الفهرس 
Heavy metal pollutants and their accumulation in aquatic molluscsOnly 14 pages are availabe for public view
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Abstract
BIOCHEMICAL AND BIOLOGICAL STUDIES ON THE EFFECT OF SOME CATIONS ON THE SNAIL INTERMEDIATE HOST OF SCHISTOSOMA MANSONl Water cation pollution due to various industrial activities and animals wastes has been found to play an important role in the development and distribution of Biomphalaria alexandrina snail the intermediate host of Schistosoma mansoni in Egypt. So, the present study was designed to investigate the effect of some cations on biochemical and biological parameters of B. alexandrina snail. The biochemical parameters studied were: The accumulation levels of tested cations in the whole soft parts and different organs of snails as well as the activities of the transaminases alanine aminotransferase (ALT) and aspartate aminotransferase (AST and total protein content in snail haemolymph. The biological parameters were; the growth rate, egg laying capacity, hatchability rate of deposited eggs and the mortality rate of adult snails. In addition histological architecture of the digestive and hermaphrodite glands and the toxic levels of tested cations against snails were studied. The cations investigated were copper, cadmium, zinc, lead, calcium, sodium, Summary A 1 potassium and magnesium. The results of this study can be summarized as follows: I. THE LC50 LEVELS OF THE CATIONS UNDER INVESTIGATION AGAINST 6. ALEXANDRINA: The results obtained showed that copper, zinc, cadmium and lead were found to be the most toxic cations to snails. The LCs0 values of these cations after an exposure period of 96 hours were 0.169 pprn of Cur 1.09 pprn of Cd, 16.85 pprn of Zn and 143.83 pprn of Pb. However, the LC95 values recorded were 0.538 pprn of Cu, 6 pprn of Cd, 70.97 pprn of Zn and 427.28 pprn of Pb. Consequently, the lethal effect of the above mentioned cations after 96 hours was in the following order: Cu > Cd > Zn > Pb:On the other hand no effect was observed in calcium, sodium, potassium and magnesium up to a concentration of 500 pprn for an exposure period of 96 hours against snails. 2. THE LETHALITY OF LONG TERM EXPOSURE OF B. ALEXANDRINA SNAILS TO THE NATURE LEVEL CONCENTRATIONS OF THE CATIONS: selection of cations concentrations was based on the analysis of water samples collected from either irrigation channels or agriculture drains. It was found that the snails exposed to cadmium and lead displayed the lowest mortality rate (55.2 % and 69.2 % ) . Summary 62 Whereas, snails exposed to copper and zinc displayed the highest mortality rate (73.8 % and 76 % ) as compared with the control group (dechlorinated tap water) in which the mortality rate was 53 %. 3. THE ACCUMULATION OF THE CATIONS IN THE DIFFERENT ORGANS OF B. ALEXANDRINA SNAILS: The results obtained showed that the soft tissues of B, alexandrina was capable of accumulating lead, cadmium, zinc and copper even when exposed to concentrations as low as 0.1 ppm of lead, 0.01 ppm of cadmium, 0.055 ppm of zinc and 0.02 ppm of copper. Accumulation of lead and cadmium was essentially in the foot and their average tissue concentrations were 0.06 mg/g and 0.01 mg/g respectively. Copper was essentially accumulated in digestive gland gonads complex (DGG Complex), since its concentration was 0.078 mg/g, while zinc was found to be accumulated in other organs rather than foot and DGG complex, since its concentration in pooled soft tissues was 0.446 mg/g. 4. EFFECT OF THE CATIONS ON THE HISTOLOGY OF THE SNAIL’S HERMAPHRODITE GLAND: The results obtained showed that the histological architecture of the hermaphrodite Summarv , - gland of snails exposed to Cu, Cd, Zn and Pb cations all displayed irregular shape of acini and destruction of the mean number of oogenic cells. Mature ova were markedly decreased. Complete degeneration of the germinal epithelium and all developmental stages of gametogenesis were also observed. 5. EFFECT OF THE CATIONS ON THE HISTOLOGY OF THE SNAIL’S DIGESTIVE GLAND: The results obtained showed that the histological architecture of the digestive gland of snails exposed to Cu, Cd, Zn and Pb cations displayed similar marked degenerative changes. The digestive tubule epithelium became irregular and reduced ’ in thickness. The digestive gland tubules showed shrinked tissue displaying vaculation in the cells. The secretory cells increased in number than digestive cells. 6. THE EFFECT OF chrONIC EXPOSURE TO THE CATIONS ON THE ENZYMATIC ACTIVITIES AND TOTAL PROTEIN CONTENT OF THE HAEMOLYMPH OF 6. ALEXANDRINA . 6.1: Aspartate aminotransferase (AST): The results showed that the level of AST activity in the haemolymph of snails exposed to these cations was found to be decreased as compared with the control group. The values Summary 64 recorded in U/ ml were 33.6 f 6 for Cu, 33.9 * 13.5 for Cd, 28.8 + 8.4 for Zn, 29 + 15.3 for Pb and 39.6 + 17.1 for the control g;oup. 6.2 : Alanine aminofransferase (ALT): The results showed that the level of ALT activity in the haernolymph of snails exposed to these cations was decreased as compared with the control group. The values recorded in U/ ml were 41.1 k 32.1 for Cu, 41.4 F 30.3 for Cd, 35.1 + 21.5 for Zn, 40.2 + 35.6 for Pb and 50.3 + 43.2 for the control group. 6.3 : Total protein content: The results also showed that the total protein concentration in the haemolymph of snails exposed to these cations decreased as compared with the control group. The values recorded in mg / ml were 24.5 + 3 for Cu, 26.4 If: 4.8 for Cd, 21.5 k 2.3 for Zn, 22.9 f 2.7 for Pb and 27.3 + 6.1 for the control group. 7. THE EFFECTS OF CALCIUM ION ON THE BIOLOGICAL ACTIVITIES OF THE SNAILS: 7. I : Effect on the growth rate of snails: The results obtained showed that the growth rate of the snails exposed to different calcium concentrations increased all over of the experiment period. Summary LC 7.2 : Effect on the egg laying capacity of the snails: The results revealed that the snails exposed to different calcium concentrations showed marked increase in the mean number of egg masses and eggs number as compared with the control group. Marked increase was observed at 75 ppm and 100 ppm concentrations. 7.3: Effect on the hatchability rate of deposited egg masses of the snails: The results obtained showed that the hatchability rate of deposited eggs exposed to calcium concentrations increased compared with those maintained in dechlorinated tap water. A1 t hough there were fluctuations in hatchability rate. It followed a time and a concentration independent pattern. 7.4 : Effect on the mortality rate of the snails : It was found that the mortality rate of the treated snails increased markedly but there was no relationship between the increase of calcium concentrations and mortality rate.