International Research Journal of Public and Environmental Health Vol.2 (11), pp. 182-190, November 2015
Available online at http://www.journalissues.org/IRJPEH/
http://dx.doi.org/10.15739/irjpeh.037
Copyright © 2015 Author(s) retain the copyright of this article
ISSN 2360-8803
Original Research Article
Neutron activation analysis of constituent elements of
edible and medicinal plant of iron stick yam (Dioscorea
opposita Thunb)
Received 15 October, 2015
Revised
Li Xuesong*1, 2,
G. Hristozova1, 3,
P. S. Nekhoroshkov1
and M.V. Frontasyeva1
1Sector of Neutron Activation
Analysis and Applied Research,
Division of Nuclear Physics, Frank
Laboratory of Neutron Physics, Joint
Institute for Nuclear Rearch, Dubna
141980, Moscow Region, Russian
Federation.
2Northwest Institute of Nuclear
Technology, Xi’an 710024, China
3Faculty of Physics, Paisii Hilendarski
University, Plovdiv 400, Bulgaria.
*Corresponding Author
Email: [email protected]
Tel.: +721638311
29 October, 2015
Accepted 2 November, 2015
Published 6 November, 2015
For the first time conventional and epithermal neutron activation analysis
(ENAA) was applied to determine the elemental content of iron stick yam
(Dioscorea opposita Thunb), an edible and medicinal plant grown in China,
well known for its high nutritional value and salutary effects: anti-aging,
anti-tumor, etc. High-resolution HPGe gamma ray spectrometer with
Genie2000 analysis software were employed to measure and analyze the
gamma-spectra of the irradiated samples. A total of 30 elements were
determined at the reactor IBR-2 of FLNP JINR (Na, Mg, Al, S, Cl, K, Ca, Sc, Ti, V,
Cr, Mn, Fe, Co, Cu, Zn, Se, As, Br, Sr, Rb, Zr, Ag, In, Sb, I, Ba, Cs, La, Ce, Nd, Eu,
Gd, Sm, Tb, Dy, Yb, Tm, Hf, Ta, W, Au, Th, and U ), 11 of which (S, Cl, Br, Rb, Sb,
Cs, Nd, Eu, Sm, Au, and U) have never been reported in previous yam studies.
Abnormally high concentrations of Al, U, Eu and Nd have been found.
Key words: NAA, iron stick yam, elemental content, Dioscorea opposita Thunb,
edible, medicinal plants.
INTRODUCTION
Yam is a type of useful food plant belonging to the Dioscorea
genus which has more than 600 species, mainly distributed
in tropical and subtropical areas. To the best of our
knowledge, the study of yam started in 1969 (Ferguson,
1969). Among several special species possessing both
nutritional and medicinal properties, iron stick yam
(Dioscorea opposita Thunb), also known as Die-hard yam or
Tie Gan yam, grows in Wenxian County, China, and is
deemed to have anti-aging, anti-tumor, anti-fatigue and
immunity enhancing qualities. Therefore, iron stick yam
has been widely used in the Chinese cuisine and traditional
medicine. Its nutritional content (Hang et al., 1992; Tang,
1987) and medical functions (Harbin Medical University,
1975; Xu et al., 2014; Zhang et al., 2007) have been the
topic of investigation for several decades.
The Chinese researchers have studied mineral and trace
elements in many local types of yams, including iron stick
yam. Twenty-nine trace elements in five types of yams were
systematically investigated in 1988 by means of inductive
coupled plasma atomic emitted spectrometry (ICP-AES)
(Hang et al., 1988). In 1996, flame photometry and atomic
absorption spectrometry (AAS) were utilized to determine
Na, K, Fe, Cu, Mn, Zn, Ca and Mg concentrations in longshape yam (Dioscorea opposita Thunb) grown in Lichuan,
Hubei province, China (Zhang and Xie, 1996). Then AAS and
ICP-AES methods were widely used in mineral and trace
elements measurements of yams (Huang et al., 2002; Liu et
al., 2010; Zhang et al., 2006). In 2003, ICP-AES was
employed to analyze 22 elements of Huai yam (Dioscorea
opposita Thunb) grown in Qinyang, Henan province, China
(Zhang and Xie, 2003). Zhou et al. (2010) compared the
concentrations of nine elements in purple yam (Dioscorea
alata Linn.) and iron stick yam determined by ICP-AES .The
results showed that all concentrations were higher in iron
stick yam. In 2011, ICP-AES was used to determine K, Ca,
Na, Mg, Cu, Zn, Fe, and Mn in iron stick yam and Huai yam
Int. Res. J. Public Environ. Health
183
a. Sampling place of iron stick yam
b. Iron stick yam
Fig. 1 Iron stick yam from China
Figure 1: Iron stick yam from China
grown in the same place, Wenxian county, China (Wu et al.,
2011). The obtained results showed that concentrations of
these elements were apparently higher in iron stick yam. In
the same year, inductive coupled plasma mass
spectrometry (ICP-MS) was used to analyze eleven
elements in five thin-coarse yam (Dioscorea opposita
Thumb) grown in different places in Shandong Province,
China (Xu et al., 2011). In 2012, X-ray fluorescence (XRF)
method was allowed determination of thirteen elements in
Qishan yams (Dioscorea opposita Thumb) from Hebei
province, China (Zhang et al., 2012).
Numerous investigations of mineral elements in various
kinds of yams were undertaken in other yam-rich countries.
Abara, (2011) reviewed the papers on mineral element
composition of the Dioscorea bulbifera tuber and reported
the mineral elements (Ca, Ma, Fe, Zn, Cu, Na, and K) in the
yam tissue and peel determined by AAS and AES (Abara,
2011). The results showed that almost all mineral element
concentrations in peel were higher than those in tissue. A
lot of investigations on elemental content of yam were
carried out in Nigeria (Okwu and Ndu, 2006; Ayele, 2009;
Ameh, 2007; Karim et al., 2013; Olajumoke et al., 2014).
Other studies were conducted mainly in India
(Shanthakumari et al., 2008), South Korea (Shin et al.,
2012), Ghana (Dufie et al., 2013; Polycarp et al., 2012), Cote
d'Ivoire (Kouadio et al., 2013), etc., where AAS and ICP-AES
have been widely used to determine mineral elemental
content.
Despite the fact that over the past, several analytical
techniques have been employed complementarily in the
elemental content studies, the obtained data are still
insufficient. With the development of nuclear research
reactors and high resolution gamma spectrometry, neutron
activation analysis (NAA), a multi-element and nondestructive technique, showed itself a reliable analytical
method used in many branches of the life science (Avino et
al., 2011; Fei et al., 2010; Frontasyeva, 2011; Marchkesbery
et al., 1981).
In the present work, the elemental content of iron stick
yam was determined by epithermal neutron activation
analysis (ENAA) (Frontasyeva, 2011) for the first time and
concentrations of thirty elements were determined, among
them eleven elements (S, Cl, Br, Rb, Sb, Cs, Nd, Eu, Sm, Au,
and U) were never reported in literature before.
MATERIALS AND METHODS
Samples of iron stick yam grown near the Yellow river (red
point in Figure1- a), Wenxian county, Jiaozuo city, Henan
province, China (Figure 1) were collected.
Neutron conditions
The IBR-2 reactor of FLNP JINR is equipped with two
irradiation channels of pneumatic transport system
REGATA (Frontasyeva, 2011) for NAA. Characteristics of
two irradiation channels, one of which is cadmium
screened for irradiation with epithermal neutrons, are
shown in Table 1. Table 2 lists selected peak energies for
NAA and method of analysis.
Quality control
To provide quality control of the results obtained, several
international standard reference materials (SRMs) were
used (see Table 3). As follows from Table 3, the deviations
for all elements are between -1% and +1%.
Samples preparation
After rinsing with high-purified water, the iron stick yam
Xuesong et al.
184
Table 1. Neutron conditions of sample irradiation
Channels
Dimensions, mm
Neutron type
Experimental fluxes, s-1cm-2
Ch1 (epithermal) (cadmium-screened)
Diameter 28, length 260
Thermal
Resonance
Fast
Cd-coated
3.6×1011
5.5×1011
Ch2 (thermal)
Diameter 28, length 260
Thermal
Resonance
Fast
1.5×1012
1.8×1011
2.7×1011
Table 2. List of isotopes, selected peak energies, half-lives, and method of analysis
Element
Na
Mg
Al
S
Cl
K
Ca
Sc
V
Mn
Fe
Co
Cu
Zn
As
Br
Sr
Rb
Zr
Sb
I
Ba
Cs
La
Nd
Eu
Sm
Au
Th
U
Isotope
24Na
27Mg
28Al
37S
38Cl
42K
49Ca
46Sc
52V
56Mn
59Fe
60Co
66Cu
65Zn
76As
82Br
85Sr
86Rb
95Zr
124Sb
128I
131Ba
134Cs
140La
147Nd
152Eu
153Sm
198Au
233Pa
239Np
Gamma peak, keV
1368.6
1014.4
1779.0
3104.0
2167.7
1524.6
3084.4
889.2
1434.1
1810.7
1099.2
1173.1
1039.0
1116.0
559.1
776.5
514.0
1076.6
724.2
1691.0
442.9
496.8
795.8
1596.5
531.04
1407.5
103.2
411.8
312.0
228.2
Half-life
14.7h
9.5min
2.2min
5.06min
37.2min
12.4h
8.7min
83.8d
3.8min
2.6h
44.5d
5.3y
5.1min
244.0d
26.3h
35.3h
64.8d
18.6d
64.4d
60.2d
25.0min
11.8d
2.1y
40.2h
10.98 d
13.3 y
46.8h
2.7 d
27.0 d
2.4 d
Method of analysis(1)
2
1
1
1
1
2
1
3
1
1
3
3
1
3
2
2
3
3
3
3
1
2
3
2
3
3
2
2
3
2
Note: (1) Method 1: conventional NAA, measured after ~3 min of decay;
Method 2: epithermal NAA, measured after 4~5 days of decay;
Method 3: epithermal NAA, measured after ~29 days of decay.
tuber was dried for 24 hours at 40 ℃. The peel was
removed from the tuber with a pair of plastic tweezers to
avoid contamination. Inner tissue was cut into ~3 mm
pieces and placed with the peel pieces in a drying unit for
72 hours at 40 ℃. Samples were homogenized by grinding
with agate ball mill into powder, and about 0.3 g powder for
each sample was packed in polyethylene bags for
determination of short-lived isotopes and in aluminum
cups of 12 mm diameter for determination of long-lived
isotopes. In total, 5 peel and 6 tuber tissue samples were
prepared.
Irradiation and measurements
Three sub-samples of peel and three sub-samples of tissue
were irradiated in cadmium-screened channel 1 for 2 days.
To determine the long-lived isotopes gamma spectra were
measured twice: for 30 minutes after 4~5 days of decay
and for 1.5 hours after ~29 days of decay. To determine
short-lived isotopes five sub-samples (two peel and three
tissue sub-samples) were irradiated for 3 minutes in
conventional Channel 2. After ~3 min of decay each
irradiated sub-sample was measured for 15 min.
Gamma-ray spectrometers based on high-resolution
HPGe detector from Canberra with 50% relative efficiency
and 1.9 keV resolution at 1.332 MeV for the line of 60Co
were used to measure gamma spectra of induced activity by
means of Genie2000. A software package developed at the
FLNP JINR (Pavlov et al., 2014) was used to calculate the
concentrations of elements based on relative method using
Int. Res. J. Public Environ. Health
185
Table 3. NAA data and certified values of reference materials, mg/kg
Element
Na
Mg
Al
S
Cl
K
Ca
Sc
V
Mn
Fe
Co
Cu
Zn
As
Br
Sr
Rb
Zr
Sb
I
Ba
Cs
La
Nd
Eu
Sm
Au
Th
U
Determined concentration
299.5±9.9
4324±40
64434±710
2400±700
579±25
24289±1200
15637±550
2.908±0.058
295.8±6.5
132.0±3.4
7339±499
12.9±0.2
2952±730
100.9±18.0
18.92±0.42
18.66±0.45
301.6±12.0
5.04±1.10
148±19
1.96±0.05
0.3014±0.0430
67.6±10.4
0.594±0.017
27.79±1.10
24.9±2.3
0.997±0.110
1.082±0.036
0.01659±0.00510
1.399±0.025
0.5128±0.0150
Certified concentration
298.8±4.8
4320±80
64400±800
2400±60
579±23
24300±300
15600±200
2.905±0.036
295.7±3.6
131.8±1.7
7350±110
12.9±0.3
2950±130
101±2
18.9±0.5
18.7±0.4
302±6
5.05±0.11
148±44
1.96±0.035
0.30±0.09
67.5±2.1
0.594±0.010
27.8±1.0
25.0±1.4
1.00±0.01
1.078±0.028
0.0166±0.0012
1.40±0.03
0.513±0.012
Deviation, %
0.2
0.1
0.05
0
0
-0.05
0.2
0.1
0.04
0.2
-0.1
0
0.04
-0.1
0.1
-0.2
-0.1
-0.2
0
0
0.5
0.1
0
-0.04
-0.4
-0.3
0.4
-0.06
-0.06
-0.04
SRM
NIST-1632c (trace elements in coal)
NIST-1547 (peach leaves)
NIST-2710 (montana soil)
NIST-2710 (montana soil)
NIST-1515 (apple leaves)
NIST-1547 (peach leaves)
NIST-1547 (peach leaves)
NIST-1632c (trace elements in coal)
NIST-1633b (coal fly ash)
NIST-1633b (coal fly ash)
NIST-1632c (trace elements in coal)
IAEA-433 (marine sediment)
NIST-2710 (montana soil)
IAEA-433 (marine sediment)
IAEA-433 (marine sediment)
NIST-1632c (trace elements in coal)
IAEA-433 (marine sediment)
NIST-1632b (trace elements in coal)
IAEA-433 (marine sediment)
IAEA-433 (marine sediment)
NIST-1547 (peach leaves)
NIST-1632b (trace elements in coal)
NIST-1632c (trace elements in coal)
BCR-667 (estuarine sediment)
BCR-667 (estuarine sediment)
BCR-667 (estuarine sediment)
NIST-1632c (trace elements in coal)
BCR-667 (estuarine sediment)
NIST-1632c (trace elements in coal)
NIST-1632c (trace elements in coal)
Note: (1) NIST: National institute of standard and technology
(2) IAEA: international atomic energy agency
(3) BCR: Community bureau of reference, the former materials program of the European commission, the certificate BCR-667 has been revised by
institute for reference materials and measurements.
the certified reference materials as mentioned in Table 3.
Descriptive statistics was applied to determine mean values
and their standard deviations for each sample.
RESULTS
Figure 2 shows one of the gamma-spectra for
determination of short-lived isotopes in sample of peel.
The NAA results of iron stick yam peel and tissue are
shown in Table 4. A total of 30 elements were determined
using the modes of measurements described in Table 2.
They are compared with the relevant literature data (Abara,
2011).
In Table 5 are compared the present results with
literature data on elemental concentrations in other yam
species as well as with the Reference Plant by Markert
(Markert, 1992).
Figure 3 directly shows the level of elemental
concentrations in yam tissue by comparing with the
Reference Plant (Markert, 1992)
DISCUSSION
The tissue/peel ratios (Table 4, column 4) shows that with
except of Sb, concentrations of other elements in peel are
much higher than those in tuber tissue, which shows the
same phenomenon as observed in (Abara, 2011). And the
concentrations of Al, Au and U are extremely high in peer.
As we all know, too much Al and U is harmful for human
body. The main reason perhaps is that different elements
have different deposit rate in the peer of iron stick yam.
Besides, it is logical that the soil particles probably still
remain on the peel despite cleaning. And Table 4 shows that
for different types of yams, the concentration radio of
tissue/peel for the same element has much difference.
Comparison with reference data (Table 5) shows that
yams grown in different places demonstrate great
variability of the elemental concentrations even between
the same species. The main reason is probably due to
different elemental content of soil in different areas.
Moreover, different yam species perhaps exhibit various
element accumulation mechanisms.
Xuesong et al.
Figure 2: Example of a gamma-spectrum for short-lived isotopes in a sample of peel
Table 4. Element concentrations (mg/kg) of iron stick yam peel and tissue and Ref. (Abara, 2011)
Present work (NAA)
element
Na
Mg
Al
P
S
Cl
K
Ca
Sc
V
Mn
Fe
Co
Cu
Zn
As
Br
Sr
Rb
Zr
Sb
I
Ba
Cs
La
Nd
Eu
Sm
Au
Th
U
iron-stick
yam (peel)
(China)
1290±20
2840±71
194±3
96±34
4255±220
19867±2400
6425±240
0.036±0.003
1.29±0.05
30±1
106±10
0.135±0.008
14±4
37.9±0.8
0.12±0.01
23.5±0.3
65.2±2.6
1.36±0.15
14.2±5.7
0.027±0.003
0.72±0.19
10.4±0.9
0.035±0.003
0.165±0.011
8.34±0.46
0.22±0.05
0.037±0.007
0.038±0.002
0.775±0.015
Ref. (Abara, 2011) (AAS+AES)
Dioscorea
iron-stick
Dioscorea
Tissue/peel
bulbifera
yam (tissue)
bulbifera (peel)
ratio
(tissue)
(China)
(Nigeria)
(Nigeria)
941±15
0.73
640
550
1440±35
0.53
161
139
12.0±0.4
0.056
184
150
82±16
0.83
2197±92
0.53
13800±1700
0.69
920
440
1496±51
0.23
316.31
205.60
5.76±0.23
0.19
18
4
17.35
5.90
6.9±1.7
0.48
8
5
15.8±0.4
0.42
4.12
1.52
7.9±0.1
0.34
14.9±0.7
0.23
0.95±0.10
0.70
0.050±0.007
1.85
1.8±0.2
0.19
0.007±0.002
0.22
2.84±0.16
0.34
0.14±0.02
0.63
0.0030±0.0003
0.0020±0.0004
0.054
0.0094±0.0007
0.015
-
Tissue/peel
ratio
0.86
0.86
0.82
0.49
0.65
0.22
0.34
0.63
0.37
-
186
Int. Res. J. Public Environ. Health
187
Table 5. Elemental concentrations (mg/kg) for different yams and the Reference Plant
Ref.(Huang
Present
Ref.(Hang et
et al.,
work
al., 1988)
2002)
(NAA)
(ICP-AES)
Element
(AAS)
iron stick
iron stick
iron-stick
yam(tissue)
yam
yam
(China)
(China)
(China)
Li
Be
Na
Mg
Al
P
S
Cl
K
Ca
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
As
Se
Br
Sr
Rb
Y
Zr
Nb
Sb
Ba
Cs
La
Ce
Nd
Eu
Yb
Sm
Au
Hg
Th
U
941
1440
12.0
82
2197
13800
1496
5.76
6.9
15.8
7.9
14.9
0.95
0.050
1.8
0.007
2.84
0.14
0.0030
0.0020
0.0094
0.0198
0.036
280.6(Na2O)
1365(MgO)
100.5(Al2O3)
1770
14220(K2O)
897.6(CaO)
3.722
0.911
33.83
7.578
368.2(Fe2O3)
0.6164
17.85
0.080
20.77
1.254
6.431
0.0611
0.2223
0.9189
3.653
0.07991
1.277
0.03961
0.8075
-
580.7
545
923.9
2.70
32.25
5.68
6.76
1.13
0.29
0.039
-
Ref.
Ref.(Zhou Ref.(Ogunlade
Ref.
(Polycarp,
The
et al.,
et al., 2006) (Shanthakumari
2012) Reference
2010)
(AAS)
et al., 2008)
(AAS)
Plant
(ICP-AES) Dioscorea
(AAS)
Dioscorea (Markert,
iron stick dumetorum
Dioscorea
Esculenta
1992)
yam
(tissue)
alata
(tissue)
(China)
(Nigeria)
(India)
(Ghana)
0.2
0.001
549.9
320
875
150
370
48.5
5661
675
2000
80
490
607.0
1101
2735
2000
3000
2000
6470
1550
7950
19000
570
161.5
3381
205
10000
0.05
0.5
1.5
0.81
53.6
27
200
10.09
4.5
331
20
150
0.2
1.5
1.56
2.1
83
1
10
3.35
40.4
12.6
78
50
0.1
0.1
0.01719
0.02
4
50
50
0.2
0.1
0.05
0.1
40
0.2
0.2
0.5
0.2
0.008
0.02
0.04
0.001
0.1
0.005
0.01
Comparison with the Reference Plant evidences that the
concentrations of Na, Cl, Br, Nd, Eu and Au are much higher
in iron stick yam tissue (Figure 3).
Na concentration determined in tissue is about 5 times
higher than that in the Reference plant but quite consistent
with other yam species reported in Ref. (Polycarp, 2012).
This probably explains the medicinal effect of iron stick
yam, as it is well-known that sodium is an essential
element, which regulates blood volume, blood pressure,
osmotic equilibrium and pH; the minimum physiological
requirement for sodium is 500 milligrams per day.
According to our results, Br concentration in dry iron
stick yam tissue is 7.9 mg/kg that is about 2 times higher
than in the Reference Plant. Bromine is also considered
essential for mammals (McCall et al., 2014), producing
positive effect on nerve system as a tranquilizer. Its
Xuesong et al.
188
Figure 3: Elemental concentrations comparison with the Reference plant
recommended daily allowance (RDA) is 1.5-2.5 mg per day
for adults (Patricelli et al., 1998; NRC, 1989).
Abnormally high concentrations of rare earth elements
(RREs), neodymium and europium, relatively to the
Reference Plant were observed. The role of REEs in human
body is under intense investigations (Rim et al., 2013). At
present there is no standard RDA for neodymium and
europium. Preliminary study shows that some lanthanides
are toxic. So the reason of so much high concentrations for
Eu and Nd need to be clarified. And the most probable clue
lies in the growing soil. Besides Nd has good magnetic
property as a constituent of Nd2Fe14B magnet and may
provide positive influence on blood and brain activity
(Hinman, 2002).
Gold is a trace element in human body and mainly
distributed in lung, liver, and spleen (Yukawa et al., 1980).
Since the ancient times, pure gold is always used as the food
decoration or additive and the constituent of drugs. And
Gold has the benefit for rheumatoid arthritis and
antitubercular (Ellman et al., 1940; Khanye, 2001).
In particular, the concentrations of Al, Au and U are
extremely high in peer, and the concentrations of Nd and Eu
are abnormally high compared to the Reference Plant.
Further studies on element accumulation mechanism in
iron stick yam and local soil elemental content will be
conducted to clarify the reason of this phenomenon.
CONCLUSION
Concentrations of thirty elements in iron stick yam were
determined by NAA. Among them, eleven elements (S, Cl,
Br, Rb, Sb, Cs, Nd, Eu, Sm, Au and U) were reported for the
first time in this kind of species. Determination of elemental
content provides the basis for explanation of the principle
and treatment effect of Chinese traditional medicine.
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