Metallic Mineral Elements and Heavy Metals in Medicinal Plants

A large proportion of the world’s population relies on medicines from the herbal sources. In this review, data about the mineral element content of medicinal and aromatic plants, including major elements, trace elements and toxic heavy metals, will be discussed and compared. Plants and drugs with remarkable elemental compositions will be pointed out. The main focus will be given on plants used in and originating from Europe and the Mediterranean region. The main metallic mineral macronutrients accumulate usually in the order K > Ca > Mg. The contents of beneficial trace elements decrease commonly from Fe > Mn > Zn > Cu > Ni > Mo. Higher concentrations occur in the leaves compared to other plant parts. Amongst the toxic heavy metals Cd, Pb and Hg are the best investigated. Due to its high mobility in the soil and good availability to plants, monitoring Cd merits special attention. A range of plants shows the tendency to accumulate higher concentrations of this element. For these plants, which may display problematic Cd levels, production measures should be taken to minimize the Cd accumulation, taking into consideration the growing site, planting material and fertilization regime. Interactions in the uptake between various elements have been described. The most prominent one occurs between Cd and Zn. Furthermore, it will be discussed that during the preparation of herbal tea using boiling water, only a proportion of the minerals is extracted. Finally regulations to set limits for toxic heavy metals at the national or international level are considered. _____________________________________________________________________________________________________________