The accumulation and the effect of heavy metals on the water fern Azolla filiculoides

Azolla filiculoides Lamarck grown for 3‐7 days in nutrient media containing 8‐15 ppm of different heavy metals was found to contain about 10000 ppm cadmium, 1990 ppm chromium, 9000 ppm copper, 9000 ppm nickel and 6500 ppm zinc. The content of heavy metal in the roots was two‐ to five‐fold higher than in the shoots, and 98% of the heavy metals were bound to the insoluble fraction of the Azolla. The content of heavy metals in dead dried Azolla was 3–7 times higher than in the living plants. Zinc and cadmium were more readily transferred from the roots to the shoots than nickel, copper and chromium. Growth in the presence of the heavy metals resulted in severe leakage of K⁺, Mg²⁺ and Na⁺ ions from the roots with less leakage of Ca²⁺. The effect of heavy metals on the loss of K⁺, Na⁺ and Mg²⁺ from the shoots was more limited. Nitrogenase activity was almost completely inhibited by cadmium, nickel and zinc, while copper and chromium had less effect. Azolla may prove useful in the detoxification of industrial effluents.