Influence of Phosphate and Iron Ions in Selective Uptake

27 In the present study, the effect of phosphate ion and iron hydroxides (Fe-plaques) on the 28 selective uptake of arsenic species by water fern (Salvinia natans L.) was investigated. The 29 plants were grown for 5 days in aqueous Murashige and Skoog (MS) culture media modified in 30 arsenic and phosphate concentrations. Arsenic accumulations in Salvinia natans L. increased 31 with the increase of arsenate and DMAA concentrations in the culture solutions. Compared to 32 the control treatment, Salvinia natans L. accumulated significantly higher amount of arsenic 33 from phosphate deficient solutions, when the source was arsenate. However, arsenic uptake was 34 not affected significantly by phosphate, when the source was dimethylarsinic acid (DMAA). 35 From solutions modified in 100 μM of phosphate and 4.0 μM of either arsenate or DMAA, the 36 Salvinia natans L. accumulated 0.14±0.02 and 0.02±0.00 μmol (g dry weight) of arsenic, 37 respectively. In contrast, plants accumulated 0.24±0.06 and 0.03±0.00 μmol (g dry weight) of 38 arsenic from solutions containing 4.0 μM of either arsenate or DMAA in the absence of 39 phosphate, respectively. Thus, it is reasonable to state that increasing phosphate concentration in 40 culture solutions decreases the arsenic uptake into the water fern significantly, when the source 41 was arsenate. Moreover, arsenic and phosphate content in plant tissue correlated significantly (r 42 = -0.66; p < 0.05), when initial source was arsenate while there were no correlation between 43 arsenic and phosphate, when initial source was DMAA (r = -0.077; p > 0.05). Similarly, 44 significant correlation was observed between arsenic and iron content in plant tissues (r = 0.66; 45 p < 0.05), when initial source was arsenate while the correlation was not significant (r = 0.23; p 46 < 0.05), when initial source was DMAA. The results indicate the adsorption of arsenate on Fe47 plaques of aquatic plant surfaces. Further, the study demonstrates that the DMAA uptake 48 mechanisms into the water fern are deferent from those of arsenate. 49 50 51 52