Influence of EDTA and chemical species on arsenic accumulation in Spirodela polyrhiza L. (duckweed).

The influence of ethylenediaminetetraacetic acid (EDTA) and chemical species on arsenic accumulation in aquatic floating macrophyte Spirodela polyrhiza L. (duckweed) was investigated. The uptake of inorganic arsenic species (arsenate; As(V) and arsenite; As(III)) into the plant tissue and their adsorption on iron plaque of plant surfaces were significantly (p<0.05) higher than those of organic species (monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA)). The addition of EDTA to the culture media increased the uptake of As(V) and As(III) into the plant tissue though the MMAA and DMAA uptake were not affected. About 4-6% of the inorganic arsenic species were desorbed or mobilized from iron plaque by EDTA. Desorption of organic arsenic species was not affected by EDTA addition because the co-precipitation occurs only with inorganic species. Phosphate uptake was not affected by EDTA though its concentration in citrate-bicarbonate-EDTA (CBE)-extract was much higher than that of plant tissue. Iron uptake into the plant increased significantly (p>0.05) by EDTA addition to the culture media while its concentration in CBE-extract decreased significantly (p<0.05). The As(inorganic)/Fe ratios in plant were higher than those of CBE-extract which indicate the increased uptake of these arsenic species into the plant relative to the iron. The lower As(organic)/Fe ratios in plant and on CBE-extract suggest the reduction of accumulation of these arsenic species relative to the iron.