Toxic effect of Pb, Cd, Ni and Zn on Azolla filiculoides in the International Anzali Wetland

The limitation of plant growth in the polluted mediums can be used as a factor to determine of plant tolerance and the toxic effect of these mediums. In this work, the effect of Pb²⁺, Cd²⁺, Ni²⁺and Znsu2+ (individually) on Azolla filiculoides growth in the aqueous solution and using this method to water post treatment were studied. During 15 days the biomass the fresh Azolla with initial mass of 20 g was grown on the nutrient solution containing these metal ions, each in a concentration 4 mg/l. The presence of these ions, caused about 25%, 42%, 31% and 17% inhibition of biomass growth, respectively, in comparison to Azolla control weight which had not heavy metals. The water salinity of 1, 2 and 4 g. NaCl/l decreased the removal of these heavy metals about 4–7%, 20–24% and 40–55%, respectively. The addition of total dissolved solids (TDS) from 50 to 300 ppm. (as CaCO₃) into the samples of containing heavy metals increased Azolla growth, but decreased the control Azolla growth.