No description available.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in, Microbiology and Biotechnology 2016. / Heavy metal contamination, of natural water resources, resulting from the large amounts of toxic waste generated by industrial practices is of great environmental concern. Lead (Pb) in particular is one of the most toxic heavy metals that leads to several health deficiencies upon human exposure. The reduction of heavy metals like Pb to acceptable levels in the water therefore becomes critical for potable and agricultural use. Removal of heavy metals by conventional methods is expensive and results in secondary pollution. Bioremediation, a process that passively removes heavy metals from solution through microbial biosorption, is a much sought after alternative because it is more eco-friendly and cost-effective. Micrococcus luteus and Paenibacillus castaneae are two bacterial species reported to be highly resistant to Pb making them favourable as metal biosorbents. The present study aimed to further characterise these species as biosorbents by evaluating the influence of environmental conditions on their rate of biosorption of Pb. Each bacterial isolate was heat-killed and exposed to 0.5 mM (150 mg/L) Pb and the maximal rate of metal uptake calculated when the pH, temperature and biomass concentration were varied. Additionally, the initial metal concentration was increased from 0.005 to 1.25 mM to determine its effect on Pb uptake by each species. The influence of competing cations (Ni2+, Co2+, Mn2+ and Zn2+) on the rate of Pb uptake by each isolate was also established. Both bacterial isolates resulted in the biosorption of at least 50% of 0.5 mM Pb ions when used at a pH of 7, temperature of 25 oC, and a biomass concentration of 2 g/L. The rate of metal uptake for M. luteus at the above mentioned parameters was found to be 24.51 mg/g biomass, while the rate of metal uptake for P. castaneae was 15.63 mg/g biomass. These findings indicated that M. luteus took up more Pb at a faster rate in comparison to P. castaneae. The present study furthermore elucidated that as the metal concentration of Pb was increased, the amount of Pb biosorbed by M. luteus decreased from 84.76% to 46.10%. Similarly, P. castaneae yielded 81.39% biosorption from 0.005 mM Pb but only 34.29% of Pb was taken up when the concentration was increased to 1.25 mM. When the bacteria were exposed to various competing cations an increase in the rate of Pb biosorption was observed for P. castaneae while the opposite effect was noted for M. luteus. Findings from this study show that under high metal concentrations, both M. luteus and P. castaneae are capable of significantly reducing the level of Pb from pure solution. The results warrant further treatment of several industrial effluents using these biosorbents for subsequent application in wastewater treatment. / MT2017

University of Macau / Institute of Chinese Medical Sciences

No description available.

No description available.

An experimental study was made of accumulation and loss of heavy metals by the aquatic moss Rhynchostegium riparioides and of the processes involved. The information gained were used to assess the effectiveness of this species as a monitor. Growth of Rhynchostegium continued throughout the year with peaks in spring and autumn. There were positive correlations between growth and water and air temperatures. Strong differences in growth rates in the four streams were not related to nutrient or heavy metal concentrations. Various patterns of mesh bag were tested as containers for transplanted Rhynchostegium to be used as a monitor. No significant differences in accumulation by moss were found between boulders or bags, or in accumulation with different patterns of bags. Accumulation was reduced slightly at the centre of bags packed with large quantities of moss. The physiology of Zn accumulation was also studied. A large part of accumulation (> 70%) in the early stages (< 12 h) was in a form readily exchanged for competing cations such as Ca and Ni; over longer time periods there was significant accumulation into a more tightly bound compartment. There was no evidence that uptake into this latter compartment was under the direct control of the plant's metabolism. There was differential accumulation of Cr(III) and Cr(VI) in laboratory experiments; during a case study it was possible to "predict" the speciation of Cr in the water by the concentrations accumulated by the moss. These results confirm that bryophytes are useful as monitors of heavy metal pollution in a wide range of circumstances. A range of such applications are outlined, along with recommendations for standard methods for using moss bags.

On-line systems for monitoring mercury in liquid and gaseous production and waste streams have been developed, utilising atomic fluorescence spectrometry (AFS) as the basis for detection. Instrumentation has been designed for unattended continuous operation. Laboratory chemistries for the vapour generation of mercury, normally performed off-line in batch mode, have been adapted and optimised for continuous, flow-injection analysis for varying sample types and chemical forms of mercury. The system has typical analysis cycle of 7 minutes, a limit of detection of 10 pg ml ˉ¹ a linear range up to 100 µg ml ˉ¹ and has been applied in industrial environments for the continuous monitoring of mercury in incineration wastewater and sulphuric acid. The system was validated by on-site trials for periods of one week, during which time comparative off-line laboratory measurements showed good agreement. An automated system for monitoring mercury in natural gas streams has also been developed and validated by laboratory and on-site industrial trials. A heated pressure let-down system was designed in order to facilitate sampling of high-pressure gas streams without condensation of heavier fractions. The heated sampling line was interfaced with an automated system for trapping mercury, from variable volumes of gas, onto gold amalgamation traps, with subsequent desorbtion and analysis by AFS. The method detection limit for a 58 litre sample of natural gas was 30 pg m ˉ³ which was sufficient to determine residual mercury in natural gas streams even after mercury scrubbing had been performed. The system was validated by laboratory trials and spiking experiments during on-site trials at a gas processing facility, which resulted in complete installation and commissioning.

The primary aim of this thesis was to establish the mode of action of the heavy metal, copper, on the cardiac physiology of the blue mussel, Mytilus edulis. Exposure of specimens of M.edulis to dissolved copper led to a decrease in heart rate and an increase in heart rate variability (HRV). The concentration of copper causing a 50% reduction in heart rate was found to be 0.8µM, while the concentration causing a 50% increase in HRV was 0.06µM (48 h EC50s). Simultaneous measurements of valve activity indicated that the observed bradycardia was not caused by valve closure. Subsequently, it was considered that copper might directly affect cardiac physiology by disrupting important cellular functions of the heart. Four different ionic currents were identified and characterised in M.edulis ventricular myocytes: two outward potassium currents, a sodium current and a calcium conductance. Copper ions had no effect on the ionic currents of M.edulis heart cells at concentrations shown to inhibit the cardiac activity of whole animals. Clearly, the bradycardia measured in whole animals was not due to a change in the configuration of the ventricular action potential. It was recognised that copper could still directly affect cardiac physiology in mussels by altering excitation-contraction coupling, contractile protein function or myocardial energy production. To determine whether this was the case, recordings of heart contractions from isolated ventricular strips were made using an isometric force transducer. Using isolated strips, inhibition of cardiac activity was only induced by exposure to copper concentrations ≥1 mM. Thus, the fall in heart rate measured in the whole animals dosed with copper could not be attributed to direct cardiomyopathy. Control of the. beating of M. edulis heart is known to be exercised by nerves from the visceral ganglion (VG) that contains both excitatory and inhibitory fibres. Following the removal of the VG (in vivo), exposure to copper had no effect on the heart rate of whole animals as occurred in the initial experiments. This suggests that copper affects the heart rate in M.edulis via a neuronal pathway. The principal cardioexcitatory and cardioinhibitory transmitters in molluscs are thought to be serotonin and acetylcholine, respectively, The effect of copper on the heart rate of M.edulis could not be abolished by depletion of the monoamine content of the animal using reserpine. However, pre-treatment of mussels with α-bungarotoxin considerably reduced the sensitivity of the heart to copper. These results indicated that the influence of copper on the heart of M.edulis might be mediated by a change in the activity of cholinergic nerves to the heart. Acetylcholine is known to have a biphasic action on the heart of M.edulis, low doses depress and high doses excite (the endpoint of both responses resulting in a cessation of the heart beat). In the final experiments of this series, mussels were injected with either benzoquinonium or D-tubocurarine, prior to copper exposure, in an attempt to selectively block the inhibitory or excitatory cholinoreceptors of the heart. Only benzoquinoniuin decreased the susceptibility of the heart to copper, suggesting that copper affects the cardiac activity of blue mussels by stimulating inhibitory cholinergic nerves to the heart. It is suggested that there may be a chemosensory mechanism present in mussels which responds to increased levels of metals in seawater leading to changes in a number of physiological functions. The last result chapter of this thesis examined the effects of the organophosphorous pesticide, dimethoate, on cardiac and acetylcholinesterase (AChE) activity in the common shore crab Carcinus maenas. Cardiac activity was measured non-invasively before and during dimethoate exposure. Heart rates decreased in a concentration-dependent manner. Serial measurements of AChE activity in haemolymph samples taken from crabs before and after exposure indicated that 2 mg 1ˉ¹ dimethoate also significantly reduced AChE activity. The percentage inhibition in AChE activity was correlated with the percentage reduction in heart rate following dimethoate exposure. This suggests that organophosphates may directly affect neuronal control of the heart. These experiments indicate that non-destructive, serial measurements of cardiac activity and AChE activity are valuable biomarkers of organophosphate exposure and adverse effects.

Thesis (Ph. D.)--Rutgers University, 2010. / "Graduate Program in Environmental Science." Includes bibliographical references (p. 104-113).

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 99-112). Also available on the World Wide Web.