Heavy metal pollution in Iranian medicinal plants, a review of sources, distribution, and health implications

Environmental pollution, particularly with heavy metals, is a critical issue in assessing the quality of medicinal plants. The concentration of heavy metals in these plants depends on factors such as growth environment, species, and processing methods. Contaminants absorbed by plants can enter the human body through consumption. This review examines the impact of heavy metals—cadmium (Cd), lead (Pb), arsenic (As), copper (Cu), chromium (Cr), zinc (Zn), and nickel (Ni)—on medicinal plants in Iran. It explores how environmental contamination affects plant quality and analyzes trends in measurement techniques and metal concentrations over time. Results show that Cd has the most significant negative impact on plant growth (63 %), followed by Pb (21 %), Cr (11 %), and Zn (5 %). Cd exceeded WHO limits in 47 % of samples, while Pb and Zn exceeded limits in 26 % and 20 %, respectively. Cd and Pb also significantly reduced germination rates. Contamination with Cd and Pb poses serious health risks, including kidney damage, bone disorders, cancer, neurological issues, and reproductive harm. Strict quality control, sustainable farming, and public awareness are essential to mitigate these risks. This study highlights the need for further research, particularly in industrial regions like Tehran, Khuzestan, Isfahan, and Fars, to ensure the safety of medicinal plants.