Arsenic and antimony bioremediation by Phragmites australis: Rhizofiltration technology

Background/Question/Methods: Arsenic (As) and Antimony (Sb) are toxic heavy metals that are often present as contaminants in the environment. High As concentration is reported in Kohsorkh, Khorasan province, northeast Iran, making it an ideal area for investigation of techniques for decontamination of these two heavy metals. As and Sb in this naturally polluted area is derived from weathering and alteration of rocks and leach into ground and surface water. The current study examines the possibility of utilizing the common reed, Phragmites australis for rhizofiltration of As and Sb by measuring the concentration of these heavy metals in samples collected from the Kohsorkh area. Phragmites australis plants were collected from five sampling sites of Kohsorkh area. Control plants collected from non contaminated area. As, Sb, phosphorus and iron concentrations in roots and shoots were determined by atomic absorption spectrometry.  The catalase, ascorbate peroxidase and guaicol peroxidase activity was also measured in the samples. Results/Conclusions: Our results show that about 80% of total As in the plant is accumulated in the roots of the plant. Maximum As and Sb accumulation in root and rhizomes were 84.5-16.20 ppb and 73-10.20 ppb respectively. As/Sb ratio of root and rhizome ranged from 35 to 194 and 10.42 to 99.9 respectively. The Arsenic contents in roots of contaminated plants were significantly higher than antimony accumulation (P<0.01). The phosphorus contents of contaminated root system (root and rhizomes) was significantly lower in comparison to control plants (P<0.05). In comparison, iron accumulation in root system of contaminated plants was significantly higher than control plants. We speculate an antagonistic interaction between As, Sb with P contents in the roots of contaminated plants. Similarly, the increased iron content may provide a protective mechanism for the plants against toxicity from the heavy metals.  The enzymatic antioxidant (Catalase, Ascorbate peroxidase and Guaicol peroxidase) activity increased significantly with increment of As uptake in root system. This increased activity makes the plants more tolerant to harmful effects of reactive oxygen species that are known to be induced by arsenic. Root As and Sb accumulation with enhanced changes in metabolic changes indicates that P. australis could be used as As, Sb rhizofiltration agent in this region and similar contaminated area all over the world. Antioxidant enzymatic activity, iron and phosphorus content may play role in the mechanism of rhizofiltration.

Keywords: Arsenic, Antimony, bioremediation, rhizofiltration, Phragmites australi