In the present Study, the effect of phosphate ion anti iron hydroxides (Fe-plaques) on the selective uptake of arsenic species by water fern (Salvinia natans L.) was investigated. The plants were grown for 5 days it) aqueous Murashige and Skoog (MS) culture media modified in arsenic and phosphate concentrations. Arsenic accumulations in S. natans L. increased with the increase of arsenate and DMAA concentrations in the culture solutions. Compared to the control treatment, S. natans L. accumulated significantly higher amount of arsenic from phosphate-deficient solutions, when the source was arsenate. However, arsenic uptake was not affected significantly by phosphate, when the source was dimethylarsinic acid (DMAA). From solutions containing 100 p M of phosphate and 4.0 mu M of either arsenate or DMAA, the S. natans L. accumulated 0.14 +/- 0.02 and 0.02 +/- 0.00 mu mol (g dry weight)(-1) of arsenic, respectively. In contrast, plants accumulated 0.24 +/- 0.06 and 0.03 +/- 0.00 mu mol (g dry weight)(-1) of arsenic from solutions containing 4.0 mu M of either arsenate and DMAA in phosphate deficient conditions, respectively. Thus, it is reasonable to state that increasing phosphate concentration in culture solutions decreased the arsenic uptake into the water fern significantly, when the source was arsenate. Moreover, arsenic and phosphate content in plant tissue correlated significantly (r=-0.66; p<0.05). when initial source was arsenate while there were no correlation between arsenic and phosphate, where initial source was DMAA (r=-0.077; p>0.05). Similarly, significant correlation was observed between arsenic anti iron content in plant tissues (r=0.66; p<0.05). when initial source was arsenate while the correlation was not significant (r=0.23; p<0.05), when initial source was DMAA. The results indicate the adsorption of arsenate on Fe-plagues of aquatic plant surfaces. Furthermore, the study demonstrates that the DMAA uptake mechanisms into the water fern are deferent from those of arsenate. (C) 2008 Elsevier B.V. All rights reserved.