The thesis concentrates on the environmental implications of Cd. The aspect being dealt with concerns the effect of cadmium on plants and particularly its effect on chlorophyll content. The thesis also deals with the relationship of Cd with pH and other trace metals particularly zinc. The first chapter is an introduction to the subject. It briefly reviews the history of studies on trace metals, their relationship and their effects on soils, animals and plants. It also includes information about factors such as pH, organic matter, interactions between elements etc. affecting the behaviour of trace metals. Chapter I contains a review on cadmium, its behaviour, its phytotoxicity and its presence in biological systems. It also reviews some previous works and suggestions and it ends by suggesting a frame work for this thesis with a brief description of each part. Chapter 2 is divided into two parts. Part (one deals with Cd as it is affected by pH which plays an important role in accounting for Cd behaviour and uptake by plants. Besides an introduction on Cd, this chapter contains a description of the experiments and the techniques used for the analysis. It also contains detailed data and the corresponding graphics. Investigations carried out in this chapter suggest that pH is undoubtedly an important factor interfering with the transport, translocation and uptake of Cd by plants. Part two of this chapter is aimed at studying the transport and distribution of Cd in a plant. It is also aimed at demonstrating the preferential localization of Cd by using radiolabelled Cd-109. The analysis was carried out using the solid scintillation technique. Information was obtained suggesting that Cd was preferably taken up by roots than by the other parts of the plant. It also indicates that leaves are less tolerant to high levels of Cd than roots and stems. Chapter 3 lays emphasis on the interaction of cadmium with other trace metals and most particularly with zinc because of their chemical similarities. The following levels of Cd and Zn are used for the investigation. Cd (mug) : 30 to 180 and Zn (mug): 2000 to 10,000. The interactions of Cd with other trace metals were also reviewed. In this chapter, some conclusions are drawn concerning the mutual effect between Cd and Zn. It also shows that the addition of Zn has a positive result in minimizing the toxic effect of Cd as is expressed in the delay of plant response to Cd compared to the findings in Chapter 2. A chemical approach is suggested to explain the nature of the interaction between Cd and Zn. Two possible types of interaction are more likely to occur: competition for sites at the root level and a direct substitution of Zn by Cd In zinc enzymes. The chemical approach seems to be valid because of the chemical similarities between the two elements. Symptoms of chlorosis or loss in chlorophyll were shown as a result of Cd effect on beans. Chapter 4 is devoted to the investigation of this matter aiming at explaining the causes of chlorophyll losses by studying the effect of Cd on chlorophyll formation and content. In Vitro and in Vivo experiments were carried out using atomic absorption and ultra violet spectroscopy. Some conclusions were drawn consequently such as: Cd suppresses chlorophyll content and also decreases Mg content. It is also suggested that Cd may disturb the formation of chlorophyll by interfering with Fe which is important for its synthesis. In this chapter some suggestions are put forward concerning the possible displacement of Mg by Cd. Chapter 5 carries out an assessment of all the points and suggestions encompassed in this thesis and considers the extent of the practicality of the results. It also assesses the prospects for future research which could be to be carried out in this area
