Phytoremediation of Depleted Uranium from Contaminated Soil and ...

Arab Journal of Nuclear Sciences and Applications, 45 (2) 315-326 (2012)

Phytoremediation of Depleted Uranium from Contaminated Soil and Sediments K. A. Al-Saad*, M. A. Amr*, A. T. Al-Kinani**, A. I. Helal*** *Department of Chemistry and Earth Sciences, Qatar University, P. O. Box 2713, Doha, Qatar. **Radiation and Chemical protection Department, Ministry of Environment, P. O. Box 7634, Doha, Qatar. ***Department of Nuclear Physics, NRC, Atomic Energy Authority, Cairo, 13759, Egypt. ABSTRACT Seedlings of sunflower (Helianthus annuus L.) was used to test the effect of pH, citric acid, phosphoric acid, and ethylene-diamine-tetraacetic acid (EDTA) on the uptake and the translocation of depleted uranium (DU). The experiments was performed in hydroponic cultures and environmental soil samples collected from Qatar. The results of hydroponic experiment indicated that DU accumulated more in the roots than leaves, in the plants that was grown in contaminated water. The presence of phosphoric acid, citric acid, or EDTA showed different patterns of DU uptake. Higher transfer factor was observed when phosphoric acid was added. When EDTA was added, higher DU uptake was observed. The data suggested the DU was mostly retained to the root when EDTA was added. Also, the experiments were applied on environmental soil samples collected from Qatar. The presence of phosphoric acid, citric acid, or EDTA showed different patterns of DU uptake for the three different soil samples. The addition of EDTA increased the DU uptake in the sunflowers planted in the three types of soils. The results indicated that, generally, DU accumulated more in the roots compared to leaves and stems, except when soil was spiked with phosphoric acid. The translocation ratio was limited but highest (1.4) in the sunflower planted in soil S2705 when spiked with phosphoric acid. In the three soils tested, the result suggested higher DU translocation of sunflower with the presence of phosphoric acid. Key Word: Depleted Uranium/ Phytoremediation/ Rhizofiltration/ ICP-MS.

INTRODUCTION Depleted uranium (DU) is a by-product of the uranium enrichment process.1 It has massive civilian and military uses. DU is used in hospitals as X-ray radiation shielding. In commercial aircrafts, it is used as a counterweight for rudders and flaps. Also, DU is applied as a counterweight for fork lifting, piling and oil well drilling equipments. In addition, DU forms the keels of sailing yachts. 2 It has as well been widely used in military conflicts primarily as armor penetrating munitions. 3 As a consequences of the past war activities, a large areas (in Kosovo and some locations in Serbia, and in Iraq) were contaminated by DU.1,4 Contamination of soil with DU has increased the public health concerns due to the radiotoxicity of DU. Inhaled DU particles that reside in the lungs for long periods of time may damage lung cells and increase the possibility of lung cancer. Other radiation-induced

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cancers, including leukemia, are also considered.5 Therefore, the select of a cost-effective technique appropriate for the remediation of large areas of contaminated waters and soils from depleted uranium, and the development of human potential trained on these techniques are of great necessities. The use of plants for the decontamination of environmental systems is an area of interest. These techniques are collectively termed phytoremediation, which is a promising cost-effective alternative to more conventional methods for decontamination.6-8 Soils and waters have frequently been the object of phytoremediation applications.9 Shahandeh and Hossner10 screened thirty four plant species for uranium accumulation from uranium-contaminated soil. The authors concluded that the effectiveness of uranium remediation of soils by plants was strongly influenced by the soil type.11 A key to the success of uranium phytoextraction is to increase the uranium accessibility to plants. Some organic acids can be added to the soils to increase uranium desorption from soil to soil solution and to trigger a rapid uranium accumulation in plants. Huang et al.12 indicated that of the organic acids tested (acetic acid, citric acid, and malic acid), citric acid was the most effective in enhancing uranium accumulation in plants. Uranium concentrations in shoot of Brassica juncea and Brassica chinensis (grown in a uranium-contaminated soil with uranium/soil=750 mg/kg) increased from 5000 mg/kg in citric acid-treated soils. It was stated that using this uranium hyperaccumulation technique, uranium accumulation in shoots of selected plant species grown in two uranium-contaminated soils (total soil uranium, 280 and 750 mg/kg) can be increased by more than 1000-fold within a few days. 12 Chang et al.13 observed that the highest uranium concentration was in plants growing in calcareous (calcium-rich) soils and the lowest in clayey acid soils with high Fe and Mn oxides and organic matter content. Addition of citric and oxalic acids increased uranium accumulation and uranium translocation to the shoots significantly. Addition of 20 mmol/kg-1 of citric acid to loamy acid soils reduced the soil pH to below 5 and increased uranium concentration in shoots to by 150-fold. Citric acid was the most effective chelater in desorption and plant accumulation of uranium. From the literature one gathers that sunflower (Helianthus annuus L.) is the most promising candidate for phytoremediation.6,14,15 It has been studied in hydroponics trials9,16 at the laboratory scale and at the field scale for the decontamination of soils and water containing low to moderate levels of heavy metals, 14 artificial radionuclides,9 and natural radionuclides.17,18 In some case, Helianthus annuus L. contains 1000 times more metal species than the soil in which it grows.19 The aim of work is to study the potential of sunflower (Helianthus annuus L.) to uptake and translocates uranium under different types of salinity of Qatari soils. The Influence of pH, citric acid, phosphates and EDTA on plant uptake of uranium were studied.

METHODOLOGY Instrumentations Measurements of depleted uranium were performed using inductively coupled plasma/mass spectrometry (ICP-MS, Agilent 7500Ce). The ICP-MS operational conditions in this experiment are summarized in Table(1). Prior to the remediation experiments, some selected samples were measured by -ray spectroscopy to determine the radioactivity of the heavy metals. -rays spectra were collected using p-type coaxial EG&G Ortec HPGe detector with relative efficiency 42.4%, 1.9 KeV at 1.33 MeV of 60Co. Also the

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mineral compositions of the soils were determined by the X-ray diffraction (XRD, CubiX3 Minerals, Panalytical, and the Netherlands). Table (1): Operating parameters of ICP-MS Agilent 7500ce. RF power Plasma gas flow Auxiliary gas flow Carrier gas flow Sampling depth Torch injector internal diameter Interface Ion lens voltages Octopole bias Quadrupole bias

1500 W 15 L/min 1 L/min 1.25 L/min 7 mm 2.5 mm Ni (1 mm sampler: 0.4 mm skimmer ) optimized for sensitivity in 10 ng/ml tune solution (Li, Y, Ce, Tl) - 17 V -13.5 V

Reagents Depleted uranium standard solution (NIST3164) and natural uranium standard solution (NIST4321C) were obtained from national institute of standard and technology (NIST, USA). Acetic acid, nitric acid, hydrogen peroxide, hydrofluoric acid, and perchloric acid were obtained from Merck, Germany. Phosphoric acid, citric acid and EDTA were obtained from Sigma-Aldrich, USA. Hydroponic experiment Prior to seedling, nutrient solution was prepared. This solution contained the following ingredients in g/L: 0.708 Ca(NO3)2-4H2O, 0.492 MgSO4-7H2O, 0.17 KNO3, 0.272 KH2PO4, 0.0083 FeCl3, 0.0025 H3BO3, 0.0015 MnCl2-4H2O, 0.0001 ZnCl2, 0.00005 CuCl2-2H20, and 0.00005 Na2MoO4-2H2O. 17 Seedling growth was prepared as described by Rodrĺguez et al.20 Briefly, seeds of sunflower were pretreated with an aqueous solution of CaCl2 (10 mM) in continuous agitation for 2 h. They were then transferred to a container with filter paper as substrate, treated with distilled water, and incubated for two days in a growth chamber until the roots presented a length of about 2 cm. Roots were grown in continuous darkness throughout the experiment. The germinated seedlings were then transferred to a 1-liter beaker containing tracer-free nutrient solution. The stems of the plant were protected with hydrophobic cotton and then were covered by a pierced lid. A second hole in the container cap was used for the air inlet from an air pump. The plants were allowed to grow for 4 weeks. After that, the nutrient solution was removed and 200 mL of fresh nutrient solutions containing the tracers (depleted uranium) were added. The plants were allowed to grow in the tracer solution for one week more prior to harvesting. The harvested plants were divided into leaves, stems and roots. After washing with de-ionized water, the plant tissues were dried at 70 °C for 24 h and weighed.

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Plant growth in soils Soil samples were collected from three regions in Qatar, namely, Abo-samara, Om-Said, and Doha. Artificial contaminated soil samples were fabricated in laboratory scale by spiking the samples with DU in the form of UO2(NO3)2.6H2O. Sunflower seeds were planted in soils held in plastic containers and irrigated daily and kept under sun light. Influence of pH, phosphoric acid, citric acid, and EDTA were studied. Preparation of artificial contaminated soil The practical part of the project depends on the classification of sample soils from the southern of Qatar. five samples were chosen from forty samples according to the physical composition of them. Each sample was divided into 5 portions. As a result, 25 portions were made. The mass of each portion was measured. The standard depleted uranium was added to each portion with specific volume needed to complete 50 ppm of depleted uranium in each sample. 20 ml of ultra-pure water was added to each portion to distribute the uranium equally in the soil. The depleted uranium remained in the soil 24 hours until the soil absorbed all the amount of uranium and homogenized in a shaker. After four days, the sunflower seeds were planted in the soils. Three seeds were planted in each portion (subsoil). An open hole (0.5 cm diameter) was made for each plastic bottles to release any excess water. The released water was collected in other plastic bottles. The soil was irrigated with deionized water for one month (from December 15/2010 – January 15/2011). After one month, the citric acid, phosphoric acid, and EDTA were added to the three portions, while the other two portions were left as a control-1 (with DU) and control-2 (without DU). A week later, after irrigating with the reagent, the plants were removed from the soil and the roots were washed. The plants were divided into three portions: (roots, stems, and leaves), dried in the furnace. These portions were grinded and digested by the procedure in the next section (2.7). Finally, uranium concentration was determined by ICP-MS. Soil digestion Soil samples were digested in order to measure the concentration of uranium and other trace elements originally found in the samples. Soil samples were dried overnight at 105 C. About 0.5 g of each sample was weighed and transferred into PTFE beaker. 10 mL of HF and 4 mL of HClO4 were slowly added and evaporated on a hot plate at 200 C until a crystalline paste was formed (2-3 h). 4 mL of HClO4 was added to each sample and evaporated to near dryness to remove any remaining HF residue. 10 mL of 5 M HNO3 was added and warmed gently until a clear solution was obtained. The clear solutions of samples were allowed to cool down and then diluted to 50 mL in polypropylene bottles for storage (producing a 1 M HNO3 solution). 1 mL of aliquot was diluted to 10 mL of deionized water, immediately prior to analysis by ICP-MS. Plant digestion Sunflowers (Helianthus annuus L.) were divided into roots, stem and leaves. About 0.5 g of each part was digested in microwave digestion system (MarsX, CEM, Germany) using 7 mL of HNO3 and 2 mL of H2O2. The maximum power of the microwave was 1200 W, percent power was 100%, pressure was 150 psi, temperature was 210 C, hold was 5:00 minute, and ramp was 20.00 min. The digested samples were then introduced to the ICP-MS for the measurement of DU.

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RESULTS AND DISCUUSSION Uptake and translocation of depleted uranium by Helianthus Annuus L. after rizofiltration of contaminated water DU was used as spiker in every experiment. Nutrient solution was spiked by 1 mg/L of DU standard solution. The parameters to be analyzed are the transfer factor (TF), defined as the ratio of the concentration in the plant to the concentration in the substrate, and the translocation ratio (TR), defined as the ratio of the DU concentrations in leaves and roots (dimensionless). These concentrations, however, can be expressed in the literature as the amount of uranium per mass unit of plant dry weight, or per unit of plants fresh weight. Table (2) shows the concentrations of DU, transfer factors (TF), and translocation ratios (TR) in parts of Helianthus Annuus L. treated by different reagents. Generally, the DU was concentrated in the roots of sunflower compared to the stems and leaves. Table (2); Concentration of DU, transfer factors (TF), and translocation ratios (TR). in different parts of Helianthus Annuus L. treated by different reagents. Reagent

pH Phosphoric acid Citric acid

EDTA

Reagent Conc. 5 7 9 1 mM 10 mM 100 mM 1 mM 10 mM 100 mM 1 mM 8 mM 10 mM 12 mM

DU concentration (g/g)/dry weight Leaves

Stem

Root

28.43±0.37 3.66±0.09 4.88±0.20 87.32±1.05 280.45±5.21 609.01±9.18 22.57±0.45 14.81±0.21 1.65±0.23 8.72±0.17 10.87±0.22 8.68±0.18 4.75±0.10

56.61±0.76 36.76±0.62 18.01±0.51 73.9±1.26 332.2±5.7 659.8±11.22 44.89±0.76 10.65±0.18 2.13±0.02 14.6±0.25 187.8±4.2 57.75±0.98 153.9±2.6

78.22±1.11 697.8±16.1 73.74±1.21 68.46±0.57 200.0±2.6 1628±31 369±9 71.03±1.13 11.17±0.26 442.3±11.2 2564±40 2851±66 1311±75

Whole plant 163.3 738.2 96.6 976.78 1065.9 2896.46 436.46 96.49 14.95 465.6 2762.7 2917.4 1469.7

TF

TR

163.3 738.2 96.6 976.78 1065.9 1896.46 436.46 96.49 14.95 465.6 2762.7 2917.4 1469.7

0.3635 0.0052 0.0662 1.2755 1.4023 0.3741 0.0612 0.2085 0.1477 0.0197 0.0042 0.0030 0.0036

Effect of pH The optimum plant-transfer factor was at pH 7 compared to the other studied condition (pH 5 and pH 9) (Fig. 1 a). The transfer factor was 738 at pH 7. Probably, at acidic aqueous solution, the free uranyl remains as water-soluble and it is less possible to form complex with the nutrients found in the solution. According to Chen et al.,20 rhizopheric organic matters increase the availability of metals to plant uptake. This is attributed to the fact that these matters may form complex with the metal ions as a result of chelation. This suggests that the DU forms a chemical compounds that are involved in the retention by the roots. Translocation ratios at pH 7 and pH 9 are approximately the same, namely 0.05, meanwhile the ratios is higher at pH 5. This is not necessarily due to the higher complex formation,

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but may be due to the less amount of DU being retained by the root. It is likely that the dissolved uranyl ions flow with the aqueous solution to the leaves. Effect of citric acid Three aliquots of spiked nutrient solution were prepared at 1mM, 10 mM, and 100 mM of citric acid. The plants were grown in these solutions for one week before harvested. The results showed reduction of the plant’s uptake at higher concentration of citric acid (Fig. 1 b). The transfer factor was 436 at 1 mM of citric acid. Evangelou et al.21 indicated a possible destruction of the natural barriers in the roots of Helianthus Annuus L. by citric acid excess. Chen et al.20 observed lower uptake of Pb and Cd to radish at as the concentration of citric acid increased from 0 to 3 mmol. This, according to the authors, was attributed to the lower pH as a result of adding citric acid. Effect of phosphoric acid Three aliquots of spiked nutrient solution were prepared at 1mM, 10 mM, and 100 mM of phosphoric acid. The plants were grown in these solutions for one week before harvested. Water-toplant transfer factor was 2896 at 100 mM. The results indicated that higher concentration of phosphoric acid caused the increase of the plant’s uptake, as shown in Fig. 1 (c). Effect of EDTA Fig. 5 presents the results of the DU concentrations in the roots, stems and leaves of sunflower for the EDTA experiments. The highest DU tissue concentrations resulted from the 10 mM of EDTA treatment. There was a big difference between the control at pH 7 and the 8mM, 10mM, and 12mM concentration of EDTA for any of the tissue sections. All EDTA dosages were effective in increasing DU translocation through the biomass. As shown in Fig. 1 (d), almost all of the DU was accumulated in the roots. Table 3 showed that the highest concentration of DU was 2762.7 and 2917.4 g/g for the 8 and 10 mM EDTA treatments. EDTA is well known as a chelater. Uptake and translocation of depleted uranium by Helianthus Annuus L. after phytoremediation of contaminated water The mathematical expression of the Helianthus annuus L. uptake that was used in the study is transfer factor (TF) and translocation ratio (TR). TF is defined as the ratio between the concentrations of a contaminant in the plant to the concentration of the same contaminant in the soil in which the plant grows,22 as shown in the equation below. Translocation ratio is the ratio between the concentration of uranium in leaves to roots.22

TF 

Concentration in plant (dry weihght ) oncentration in soil (dry weight )

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Arab Journal of Nuclear Sciences and Applications, 45 (2) 315-326 (2012)

(b)

(a) TF TF

(d)

(c)

Fig. (1): Effect of pH (a), citric acid (b), phosphoric acid (c), EDTA (d) on the uptake and translocation of DU in Helianthus Annuus L. Environmental soil sample characterization Mineral compositions of the five environmental soil samples were determined by X-ray diffraction, as shown in Table 3. These data were obtained from the XRD spectra. The elemental compositions of the soils were measured by ICP-MS, as shown in Table (4). Table (3): Mineral composition of the environmental soil samples measured by XRD. Minerals composition (Weight %) of minerals in different soil samples Sample Code Mineral name Mineral formula 2605 2714 2617 2705 Silicon oxide SiO2 52.74 ND ND 75.35 Calcite CaCO3 47.26 44.99 ND 24.65 Alarsite AlAsO4 ND 14.07 ND ND Microsommite [Na4K2(SO4)] ND ND 29.11 ND [Ca2Cl2][Si6Al6O24] Meionite Ca4[CO3(Al2Si2O8)3] ND ND 70.89 ND Dolomite CaMg(CO3)2 ND ND ND ND ND: Not detected

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2770 36.16 30.12 ND ND ND 33.72

Arab Journal of Nuclear Sciences and Applications, 45 (2) 315-326 (2012)

Table (4): Elemental composition (g/g) of environmental soil samples measured by ICP-MS. Metal Na Mg Al K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn As Se Rb Sr Y Zr

S2617 7080±25 15700±80 27060±322 4411±38 40330±553 9.85±0.04 3009±32 46.14±0.81 73.92±2.65 362±4 11060±39 10.51±0.08 40.37±0.67 12.96±0.05 28.57±0.46 9.87±0.21 7.51±0.67 30.28±0.19 525.5±2.2 12.96±0.09 55.98±1.33

S2770 8286±12 20040±168 25580±138 4134±9 38040±179 9.07±0.02 2960±18 42.52±0.49 83.70±0.97 36.53±0.39 9235±11 9.60±0.05 30.53±0.71 11.92±0.07 25.20±0.05 10.37±0.09 7.66±0.69 28.72±0.17 485±3 12.45±0.04 48.35±4.36

S2705 2523±15 7749±38 19460±119 3009±7 55040±396 8.77±0.09 1327.00±15.3 47.98±0.63 42.18±0.35 213.10±1.4 9764±92 9.89±0.05 28.01±0.38 14.62±0.17 26.93±0.66 12.54±0.26 10.76±1.02 24.75±0.44 2998±56 10.57±0.12 33.02±0.30

Metal Nb Mo Tc Cd Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Pb

S2617 11.68±0.04 4.45±0.12 3.00±0.004 3.69±0.19 7.85±0.01 261.60±1.99 17.59±0.04 28.22±0.42 9.50±0.05 15.89±0.37 6.07±0.05 4.30±0.02 6.25±0.12 7.78±0.02 5.77±0.07 7.97±0.02 4.95±.077 7.81±0.01 5.08±0.08 7.94±0.02 11.17±0.15

S2770 11.83±0.08 4.55±0.063 3.03±0.01 3.49±0.13 7.63±0.01 352.50±1.83 17.03±0.05 26.81±0.13 9.27±0.04 14.36±0.19 5.83±0.14 4.28±0.04 6.00±0.13 7.76±0.003 5.57±0.05 7.94±0.01 4.90±0.04 7.79±0.01 5.11±0.02 7.93±0.02 10.30±0.03

S2705 10.93±0.15 4.92±0.12 3.01±0.03 3.43±0.05 7.94±0.04 163.7±2.9 13.51±0.11 21.43±0.28 8.61±0.02 11.80±0.11 5.45±0.10 4.08±0.03 5.49±0.07 7.71±0.01 5.14±0.06 7.88±0.02 4.58±0.03 7.78±0.01 4.73±0.02 7.89±0.001 8.71±0.14

Effect of soil texture and chemical reagents on the uptake and translocations of DU in Helianthus Annuus L. Table (5) shows the concentration of DU in the three parts of Helianthus Annuus L. (leaves, stems and roots) treated by different reagents (citric acid, phosphoric acid, and EDTA) in addition to the control-1 (without any uranium or reagent added) and control-2 (with only uranium added, but with no reagents). The transfer factors (TF), and translocation ratios (TR) are also listed in the Table. The concentration of DU in the different parts of the plants as well as the TF and TR (listed in Table 5) are plotted for the control and the three types of soils in Fig.2 a-e. The total concentration of DU in the sunflower planted in control-1 soils (that had no uranium or reagents added) did not exceed a total of 900 g/g. When the soils were spiked with DU (50 ppm) and with no reagent added (control-2), the concentration of DU in the planted sunflowers increased to a level between 1800 and 2700 g/g. The soil with the code S2770 adsorbed the highest amount of DU (2654 g/g) as a total concentration when spiked with uranium. This soil (S2770) contains about 34% CaMg(CO3)2, unlike the other soils tested, which do not contain this mineral. Also, soil S2770 contains 30.12% CaCO3.

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Table (5): Concentration of DU, transfer factors (TF), and translocation ratios (TR) In different parts of Helianthus Annuus L. treated by different reagents. DU concentration (g/g)/dry weight Reagent

Control-1 (without spiking with DU or reagents)

Control-2 (with DU, but with no reagents)

Phosphoric acid

Citric acid

EDTA

Soil samples codes

TR

Stem

Leaves

Whole plant

TF

Root

S 2617

267±5.91

3.45±0.05

178.39±0.61

449±7

8.977

0.668

S2770

525.70±11.72

1.681±0.023

354.6±1.2

882±13

17.640

0.675

S 2705

8.3±0.1

5.223±0.081

2.175±0.041

15.7±0

0.314

0.262

S 2617

1797±213

7.75±1.51

76.87±9.09

1881.62

37.63

0.0428

S2770

2421±311

198.7±24.1

35.06±2.56

2654.76

53.10

0.0145

S 2705

2011±137

97.25±8.64

65.15±5.15

2173.4

43.47

0.0324

S 2617

4.72±0.61

1440±187

304.5±36.2

1749.22

34.98

0.0155

S 2770

672±88

1356±157

156.6±18.4

2184.6

43.69

0.2330

S 2705

1757±277

1206±167

2467±221

5430

108.60

1.4041

S 2617

2038±214

41.2±5.2

293.8±28.2

2373

47.46

0.1442

S2770

1457±241

287.6±31.3

81.23±10.24

1825.83

36.52

0.0557

S 2705

1621±201

100.5±13.1

189.5±24.6

1911

38.22

0.1169

S 2617

3015±312

18.96±2.06

62.3±8.1

3096.26

61.93

0.0207

S 2770

3793±383

67.34±7.75

17.27±1.25

3877.61

77.55

0.0046

S 2705

3079±400

1688±119

605.1±58.7

5372.1

107.44

0.1965

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b

a

d

c

e

Fig. (2): Effect of soil texture and chemical reagents of uptake and translocation of DU in Helianthus Annuus L.

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Although the distribution pattern between the three parts of the plants varied, DU uptake by the Helianthus annuus L. was always the highest in the roots compared to the stems and leaves, except in the case of soils spiked with phosphoric acid (Fig.2 d). This may suggest that phosphoric acid could enhance translocation. The translocation ratio (when spiked with phosphoric acid) was highest (1.4) in the sunflower planted in soil S2705, the one containing microsommite (29%) and meionite (71%), see Table 4. It is concluded from its mineral composition that soil S2705 has the least fraction of CO32compared to the other two tested soils (S2617 and S2770). In the three soils tested, the result suggested higher DU translocation of sunflower with the presence of phosphoric acid. Phosphoric acid may forms a compound with uranium that reaches the leaves rather than accumulate in the roots. The addition of EDTA always (in the three types of soils tested) increased the DU uptake (as shown in Fig.2 e), compared to those spiked by citric acid and phosphoric acid. The concentration of DU in the sunflower planted in soils spiked with EDTA reached a level between 3000-5000 g/g. Higher translocation was observed in soil S2705, when spiked with EDTA. Soil S2705 likely contains the least amount of CO32-, attributed to the fact that it does not contain calcite (CaCO3) nor dolomite (CaMg(CO3)2) (see Table 3, mineral composition of soils). According to, Vera Tomé18 CaCO3 could occlude the uranium and fix it into the wall of the root. Higher translocation of DU may be due to the lack of CO3 in soil S2705. According to Jean et al.,23 the addition to of EDTA increases the Pb concentration in Indian mustered by 1.5% in dry weigh of shoot. However, Nowack 24 indicated that the EDTA is persistent in the environment, so it causes unlimited leaching of metals from soil. As a result, EDTA is not recommended to be used in phytoremediation. Some alternative additive can be used instead of EDTA such as EDDT and citric acid. These molecules are biodegradable and enhance the uptake of metals by the plants’ roots.

CONCLUSION Examining the transfer factor (TF) hydroponically, it is observed that phosphoric acid allows the highest TF of DU compared to the other reagents (citric acid and EDTA). This suggests that phosphoric acid, similar to EDTA, can undergo chelation with DU. However, unlike EDTA, it is not strongly retained by the root of sunflower due to the fact that phosphoric acid complex is more polarizable, leading to higher translocation ratio. According to the phytoremediation study in soils it is indicated that EDTA and CO32-, when found in soils seem to cause higher DU uptake. The DU, however, is fixed in the roots of Helianthus annuus L. rather than translocated to the leaves. The presence of phosphate in the soil, on the other hand, promotes more translocation suggesting the formation of complex with uranium that unleashes the adsorbed uranium from the root and moved it to the leaves. With the soil lacking CO32-, this effect is more perceptible. ACKNOWLEDGMENT This article was made possible by NPRP award [NPRP 08-187-1-034] from the Qatar National Research Fund (a member of The Qatar Foundation). The statements made herein are solely the responsibility of the authors.

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