Journal of Applied Mathematics and Physics, 2014, 2, 848-854
Published Online August 2014 in SciRes. http://www.scirp.org/journal/jamp
http://dx.doi.org/10.4236/jamp.2014.29095
How to cite this paper: Song, G., Zhu, Q.P., Lu, M.X., Chen, D.Y. and Chen, Y.H. (2014) Natural Radioactivity in Miscanthus
floridul u Plant from the Uranium Tailing Pile at Guangdong, South China. Journal of Applied Mathematics and Physics, 2,
848-854. http://dx.doi.org/10.4236/jamp.2014.29095
Natural Radioactivity in Miscanthus floridulu
Plant from the Uranium Tailing Pile at
Guangdong, South China
Gang Song1,2,3*, Qiuping Zhu1,2,3, Minxing Lu1,2,3, Diyun Chen1,2,3, Yongheng Chen1,2,3
1School of Environmental Science & Engineering, Guangzhou University, Guangzhou, China
2Guangdong Province Key Laboratory of Radionuclides Pollution Control and Resou rces, Guangzhou, China
3Key Laboratory of Water Safety & Protection in the Pearl River Delta, Ministry of Education & Guangdong
Province, Guangzhou, China
Received 28 May 2014
Abstract
Large amounts of uranium waste rocks and tailings resulting from the exploitation and treatment
of uranium ore at the Northern Guangdong mine (South China) have been accumulated in dams
(tailing ponds). To reduce the dispersion of natural radionuclides into the environment, some
dams were reveg eta ted with arbor, bush and sward. Besides these plants, Miscanthus floridulu is
the dominant plant growing in some of the dams. The uptake and distribution of naturally occur-
ring uranium (238U) , thorium (232Th), radium (226Ra) and potassium (40K) by Miscanthus floridulu
plant from different sample sites of uranium mine were studied under native conditions. The bio-
concentration factors (BC F s) of soil to Miscanthus floridulu abov e-ground and root were calculated
and observed to be in the range of 0.14 to 7 .74 and 2.71 to 17.83 for 238U, 0 to 3.02 and 0 to 3.29 for
232Th, 0.15 to 79.76 and 1 . 01 to 50.22 for 226Ra and 3.00 to 8.41 and 2.69 to 11.22 for 40K, respec-
tively. The transfer factors (TFs) of Miscanthus floridulu root to aboveground were also calculated
and observed to be in the range of 0. 01 to 0.7 3 for 238U, 0 to 0.99 for 232Th, 0.08 to 1.50 for 226Ra
and 0.57 to 1.94 for 40K, respectively. The results showed that, Miscanthus floridulu is 238U and
226Ra-accumulating plant with significant absorption and accumulation characteristics.
Keywords
Natural Radionuclides, Uranium Tailings, Miscanthus floridulu, BCFs and TFs
1. Introduction
Over the past 50 years, large amounts of uranium waste rocks and tailings resulting from the exploitation and
treatment of uranium ore at the Northern Guangdong mine (South China) have been accumulated in dams (tail-
ing ponds). These radioactive solid wastes are exposed in the environment, long-term subjected to wind erosion
and rain leaching. The water and soil in the surrounding environment would be polluted with higher 238U, 226Ra
*
Corresponding author.

G. Song et al.
849
and other heavy metals; it will threaten the safety of the local ecological environment.
The traditional method of repair of uranium mine contaminated soil with physical and chemical methods, but
it is expens i ve and requires specialized equipment and technical personnel. Repair is not complete and causes
secondary pollution problems. Phytoremediation attracts much attention definitely with low cost and small en-
vironmental disturbance.
The study on transfer of natural radionuclides like 23 8U and 232Th along with their daughter products through
the biosphere is important because of their ubiquitous presence and persistence in the environment [1] [2] (P u l-
hani, 2005; Vino gr a dov, 1959). These long-lived naturally occurring radionuclides may get transferred to plants
along with the nutrients during mineral uptake, accumulate in various parts and even reach the edible portions
[1]. Most of the available literature refers to studie s of the accumulator plants including Helianthus annuus,
Brassica juncea, Lactuca dolichophylla, Cyperus iria L., Miscanthus sinensis and others. However, the accu-
mulator plant’s individual short stature, slow growth and small biomass, constitute the bottleneck of application
of phytoremediation. The key to break the bottleneck lies in two aspects; first is to improve the bioavailability of
radionuclides, and secondly is to improve the plant biomass. The screening of hyperaccumulator is one of im-
portant problems that the plant repair technology should solve.
Fro m the practical point of view, short growth cycle and biomass rapid accumulation of herbs have screened
quite large value. At home and abroad currently, the enrichment plants and hyperaccumulators for heavy metals
mainly are herbaceous plants. The enrichment plants for 238U and 226 Ra are mostly economic crops or foods
(such as Helianthus annuus [3]-[5], Brassica juncea [6] [7], Lactuca dolichophylla, Cyperus iria L., soybean,
etc.). These plants are low biomass, slow growth and longer repair time. The food safety and other defects also
decided the limitations of the practical application for these kinds of plants.
The field investigation found that there grows a single, dominant plant species—Miscanthus floridulus—in
the uranium mill tailings piles and waste rock heap. It is the Gramineae Miscanthus perennial herbaceous plants,
alias M. sinensis. It is mainly distributed in tropical Asia. Miscanthus floridulus has the advantages of root sys-
tem develops, large biomass, fast growth and strong resistance. It often grows in rock crevices and gravel pile. It
also can closure rain, conserve water and prevent the topsoil runoff and landslides and has very high value of
water and soil conservation. Therefore, the main goal of this study was to evaluate 238U, 232Th, 226Ra and 40K
uptake and distribution from uranium mill tailings by quantifying the total and available fraction of radionuc-
lides in the solid wastes and to estimate its transfer to plants growing on the tailing piles. Gamma spectrometry
was used to estimate 238U, 232 Th, 226Ra and 40K concentrations in soil, solid waste and plant.
2. Materials and Methods
2.1. The Study Area and Sampling Location
The Northern Guangdong uranium mine is located in the north of Guangdong province near Jiangxi province,
South China. The mine’s exploitation began in 1950s for uranium extraction. At present, uranium mine contin-
ues to production, but the extensive exploitation and treatment of the uranium ore in this mine, has led to an ac-
cumulation of large amounts of solid wastes (tailings). The solid wastes are composed mainly of tails and silt
particles that resulted from sulphuric acid-leaching of uranium, after ore crushing and grinding. The aqueous
phase containing the chemical components resulting from solvent extraction and/or ion-exchange separation to
concentrate uranium from the leaching solution is also deposited at the dams. Thus, the chemical composition is
complex and variable, depending not only on the nature of the original ore and added milling reagents, but also
on climatic conditions and on weathering reactions that occurred following the disposal.
2.2. Sample Collection and Proces sing
Miscanthus floridulus and tailing (solid waste) samp l e s from the soil within the rooting zone of the plants were
collected from uranium tailing piles in the above mentioned sample sites between May 2010 and December
2011. Reference samples of plants and soils were also collected from areas within 0.5 km of the tailing piles.
Plants were harvested and washed to remove adhering soil particles. Roots were separated from the above-
ground parts of the plants, air-dried and weighed. They were then dried at 110˚C until the weight was constant,
cooled and weighed again. The dried samples were ashed at 550˚C for 8 h (or until they formed a white ash) in a
muffle furnace, cooled and weighed.

G. Song et al.
850
Tailings and soil reference samples were collected from the rooting zone of the plants. They were homoge-
nised to obtain a representative sample. The tailing and soil samples were dried at room temperature and the
fraction less than ≤0.25 mm was retained for analysis.
Tailings (about 300 g), soil (about 250 g) and ashed plant (aerial parts about 30 g and roots about 40 g) sam-
ples were counted for 4 (tailings and soils) and 24 (plants) hours in sealed containers (70 mm × 75 mm), after
one month’s delay to allow equilibrium of 226Ra with its short-lived daughters.
2.3. Radioactivity Measurement
The activity concentrations of the natural radionuclides 238U, 226Ra, 232Th and 40K were determined in tailings,
soil and plant samples by gamma-spectrometry using a Canberra HPGe detector, with a relative efficiency of 30%
and an energy resolution of 1.8 keV for 60Co γ-ray energy line at 1332 keV, with 3800 mm2 active area and 70
mm2 active diameter [8].
2.4. Data Processing and Analysis
A common approach to quantifying the availability of soil radionuclides for plant uptake is the ratio between
plant activity concentration (B q ∙ kg−1) and total soil activity concentration (B q∙kg−1), usually termed as biocon-
centration factors (BCFs = activity concentration of radionuclides in plants Bq∙kg−1 dry weight/ activity concen-
tration of radionuclides in soil Bq∙ kg−1 dry weight) and transfer factors (TFs = activity concentration of radio-
nuclides in aboveground parts of plants B q ∙ kg−1 dry weight/ activity concentration of radionuclides in roots of
plants Bq ∙ kg −1 dry weight).
3. Results and Discussion
The uptake and distribution of naturally occurring uranium (238U), thorium (232Th), radium (226Ra) and potassium
(40K) by Miscanthus floridulu plant from different sample sites of uranium mine were studied under native con-
ditions.
3.1. Natural Radioactivity in Root Soils
Table 1 gives the concentration of 238U, 232Th, 226Ra and 40K in the root soils collected from all the fields. The
Table 1. Activity concentrations of 238U, 232Th, 226Ra and 40K in the root soils (Bq ∙ kg −1).
Samples
238
U
226
Ra
232
Th
40
K
S1 20338.2 16235.2 184.3 1357.2
S2 8127.5 3022.7 84.8 1757.0
S3 2938.3 1048.6 123.5 2629 .5
S4 11719.2 950.7 84.3 1523.8
S5 187917.0 176007.0 248.1 1857.5
S6 39064.3 103375.3 414.2 1252.9
S7 50010.2 175620.7 95.3 1089 .5
S8 29615.6 102558.4 114.6 1423.3
S9 74171.1 263621.9 117.8 1974.0
S10 30215.2 110054.7 121.8 1503.6
S11 1073.2 4253.5 274.4 986.5
S12 1154.5 3087.1 298.0 1400.4
S13 2529.9 1304.7 198.0 1654.4
S14 4519.6 3244.1 106.3 1277.8
S15 157.3 132.6 96.7 830.7
S16 153.0 99.8 86. 6 660.9
S17 163.2 90.8 99. 2 666.6

G. Song et al.
851
radionuclide contents of the different root soils are showing regional variations and strong dependence on their
geological precursor or the parent rock during its genesis. There were higher 238U and 226Ra contents in the root
soils from the tailing ponds
3.2. Natural Radioactivity Distribution in Different Parts of the Miscanthus flori du lus
In order to study the translocation and preferred site of accumulation of a radionuclide the total content of a ra-
dionuclide in whole plant has been normalized for fresh weight fraction of each plant part. The percent distribu-
tions of the radionuclides in various parts of the Miscanthus floridulus are shown in Tab le 2.
The distribution of 238U, 232Th, 226Ra and 40K in different parts of the Miscanthus floridulus showed the de-
creasing trend as root > above gr o und .
3.3. Transfer Factors (TFs) and Bioconcentration Factors (BCFs) for Natural Radioactivity
Transfer factors (TFs) were calculated as the ratio of the radionuclide concentration in plant aboveground
(Bq∙ kg−1 plant) to its concentration in root (Bq/kg root). And bioconcentration factors (BCFs) were calculated as
the ratio of the radionuclide concentration in root (Bq∙kg−1 root) to its concentration in so i l (Bq/kg soil). The
calculated results are given in Table 3 and Table 4.
The bioconcentration factors (BCFs) of soil to Miscanthus floridulu aboveground and root were calculated
and observed to be in the range of 0.06 to 8.95 (1.77 ± 2.63) and 0.22 to 19 . 60 (6.96 ± 6.06) for 238U, 0.13 to
4.89 (1.72 ± 1.42) and 0.48 to 6.41 (2.55 ± 1.61) for 232Th, 0.15 to 43.87 (8.44 ± 13.86) and 0.45 to 103.94
(20.50 ± 29.18) for 226Ra and 1.66 to 28.99 (6.72 ± 6.29) and 2.67 to 35. 79 ( 10 . 59 ± 8.77) for 40K, respectively.
Table 2. 238U, 232Th, 226Ra and 40K distribution in the roo ts and abovegrounds (fresh) of Miscanthus floridulus.
Samples
238U(Bq∙kg−1) 226Ra(Bq∙kg−1) 232Th(Bq∙kg−1) 40K(Bq∙kg−1)
Root AG Root AG Root AG Root AG
S1 83270.5 2868.6 29864.5 2 440.1 130.2 23.2 15226.3 9890.6
S2 35019.1 3852.3 17595.2 6 736.9 121.4 49.4 13487.0 8580.1
S3 29445.1 1359.7 5715.5 2290 .8 357.4 94.6 11397.8 8654.1
S4 4278.0 1436.3 9881 9.0 16834.5 40.7 29.5 54530.0 4696.8
S5 41252.2 13645.1 7970 5.4 46965.1 872.3 591.8 7665 .2 7165.7
S6 318591.0 18513.4 280150.3 4 7635.1 268.7 74.0 8925.4 4205.4
S7 135542.5 24933.0 177146.9 7 8166.3 610.4 268.3 5271.5 3271 .0
S8 52776.7 7440.3 1788 88.7 26623.0 522.7 248.6 3830 .8 7424.3
S9 92698.5 4418.1 2517 94.6 78166.3 365.7 130.4 5271 .5 3271.0
S10 225034.1 56276.3 1842979.7 2656 37.4 459.2 182.4 5970 .3 4913.1
S11 5659.8 4135.4 6 656.4 10571.9 812.6 744.9 9693.8 9410.8
S12 14821.8 388.8 99142.9 1480.2 167.6 40.7 3695 5.2 7297.1
S13 8175.4 3024.1 2 4910.2 8853.2 558.0 310.2 2411 4.1 14812.6
S14 19140.6 1558.9 10917.7 4203.3 124.4 123.5 11855.7 6 767.9
S15 2498.7 671.8 4242.2 3508.2 282.9 414.3 12946.4 2408 2.2
S16 2999.4 1023.5 6 107.3 4378.6 301.4 423.7 6780.3 7246.4
S17 2747.9 1460.7 5 319.5 3244.1 190.0 247.1 6504.2 4205.1
Note: AG―Above ground.

G. Song et al.
852
Table 3. Calculat ed BCFs fo r the roots and abovegrounds of Miscanthus floridulus.
BCFs
238U 226Ra 232Th 40K
Samples R oot AG1 Root AG Root AG Root AG
S1 4.09 0.14 1.84 0.15 0.71 0.13 11.22 7.29
S2 4.31 0.47 5.82 2.23 1.43 0.58 7.68 4.88
S3 10.02 0.46 5.45 2.18 2.89 0.77 4.33 3.29
S4 0.37 0.12 103.94 17.71 0.48 0.35 35.79 3.08
S5 0.22 0.07 0.45 0.27 3.52 2.39 4.13 3.86
S6 8.16 0.47 2.71 0.46 0.65 0.18 7.12 3.36
S7 2.71 0.50 1.01 0.45 6.41 2.82 4.84 3.00
S8 1.78 0.25 1.74 0.26 4.56 2.17 2.69 5.22
S9 1.25 0.06 0.96 0.30 3.10 1.11 2.67 1.66
S10 7.45 1.86 16.75 2.41 3.77 1.50 3.97 3.27
S11 5.27 3.85 1.56 2.49 2.96 2.71 9.83 9.54
S12 12. 84 0.34 32.12 0.48 0.56 0.14 26.39 5.21
S13 3.23 1.20 19.09 6.79 2.82 1.57 14.58 8.95
S14 4.24 0.34 3.37 1.30 1.17 1.16 9.28 5.30
S15 15. 88 4.27 31.99 26.46 2.93 4.28 15.58 28.99
S16 19. 60 6.69 61.20 43.87 3.48 4.89 10.26 10.96
S17 16. 84 8.95 58.58 35.73 1.92 2.49 9.76 6.31
Table 4. Calculated TFs for the roots and abovegrounds of Miscanthus floridulus.
TFs
Samples 238U 226Ra 232Th 40K
S1 0.08 0.18 0.65 2.37
S2 0.38 0.41 0.64 3.48
S3 0.40 0.26 0.76 8.68
S4 0.17 0.72 0.09 0.51
S5 0.59 0.68 0.93 1.78
S6 0.17 0.28 0.47 2.93
S7 0.44 0.44 0.62 2.40
S8 0.15 0.48 1.94 1.06
S9 0.31 0.36 0.62 6.51
S10 0.14 0.40 0.82 0.58
S11 1.59 0.92 0.97 2.17
S12 0.01 0.24 0.20 0.57
S13 0.36 0.56 0.61 0.96
S14 0.38 0.99 0.57 4.73
S15 0.83 1.46 1.86 3.08
S16 0.72 1.41 1.07 2.10
S17 0.61 1.30 0.65 1.15

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853
The transfer factors (TFs) of Miscanthus floridulu root to aboveground were also calculated and observed to
be in the range of 0.03 to 0.73 (0.23 ± 0.20) for 238U, 0.1 8 to 1.46 (0.65 ± 0.42) for 232Th, 0.01 to 1.59 (0.43 ±
0.37) for 226Ra and 0.09 to 1.94 (0.79 ± 0.48) for 40K, respectively. A major average percentage of total 83%
(57% - 97%) for 238U, 64% (40% - 85%) for 232Th and 73% (39% - 98%) for 226Ra activity in the plant is con-
centrated in the roots, and only about 17% (2.6% - 42%) for 238U, 36% (15% - 49%) for 232Th and 27% (1.5% -
61%) for 226Ra was distributed in the aboveground, whereas about 59% of 40K activity accumulated in the roots
and 41% in the aboveground. The results showed that, Miscanthus floridulu is 238U and 226Ra -accumulating plant
with significant absorption and accumulation characteristics, but their BCFs and TFs are not in accord with tra-
ditional hyperaccumulator definition.
The nearly comparable value of transfer factors for radionuclides in spite of their different concentration le-
vels in soil is a result of very complex behavior of elements in soil. Yunoki [9] have reported that the degrees of
accumulation of natural radioactive elements are affected by the metal-selective function of plants during uptake
of elements so as to maintain the mechanism of homeostasis in normal environment.
4. Conclusions
The soils show characteristics of the pollution from the uranium waste rocks and tailings, with regards to their
radionuclide contents. The uptake of uranium, thorium and radium appears to be regulated by the requirement of
the Miscanthus floridulu for essential nutrients. Radium uptake by Miscanthus floridulu is more than uranium
for the soils polluted by the uranium waste rocks and tailings. Under natural field conditions, the concentration
of a radionuclide in the receptor compartment (root or aboveground) changed with the concentration in the
source compartment (soil) is high or low.
To reduce the dispersion of natural radionuclides into the environment, some uranium tailings dams were re-
vegetated with arbor, bush and sward. Besides these plants, Miscanthus floridulus is the dominant plant gro wi ng
in some of the dams. The results showed that, Miscanthus floridulu is 238U and 226Ra -accumulating plant with
significant absorption and accumulation characteristics, but their BCFs and TFs are not in accord with tradition-
al hyperaccumulator definition. Even the BCFs and TFs of some plants do not reach a certain threshold, but their
large biomass also can make them a hyperaccumulator. Miscanthus floridulus has outstanding characteristics of
fast growth and large biomass; it will provide us a new plant material to study hyperaccumulator selection and
phytoremediation engineering in uranium tailings environment.
Acknowledgements
Supports by the National Natural Science Foundation of China (No.41373117, 40930743) are gratefully ac-
knowle dged .
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