Detection of environmental pollution (radionuclides and heavy metals) using microorganisms.

Radionuclide and heavy metal pollutants are a major concern for the environment nowadays as thousands of waste sites around the world pose a serious threat to all living organisms and humans in particular. In order to find an effective technique for the detection of these pollutants and their disposal, great efforts have been made. This is one of the most important reasons and motivation for research in this important field. In the present work bacteria cells were used as a sensitive material in biosensor for the detection of gamma radiation and heavy metals (cadmium chloride and nickel chloride) dissolved in water. The main aim of this project is to develop novel sensing technologies for the detection of environmental pollution; the project utilized two types of bacteria samples, E. coli and D. radiodurans, for this task. The biomass (bacteria density or concentration) was firstly characterised by the optical techniques,including fluorescence microscopy, fluorescence spectroscopy, optical density OD600 and UV-visible spectroscopy and was evaluated or estimated according to or attributed to the time of exposure to gamma radiation, which are emitted from CO57 radiation source. From the exponentially decaying response it was shown that the E. coli bacteria (DH5alpha strain, belong gram-negative bacteria) are very sensitive to gamma radiation and the time constant is around 40 hours, that it can be relied upon in determining the low level of radiation. While, D. radiodurans (R1 Anderson strain, which belongs to gram positive bacteria) appeared to be much less affected by gamma radiation and showed even smaller increase in the bacteria counts at low radiation doses followed by rather moderate decay at intermediate and high doses; the time constant is around 240 hours. A series of DC and AC electrical measurements were carried out on the same bacteria samples. As a first step, a correlation between DC and AC electrical conductivity and capacitance with bacteria concentration in solution was established. The study of the effect of gamma-radiation on DC and AC electrical characteristics of bacteria revealed a possibility of pattern recognition of the above inhibition factors. The electrical results showed some match or consistency with the optical results. The optical and electrical techniques were also used to study the effect of heavy metals, mainly NiCb and CdCb on bacteria samples. The relations between the optical and electrical properties with metals concentration were established. The electrical characteristics showed clear sequences according to metals concentration. Pattern recognition seems very interesting and proved to provide a simple method to calculate the environmental contamination levels. The equivalent circuit was investigated and their results were compared with the experimental results; significant match to some extent between the practical and theoretical results was established.