Tissue sequestration and biliary elimination are two of the important mechanisms by which mammalian body defends against heavy metal insults. In rats or rabbits that had received Pb, Cd, Hg, As and ²¹⁰Po, these metal ions were sequestered in the choroid plexus at concentrations of Pb, Cd, Hg, As and Po that were 57, 33, 12, 13 and 5 times higher, respectively, than those found in the brain cortex. In addition, the concentrations of these heavy metal ions were many fold greater in the choroid plexus than in the CSF or blood. The accumulation of Pb in the choroid plexus was dose-dependent and time-related. When the choroid plexus was incubated, in vitro, with ouabain, the latter significantly inhibited the uptake of Cd from the CSF side of the choroid plexus. Cystine concentration was four times greater in the choroid plexus than in brain cortex. Results suggest that the choroid plexus sequesters toxic metal and metalloid ions. It appears to do this in order to protect the CSF and brain from toxic heavy metals in the blood. The effect of N-(2,3-dimercaptopropyl) phthalamidic acid (DMPA), meso-dimercaptosuccinic acid (DMSA) and 2,3-dimercapto-1-propane sulfonic acid (DMPS) on biliary excretion of Cd was studied in rat chronic intoxication mode. DMPA (0.10 mmol/kg, iv), when given to rats three days after exposure to Cd, elicited within 30 min a 20-fold increase in biliary Cd excretion. GSH in rat bile was also increased three fold as compared to control. Neither DMSA nor DMPS increased biliary Cd or GSH. Upon iv administration, DMPA, not DMSA, appeared in bile. An altered, presumably disulfide, form of DMPS was also found in bile. Incubation of DMPA or DMSA with Cd-saturated MT resulted in the removal of Cd from MT. DMPS, however, promoted the formation of MT polymers. DMPA protected biliary GSH from autoxidation. Gel filtration and autoradiographic study of rat bile samples showed that the radioactivity of Cd was correlated with both GSH and DMPA. The evidence supports the mechanism that the increase of biliary Cd by DMPA is the result of DMPA entering cells and removing Cd from MT. Protection of GSH autoxidation by DMPA may facilitate Cd elimination via the bile.

No description available.

No description available.

Thesis (M.Sc.) -- University of Limpopo, 2005 / Six aerobic bacterial strains [GM 10(1), GM 10 (2), GM 14, GM 15, GM 16 and GM 17] were isolated from an antimony mine in South Africa. Heavy-metal resistance and biosorptive capacities of the isolates were studied. Three of the isolates (GM 15, GM 16 and GM 17) showed different degrees of resistance to antimony and arsenic oxyanions in TYG media. The most resistant isolate GM 16 showed 90 % resistance, followed by GM 17 showing 60 % resistance and GM 15 was least resistant showing 58 % resistance to 80 mM arsenate (AsO4 3-). GM 15 also showed 90 % resistance whereas isolates GM 16 and GM 17 showed 80 % and 45 % resistance respectively to 20 mM antimonate (SbO4 3-). Arsenite (AsO2 -) was the most toxic oxyanion to all the isolates. Media composition influenced the degrees of resistance of the isolates to some divalent metal ions (Zn2+, Ni2+, Co2+, Cu2+ and Cd2+). Higher resistances were found in MH than in TYG media. All the isolates could tolerate up to 5 mM of the divalent metal ions in MH media, but in TYG media, they could only survive at concentrations below 1 mM. Also, from the toxicity studies, high MICs were observed in MH media than TRIS-buffered mineral salt media. Zn2+ was the most tolerated metal by all the isolates while Co2+ was toxic to the isolates. The biosorptive capacities of the isolates were studied in MH medium containing different concentrations of the metal ions, and the residual metal ions were determined using atomic absorption spectroscopy. GM 16 was effective in the removal of Cu2+ and Cd2+ from the contaminated medium. It was capable of removing 65 % of Cu2+ and 48 % of Cd2+ when the initial concentrations were 100 mg/l, whereas GM 15 was found to be effective in the biosorption of Ni2+ from the aqueous solutions. It was capable of removing 44 % of Ni2+ when the initial concentration was 50 mg/l. GM 17 could only remove 20 % of Cu2+ or Cd2+. These observations indicated that GM 16 could be used for bioremediation of xvi Cu2+ and Cd2+ ions from Cu2+ and Cd2+-contaminated aqueous environment, whereas GM 15 could be used for bioremediation of Ni2+. / National Research Foundation and the University of the North Research Unit

Graduation date: 1993 / Figures in original are black and white photocopies. Best scan available.

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

published_or_final_version / Zoology / Master / Master of Philosophy

Acid rmne drainage (AMD) is a major pollution problem througbout the world, adversely affecting both surface and groundwaters. AMD is principally associated with the mining of sulphide ores. The most commonly associated minerals being sulphur, copper, zinc, silver, gold, lead and uranium. As conventional methods for removing heavy metals from wastewater are often prohibitively expensive, the implementation of biological processes for the removal of heavy metals has become a realistic practice. The objectives of this project was firstly to establish the effect of copper, lead and nickel, heavy metals commonly found in AMD waters, on the enzyme carbonic anhydrase, which is an integral part of the carbon concentrating mechanism (CCM) and secondly, to determine the feasibility of using the alkalinity generated by Spindina for the precipitation of heavy metals from solution. Initially, batch flask experiments were performed and it was found that the algae were able to utilise the bicarbonate supplied in the medium, under CO, limiting conditions, through the induction of their CCM, resulting in the generation of carbonate. The effect of the inhibitors, acetazolamide (AZ) and ethoxyzolamide (EZ), were also investigated in order to determine the importance of carbonic anhydrase (CA) in inorganic carbon accumulation and photosynthesis. Results obtained were consistent with those observed in literature and it was found that at IOOf.LM AZ and EZ, complete inhibition of photosynthesis and carbonic anhydrase occurred, with no oxygen being evolved. The results obtained from the inhibitor experiments substantiate the findings that carbonic anhydrase is an important part of the CCM, and that the dehydration of bicarbonate to carbon dioxide and hydroxide ions, is in fact an enzymatic process regulated by the enzyme carbonic anhydrase and is essential for efficient photosynthesis. The effect of heavy metals on Spirulina was also investigated. Lead, copper and nickel were all found to cause a reduction in the synthesis of chlorophyll a, which resulted in a decrease in photosynthetic efficiency and eventually death of the culture. The morphology of the algae was also severely affected by heavy metals, with degradation and aJmost complete disintegration of the algal filaments occurring. Using the Wilbur-Anderson assay method, carbonic anhydrase activity was found to be lower in the experimental flasks containing heavy metals, than the control flasks, reducing the algae's ability to utilise the bicarbonate in solution for effective photosynthesis. The Wilbur-Anderson assay method did not prove to be a reliable method for measuring changes in enzyme activity as results were found to be erratic. Therefore attempts were made to use an oxygen electrode as an alternative method for determining the effects of various parameters on enzyme activity and photosynthesis, this proved to be more successful. Because of the toxic effects of heavy metals on Spirulina it was decided that the use of the biogenic alkalinity generated by the algae for the precipitation of heavy metals may be successfully employed as an alternative method for bioremediation and metal recovery. Carbonate reacts readily with metals, therefore the carbonate produced by this algal system was used for the precipitation of metals. It was possible to categorise the precipitation reactions observed into three groups, namely those metals which, a) precipitate as hydroxides, b) precipitate as carbonates generated from the dissociation of bicarbonate and c) metals which can only precipitate if there is free carbonate present in solution.

Thesis (MScEng (Process Engineering))--Stellenbosch University, 2008. / A substance called CRUD (Chalk River Unidentified Deposit) was deposited together with gold tailings to the East Paydam tailings dam. Previous research conducted on the material has shown that the crud leaches Mn and Ni at concentrations that are above their acceptable risks limits as well as Zn which leaches at concentration slightly below its acceptable limits thereby posing an environmental risk. The main objective of the research was to test the hypothesis stating that soil washing in series with bioremediation can be used to remove the heavy metals from the material from the East Paydam tailings dam. Various laboratory and pilot scale tests were conducted to investigate critical soil washing and bioremediation parameters and their respective influence on the treatment process. Laboratory work involved column tests and batch tests. These tests were crucial in determining the critical parameters for the pilot scale tests such as the selection of the suitable lixiviant from the four that were investigated. The optimal concentration of the lixiviant was also determined together with the optimum soil: liquid ratio. These parameters were employed in the pilot scale tests. Pilot scale tests involved soil washing in series with bioremediation. The bacterial growth over the bioremediation period was also determined. Precipitation of the heavy metals from leachate was investigated by varying the pH and temperature. Results showed that the soil from the East Paydam can effectively be treated by soil washing in series with bioremediation. Oxalic acid was selected for soil washing of the payable slimes at a concentration of 0.001M. However, material that contains high amount of CRUD (deeper down the slime dam) required the relatively concentrated 0.1M oxalic acid and mechanical agitation. Bioremediation was determined to increase the amount of heavy metals that was leached from the material from the East Paydam slimes dam. Precipitation of the heavy metals at a pH of 12 achieved up to 98% removal of heavy metals from leachate.

M.Sc. (Zoology) / The production of nanoparticles started as early as 1990s (Alkilany & Murphy, 2010). Nanoparticles are utilised in a range of products such as electronics, optics, textiles, medical, devices, cosmetics, food packaging, water treatment technology, fuel cells, catalysts, biosensors and agents for environmental remediation (Handy et al., 2008). Unlike natural particles, which dissolve or aggregate and are often temporary in the environment, engineered nanoparticles (ENPs) maybe persistent due to the stabilization properties of their capping agent (surfactant or organic material). Thus, there is growing concern about the production and fate of ENPs in the environment (Handy et al., 2008).As ENPs pass through the water system they become exposed to different salinities, ionic concentrations and pH changes (Lapresta-Fernández et al., 2012). During this process the ENPs are degraded, transported, altered and accumulated in various ways. Nanoparticles have been found to aggregate in various organelles, for example endocytotic vesicles (Elsaesser & Howard, 2011; Lapresta-Fernández et al., 2012), cytoplasm and the perinuclear region (Mirkin et al., 2010). This can take place via ingestion, endocytosis and or by diffusion (Nowack & Bucheli, 2007). The major question is are NPs toxic and are they more toxic than their metal salts? While bulk gold is distinguished as a chemically inert and a non-toxic substance, (Alkilany & Murphy, 2010) GNPs may be toxic due to their different physicochemical properties such as small particle size, configuration, charge and specific surface area and easy surface alterations (Cho et al., 2009; Goodman et al., 2004; Lapresta-Fernández et al., 2012)...