This manuscript reports the toxic effects of As2O3 (arsenic trioxide) and As2O5 (arsenic pentoxide) on S. kali as well as the arsenic and phosphate uptake and arsenic coordination within plant tissues. Plants were germinated and grown for 15 days on a Hoagland-modified medium containing either As(III) (arsenic trioxide) or As(V) (arsenic pentoxide). Subsequently, the seedlings were measured and analyzed using inductively coupled plasma optical emission spectroscopy and X-ray absorption spectroscopy techniques. Plants stressed with 2 mg L(-1) of whichever As(III) or As(V) concentrated 245 +/- 19, 30 +/- 1, and 60 +/- 3 mg As kg(-1) dry weight or 70 +/- 6, 10 +/- 0.3, and 27 +/- 3 mg As kg(-1) dry weight in roots, stems, and leaves, respectively. Arsenate was less toxic, and more As translocation occurred from the roots to the leaves. All treatments reduced P concentration at root level; however, only As(V) at 2 and 4 mg L(-1) reduced P concentration at leaf level. Regardless the arsenic species supplied to the plants, arsenic was found in plant tissues as As(III) coordinated to three sulfur ligands with an interatomic distance of approximately 2.25 angstroms.