| Summary: | Three toxicity experiments were carried out separately to study the toxicity effects of Zn, Fe and Pb on adult freshwater snail Theodoxus niloticus (Gastropod, Prosobranchia, Nertidae). The LC50 values for the 96 hr exposures of Zn, Fe and Pb on Theodoxus niloticus were 12.199, 8.6 and 18 mg/l respectively. These values increased by decreasing the time of exposure. Fe was more toxic followed by Zn and Pb to Theodoxus niloticus. The rate of mortality increased by increasing the exposure period and concentration of metals in solution. Moreover, bioconcentration of Zn, Fe and Pb in soft parts and shell increased gradually by increasing the concentrations of each metal in solutions. After 96 hr of exposure, the bioaccumulation factors for each metal were decreased from highest values in the control to the lowest one with the highest concentration of the metal. It is difficult to compare LC50 values for metals for this species with those for other gastropod species due to different abilities of closely related taxa or the species belonging to the same genus, which live in the same habitats, to accumulate metals. Keywords: Toxicity, LC50, Theodoxus niloticus, Zn, Fe, Pb
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