Arsenic accumulation in duckweed (Spirodela polyrhiza L.): A good option for phytoremediation

Some unavoidable drawbacks of traditional technologies have made phytoremediation a promising alternative for removal of arsenic from contaminated soil and water. In the present study, the potential of an aquatic macrophyte Spirodela polyrhiza L. for phytofiltration of arsenic, and the mechanism of the arsenic uptake were investigated. The S. polyrhiza L. were grown in three test concentrations of arsenate and dimethylarsinic acid (DMAA) (i.e. 1.0, 2.0 and 4.0 μM) with 0 (control), 100 or 500 μM of phosphate. One control treatment was also set for each test concentrations of arsenic. The PO43- concentration in control treatment was 0.02 μM. When S. polyrhiza L. was cultivated hydroponically for 6 d in culture solution containing 0.02 μM phosphate and 4.0 μM arsenate or DMAA, the arsenic uptake was 0.353 ± 0.003 μmol g−1 and 7.65 ± 0.27 nmol g−1, respectively. Arsenic uptake into S. polyrhiza L. was negatively (p < 0.05) correlated with phosphate uptake when arsenate was applied to the culture solutions owing to similar in the sorption mechanism between AsO43- and PO43-, and positively (p < 0.05) correlated with iron uptake due to adsorption of AsO43- onto iron oxides. Thus, the S. polyrhiza L. accumulates arsenic by physico-chemical adsorption and via the phosphate uptake pathway when arsenate was added to the solutions. These results indicate that S. polyrhiza L. would be a good arsenic phytofiltrator. In contrast, DMAA accumulation into S. polyrhiza L. was neither affected by the phosphate concentration in the culture nor correlated (p > 0.05) with iron accumulation in plant tissues, which indicates that S. polyrhiza L. uses different mechanisms for DMAA uptake.