Uptake of heavy metals by Typha capensis from wetland sites polluted by effluent from mineral processing plants: implications of metal-metal interactions.

The aim of the present work was to demonstrate the existence of metal-metal interactions in plants and their implications for the absorption of toxic elements like Cr. Typha capensis, a good accumulator of heavy metals, was chosen for the study. Levels of Fe, Cr, Ni, Cd, Pb, Cu and Zn were determined in the soil and roots, rhizomes, stems and leaves of T. capensis from three Sites A, B and C polluted by effluent from a chrome ore processing plant, a gold ore processing plant, and a nickel ore processing plant, respectively. The levels of Cr were extremely high at Site A at 5415 and 786-16,047 µg g-1 dry weight in the soil and the plant, respectively, while the levels of Ni were high at Site C at 176 and 24-891 µg g-1 in the soil and the plant, respectively. The levels of Fe were high at all three sites at 2502-7500 and 906-13,833 µg g-1 in the soil and plant, respectively. For the rest of the metals, levels were modest at 8.5-148 and 2-264 µg g-1 in the soil and plant, respectively. Pearson's correlation analysis confirmed mutual synergistic metal-metal interactions in the uptake of Zn, Cu, Co, Ni, Fe, and Cr, which are attributed to the similarity in the radii and coordination geometry of the cations of these elements. The implications of such metal-metal interactions (or effects of one metal on the behaviour of another) on the uptake of Cr, a toxic element, and possible Cr detoxification mechanism within the plant, are discussed.

Potential marker enzymes and metal-metal interactions in Helisoma duryi and Lymnaea natalensis exposed to cadmium.

In this study, we investigate the effects of exposure to cadmium and copper on Lymnaea natalensis and Helisoma duryi. The snails were dosed with Cd2+ or Cu2+ for a period of 96h. Snails dosed with Cd accumulated the metal significantly (P<0.05) in tissues but not in shells. Mortality was observed at approximately 1mg Cd/l of culture water. In tissues and shells of snails dosed with Cd or Cu, synergistic and antagonistic metal-metal interactions involving Cd, Cu, Zn, and Pb were observed and these may affect metal toxicity. Glutamate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase were assayed in whole snail tissue sub-cellular fractions of Cd-dosed snails. Generally, enzyme activity significantly increased at lower concentrations of Cd but decreased at high concentrations of the metal. However, mitochondrial alanine aminotransferase activity progressively declined with increasing Cd concentration. The changes in some of the enzymes' activities suggest biomarker potential.

Activities of glutamate dehydrogenase and aspartate and alanine aminotransferases in freshwater snails Helisoma duryi and Lymnaea natalensis exposed to copper.

In this paper we investigate the potential of glutamate dehydrogenase (GDH) and aspartate and alanine aminotransferases (AST and ALT) as biomarkers of water pollution due to copper in the freshwater snails Helisoma duryi and Lymnaea natalensis. Snails were dosed with copper(II) ion concentrations of 0.01, 0.1 and 1 mg kg(-1) breeding water for a period of 96 h, after which those surviving were shelled. The copper content in the breeding water, in whole snail tissue and in the snail shells was determined at the end of the period of exposure. For enzyme determinations, whole snail tissue was first homogenized and fractionated by centrifugation at 500 g to remove the nuclei. The resulting supernatant was then centrifuged at 10,000 g to give a pellet fraction representing the mitochondrial fraction and a supernatant representing the cytosolic fraction. Copper was very toxic to both snail species at concentrations above 0.2 mg l(-1), with only 3% of the Helisoma and 12% of the Lymnaea surviving at concentrations of approximately 1 mg l(-1). The copper content in the shells and tissues of snails rose with increasing copper concentration in the breeding water, and was 2.1- to 4.9-fold in snails exposed to copper ion at a dose of 1 mg kg(-1) water compared with undosed snails. Similarly, the activities of GDH and AST rose by up to 4.7-fold in the homogenate and the mitochondrial and cytosolic fractions with increasing concentrations of copper. These activities, however, fell at copper concentrations of approximately 1 mg l(-1), which coincided with massive death of snails. Mitochondrial ALT disappeared at copper ion concentrations of approximately 0.2 mg l(-1) for Lymnaea and 1 mg l(-1) for Helisoma, possibly indicating mitochondrial degeneration. These results show that GDH, AST and ALT have the potential to be biomarkers of sublethal copper pollution in these two snail species, since their activities were significantly altered by low copper concentrations.

A possible steady state kinetic model for the atomization and excitation processes during inductively coupled plasma atomic emission spectrometry: application to interference effects of lithium on calcium.

A possible steady state kinetic model is presented for the atomization and excitation processes during inductively coupled plasma atomic emission spectrometry. The model takes into account the relative rates of (a) thermal dissociation of analyte salt, (b) recombination of counter atom and analyte atoms, (c) charge transfer between analyte and interferent species, (d) charge transfer between analyte and argon species, and (e) ion/electron collisional de-ionization. Number density ratio data, n(u)'/n(u), where n(u) denotes the excited state and the prime denotes the presence of an interferent element, are presented showing that the predictions of the model are consistent with the signal enhancement observed at low analyte concentrations when Ca is determined by ICP in the presence of excess Li.