For ICP-MS method, 0.003g (+-0.001g) dried samples of plants were thansferred to a Teflon vessel, digested with 6ml of concentrated ultrapure nitric acid (65%) and 2 ml of ultrapure hydrogen peroxide(30%). Decomposition of the samples was carried out in a microwave digestion system (Milestone Srl, Ethos One, ltaly). A one-step microwave program, ramping for 15 min up to 200 °C at 1000W, was applied to the samples. The undissolved parts were separated with 25 mm polyethylene syringe filters(Millex,Merck KGaA,Germany)