Determination of the Elements Composition in Sempervivum tectorum L. from Bulgaria

Abstract

Sempervivumtectorum L. is an evergreen plant with fleshy blue-green leaves forming a rosette. The plant is well-known in alternative medicine and has been used for thousands of years. Traditionally for medicinal purposes, the plant is used as a juice obtained by simple squeezing of fresh plants leaves. The total content of Ca, K, Na, Mg, Mn, Fe, Zn, Cu, Co, Al, V, Cr, Ni, Mo, Ba, Pb, Cd, Hg, As, and Tl in plant leaves of Sempervivum tectorum L. sampled from different habitats in Bulgaria was determined after microwave digestion and measurements by inductively coupled plasma mass spectrometry and flame atomic absorption spectrometry. Furthermore, the bioavailable fraction of essential elements Ca, Mg, Fe, Mn, and Zn was defined after extraction with a hydrochloric acid solution, mimicking stomach juice. The total element content showed a high bioavailability of essential human health elements, such as Ca, Mg, Fe, and Zn. Additionally, essential and toxic elements concentrations were quantified in a fresh juice, obtained by squeezing from plant leaves, as most frequently used in folk medicine. The results obtained demonstrated high concentrations of K, Mg, Ca, Zn, and Cu, which could be accepted as an explanation and a further confirmation of the anti-inflammatory action of this plant.

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horticulturae
Article
Determination of the Elements Composition in Sempervivum
tectorum L. from Bulgaria
Galia Gentscheva 1,2, Irina Karadjova 3, Poli Radusheva 4, Stefka Minkova 4, Krastena Nikolova 4, *,
Yoana Sotirova 5, Ina Yotkovska 1and Velichka Andonova 5,*


Citation: Gentscheva, G.; Karadjova,
I.; Radusheva, P.; Minkova, S.;
Nikolova, K.; Sotirova, Y.; Yotkovska,
I.; Andonova, V. Determination of the
Elements Composition in
Sempervivum tectorum L. from
Bulgaria. Horticulturae 2021,7, 306.
https://doi.org/10.3390/
horticulturae7090306
Academic Editors: Dasha Mihaylova
and Aneta Popova
Received: 12 August 2021
Accepted: 9 September 2021
Published: 12 September 2021
Publisher’s Note: MDPI stays neutral
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Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
1Department of Chemistry and Biochemistry, Medical University of Pleven, 5800 Pleven, Bulgaria;
gentscheva@mu-pleven.bg (G.G.); ina.iotkovska@mu-pleven.bg (I.Y.)
2Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
3Faculty of Chemistry and Pharmacy, University of Sofia, 1164 Sofia, Bulgaria; Karadjova@chem.uni-sofia.bg
4Department of Physics and Biophysics, Medical University of Varna, 9000 Varna, Bulgaria;
radusheva@mu-varna.bg (P.R.); stefka.minkova@yahoo.com (S.M.)
5Department of Pharmaceutical Technologies, Medical University of Varna, 9000 Varna, Bulgaria;
Yoana.Sotirova@mu-varna.bg
*Correspondence: kr.nikolova@abv.bg (K.N.); velichka.andonova@mu-varna.bg (V.A.);
Tel.: +35-988-860-3272 (K.N.); +35-989-783-2753 (V.A.)
Abstract:
Sempervivum tectorum L. is an evergreen plant with fleshy blue-green leaves forming a
rosette. The plant is well-known in alternative medicine and has been used for thousands of years.
Traditionally for medicinal purposes, the plant is used as a juice obtained by simple squeezing of
fresh plants leaves. The total content of Ca, K, Na, Mg, Mn, Fe, Zn, Cu, Co, Al, V, Cr, Ni, Mo, Ba,
Pb, Cd, Hg, As, and Tl in plant leaves of Sempervivum tectorum L. sampled from different habitats
in Bulgaria was determined after microwave digestion and measurements by inductively coupled
plasma mass spectrometry and flame atomic absorption spectrometry. Furthermore, the bioavailable
fraction of essential elements Ca, Mg, Fe, Mn, and Zn was defined after extraction with a hydrochloric
acid solution, mimicking stomach juice. The total element content showed a high bioavailability
of essential human health elements, such as Ca, Mg, Fe, and Zn. Additionally, essential and toxic
elements concentrations were quantified in a fresh juice, obtained by squeezing from plant leaves, as
most frequently used in folk medicine. The results obtained demonstrated high concentrations of K,
Mg, Ca, Zn, and Cu, which could be accepted as an explanation and a further confirmation of the
anti-inflammatory action of this plant.
Keywords: Sempervivum tectorum L.; mineral content; bioavailable fraction; heavy metals
1. Introduction
There are over 3000 plant species in Bulgaria, of which more than 600 are used for
medicinal purposes. Bulgarian herbs contain a high percentage of biologically active sub-
stances [
1
]. They are rich in various chemical compounds: alkaloids, glycosides, saponins,
polysaccharides, tannins, flavonoids, coumarins, essential oils, vitamins, and trace elements.
The pharmacological and medicinal action and application of Bulgarian herbs has been an
important topic and subject of many studies. One of the most outstanding achievements
of the Bulgarian pharmaceutical industry was the creation of the medicinal preparation
“Nivalin” by Prof. D. Paskov. The active substance of which is the alkaloid galantamine,
extracted from Leucojum aestivum L. [
2
]. Most of the achievements of contemporary medical
science are based on bioactive compounds extracted from medicinal plants [3].
Sempervivum tectorum L. (synonym: Sempervivum tectorum var. arvernense (Lecoq &
Lamotte) Zonn., Sempervivum tectorum var. andreanum (Wale) O.Bolòs & Vigo) belongs to
a large family of Crassulaceae with crassulacean acid metabolism, native to the mountains
of southern Europe and cultivated in the whole of Europe.
Horticulturae 2021,7, 306. https://doi.org/10.3390/horticulturae7090306 https://www.mdpi.com/journal/horticulturae

Horticulturae 2021,7, 306 2 of 9
Sempervivum tectorum L. (houseleek) is an evergreen plant with fleshy blue-green
leaves forming a rosette, which grows on dry to fresh sandy soils and in sunny to semi-
sunny places. The plant is well-known in folk medicine and has been used for thousands
of years.
In recent years, researchers have focused on studies of the characterization of the
bioactive ingredients of this plant and their ability to restore liver function [
4
], their an-
tioxidant properties [
5
], the potential for wound healing [
6
], anti-inflammatory action,
and analgesic and detoxicating properties [
7
–
9
]. Most of these properties of Sempervivum
tectorum L. are connected with phenolic compounds identified in fresh juices squeezed
from plant leaves [
10
,
11
]. However, according to the author’s knowledge, despite of the nu-
merous uses of Sempervivum tectorum L. in folk medicine, it remains poorly known from the
viewpoint of systematic investigations into trace element content, element bioavailability,
and correlation between essential element content and antioxidant activity.
The trace element content is an essential characteristic of any plant. However, there
are no such data for Sempervivum tectorum L., neither for environmental safety, nor the effect
on human health. The objective of this study was to investigate the level of the elements Ca,
K, Na, Mg, Mn, Fe, Zn, Cu, Co, Al, V, Cr, Ni, Mo, Ba. Pb, Cd, Hg, and As as a total content
in plant samples of Sempervivum tectorum L. obtained from different sampling sites; natural
and affected at different levels by human activities. The urban soil (A) is from an urban
park close to center of the city, and the fertilized soil (C) is from land used for agriculture
purposes for many years. The rural soil (B) and mountain soil (D) might be accepted as
natural; however, with varying composition. The bioavailable fraction of essential elements
Ca, Mg, Fe, Mn, and Zn, defined according to a standard procedure for element migration
in hydrochloric acid that mimics food digestion processes in the stomach, was quantified.
Additionally, K, Ca, Mg, Na, Fe, Mn, Zn, Al, Cu, and Cr were determined in the freshly
squeezed juice from plant leaves, as directly used in folk medicine against ear pain.
2. Materials and Methods
Plant Material.S. tectorum plants were from different habitats, grown on city soils
(A), village soils (B), fertilized soils (C), and mountain soils (D). The leaves of the plants
were removed, thoroughly washed with deionized water to remove all possible external
contaminants, and used immediately for:
(i).
the preparation of fresh juice after squeezing;
(ii). the preparation of a fresh homogeneous sample mix after milling for the determination
of bioavailable fraction;
(iii).
the preparation of dry mass after oven drying to a constant weight at 40
◦
C and
homogenization by careful grinding.
Sample preparation before analysis:
Reagents: 67% HNO
3
(supra pure, Merck, Darmstadt Germany); 30% H
2
O
2
(supra
pure, Merck, Darmstadt Germany); 37% HCl (p.a. Sigma-Aldrich, Darmstadt Germany).
2.1. Determination of Total Content of Elements
A dry sample of around 0.5 g was weighed in Teflon vessels of a microwave digestion
system, 6 mL 67% HNO
3
and 2 mL 30% H
2
O
2
were added, and samples were left overnight.
Microwave digestion was performed for 20 min: 10 min to reach 180
◦
C and 10 min
maintained at this temperature. After cooling, samples were transferred to a 50 mL
volumetric flask and diluted up to the mark with deionized water. A blank sample was
passed through the whole analytical procedure.
2.2. Determination of Bioavailable Fraction in Fresh Leaves
A sample of 2.0 g of fresh leaves was milled with 50 mL deionized water in a plastic
container. After that, 50 mL 0.14 mol L
−1
HCl were added, and the mixture was shaken
for at least 1 min. The suspension was left for several minutes to settle, and the pH of
the clear supernatant was measured. If the pH was above 1.5, 2 mol L
−1
HCl solution

Horticulturae 2021,7, 306 3 of 9
was added drop-wise while mixing until the pH reached values between 1.0 and 1.5. The
container was closed and agitated at 37
±
2
◦
C for 1 h. After that, the suspension was left
for a further 1 h at 37
±
2
◦
C. The mixture was protected from daylight. The solid matter
was separated by centrifugation and, if necessary, filtrated through a membrane filter
(0.22
µ
m) to remove all solid particles. The separation should be completed as soon as
possible after completing the standing time; centrifuging should take no longer than
10 min. Next, the obtained solution was evaporated on a hot plate to 2–3 mL, 3 mL of conc.
HNO
3
was added for digestion of the organic components, and, finally, the sample was
quantitatively transferred to a 25 mL flask and made up with deionized water [12].
2.3. Determination of Elements in Juice Obtained by Squeezing of Fresh Leaves
A sample of 2.0 g juice (obtained after filtration of fresh juice through a 0.22
µ
m
membrane filter) was transferred in a glass beaker and treated with 1 mL 67% HNO
3
on a
hot plate. After 1 h, the solution was cooled and diluted in a 10 mL volumetric flask with
distilled water.
Apparatus for quantitative measurement of chemical elements:
Flame atomic absorption spectrometry: The content of Fe, K, Mn, Mg, Na, and Zn
was measured by flame atomic absorption spectrometry (Thermo Electron—SOLAAR Mkll
M5 series, UK) in an air/acetylene flame under optimized instrumental parameters. The
content of Ca was measured in N
2
O/acetylene flame, using the same instrument. Stock
standard solutions of Ca, Fe, K, Mn, Mg, Na, and Zn (1.000 g L
−1
(Merck)) were used for
the preparation of diluted working standards.
Inductively coupled plasma mass spectrometry: The content of As, Al, Ba, Cd, Co, Cr,
Cu, Hg, Mo, Ni, Pb, and V was measured by ICP-MS using an inductively coupled plasma
mass spectrometer “X SERIES 2”—Thermo Scientific, USA with a 3 channel peristaltic
pump; concentric nebulizer; Peltier-cooled spray chamber (4
◦
C); Xt interface option; Ni
cones. Optimized instrumental parameters: forward plasma power of 1400 W; plasma gas
flow 13 L min/L; nebulizer flow 0.85 L/min; dwell time 30 ms; measurements 3
×
30 scans.
Stock standard solutions: multielement standard solution 5 for ICP (TraceCERT
®
, Merck),
1000 mg/L As (Fluka, Sigma-Aldrich) and 1000 mg/L Hg (Fluka, Sigma-Aldrich) were
used for the preparation of diluted working standard solutions for calibration of ICP-MS.
The accuracy of the analytical procedure used was validated by the analysis of certified
reference material NIST SRM 1573a Tomato leaves. The very good agreement with the
certified values and the recoveries above 95% achieved for all certified elements confirmed
the reliability of the results obtained for total element contents (see Table 1). Limit of
detection and limit of quantification was calculated for each element based on standard
deviation of blanks sample for the respective procedures using 3
σ
criterium (LOD) and
10 σcriterium (LOQ). Calculated values for LOD and LOQ are presented in Table 1.
2.4. Statistical Analysis
Data for the concentrations of chemical elements were processed to obtain the mean
and standard deviation of the mean (SD). One-way analysis of variance, followed by a
Student’s t-test was used to compare the mean values. A value of p< 0.05 was considered
to be statistically significant.

Horticulturae 2021,7, 306 4 of 9
Table 1.
Results and recoveries for chemical element contents (mg/kg) determined in NIST SRM
1573a Tomato leaves (three parallel determinations).
Element,
mg/kg
Determined
(Mean ±sd)
Certified
(Mean ±sd)
Recovery, %
(Mean)
LOQ/LOD,
mg/kg
Al (ICP-MS) 594 ±4 598.4 ±7.1 99.3 0.10/0.35
As (ICP-MS) 0.1088 ±0.056 0.1126 ±0.0024 96.6 0.02/0.06
Cd (ICP-MS) 1.456 ±0.016 1.517 ±0.027 96 0.02/0.05
Ca (FAAS) 49,441 ±342 50,450 ±550 98 2/6
Cr (ICP-MS) 1.92 ±0.04 1.988 ±0.034 96.6 0.05/0.15
Co (ICP-MS) 0.5588 ±0.021 0.5773 ±0.0071 96.8 0.02/0.06
Cu (ICP-MS) 4.56 ±0.11 4.70 ±0.14 97 0.1/0.3
Fe (FAAS) 363.8 ±2.1 367.5 ±4.3 99 3/10
Mn (FAAS) 243.8 ±9.3 246.3 ±7.1 99 3/10
Hg (ICP-MS) 0.0329 ±0.0043 0.0341 ±0.0015 96.5 0.02/0.06
Ni (ICP-MS) 1.536 ±0.031 1.582 ±0.041 97.1 0.02/0.05
K (FAAS) 26,490 ±312 26,760 ±480 99 5/15
Na (FAAS) 134.3 ±2.5 136.1 ±3.7 98,7 5/15
V (ICP-MS) 0.809 ±0.042 0.835 ±0.034 96.9 0.02/0.06
Zn (FAAS) 30.02 ±0.56 30.94 ±0.55 97 1/3
3. Results
The profile of chemical elements in plants depends on the geochemical characteristics
of the soil [
13
] and on the ability of plants to selectively accumulate minerals essential for
their growth. For given plants, the content of mineral and trace elements is characteristic
and will be affected by different factors, such as the physical and chemical properties
of the soil, application of natural and artificial fertilizers, and climatic conditions of the
region. The results obtained for the total content of elements in Sempervivum tectorum L. are
presented in Tables 2–4.
Table 2. Essential (basic) element contents in dry samples.
K
g kg−1
Ca
g kg−1
Mg
g kg−1
Na
mg kg−1
Fe
mg kg−1
Mn
mg kg−1
Zn
mg kg−1
city soils (A), number of plant samples-4
mean 18.0 107 10.6 93.6 325 35.4 49.2
min 9.36 102 4.39 16.4 188 13.9 45.1
max 29.9 115 12.3 234.9 398 65.4 51.7
village soils (B), number of plant samples-5
mean 11.1 116 11.6 206 384 30.7 79.0
min 7.59 84.7 7.71 176 328 17.4 42.2
max 12.9 132 18.2 230 491 50.9 135
fertilized soils (C), number of plant samples-4
mean 26.3 66.2 5.97 74.4 358 273 30.5
min 10.7 60.7 3.4 67.2 243 102 26.7
max 31.4 103 7.81 112 427 283 44.8
mountain soils (D), number of plant samples-4
mean 15.7 61.0 5.68 125 247 12.1 29.2
min 7.21 57.3 3.84 102 197 10.5 25.5
max 21.3 85.1 10.5 131 343 18.4 37.8

Horticulturae 2021,7, 306 5 of 9
Table 3. The content (mg/kg) of non-essential elements in dry samples.
Al
mg kg−1
Co
mg kg−1
Cu
mg kg−1
Ba
mg kg−1
Mo
mg kg−1
V
mg kg−1
Cr
mg kg−1
A
mean 23.3 0.46 7.91 51.0 0.86 <0.02 0.42
min 17.0 0.32 5.63 48.5 <0.02 * <0.02 0.37
max 32.6 0.56 11.0 53.9 2.53 <0.02 0.45
B
mean 61.1 0.39 8.12 65.4 1.96 0.10 0.63
min 38.5 0.35 5.33 50.6 <0.02 <0.02 0.49
max 99.6 0.47 10.7 74.0 5.62 0.23 0.90
C
mean 257.6 2.13 9.14 145.8 <0.02 0.05 0.76
min 94.5 1.12 7.43 85.3 <0.02 <0.02 0.37
max 301.2 2.54 12.32 153.2 <0.02 0.17 0.94
D
mean 18.5 0.24 7.32 38.7 <0.02 <0.02 0.38
min 13.4 0.05 4.91 29.5 <0.02 <0.02 0.23
max 21.3 0.32 8.94 50.4 <0.02 <0.02 0.42
* Limit of detection.
Table 4. The total content (mg/kg) of toxic elements (Cd, Pb, As, Hg, and Ni) in dry samples.
Cd
mg kg−1
Pb
mg kg−1
As
mg kg−1
Hg
mg kg−1
Ni
mg kg−1
A
mean 0.27 2.66 0.14 0.05 2.03
min 0.17 1.56 <0.02 <0.02 1.32
max 0.46 3.99 0.36 0.10 2.38
B
mean 0.23 1.05 0.05 0.03 2.40
min <0.02 0.63 0.03 <0.02 2.19
max 0.26 1.42 0.09 0.05 2.73
C
mean 0.10 3.18 0.07 0.03 4.51
min <0.02 1.43 <0.02 <0.02 1.29
max 0.27 4.02 0.12 0.05 4.78
D
mean <0.02 1.29 0.08 0.02 0.89
min <0.02 0.54 <0.02 <0.02 0.32
max <0.02 1.78 0.11 0.05 1.15
The bioavailable content of Ca, Mg, Zn, Mn, and Fe in fresh leaves of Sempervivum
tectorum L. is depicted in Table 5.
The concentrations of elements in juice obtained from fresh leaves are presented in
Table 6.

Horticulturae 2021,7, 306 6 of 9
Table 5.
Bioavailable content of Ca, Mg, Zn, Mn, and Fe in fresh leaves of Sempervivum tectorum L. as
a mean values (RSD for all samples varied between 3–8%).
Ca
g kg−1
Mg
g kg−1
Zn
mg kg−1
Mn
mg kg−1
Fe
mg kg−1
B5.07 0.40 3.55 1.97 16.5
C2.95 0.44 3.58 9.02 20.0
D3.16 0.37 2.37 1.71 12.3
Table 6. Element concentrations (mg/L) in fresh juice from Sempervivum tectorum L.
Elements A Elements A
K, mg L−1133 Na, mg L−10.7
Ca, mg L−1561 Zn, mg L−11.95
Mg, mg L−12845 Al, mg L−13.45
Fe, mg L−10.07 Cu, mg L−10.28
Mn, mg L−12.40 Cr, mg L−10.29
4. Discussion
As seen from Table 1,Sempervivum tectorum L. contains an extremely high calcium
content, exceeding by between 3–10 times the concentrations of the second highest content
element, K. No statistically significant differences were found for the total content of
essential elements (except Ca and Mn) in plants from different regions, confirming the bio-
uptake ability of plant toward essential elements [
14
]. Unexpectedly a higher total content
of Ca was observed in rural and urban plants in comparison with plants from fertilized
and mountain regions. Significantly higher concentrations of Mn were determined in the
plants grown on fertilized soils, which might be explained by the high bioavailable Mn
content in these soils, as the same concentrations were measured in other herbs from the
same region. The total content of essential elements presented at lower concentration levels
in Sempervivum tectorum L. is close to the content of these elements in other herbs from
these regions [15,16].
Table 2lists the results obtained for some nonessential elements. As can be seen, the
plants grown on agricultural (fertilized) soils differed from the others with their higher con-
centrations of Al, Co, and Ba. However, only the concentrations of cobalt were surprising,
as Al of such and higher concentrations is found in herbs from this region [15].
Another critical aspect is the good quality control of medicinal herbs, to protect
consumers from contamination, as many medicinal herbs and their mixtures can present a
health risk due to toxic elements [17].
Toxic element levels in raw plant material or prepared products/extracts/infusions is
regulated by documents at global, national, or regional level. Strict control of contaminant
levels and their minimization is required by the World Health Organization (WHO) through
guidelines such as the good agricultural and collection practices (GACP) for medicinal
plants and good manufacturing practices (GMP) for herbal medicines. Maximal values for
toxic elements in herbal drugs and extracts have been discussed and compared by several
authors [18–20].
According to the World Health Organization, cadmium concentrations and lead in
herbal medicines and products are regulated at 0.3 mg kg
−1
Cd and 10.0 mg kg
−1
Pb [
18
].
In different countries, the law sets lower limits, and a very good comparison of the various
permissible limits is presented by Luo et al. [
20
]. As shown in Table 3, the concentrations
of toxic elements meet the requirements of the WHO, and only in one single case was
the cadmium concentration exceeded, for urban soil. Expectedly, the results for elements
such as As, Cd, and Pb are highest in plants grown on urban soils. Most probably, in this
case both soil pollution and aerosol deposition are responsible for the high toxic element
content. Although, it is clearly important to harvest medicinal plants from clean sites

Horticulturae 2021,7, 306 7 of 9
without anthropogenic influences such as mountain regions. A relatively high content was
determined for Ni and Pb in plants grown on fertilized soils, most likely connected with
Ni and Pb contamination by the phosphate fertilizers applied.
In this study, sampling for all studied plants and sampling sites was performed in the
summer season, with some efforts to use plants in the same vegetation period. Taking into
account that Sempervivum tectorum L. is a perennial plant, additional research is required to
elucidate any correlation between plant age and chemical element content.
In Table 4, the results found for the operationally defined bioavailable content (see
Section 2.3) of Ca, Mg, Zn, Mn, and Fe in fresh leaves of Sempervivum tectorum L. (after two
hours of treatment in pH 1.0–1.5) are depicted. Plants growing on mountains, villages, and
fertilized soils were used. The percentage content of bioavailable fraction varied between
4–14% for all studied essential elements (Table 7). It should be pointed out that the content
of Ca and Fe, which might be accepted as being most responsible for the health functions
of Sempervivum tectorum L., is almost constant in the bioavailable fractions from all samples.
High concentrations of Ca in this fraction justify the use of Sempervivum tectorum L. as
a national remedy for the treatment of gastric ulcers, possibly because of the beneficial
calcification effect.
Table 7. Bioavailable concentrations of Ca, Mg, Zn, Mn, and Fe as a percentage of total content.
Ca
Bioavaible
Fraction, %
Mg
Bioavaible
Fraction, %
Zn
Bioavaible
Fraction, %
Mn
Bioavaible
Fraction, %
Fe
Bioavaible
Fraction, %
B4.37 3.45 4.49 6.42 4.30
C4.46 5.63 11.7 3.30 5.59
D5.18 6.51 8.12 14.1 4.98
Although the concentration of Mn is still highest as a bioavailable concentration, the
degree of extraction was significantly lower, most probably depending on the different Mn
species present in the leaves. Therefore, it might be assumed that the Mn bio-uptake would
be highest from agricultural (fertilized) soils, most probably because of suitable pH values.
Determination of elements in juice from fresh leaves. Fresh juice obtained by squeezing
leaves from Sempervivum tectorum L. was widely used as folk medicine against ear pain. As
shown in Table 6, this effect can most probably be explained by the high Mg concentrations,
analogous to the pharmaceuticals used for external application (Mg-gels or Mg-oils) with
anti-inflammatory and regenerative actions and improved blood circulation [21–23]
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.

Horticulturae 2021,7, 306 8 of 9
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.
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