**5. Conclusions**

The total element contents and the bioavailable fraction of essential elements Ca, Mg, Zn, Mn, and Fe were determined in leaves of *Sempervivum tectorum* L. The control of the quality of medicinal plants used in traditional medicine and pharmacy is an important step for consumer protection from contamination and health risks. The determination of toxic element content in plants grown on different soils clearly shows the contamination of plants from urban soils and plants fertilized with phosphate fertilizers. The high bioavailable concentrations of essential elements could explain the wide use of this plant in folk medicine. For example, the high Mg content in fresh juice is responsible for its anti-inflammatory action and application as an ear pain reliever.

**Author Contributions:** K.N. constructed and conceived the project. G.G. and I.K. designed the study. P.R., S.M., Y.S. and I.Y. performed the study. V.A. and Y.S. analyzed the data. G.G. and I.K. wrote the newspaper. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Bulgarian Ministry of Education and Science under the National Research Programme "Healthy Foods for a Strong Bio-Economy and Quality of Life" approved by DCM # 577/17.08.2018.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Datasets from the time of this study are available from the respective author upon reasonable request.

**Acknowledgments:** Special thanks to Medical University–Varna for the provided financial support for paper publication.

**Conflicts of Interest:** The authors declare no conflict of interest.
