Analysis of Mercury Content in Medicinal Plants Popular in Poland

The use of herbal medicinal products and dietary supplements has increased significantly in recent years. Insufficient knowledge regarding the effects of herbal raw materials, as well as their potential adverse effects and interactions with medications and food, poses a considerable risk in therapies involving these products. Furthermore, contamination with heavy metals, including mercury, may constitute an additional health hazard. The aim of this study was to determine the mercury (Hg) content in wild-growing herbal raw materials collected independently and in commercial products, namely herbal teas derived from the same plant species under investigation. The measured Hg levels were compared with the limits established by the applicable standard set out in Commission Regulation (EU) 2018/73. For the study, five medicinal plant species commonly used in Poland were selected: wild rose (Rosa canina L.), common hawthorn (Crataegus monogyna L.), dandelion (Taraxacum officinale), common nettle (Urtica dioica L.) and silver birch (Betula pendula). The determination of Hg concentrations was carried out using an AMA 254 (Altec, Prague, Czech Republic) atomic absorption spectrometer. The arithmetic mean Hg concentration across all analyzed samples was 18.68 µg/kg, with values ranging from 0.19 to 202.83 µg/kg. The highest median Hg concentrations were found in common nettle (23.80 µg/kg), followed by dandelion (13.00 µg/kg) and silver birch (12.68 µg/kg). Considerably lower concentrations were observed in common hawthorn (5.91 µg/kg) and wild rose (0.61 µg/kg). Statistically significant differences in Hg content were detected among the studied plant species (p < 0.001). With regard to individual morphological plant parts, the highest accumulation of Hg was observed in roots, followed by herbs, leaves, and buds. Among all analyzed samples, 32% exceeded the permissible Hg limit, with the majority of these being self-collected samples. Self-collection of medicinal plant materials, including common nettle (Urtica dioica), dandelion (Taraxacum officinale), and silver birch (Betula pendula), may pose a risk associated with Hg contamination. Given the continuously increasing demand for and market value of herbal medicines, ensuring the safety, quality, and efficacy of medicinal plants and herbal products is of great importance. Therefore, regular monitoring of toxic element levels in plant materials used in phytotherapy is justified and essential.