr (10%) at 150 W of microwave oven for 30 min achieved the best result. The PFBBr derivatization method had the detection limit of 0.07 μg l⁻¹ of PCP. Extraction by a mixture of hexane and acetone (1:1) showed the best recoveries. The recommended method was used to determine the low PCP in soils irrigated by wastewater and earthworms incubated in the corresponding soils. The concentrations of PCP in soils were in the range of 1.38–179 ng g⁻¹, while those in earthworms were 11.2–262 ng g⁻¹. The recoveries of the surrogate standard (trichlorophenol) ranged from 81.1% to 107%, demonstrating the merit of the method.     

Lead Adsorption on a Soil: A Polarographic Study

The adsorption of lead by a non‐contaminated loamy sand soil (Guarda, Portugal) was studied by voltammetric titrations using differential pulse polarography for pH values of 6.0, 6.8 and 7.2 and I of 0.5, 0.1 and 0.01 mol L^?1. After lead or soil additions, residual lead in solution was measured in the presence of the soil particles after an equilibration period, thus with minimum sample manipulation. The characteristics of the surface groups were studied by acid base potentiometric titrations. Lead retention by the soil is influenced both by pH and ionic strength of the medium. From the voltammetric data surface constants and total available binding groups have been estimated according to a complex surface model for the different experimental conditions and the results interpreted in terms of the surface characteristics of the soil and the support medium. Surface binding capacities in the range 1 to 70 mmol Pb kg^?1 were found depending on the pH and the ionic strength. The behavior found is in agreement with what is known in soil chemistry thus supporting the conclusion that voltammetric methods are quite appropriate for determining the extent of interaction between metal ions and soils.     

Application of data fusion techniques to direct geographical traceability indicators

A hierarchical data fusion approach has been developed proposing multivariate curve resolution (MCR) as a variable reduction tool.     

Uptake of Heavy Metals by Lupin Plants in Artificially Contaminated Sand: Preliminary Results

The aim of this study was to investigate the tolerance, uptake and accumulation of several metals of environmental interest by lupin plants. The effects of different metals on those parameters were evaluated individually as well as in groups, since the latter matches more closely real environmental conditions. The chemical form of some metals was also taken into consideration. Lupin plants were grown in different batches of sand artificially contaminated with Pb(II), Cd(II), Cr(III), Cr(VI), CH 3 Hg + and Hg(II) (each metal at the 50 mg L m 1 level) or their combinations. After 4 weeks of growth, the results indicated that lupins were quite tolerant to Cd(II), Pb(II), Cr(III) and Hg(II) since contamination with those metals did not cause significant weight differences between metal-treated and control plants. On the other hand, the presence of Cr(VI) and CH 3 Hg + induced severe signs of toxicity. Metal accumulation in lupins plants was influenced not only by the chemical form of the analyte but also by the co-presence of other metals. Metal concentration in the plants once harvested were found to be 4.9 g kg m 1 , 2.3 g kg m 1 , 0.4 g kg m 1 and 0.2 g kg m 1 for Cd(II), Hg(II), Pb(II) and Cr(III), respectively. Metals were preferentially accumulated in roots although a fast translocation to shoots was detected for Hg(II).