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 29 October, 2015 Accepted 2 November, 2015 Published 6 November, 2015

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: cedar761107@126.com

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.

Tel.: +721638311 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 long-shape 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 non-destructive 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 Ch1 (epithermal) (cadmium-screened) Ch2 (thermal) Dimensions, mm Diameter 28, length 260 Diameter 28, length 260 Neutron type Thermal Resonance Fast Thermal Resonance Fast Experimental fluxes, s-1cm-2 Cd-coated 3.6×1011 5.5×1011 1.5×1012 1.8×1011 2.7×1011

Table 2. List of isotopes, selected peak energies, half-lives, and method of analysis

Element Isotope Gamma peak, keV Half-life Method of analysis(1) Na 24Na 1368.6 14.7h 2 Mg 27Mg 1014.4 9.5min 1 Al 28Al 1779.0 2.2min 1 S 37S 3104.0 5.06min 1 Cl 38Cl 2167.7 37.2min 1 K 42K 1524.6 12.4h 2 Ca 49Ca 3084.4 8.7min 1 Sc 46Sc 889.2 83.8d 3 V 52V 1434.1 3.8min 1 Mn 56Mn 1810.7 2.6h 1 Fe 59Fe 1099.2 44.5d 3 Co 60Co 1173.1 5.3y 3 Cu 66Cu 1039.0 5.1min 1 Zn 65Zn 1116.0 244.0d 3 As 76As 559.1 26.3h 2 Br 82Br 776.5 35.3h 2 Sr 85Sr 514.0 64.8d 3 Rb 86Rb 1076.6 18.6d 3 Zr 95Zr 724.2 64.4d 3 Sb 124Sb 1691.0 60.2d 3 I 128I 442.9 25.0min 1 Ba 131Ba 496.8 11.8d 2 Cs 134Cs 795.8 2.1y 3 La 140La 1596.5 40.2h 2 Nd 147Nd 531.04 10.98 d 3 Eu 152Eu 1407.5 13.3 y 3 Sm 153Sm 103.2 46.8h 2 Au 198Au 411.8 2.7 d 2 Th 233Pa 312.0 27.0 d 3 U 239Np 228.2 2.4 d 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 Determined concentration Certified concentration Deviation, % SRM Na 299.5±9.9 298.8±4.8 0.2 NIST-1632c (trace elements in coal) Mg 4324±40 4320±80 0.1 NIST-1547 (peach leaves) Al 64434±710 64400±800 0.05 NIST-2710 (montana soil) S 2400±700 2400±60 0 NIST-2710 (montana soil) Cl 579±25 579±23 0 NIST-1515 (apple leaves) K 24289±1200 24300±300 -0.05 NIST-1547 (peach leaves) Ca 15637±550 15600±200 0.2 NIST-1547 (peach leaves) Sc 2.908±0.058 2.905±0.036 0.1 NIST-1632c (trace elements in coal) V 295.8±6.5 295.7±3.6 0.04 NIST-1633b (coal fly ash) Mn 132.0±3.4 131.8±1.7 0.2 NIST-1633b (coal fly ash) Fe 7339±499 7350±110 -0.1 NIST-1632c (trace elements in coal) Co 12.9±0.2 12.9±0.3 0 IAEA-433 (marine sediment) Cu 2952±730 2950±130 0.04 NIST-2710 (montana soil) Zn 100.9±18.0 101±2 -0.1 IAEA-433 (marine sediment) As 18.92±0.42 18.9±0.5 0.1 IAEA-433 (marine sediment) Br 18.66±0.45 18.7±0.4 -0.2 NIST-1632c (trace elements in coal) Sr 301.6±12.0 302±6 -0.1 IAEA-433 (marine sediment) Rb 5.04±1.10 5.05±0.11 -0.2 NIST-1632b (trace elements in coal) Zr 148±19 148±44 0 IAEA-433 (marine sediment) Sb 1.96±0.05 1.96±0.035 0 IAEA-433 (marine sediment) I 0.3014±0.0430 0.30±0.09 0.5 NIST-1547 (peach leaves) Ba 67.6±10.4 67.5±2.1 0.1 NIST-1632b (trace elements in coal) Cs 0.594±0.017 0.594±0.010 0 NIST-1632c (trace elements in coal) La 27.79±1.10 27.8±1.0 -0.04 BCR-667 (estuarine sediment) Nd 24.9±2.3 25.0±1.4 -0.4 BCR-667 (estuarine sediment) Eu 0.997±0.110 1.00±0.01 -0.3 BCR-667 (estuarine sediment) Sm 1.082±0.036 1.078±0.028 0.4 NIST-1632c (trace elements in coal) Au 0.01659±0.00510 0.0166±0.0012 -0.06 BCR-667 (estuarine sediment) Th 1.399±0.025 1.40±0.03 -0.06 NIST-1632c (trace elements in coal) U 0.5128±0.0150 0.513±0.012 -0.04 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. 186

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)

element

Present work (NAA) Ref. (Abara, 2011) (AAS+AES)

iron-stick yam (peel)

(China)

iron-stick yam (tissue)

(China)

Tissue/peel ratio

Dioscorea bulbifera (peel)

(Nigeria)

Dioscorea bulbifera (tissue)

(Nigeria)

Tissue/peel ratio

Na 1290±20 941±15 0.73 640 550 0.86 Mg 2840±71 1440±35 0.53 161 139 0.86 Al 194±3 12.0±0.4 0.056 - - - P - - - 184 150 0.82 S 96±34 82±16 0.83 - - - Cl 4255±220 2197±92 0.53 - - - K 19867±2400 13800±1700 0.69 920 440 0.49 Ca 6425±240 1496±51 0.23 316.31 205.60 0.65 Sc 0.036±0.003 - - - - - V 1.29±0.05 - - - - - Mn 30±1 5.76±0.23 0.19 18 4 0.22 Fe 106±10 - - 17.35 5.90 0.34 Co 0.135±0.008 - - - - - Cu 14±4 6.9±1.7 0.48 8 5 0.63 Zn 37.9±0.8 15.8±0.4 0.42 4.12 1.52 0.37 As 0.12±0.01 - - - - - Br 23.5±0.3 7.9±0.1 0.34 - - - Sr 65.2±2.6 14.9±0.7 0.23 - - - Rb 1.36±0.15 0.95±0.10 0.70 - - - Zr 14.2±5.7 - - - - - Sb 0.027±0.003 0.050±0.007 1.85 - - - I 0.72±0.19 - - - - - Ba 10.4±0.9 1.8±0.2 0.19 - - - Cs 0.035±0.003 0.007±0.002 0.22 - - - La 0.165±0.011 - - - - - Nd 8.34±0.46 2.84±0.16 0.34 - - - Eu 0.22±0.05 0.14±0.02 0.63 - - - Sm - 0.0030±0.0003 - - - - Au 0.037±0.007 0.0020±0.0004 0.054 - - - Th 0.038±0.002 - - - - - U 0.775±0.015 0.0094±0.0007 0.015 - - -

Int. Res. J. Public Environ. Health 187

Table 5. Elemental concentrations (mg/kg) for different yams and the Reference Plant

Element

Present work (NAA)

iron stick yam(tissue)

(China)

Ref.(Hang et al., 1988) (ICP-AES) iron stick

yam (China)

Ref.(Huang et al., 2002) (AAS)

iron-stick yam

(China)

Ref.(Zhou et al., 2010)

(ICP-AES) iron stick

yam (China)

Ref.(Ogunlade et al., 2006)

(AAS) Dioscorea

dumetorum (tissue)

(Nigeria)

Ref. (Shanthakumari

et al., 2008) (AAS)

Dioscorea alata

(India)

Ref. (Polycarp,

2012) (AAS)

Dioscorea Esculenta

(tissue) (Ghana)

The Reference

Plant (Markert,

1992)

Li - 0.0198 - - - - - 0.2 Be - 0.036 - - - - - 0.001 Na 941 280.6(Na2O) - - 549.9 320 875 150 Mg 1440 1365(MgO) 580.7 370 48.5 5661 675 2000 Al 12.0 100.5(Al2O3) - - - - - 80 P - 1770 545 490 607.0 1101 2735 2000 S 82 - - - - - - 3000 Cl 2197 - - - - - - 2000 K 13800 14220(K2O) - 6470 - 1550 7950 19000 Ca 1496 897.6(CaO) 923.9 570 161.5 3381 205 10000 Ti - 3.722 - - - - - 0.05 V - 0.911 - - - - - 0.5 Cr - 33.83 - - - - - 1.5 Mn 5.76 7.578 2.70 0.81 - 53.6 27 200 Fe - 368.2(Fe2O3) 32.25 10.09 4.5 331 20 150 Co - 0.6164 - - - - - 0.2 Ni - 17.85 - - - - - 1.5 Cu 6.9 0.080 5.68 1.56 2.1 83 1 10 Zn 15.8 20.77 6.76 3.35 40.4 12.6 78 50 Ga - 1.254 - - - - - 0.1

As - - 1.13 - - - - 0.1 Se - - 0.29 0.01719 - - - 0.02 Br 7.9 - - - - - - 4 Sr 14.9 6.431 - - - - - 50 Rb 0.95 - - - - - - 50 Y - 0.0611 - - - - - 0.2 Zr - 0.2223 - - - - - 0.1 Nb - 0.9189 - - - - - 0.05 Sb 0.050 - - - - - - 0.1 Ba 1.8 3.653 - - - - - 40 Cs 0.007 - - - - - - 0.2 La - 0.07991 - - - - - 0.2 Ce - 1.277 - - - - - 0.5 Nd 2.84 - - - - - - 0.2 Eu 0.14 - - - - - - 0.008 Yb - 0.03961 - - - - - 0.02 Sm 0.0030 - - - - - - 0.04 Au 0.0020 - - - - - - 0.001

Hg - - 0.039 - - - - 0.1 Th - 0.8075 - - - - - 0.005

U 0.0094 - - - - - - 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. REFERENCES Abara AE (2011). Proximate and mineral elements

composition of the tissue and peel of Dioscorea bulbifera tuber. Pakistan J. Nutri., 10: 543-551.

Ameh IG (2007). Proximate and mineral composition of seed and tuber of African yam bean, sphenostylis stenocarpa (Hoechst. ex. a. rich.) Harms. ASSET: An International J. (Series B), 6(1): 1-10.

Avino P, Capannesi G, Manigrasso M, Sabbioni E, Rosada A (2011). Element assessment in whole blood, serum and urine of three Italian healthy sub-populations by INAA. Microchem. J., 99(2): 548-555.

Ayele E (2009). Effect of Boiling Temperature on Mineral Content and Antinutritional Factors of Yam and Taro Grown in Southern Ethiopia. Thesis. Addis Ababa University.

Dufie WMF, Oduro I, Ellis WO, Robert Asiedu, and Bussie Maziya-Dixon (2013). Potential health benefits of water yam (Dioscorea alata). Food & function, 4:1496-1501.

Ellman P, Lawrence JS, Thorold GP (1940). Gold therapy in rheumatoid arthritis. The British medical journal, 2: 314.

Fei T, Dehong L, Fengqun Z, Junhua L, Hua T, Xiangzhong K (2010). Determination of trace elements in Chinese medicinal plants by instrumental neutron activation analysis. J. Radioanal. Nucl. Chem., 284(3): 507-511.

Ferguson TU (1969). Mineral and calorie content of yam tubers. Trinidad, Annual report 1968-1969, Faculty of Agr., Univ. West Indies.

Frontasyeva MV (2011). Neutron activation analysis in the

Int. Res. J. Public Environ. Health 189

life sciences. Physics of Particles and Nuclei, 42: 332-378. Hang Y, Qin H, Ding Z (1992). A survey and quality research

on new resources of Shan Yao (Rhizoma Dioscoreae). J. of plant resources and environment, 1(2): 10-15. (in Chinese)

Hang Y, Zhou T, Ding Z, Yuan C (1988). Analysis and comparison of amino acids and trace elements of rhizome diosoreae. China Journal of Chinese Materia Medica. China J. Chinese Materia Medica, 07: 37-39, 63. (in Chinese)

Harbin Medical University (1975). Preliminary observation of treatment effect on canker using compound yam powder. J. Harbin Med. Uni., Z1: 78. (in Chinese)

Hinman MR (2002). Cytotoxicity of the rare earth metals cerium, lanthanum, and neodymium in vitro: comparisons with cadmium in a pulmonary macrophage primary culture system. Clinical rehabilitation, 16: 669-674.

Huang D, Mo J, Lao Y, Huang Y, He Y, He B (2002). Analysis of comparison of sixteen kinds of elements in Guangshanyao and Huaishanyao. Trace Elements Science, 02: 47-50. (in Chinese)

Karim OR, Kayode RMO, Oyeyinka SA, Oyeyinka AT (2013). Proximate, Mineral and Sensory Qualities of ‘Amala’Prepared from Yam flour fortified with Moringa leaf powder. Food Sci. Quality Manage., 12: 10-22.

Khanye SD, Wan B, Franzblau SG, Gut J, Rosenthal PJ, Smith GS, Chibale K (2011). Synthesis and in vitro antimalarial and antitubercular activity of gold (III) complexes containing thiosemicarbazone ligands. J. Organomet. Chem., 696(21): 3392-3396.

Kouadio CD, Yao DN, Achille FT, Charlemagne N, Georges NA, Adama B (2013). Partial Study of Yam Tuber (Dioscorea spp.) Parts during the Growth Period. Adv. J. Food Sci. Technol., 5: 1120-1131.

Liu Y, Shi S, Wang C (2010). Determination of Nutritious Compositions and Diosgen in Contents of Purple Yam(Dioscorea batatas Decne.). J. Anhui Agri. Sci. 38: 4563- 4564, 4567. (in Chinese)

Marchkesbery WR, Ehmann WD, Hossain TIM, Alauddin M, Goodin DT (1981). Instrumental neutron activation analysis of brain aluminum in Alzheimer disease and aging. Annals of Neurol., 10(6): 511-516.

Markert B (1992). Establishing of ‘Reference Plant’ for inorganic characterization of different plant species by chemical finger printing. Water, Air and Soil Pollution, 64: 533-538.

McCall AS, Cummings CF, Bhave Vanacore GR, Page-McCall A, Hudson BG (2014). Bromine is an essential trace element for assembly of collagen IV scaffolds in tissue development and architecture. Cell, 157: 1380-1392.

NRC (1989). Recommended dietary allowances (pp.241). National research council (US) sub-committee. Washington, DC: National Academy Press.

Okwu DE, Ndu CU (2006). Evaluation of the Phytonutrients, Mineral and Vitamin Content of Some Varieties of Yam (Dioscorea, sp). Int. J. Molecular Med. Adv. Sci., 2(2): 199-203.

Olajumoke OL, Margaret AA, Ima OW, Yetunde EA, Mbeh

UE (2014). Mineral and toxicant levels in yam (Dioscorea rotundata) diets. Euro. J. Experim. Biol., 4: 656-661.

Patricelli MP, Patterson JE, Boger DL, Cravatt BF (1998). An endogenous sleep-inducing compound is a novel competitive inhibitor of fatty acid amide hydrolase. Bioorganic & medicinal chemistry letters, 8: 613-618.

Pavlov SS, Dmitriev AYU, Chepurchenko IA, Frontasyeva MV (2014). Automation system for measurement of gamma-ray spectra of induced activity for neutron activation analysis at the reactor IBRr-2 of Frank Laboratory of Neutron Phsyics at the Joint Institute for Nuclear Research. Physics of Elementary Particles and Niclei. 11(6): 737–742.

Polycarp D, Afoakwa EO, Budu AS, Otoo E (2012). Characterization of chemical composition and anti-nutritional factors in seven species within the Ghanaian yam (Dioscorea) germplasm. Int. Food Res. J., 19: 985-992.

Rim KT, Koo KH, Park JS (2013). Toxicological evaluations of rare earths and their health impacts to workers: a literature review. Safety and health at work, 4:12-26.

Shanthakumari S, Mohan VR, John de B (2008). Nutritional evaluation and elimination of toxic principles in wild yam (Dioscorea spp.). Tropical and Subtropical Agroecosystems, 8: 319-325.

Mee-Young S, Young-Eun C, Park C, Ho-Yong S, Jae-Hwan L, In-Sook K (2012). The Supplementation of Yam Powder Products Can Give the Nutritional Benefits of the Antioxidant Mineral (Cu, Zn, Mn, Fe and Se) Intakes. Preventive nutrition and food science, 17: 299-305.

Tang S (1987). Analysis of nutrition constituent of yam. China Journal of Chinese Materia Medica, 12(4): 32. (in Chinese)

Wu Y, Yan Z, Han W, Liu R, Guo K (2011). Determination of trace elements in Dioscorea opposite Thumb by ICP-AES. Chinese Journal of Spectrometry Laboratory, 28: 842-845. (in Chinese)

Xu H, Li C, Gong X (2011). Contents of Mineral Elements in Different Yam Varieties. Crops, 6: 63-67. (in Chinese)

Xu X, Yu L, Ma S, Zhang T, Meng D (2014). Effect of nano CYP on immune organ and macrophage phagocytosis of wistar rats. Chinese J. Microecol., 12: 1376-1378. (in Chinese)

Yukawa M, Amano K, Yasumoto MS, Terai M (1980). Distribution of trace elements in the human body determined by neutron activation analysis. Archives of Environmental Health, (1980), 35, 36-44. Erratum, Archives of Environmental Health, 35: 191-191.

Zhang B, Xie J (1996). Study on nutrition constituent of yam. Hubei Agricultural Science, 06: 56-58. (in Chinese)

Zhang C, Xie C (2003). Analysis on the characteristics of inorganic elements in Dioscorea opposite Thumb. Special wild economic animal and plant research, 1: 41-45. (in Chinese)

Zhang H, Cui B, Wang Y (2007). Effects of ioscorea opposite polysaccharide on immune function in chickens. J. Trad. Chinese Vet. Med., 1: 11-13. (in Chinese)

Zhang J, Zhu Y, Ding X, Liu M, Guo X, Wu P, Guan Y (2012).

Study of Dioscorea opposite Thumb from different producing areas with XRF and PXRD. Spectroscopy and Spectral Analysis, 32: 1972-1975. (in Chinese)

Zhang W, Zhang Z, Shi Y, Fan G (2006). Determination of nine trace elements in Dioscorea opposite Thumb by flame atomic absorption spectrophotometry.

Xuesong et al. 190

Spectroscopy and Spectral Analysis, 05: 963-965. (in Chinese)

Zhou X, Song S, Wang W, Luo H (2010). Determination of the nutrient contents in the purple D. alata L. and the Dioscorea opposite Thumb. Journal of Anhui Agri. Sci., 38: 20005-20007. (in Chinese)