URANIUM ACCUMULATION IN SANDY SOIL IN AN ARID REGION DUE TO AGRICULTURAL ACTIVITIES Dr. Ashraf E. Khater King Saud University, Saudi Arabia Atomic Energy authority, Egypt Dr. Ashraf E. Khater King Saud University, Saudi Arabia Atomic Energy authority, Egypt

OUTLLINES Introduction Aim of the work Experimental work Results and discussion Conclusions Introduction Aim of the work Experimental work Results and discussion Conclusions

INTRODUCTION Environmental migration of long lived radionuclides, (e.g. I- 129, Am-241 and U-238) of different origins, potentially leads to contamination of soil water and consequently food-chain. The mobilization and accumulation behavior of long-lived radionuclides in soil plays a key role in risk assessment studies. Their behavior in soil is affected by soil physical and chemical properties (e.g. clay%, pH and redox potential), and processes such as sorption to organic and inorganic component of soil. Environmental migration of long lived radionuclides, (e.g. I- 129, Am-241 and U-238) of different origins, potentially leads to contamination of soil water and consequently food-chain. The mobilization and accumulation behavior of long-lived radionuclides in soil plays a key role in risk assessment studies. Their behavior in soil is affected by soil physical and chemical properties (e.g. clay%, pH and redox potential), and processes such as sorption to organic and inorganic component of soil.

Farming practices and land reclamation are adding radioactive materials and could change some soil properties and then affect the environmental behavior and migration of long lived radionuclides. Due to the continuous and long time application of phosphate fertilizers, uranium input and accumulation has been considered as potential source of soil contamination. The behavior of uranium in soil is of particular importance since the contaminated soil act as a long term source for radionuclides in food (Koch-Steindl and Prohl, 2001) Farming practices and land reclamation are adding radioactive materials and could change some soil properties and then affect the environmental behavior and migration of long lived radionuclides. Due to the continuous and long time application of phosphate fertilizers, uranium input and accumulation has been considered as potential source of soil contamination. The behavior of uranium in soil is of particular importance since the contaminated soil act as a long term source for radionuclides in food (Koch-Steindl and Prohl, 2001)

Various experimental and field studies had investigated environmental behavior and accumulation of uranium in soil (………….) Taylor (2007) assessed the accumulation of uranium in soil over 40 years from impurities in phosphate fertilizers and found that nearly all the U accumulated in soil. (undg w &plU) Rothbaum et al (1979) found that most of the U applied in SPF to CL soil during period up to 100 y was retained in the surface 23 cm layer of soil. Various experimental and field studies had investigated environmental behavior and accumulation of uranium in soil (………….) Taylor (2007) assessed the accumulation of uranium in soil over 40 years from impurities in phosphate fertilizers and found that nearly all the U accumulated in soil. (undg w &plU) Rothbaum et al (1979) found that most of the U applied in SPF to CL soil during period up to 100 y was retained in the surface 23 cm layer of soil.

Takeda et al (2006) report thee same results for the soil of experimental fields. Their results suggested that OM and non- cystalline clay minerals in soil should play an important role of uranium derived from PF in soil. Brisic et al (1992) suggest that more than 20 % of fertilizers applied U is leached to water ways as elevated U concentration, up to 0.5 mg.L -1, in surface waters have been reported in Eastern Slovenia and Mexico. The geochemical behavior of U has been investigated to an significant extent. However there is limited information on how soil physico-chemical characteristics and processes in the root environment affect U-speciation (Vandenhove et al 2007) Takeda et al (2006) report thee same results for the soil of experimental fields. Their results suggested that OM and non- cystalline clay minerals in soil should play an important role of uranium derived from PF in soil. Brisic et al (1992) suggest that more than 20 % of fertilizers applied U is leached to water ways as elevated U concentration, up to 0.5 mg.L -1, in surface waters have been reported in Eastern Slovenia and Mexico. The geochemical behavior of U has been investigated to an significant extent. However there is limited information on how soil physico-chemical characteristics and processes in the root environment affect U-speciation (Vandenhove et al 2007)

AIM OF THE WORK Shading more light on the accumulation of uranium in top surface of sandy soil in arid environment, The influences of soil physico-chemical properties on uranium behavior in soil

Twenty eight soil samples were collected from 14 location in 25 year old farm, where one cultivated (in) and another uncultivated soil (out) from each location. Fourteen water sample were collected from 14 underground water wells, as shown (map) All soil samples were dried, crushed, homogenized and sieved through 2 mm sieve Twenty eight soil samples were collected from 14 location in 25 year old farm, where one cultivated (in) and another uncultivated soil (out) from each location. Fourteen water sample were collected from 14 underground water wells, as shown (map) All soil samples were dried, crushed, homogenized and sieved through 2 mm sieve Experimental work

All soil samples were leached using Aqua Rigia and selected (10) samples were completely dissolved using mineral acid (HF, HNO 3, HCl) Uranium in soil and water samples were measured using Perkin Elmmer ICP-MS model ELAN-9000 at ALS Chemex – Canada. Soil physical and chemical properties (pH, EC, organic matter %, CaCo 3 %, soluble anions and soluble cations) and soil texture (clay%, silt% and sand %) were determined using standard method (Omran 1987) All soil samples were leached using Aqua Rigia and selected (10) samples were completely dissolved using mineral acid (HF, HNO 3, HCl) Uranium in soil and water samples were measured using Perkin Elmmer ICP-MS model ELAN-9000 at ALS Chemex – Canada. Soil physical and chemical properties (pH, EC, organic matter %, CaCo 3 %, soluble anions and soluble cations) and soil texture (clay%, silt% and sand %) were determined using standard method (Omran 1987) Cont.; Experimental work

Results and discussion Soil

Uranium activity concentration in Bq/kg

MeanRangeCountry S.A Canada < 0.01 – 45 U.S.A Europe Average uranium concentration, mg/kg in different countries soil Kabata- Pendias, 2001 & Salminen 2005

Leachable U in Soil

Total U in Soil

Organic matter المادة العضوية  Interaction of radionuclides with OM leads to formation of mineral-organic complexes and chelates, which is more important than metals hydroxo complex.  OM is extremely heterogeneous. There are a large number of possible reaction and interaction of radionuclides with OM.  The stability of these complexes depends on the pH of the soil, the cation concentration in the soil, the functional gp and the degree of saturation of the potential sorption site  Interaction of radionuclides with OM leads to formation of mineral-organic complexes and chelates, which is more important than metals hydroxo complex.  OM is extremely heterogeneous. There are a large number of possible reaction and interaction of radionuclides with OM.  The stability of these complexes depends on the pH of the soil, the cation concentration in the soil, the functional gp and the degree of saturation of the potential sorption site

CaCO 3 A higher soil cation exchange capacity will retain more U, while carbonate in the soil increase the mobility of uranium through the formation of soluble anionic U and CO3 complexes (Allard et al 1982)

pH Speciation of uranium in soil and aqueous systems is pH-dependent. Therefore, under acidic conditions, UO 2 2+ is the predominant U species in the soil, under neutral conditions, hydroxide complexes and phosphate complexes; under alkaline conditions, carbonate complexes predominant (Ebbs et al, 1998). Soil properties reported to increase mobility and plant accumulation of uranium include acidic soil with low adsorptive potential, alkaline soils with carbonate minerals, and the presence of chelates (citric acid) (Shahandeh and Hossner,2002)

EC

Soil Texture Clay %  Soils contain a number of radionuclides adsorbing components in the silt and clay fractions. The most important are minerals such as smectite, illite, chlorite, as well as the oxides and hydroxides of silica, aluminum, iron and manganese.  the adsorption is due to charge at the surface and the three-dimentional structure of the adsorbing minerals (Koch-Steindl, Prohl, 2001)  Soils contain a number of radionuclides adsorbing components in the silt and clay fractions. The most important are minerals such as smectite, illite, chlorite, as well as the oxides and hydroxides of silica, aluminum, iron and manganese.  the adsorption is due to charge at the surface and the three-dimentional structure of the adsorbing minerals (Koch-Steindl, Prohl, 2001) Clay mineral carry different kinds of charge which, can be either negative or positive.

Silt %

Sand %

Uranium in water

Conclusions Although, it is well known that U introduced into agricultural soil via phosphate fertilizers application, there is a clear evidence of U enhancement in soil samples. The effects of farming practice on uranium concentration in soils are more clear for soil with relatively low U concentration. There are various complex reactions and interactions of uranium and soil component that control U concentration and behavior in soil More research should be done to understand more the effects of soil physico-chemical properties on the accumaulation of uranium and other radionuclides

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