Assessment of Trace and Macro Elements in Medicinal Plants: Implications for Safety and Phytoremediation

The utilization of medicinal plants in Iran and other parts of the world is increasing, and there is a need to study the levels of macro and trace elements, including toxic elements, in medicinal plants. This study analyzed trace and macro elements in 42 medicinal plant samples from a medicinal plant garden in Hamadan city, western Iran. The average trace element contents (mg kg^-1 dry weight) in the aerial parts were 1.29 mg kg^-1 for Cd, 10.5 mg kg^-1 for Cu, 75.5 mg kg^-1 for Fe, 41.3 mg kg^-1 for Mn, 3.22 mg kg^-1 for Ni, and 19.7 mg kg^-1 for Zn. Iron was highest in Origanum majorana (96.7 mg kg^-1), while Cd was lowest in Inula helenium (0.85 mg kg^-1). For macro elements, the highest values were Ca in Urtica dioica (27,800 mg kg^-1), K in Echium amoenum (34,600 mg kg^-1), Mg in Verbascum thapsus (9080 mg kg^-1), and Na in Borago officinalis (10,500 mg kg^-1). Relative to adult RDAs, Marrubium vulgare is a key source of Ca (64%) and K (22%), Achillea millefolium provides Mg (98%), Fe (54%), and Mn (97%), and Matricaria chamomilla contributes Cu (86%). The bioaccumulation factor (BCF) averaged 0.68 for Cd, 0.27 for Cu, 0.005 for Fe, 0.26 for Mn, 0.05 for Ni, and 0.44 for Zn, with the highest BCF for Cd (0.92 in Urtica dioica) and lowest for Fe (0.0031 in Marrubium vulgare). The Alcea kurdica, Plantago major, and Urtica dioica may be considered in phytoremediation due to the higher Cd and Ni accumulation. Among studied trace elements, Cd had the highest hazard quotient. This study highlights both the nutritional benefits and safety hazards linked to medicinal plants and proposes some medicinal plants for possible phytoremediation of contaminated soils.