were digested with a mixture of HNO
3
H
2
O
[21], and plant samples were digested with a mixture of HNO
3
HClO
4
2
[20]. Concentrations of As, Cd and Pb in solutions were determined using an inductively coupled plasma optical emission spectrometer (ICPOES, IRIS Intrepid II XSP, USA). Blank and standard reference materials for plant (GBW