Bioconcentration of Cr and Zn in Azolla filiculoides in Anzali Lagoon

Azolla filiculoides Lam. a small aquatic and planktonic fern, is found floating on the surface of canals, lakes, wetlands and ponds. Azolla can be used as a bio-filter in the entrance pathway of industrial waste materials to wetlands and rivers, to absorb and remove heavy metals. This research was done in the summer (hot season) and the winter (cold season) of 2011-2012, in three stations Pesikhan (Eastern region), Siah Darvishan (Central region) and Siah Kashim and Abkenr (Western region), in Anzali lagoon. Roots and leaves of sampled Azolla were separated and after digestion, the concentration of chromium and zinc, in mg/kg of the dry weight, was measured using electrothermal atomic absorption. Results showed that the concentrations of zinc and chromium in the east of Anzali Lagoon were higher than the west and central regions. Average concentrations of zinc and chromium in the eastern section of the lagoon were (62/84 ±3/13, 3/14 ± 1/07), in the west (27/64 ±22/03, 1/3 ± 1/1) and in the center (29/97 ±23/3, 2/33 ±1/8) ppm, respectively. The highest contamination was noticed in the eastern area, then central, and finally in the western region of Anzali Lagoon. Results showed that in all regions of Anzali Lagoon, concentration of Cr and Zn were significantly higher in roots in comparison to leaves of Azolla (P<0.05). Also, in summer there were higher levels of heavy metals in roots and leaves than in winter. In present research, there were a positive correlation between concentration of heavy metals and temperature, but there was no correlation with other parameters. According to the results, the mean concentration ​​ of chromium (2.25 ppm) in Azolla was significantly higher than the permissible limit of chromium for plants (1.30mg/kg), recommended by WHO, while zinc (40.15 ppm) was lower than WHO’s recommended limit for zinc in plants (50 mg/kg).