Quantification, source apportionment and risk assessment of polycyclic aromatic hydrocarbons in sediments from Mokolo and Blood Rivers in Limpopo Province, South Africa.

The presence of polycyclic aromatic hydrocarbons (PAHs) in the environment is of major concern since some of these compounds are highly persistent, toxic (causing cancer) and wide spread pollutants. The objective of this study was to evaluate the levels of PAHs in sediment samples collected from Blood and Mokolo Rivers in Limpopo Province, South Africa. The PAHs in sediments were extracted using optimized microwave-assisted extraction (MAE) method. The quantification of sixteen (16) PAHs in sediments was done by gas chromatography-flame ionization detector (GC-FID). The levels of PAHs recorded in sediment samples from Blood River ranged between 0.015 and 3.25 mg kg-1. The concentrations of PAHs obtained in sediments from Mokolo River (0.047 to 52.7 mg kg-1) were higher than those recorded in sediments from Blood River. The PAHs ratios indicated that both pyrogenic and petrogenic could be the sources of these compounds in both rivers. Toxic equivalency factors (TEFs) and benzo(a)pyrene equivalent (BaPE) were used to estimate the potential human health risk of PAHs in quantitative terms. The assessment of ecotoxicological risk indicated that the sediment samples collected from Mokolo River are at high toxicity risk while sediments from Blood River are at low sediment toxicity risk.

Speciation of major and trace elements leached from coal fly ash and the kinetics involved.

The combustion of coal in thermal power plants may result in high concentrations of elements in the coal fly ash remaining that may be toxic to living organisms or pose a risk to the environment. This study was aimed at determining the concentrations of potentially toxic elements in coal fly ash leachates, in an attempt to simulate natural processes that influence the environment. Powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and elemental composition studies were employed to characterize the physicochemical properties of the parent coal fly ash. The effect of various leaching parameters, including the pH of leaching solutions, the volume ratio of leaching solutions to the mass of coal fly ash, leaching time and temperature, were investigated. Moreover, the kinetics of the leaching of toxic elements from coal fly ash was also investigated by considering that the leaching process is governed by dissolution. Zero order, pseudo-first order, pseudo-second order, power function, simple Elovich and parabolic diffusion kinetic models were used to evaluate the leaching process. The experimental results indicate that the pH and leaching time had the most significant effect on the leaching behavior of elements from coal fly ash.

Levels of potentially toxic metals in water, sediment and peat from Wonderfonteinspruit, North West Province, South Africa.

Environmental monitoring of the levels of potentially toxic metals is of importance because of possible adverse effects on living species. This study was conducted to assess the levels of Cd, Cr, Cu, Hg, Mn, Pb, U and V in water, sediment and peat samples collected from the region of Wonderfonteinspruit. Water samples were simply filtered and acidified with HNO3 prior to analysis. Sediment and peat were oven-dried, ground, sieved and mineralised using a microwave digestion system. Concentrations of the selected elements in all samples were determined by inductively coupled plasma-mass spectrometry. A Zeeman mercury analyser was also used for quantification of Hg in the same sediment and peat samples. The method validation was carried out using SRM 1643e water and BCR 320R sediment certified reference materials. The results showed no significant difference at 95% level of confidence between the certified and measured values after using the Student's t-test. The levels of Cd, Cr, Cu, Pb, V and U found in rivers and dams were lower than the tentative South African water quality range guideline for domestic and irrigation purposes. However, water from dams and certain rivers was unsuitable for irrigation and domestic use.

Binding of RDX to Cell Wall Components of Pinus sylvestris and Picea glauca and Three-Year Mineralisation Study of Tissue-Associated RDX Residues.

Contamination of soils with the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX, Research Department Explosive) as a result of military applications is a large-area problem globally. Since coniferous trees dominate the vegetation of large areas of military land in Central Europe, particularly in Germany, the long-term fate of (14)C-RDX in the conifers Scots pine and Dwarf Alberta spruce was studied. Acetic acid was the most effective solvent for the removal of extractable RDX residues from homogenates of RDX-laden tree material (85%, 80-90% and 64-80% for roots, wood and needles, respectively). On average, only a fifth of RDX-derived (14)C was bound in non-extractable residues (NER). Within the main cell wall compartments, lignin was the dominant binding site for NER (needles: 32-62%; roots: 38-42%). Hemicellulose (needles: 11-18%; roots: 6-11%) and cellulose (needles: 12-24%; roots: 1-2%) were less involved in binding and a considerable proportion of NER (needles: 15-24%; roots: 59-51%) was indigestible. After three-year incubation in rot chambers, mineralisation of tree-associated (14)C-RDX to (14)CO2 clearly dominated the mass balance in both tree species with 48-83%. 13-33% of (14)C-RDX-derived radioactivity remained in an unleachable form and the remobilisation by water leaching was negligible (< 2%).

Occurrence, distribution, and ecological risk assessment of potentially toxic elements in surface sediments of Lake Awassa and Lake Ziway, Ethiopia.

Microwave-assisted acid digestion and modified aqua regia (HNO3:HCl:HF:H3BO3) leaching techniques were used for the determination of 15 potentially toxic elements (V, Cr, Fe, Mn, Co, Ni, Cu, Zn, As, Se, Ag, Cd, Sn, Hg and Pb) in sediment samples from Lake Awassa and Lake Ziway, Ethiopia. The digests were subsequently analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-optical emission spectrometry (ICP-OES). Mercury was directly determined in the solid samples using an elemental mercury analyzer. The precision and accuracy of the digestion procedures were verified using certified reference materials. The experimental results were in good agreement with the certified values (P < 0.05) and the recoveries were quantitative (>90%). The average relative standard deviations were below 10%. There is significant correlation between the two lakes at the 0.01 level (2-tailed). Using the sediment quality guidelines, both lakes are heavily polluted with Zn and some of the sites are heavily polluted with Cu, Ni and Pb. Based on effect range low (ERL) - effect range medium (ERM), in both lakes for Ag were greater than the ERM, indicating that the areas could be toxic to aquatic organisms, while for Cr, Cu, As and Hg the values were less than ERL.

The effect of calcination on multi-walled carbon nanotubes produced by dc-arc discharge.

Multi-walled carbon nanotubes were synthesized by dc-arc discharge in helium atmosphere and the effect of calcination at different temperatures ranging from 300-600 degrees C was studied in detail. The degree of degradation to the structural integrity of the multi-walled carbon nanotubes during the thermal process was studied by Raman spectroscopy, Scanning electron microscopy and High resolution transmission electron microscopy. The thermal behaviour of the as prepared and calcined samples was investigated by thermogravimetric analysis. Calcination in air at 400 degrees C for 2 hours was found to be an efficient and simple method to eliminate carbonaceous impurities from the nanotube bundles with minimal damage to the tube walls and length. The impurities were oxidized at a faster rate when compared to the nanotubes and gave good yield of about 50%. The nanotubes were observed to be damaged at temperature higher than 450 degrees C. The results show that this method is less destructive when compared liquid phase oxidation with 5 M HNO3.

Use of a simplified generalized standard additions method for the analysis of cement, gypsum and basic slag by slurry nebulization ICP-OES.

The simplified generalized standard additions method (GSAM) was investigated as an alternative method for the ICP-OES analysis of solid materials, introduced into the plasma in the form of slurries. The method is an expansion of the conventional standard additions method. It is based on the principle of varying both the sample mass and the amount of standard solution added. The relationship between the sample mass, standard solution added and signal intensity is assumed to be linear. Concentration of the analyte can be found either geometrically from the slope of the two-dimensional response plane in a three-dimensional space or mathematically from the ratio of the parameters estimated by multiple linear regression. The analysis of a series of certified reference materials (CRMs) (cement CRM-BCS No 353, gypsum CRM-Gyp A and basic slag CRM No 382/I) introduced into the plasma in the form of slurry is described. The slurries contained glycerol and hydrochloric acid and were placed in an ultrasonic bath to ensure good dispersion. "Table curve 3D" software was used to fit the data. Results obtained showed that the method could be successfully applied to the analysis of cement, gypsum and slag samples, without the need to dissolve them. In this way, we could avoid the use of hazardous chemicals (concentrated acids), incomplete dissolution and loss of some volatiles. The application of the simplified GSAM for the analysis did not require a CRM with similar chemical and mineralogical properties for the calibration of the instrument.

Spectral moments of polycyclic aromatic hydrocarbons. Solution of a kinetic problem.

The relationship between the rate of supercritical fluid extraction of polycyclic aromatic hydrocarbons (PAHs) from coal-tar pitch and some topological invariants are examined. The aim is to explain the appearance of a minimum value on the activation energy/molar mass curve of the PAHs. Rate constants are approximated using spectral moment expansion. It is shown that the size of the PAHs determines more than 95% of the extraction rate. Activation energy for the extraction of the PAHs was found to increase with increasing molar mass. The appearance of a minimum value on the activation energy/molar mass curve is the consequence of experimental difficulties resulting from the tendency of lower members of the PAHs to sublime.

Slurry nebulization for the analysis of gypsum and cement by inductively coupled plasma spectrometry.

The usual form of presentation for a sample to be analyzed by an inductively coupled plasma-optical emission spectrometer is in the form of a liquid. For the analysis of solids, this involves a dissolution step and in the case of complex matrices this may be long and difficult. Should it be possible to analyse the sample without prior dissolution, then the problems associated with obtaining a solution would be resolved. A method for analyzing samples is to make use of slurry nebulization. Samples with complex matrices, such as cement and gypsum were selected and analysed as in the form of a slurry. Using different concentrations of a certified reference materials, calibration curves were obtained, from which the unknown samples could be determined directly. Use of aqueous solutions for calibration was also investigated. The method was evaluated using other reference materials or results obtained by an independent laboratory using different technique for the analysis. The slurry method was found to be accurate and precise.