Contamination of medicinal plants with heavy metals and its allowable level

-Contamination of soils and waters, and consequently plants, with heavy metals is one of the most important environmental issues. If these plants are medicinal plants, the excess amounts of metal ions threaten human health. Numerous reports indicate the contamination of medicinal and aromatic plants and the high potential of these plants in the absorption of heavy metals, their transfer to the food sector and even its entry into herbal medicines. Contamination of medicinal plants and by-products with heavy metals during the growing season, processing of crops or intentional addition of plant products in traditional medicine of India and China by claiming their healing properties. Since the use of medicinal plants in the treatment of many diseases is considered and it is mainly believed that medicinal plants do not have side effects due to their natural origin, so medicinal plants and their products should be free of heavy toxic metals. Therefore, the World Health Organization (WHO) has emphasized that plants with medicinal and therapeutic functions must be tested to confirm the presence of heavy metals. Since it is not possible to completely remove heavy metals in plant products, it is necessary to define a permissible limit of heavy and toxic metals. In this paper, the reaction of medicinal plants to heavy metals, the allowable limit of heavy metals according to the standards of the World Health Organization and pharmacies of different countries, and the tolerable weekly consumption of heavy metals are presented.