Medicinal plants are widely used in the Kingdom of Saudi Arabia to treat various ailments in the form of folk medicine. Forty four such medicinal plant samples were collected from local markets and evaluated for the presence of 14 elements (Mn, Cr, Co, Ni, Cu, Mo, Al, Pb, Ba, Zn, Ag, Hg, Bi, Cd). Microwave-assisted digestion with inductively coupled plasma-mass spectrometry (ICP-MS) was applied to determine the elemental composition in these medicinal plants. Widespread occurrence of these elements was observed in all plant samples, except for Bi and Co where the lowest mean values of 0.03 ± 0.04 and 0.03 ± 0.15 were observed, respectively. The descending order for mean (μg/g) elemental occurrence observed was as follows: Ba > Al > Zn > Ni > Mn > Ba > Hg > Mo > Cu > Cr > Ag > Cd > Co > Bi, whereas the range for these elements in the 44-medicinal plants was as follows: Pb > Al > Zn > Ni > Mn > Cu > Mo > Ag > Ba > Hg > Co > Cd > Cr > Bi. Pb, Hg and Cd were found beyond the maximum limits in these medicinal plants, while the remaining elements were found well within the range of maximum limits. A number of medicinal plants showed high amounts of these elements. Some plants contained more than one element, such as Foeniculum vulgare Mill (Pb, Hg, Cd), Ricinus communis (Pb, Cd), Vigna radiata (Pb, Cd) and Sesamum indicum (Pb, Hg). The data matrix was validated through the statistical tools of principal component analysis (X2 = 160.44, P = .00), Pearson's correlation (P = .01 and 0.05), and K-mean cluster analysis (F = 104.55, P = .00). The findings of the study provide baseline data for the comparative analysis of these medicinal plants, which may help select safe medicinal plants in terms of consumer-based use and its utilisation for the treatment of various ailments.
Keywords: ICP-MS; K-mean analysis; Microwave digestion; Saudi plants; heavy metals.