الفهرس 
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Abstract
The present study aimed to investigates the toxic effect of three tested metals (Cobalt, Nickel and Mercury) on the green alga Scenedesmus biguja isolated from Ibrahemia canal water. It is divided in two parts, the first part deals with heavy metals toxicity from a physiological stand point, the second part deals with interaction of some environmental factors in attenuation the toxicity of heavy metals from a chemical equilibrium stand point with special references to the role of algae on bioremediation. The following points were reached:-
1. Four concentrations of the three metals (10-9, 10-8, 10-7 and 10-6M) were suggested .
2. The lower doses of cobalt and nickel had a stimulating effect in Scenedesmus biguja biomass yield whereas the higher doses were inhibitory depending on the metal type.
3. The inhibitory effect of mercury on Scenedesmus biguja ’s growth parameters was more pronounced than two further metals tested.
4. The three tested metals affected negatively the total protein content of the tested green alga Scenedesmus biguja.
5. The supplementation of cobalt and nickel by concentration 10-8 M increases the total protein content as compared to the control, whereas decreased in mercury treated samples with increasing metal concentrations compared to the metals free media (control).
6. Scenedesmus bijuga ’s total carbohydrate content also declined depending on the metal concentration in the medium, but the inhibitory effect of the three metals tested was not as pronounced as that of the protein content. The three metals tested initiated the accumulation of total carbohydrates at the crop, supplemented by 10-8 M.
7. The total free amino acids of Scenedesmus bijuga gradually increased with rise of metals concentration. Cobalt and nickel stimulated the biosynthesis of total free amino acids more than that obtained with mercury.
8. Bioaccumulation of cobalt, nickel and mercury by Scenedesmus biguja cells were parallel to increasing the concentrations in the culture medium. The bioaccumulation of metals was on the following order: Co > Ni > Hg.
9. The protein profile of Scenedesmus bijuga under stress of metals cobalt and mercury was studied. The data illustrated that cobalt treatment caused an induction in the synthesis of some new polypeptides in green alga Scenedesmus bijuga as compared to control.
10. The electrophoretically separated protein under heavy metals as compared with control revealed; quantitative decline in certain proteins; Rise in levels of other proteins (density of protein bands); Some proteins remained unchanged; de novo induction of specific proteins.
11. The band numbers from (5:7) were detected under different concentrations of cobalt. Three protein bands at molecular weights 139.36, 52.47 and 19.88 kDa polypeptides were common bands under different concentrations of cobalt. On other hand, two bands (98.04 and 10.53 kDa) were commonly induced under moderate concentration of cobalt, while, the (95.52 KDa) protein band was newly expressed under low concentration of cobalt (10-9M) alone. Under high concentration of cobalt (10-5M) there were a specific bands disappeared at molecular weight (12.04kDa).
12. The band numbers from (3:5) were detected under different concentrations of Hg. one protein band at molecular weights 47.82 kDa polypeptide was common band under different concentrations of Hg. Two bands (28.81 and 14.52 kDa) were commonly induced under moderate concentrations of mercury (Hg 10-9 and Hg 10-8M). Protein band (14.65 KDa) was newly expressed under high concentration of mercury (10-6 M).
13. The changes in esterase activity in Scenedesmus bijuga under stress of two cobalt and mercury were investigated, whereas, three bands of EST esterase were detected under different concentrations of Hg. The intensity of the bands varied between treatments due to changes in total enzyme activity.
14. The metal toxicity can be heavily influenced by environmental conditions. The use of pH, carbonate and EDTA to reduce the toxicity of mercury at sub lethal concentration indicating role of these factors in reducing metal toxicity.
15. A metal’s toxicity is controlled by the concentrations of the metal free ions (available forms) and not by the metal ’s total concentration. The availability and toxicity of metals in their natural environments depend on the concentrations of the different physico-chemical forms (specification) of the metals.
16. The study tested the role of green alga Scenedesmus bijuga on phycoremediation of waste water. The data shows that the green alga Scenedesmus bijuga can be used for removal of the major inorganic elements form the wastewater.