113 5 Radionuclide Concentrations in Soils Guillermo Manjón Collado CONTENTS 5.1 Introduction 113 5.2 Behavior of Long-Lived Radionuclides in Soil 114 5.2.1 Fractionation 115 5.2.2 Vertical Distribution 117 5.2.3 Influence of Microorganisms on the Behavior of Radionuclides 122 5.2.4 Soil to Plant Transfer and Bioavailability of Radionuclides 127 5.3 Radioactive Contamination and Countermeasures 137 5.4 Scientific and Social Applications 140 5.4.1 Dose Assessment 140 5.4.2 Radon in Soil and Earthquakes 142 5.4.3 Dating 144 5.4.4 Tracers in Soil Erosion 145 References 148 5.1 INTRODUCTION Long-lived radionuclides can easily be studied in zones not affected by recent (days) nuclear accidents. This is one of the reasons that short-lived radionuclides are not included in this chapter. Two different origins of long-lived radionuclides in soils can be considered. First, artificial radionuclides are transuranic elements (plutonium isotopes) and long-lived fission products ( 137 Cs, 90 Sr). In both cases, the presence in the environment of these kinds of radionuclides is due to nuclear weapons tests or the nuclear power industry. Next, natural radionuclides are radionuclides belonging to the three natural decay chains ( 238 U, 235 U, 232 Th), 40 K, and cosmogenic radioisotopes ( 3 H, 7 Be, 14 C). In the case of natural decay chains, radioelements might be inside the silicon dioxide crystals in soils. A fraction of the radon (gas) can be transferred from soils into the atmosphere by emanation. Then, 222 Rn decays in 210 Pb, which falls back, associated with aerosols, onto the Earth’s surface. DK594X_book.fm Page 113 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 114 Radionuclide Concentrations in Food and the Environment On the other hand, artificial radionuclides are stored in the stratosphere and fall to the Earth’s surface according to atmospheric dynamics. Artificial and cosmogenic radionuclides and 210 Pb are typical fallout radionuclides that are being deposited. In this chapter, the behavior of radionuclides in soils is studied. The main characteristics of the mentioned radionuclides are analyzed, experimental proce- dures are exhaustively discussed, and obtained data are analyzed. The study of the behavior of radionuclides has been divided into four items. First, the fractionation of radionuclides in soils is considered, according to the soil fraction (soil solution, organic matter, residual) associated with the radionu- clides. Second, radionuclide migration along the soil profile is studied. Third, the role of microorganisms is presented (e.g., in the remediation of contaminated soil). Finally, radionuclide bioavailability and transfer into plants is considered. Knowledge of the behavior of radionuclides in soil can lead to countermeasures in case of soil contamination. Finally, some scientific and social applications of radionuclide concentration measurements in soils, such as dose assessment, earthquake prediction through radon measurements, and dating of soil cores and erosion, are explained. 5.2 BEHAVIOR OF LONG-LIVED RADIONUCLIDES IN SOIL If the scientific literature is reviewed, environmental studies on the presence of radionuclide concentrations include in-depth discussions of the fractionation, vertical distribution, the influence of microorganisms, and the soil to plant transfer of radionuclides. Fewer articles can be found on the behavior of long-lived radionuclides in soil. Factors influencing the behavior of radionuclides in soils are mainly the chemical properties of the radioelement and the characteristics of the soil, includ- ing mineral composition, organic matter content, and chemical reaction milieu [1]. Other factors also affecting the behavior of radionuclides in soil are rainfall amounts, temperature, and soil management. Finally, the pH value is an important parameter controlling the kinetics of elements in soil and consequently the kinet- ics of radionuclides. In order to understand the mobility of radionuclides in soil, it is important to study the inorganic and organic composition of soils. The presence of inorganic matter (clay minerals and oxides) can cause processes of sorption and complexation. On the other hand, biological activity can increase radioelement mobility. Radionuclides can be absorbed by some mineral fractions of the soil (silt and clay fractions). The main minerals in these fractions are smectite, illite, vermicu- lite, chlorite, allophone, and imogolite. Other contributors to the absorption pro- cess are the oxides and hydroxides of silica, aluminum, iron, and manganese. Soils with a high content of illite, smectite, vermiculite, or mica within the clay fraction absorb large amounts of cations due to their intrinsic negative charge [1]. On the other hand, anions can be absorbed by aluminum and iron oxides at DK594X_book.fm Page 114 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Radionuclide Concentrations in Soils 115 pH values in the range of 8 to 9. Water-soluble anionic compounds such as phosphate, selenite, molybdate, and arsenate can be absorbed by the formation of stable complexes and the exchange of ligands with aluminum and iron oxides. The presence of organic matter reduces anion absorption. Organic matter is extremely heterogeneous and consists of organic acids, lipids, lignin, and fulvic and humic acids. The number of interactions and reac- tions of radionuclides with organic matter is high. These processes are affected by the pH and the cation concentration in soil. The dynamics of soil water, as well as the texture and structure of soil, have a direct impact on radionuclide speciation. Chemically unchanged substances can be partially transferred through water flow, whereas slow infiltration favors inter- action with the soil matrix and soil solution. 5.2.1 F RACTIONATION The speciation of the soils, based on a sequential extraction protocol used by Krouglov et al. [2], was applied by Baeza et al. [3], to samples collected in La Bazagona and Muñoveros, Extremadura (western Spain). These authors have considered different fractions in a soil as follows: • Exchangeable fraction: Dried samples of soil are treated with NH 4 OAc, where the exchangeable fraction is dissolved. • Dilute acid soluble fraction: The solid residue is attacked with 1M HCl, where the dilute acid soluble fraction is dissolved. This fraction is bound to organic matter. • Concentrated acid extractable acid fraction: The solid residue obtained in the last step is attacked with 6M HCl at boiling temperature. This fraction is bound to carbonates and oxides (iron or manganese). • Residual fraction: This is the final residue. This is the fraction more strongly bound to the soil matrix. However, five fractions may be observed in the sequential extraction. Thus Blanco et al. [4] compare two classical experimental procedures [5,6] that con- sider five different fractions in soils: exchangeable fraction, fraction bound to organic matter, fraction bound to carbonates, fraction bound to iron and manga- nese oxides, and residual fraction. In this work, the residual fractions were totally dissolved by HNO 3 /HF digestion under pressure using a microwave oven. Table 5.1 shows the main steps of both procedures. These two methods were checked by measuring isotopes of radium, uranium, and thorium. In the conclusion of this work, the authors found that the method of Schultz et al. [6] improves some of the defects recognized in the method of Tessier et al. [5]. For this reason, the method of Schultz et al. is usually applied in studies of the behavior of radionuclides in soil [7]. However, the unsystematic nature of the differences in results does not permit a direct comparison of the historical results obtained by both methods [7]. DK594X_book.fm Page 115 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 116 Radionuclide Concentrations in Food and the Environment The distribution of radionuclides in soil can be studied using particle size fractions [8]. In this case, soil samples are homogenized and different particle size fractions are separated by physical procedures [9] such as sieving and settling. Usually the sample depth must be large enough to collect all the artificial radio- nuclides deposited in the soil in order to establish the total amount of fallout in an area. For such a study, three size fractions must be considered: the sand-size fraction (larger than 63 µm), the silt-size fraction (2 to 63 µm), and the clay-size fraction (smaller than 2 µm). In the work of Spezzano [8], seven types of soils from the same area (Viverone Lake in southwest Italy) were studied. In this case, the physical and chemical characteristics of the different soils were determined in order to discuss the different behavior of 137 Cs from global fallout and 137 Cs from the Chernobyl accident. Table 5.2 shows the results obtained. In this work, organic matter was determined by the Walkley and Black method [10,11], cation exchange capacity by the BaCl 2 -triethanolamine method, and pH (in 0.1M KCl, 1:2 solid:liquid ratio) following standard methods [12]. Soil bulk densities (in kg/m 3 ) are evaluated by dividing the mass of dried soil sample by the volume of the soil core. The concentration of the most abundant element was determined by microwave digestion of the soil using high-purity reagents and Teflon vessels, and analysis by atomic absorption spectrometry [8]. Soluble and exchangeable cesium was determined by extraction with 1M NH 4 Ac at pH 7 (1:20 solid:liquid ratio, 24 h equilibration). Table 5.3 shows the concentrations of 137 Cs for each size fraction of the studied soils (corrected for decay to May 1986). In this table the strong binding of 137 Cs to clay minerals is easily observed. TABLE 5.1 Sequential Extraction Processes According to the Methods of Tessier et al. [5] and Schultz et al. [6] Fraction Reagents Method of Tessier et al. [5] Method of Schultz et al. [6] Exchangeable 1M MgCl 2 pH 7, 1 h, room temperature 0.4M MgCl 2 pH 5, 1 h, room temperature Organic matter (1) 0.02M HNO 3 + H 2 O 2 30%, pH 2, 2 h, 85˚C (2) H 2 O 2 30%, pH 2, 3 h, 85˚C (3) 3.2M NH 4 OAc in HNO 3 20%, 30 min, room temperature NaOCl 5–6%, pH 7.5, 2 × 0.5 h, 96˚C Carbonates 1M NaAc, pH 5 (HOAc), 5 h, room temperature 1M NaAc in 25% HAc, pH 4, 2 × 2 h, room temperature Oxides (iron or manganese) 0.04M NH 2 OH·HCl in 25% HOAc, pH 2, 6 h, 96˚C 0.04M, NH 2 OH·HCl, pH 2 (HNO 3 ), 5 h, room temperature DK594X_book.fm Page 116 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Radionuclide Concentrations in Soils 117 5.2.2 V ERTICAL D ISTRIBUTION The information obtained by a fractionation analysis of radionuclides in soil can be very useful for designing predictive models or to decide realistic countermea- sures. In addition, several horizons or layers are usually examined due to their quite different physicochemical properties [13]. Thus three organic horizons are easily distinguished: Of1 (litter, only slightly decomposed), Of2 (fragmented litter, partially decomposed by fermentation processes), and Oh (well-humified organic matter). The mineral soil horizons that can be analyzed are Aeh (0 to 5 cm), Alh (5 to 10 cm), Al (10 to 36 cm), and Bt (36 to 50 cm) [14]. This method was applied to soil collected in a spruce forest 50 km northwest of Munich, Germany. However, these horizons are different in other works. Actually these horizons can be separately studied for a better understanding of radionuclide behavior and the deepest layer can be neglected if artificial radionuclide fallout is the objective of the work [13]. TABLE 5.2 Chemical and Physical Characteristics in Soil [8] Land Use Woodland Peat Bog Cultivated Pasture Bulk density (kg/m 3 ) 1650 700 1440 1350 pH (0.1M KCl) 3.63 4.24 4.72 4.07 Organic carbon (%) 1.4 18 3.0 2.9 CEC (mEq/kg) 28 499 148 112 Clay (<2 µm) (%) 15 9 30 16 Silt (2–63 µm) (%) 47 62 61 57 Sand (>63 µm) (%) 38 29 9 27 Na (g/kg) 14.4 6.5 9.8 12.3 K (g/kg) 9.2 9.4 16.4 11.6 Ca (g/kg) 5.6 3.9 3.3 5.2 Mg (g/kg) 14.2 16.8 25.7 28.6 TABLE 5.3 Concentrations of 137 Cs (in Bq/kg) in the Particle Size Fractions of the Investigated Soils (Corrected for Decay to May 1986) [8] Land Use Woodland Peat Bog Cultivated Pasture Clay (<2 µm) 303 ± 10 578 ± 17 788 ± 20 265 ± 9 Silt (2–63 µm) 32 ± 3 271 ± 11 122 ± 6 63 ± 4 Sand (>63 µm) 7 ± 1 130 ± 11 67 ± 4 16 ± 2 DK594X_book.fm Page 117 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 118 Radionuclide Concentrations in Food and the Environment In general, physicochemical properties of soil samples are analyzed. Table 5.4 shows some of these properties and results obtained in a forest soil [13]. Other parameters such as density, cation exchange capacity, and exchangeable cations are also determined. Before the sequential analysis, the air-dried soil of each layer is usually sieved to 2 mm for the removal of stones and roots. Figure 5.1 shows the results obtained by Bunzl et al. [13] in a study of 137 Cs distribution in a soil profile. The total amount of 137 Cs in this soil is due to global fallout and the Chernobyl accident. The Chernobyl contribution was determined through the 134 Cs/ 137 Cs activity ratio. The highest 137 Cs activity was determined in the first mineral soil layer (0 to 2 cm). The percentage of 137 Cs (means of five soil cores) found after sequential extraction (method of Tessier et al. [5]) in fractions I to V in the seven layers of soil is presented in Figure 5.2. It is clear that radiocesium is mainly bound to TABLE 5.4 Physicochemical Properties of a Forest Soil in Different Layers [13] Horizon Depth (cm) pH (CaCl 2 ) Organic Carbon (%) Clay (%) Organic Layer Of1 7–4.5 3.2 49 Of2 4.5–2 3.2 49 Oh 2–0 2.9 40 Mineral Soil Aeh 0–5 3.2 2.8 19 Alh 5–10 3.6 1.3 21 Al 10–40 3.9 0.9 28 FIGURE 5.1 Total activity of 137 Cs per unit area in the various soil layers. For the organic layers, the name of the horizons is given. Within the mineral soil, the depth is given in centimeters [13]. 137 Cs 0 4 8 12 Of1 Of2 Oh 0–2 2–5 5–10 10–20 kBq m −2 DK594X_book.fm Page 118 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Radionuclide Concentrations in Soils 119 fraction IV (40 to 60%), but the presence of 137 Cs in the residual fraction is also important in mineral soil layers. The percentage in fraction I increases with depth for the mineral soil layers and the amounts in fraction II and III are negligible. The corresponding values decrease with the depth in fraction V. If we consider the organic layers, 137 Cs is bound to fraction IV. If a short-term fallout of radionuclides is deposited onto the surface of a soil as a pulse, a typical fast-moving tail is observed in soil layers below the peak concentration. This phenomenon can be explained by assuming that either the hydraulic properties of the soil or the sorption properties of the soil, or both, exhibit a horizontal variability. This fact can be demonstrated by Monte Carlo calculations, assuming a convection-dispersion model [14]. For example, we have the case of the zone close to the Chernobyl nuclear power plant. The soil in this zone was affected by a pulse of contamination of artificial radionuclides (e.g., 137 Cs). A typical study of the vertical distribution and migration of radionuclides was published by Bossew et al. [15]. The sampling site was located in the exclusion zone of the Chernobyl nuclear power plant and is shown in Figure 5.3. According to this map, a 137 Cs deposition of 2 to 4 MBq/m 2 is estimated. Figure 5.4 shows the shape of a 137 Cs profile in an undisturbed soil sample. The maximum of 137 Cs and the shapes observed in all the samples analyzed in this work were quite different in spite of the close proximity of the sampling sites (10 m). The apparent migration velocity, v (in cm/year), and the apparent dispersion coefficient, D (in cm 2 /year), were selected as migration parameters. These param- eters were evaluated by fitting the 137 Cs profiles to a Gauss-type function. The apparent migration velocity ranged from 0.14 to 0.22 cm/year and the apparent FIGURE 5.2 Percentage of 137 Cs (means from five plots in a spruce stand) found for the various soil layers in five fractions according to Tessier et al.’s [5] method: I, readily exchangeable; II, bound to sesquioxides; III, bound to organic matter; IV, persistently bound; V, residual. For the organic layers, the names of the horizons are given. Within the mineral soil, the depth is given in centimeters [13]. 137 Cs 0 10 20 30 40 50 60 Of1 Of2 Oh 0–2 2–5 5–10 10–20 % Extracted I II III IV V DK594X_book.fm Page 119 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 120 Radionuclide Concentrations in Food and the Environment dispersion coefficient ranged from 0.04 to 0.07 cm 2 /year. The uncertainties of the fitted parameters ranged from less than 1% to 10% for v and less than 5% to 35% for D . This study was extended to other fallout radionuclides and migration FIGURE 5.3 137 Cs contamination map of the area around the Chernobyl nuclear power plant [61] with contamination isolines in kBq/m 2 . The location of the investigation site is marked with an asterisk [15]. FIGURE 5.4 Vertical distribution of 137 Cs in a soil core collected in the exclusion area of Chernobyl nuclear power plant in 2000 [15]. 137 Cs 0 20 40 60 0–1 1–2 2–3 3–4 4–5 5–6 6–7 7–8 8–9 9–10 10–11 11–12 Depth (cm) Bq cm −3 DK594X_book.fm Page 120 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Radionuclide Concentrations in Soils 121 parameters. There are essentially three mobility groups. Strontium, cesium, cobalt, antimony, niobium, and plutonium show low mobility, americium is more mobile, and europium is the most mobile of all the investigated elements. This is explained by the different interactions between soils (sorption) and elements. Fujiyoshi and Sawamura [16] studied the vertical distribution in soils of natural radionuclides ( 40 K, 226 Ra, 210 Pb). In the case of natural radionuclides, the geological characteristics of the soil are very important in order to determine the vertical distribution and the total content. For instance, the vertical distribution of 40 K is related to biological activity (root uptake of nutrients). Profiles of 226 Ra can be used to determine a possible heterogeneity within a soil horizon. 210 Pb is probably the most interesting natural radionuclide because of its double natural origin in the soil profile. 210 Pb is a radionuclide daughter of 222 Rn (gas), which is in the atmosphere as a result of emanation from the soil surface. Then a fraction (unsupported) of 210 Pb in the soil is derived from the atmosphere via fallout or wet deposition. The origin of the other natural fraction (supported) is the activity of 226 Ra in the soil profile. The remaining 210 Pb is anthropogenic (e.g., from the combustion of fossil fuels) [16]. A profile of the 210 Pb/ 226 Ra activity ratio is plotted against depth in Figure 5.5 [16]. A peak in the 210 Pb/ 226 Ra activity ratio is at a depth of 32 cm. This depth corresponds to a time in the 18th century. This fact could be related to the progressive clearing started in the 17th century, but the discussion is not closed. Humic substances such as humic acid (HA) and fulvic acid (FA) are a fraction of the organic matter in a soil. These have a high affinity for actinide and lanthanide metal ions in a terrestrial system. Chung et al. [17] investigated the possibility of retaining fallout radionuclides in an organic matter-rich soil of Jeju Island, Korea. In order to simulate the behavior of actinide metals, Eu(III) was used as a tracer. Synchronous fluorescence spectroscopy (SyFS) was used to characterize the Eu(III) binding to humic substances. The element composition of HA and FA (carbon, hydrogen, nitrogen, and sulfur) was determined by a combustion method. The amounts of humic substances extracted from the soil samples at different depths are shown in Table 5.5. The results show that HA and FA are distributed FIGURE 5.5 Profiles of the activity ratio of 210 Pb/ 226 Ra with soil depth in a 95-year-old Tharandt coniferous forest [16]. 210 Pb/ 226 Ra 40 30 20 10 0 0.00 1.00 2.00 3.00 Depth (cm) DK594X_book.fm Page 121 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 122 Radionuclide Concentrations in Food and the Environment into the deep soil, while the ratio of FA/HA tends to slightly increase across the soil depth. The increased ratio of FA/HA may be ascribed to the higher mobility of FA due to its low molecular weight, high acidic functional group content, and relatively high solubility [18]. In order to better understand the effects of soil humic substances on radionuclide distribution, the physicochemical and binding properties of humic substances with Eu(III) were further characterized. The stability of the complexes tends to increase as the soil depth increases, and HA has a slightly stronger binding ability to the Eu(III) ions than FA. Conclusions of this work are • The increased ratio of FA/HA with soil depth may be caused by the solubility and mobility of FA with high acidic functional group contents and low metal ion loading. • The high solubility of FA compared to HA was also confirmed by elemental analysis (the high oxygen/carbon ratio), direct pH titration results, and 13 C nuclear magnetic resonance (NMR) spectral analysis (high carboxylic carbon contents). The basic information for the soil humic substances in this work may be useful in understanding and modeling the radionuclide (actinides) transport in the soil layer. 5.2.3 I NFLUENCE OF M ICROORGANISMS ON THE B EHAVIOR OF R ADIONUCLIDES The presence of microorganisms (bacteria) can change the behavior of radionu- clides in soil, mainly by reduction reactions that change the oxidation state of an element. As an example, the case of 99 Tc, which is a fission product of 235 U or 239 Pu, is discussed. Its long half-life (2.1 × 10 5 years) makes the presence of 99 Tc in the environment a certainty for a long time. The behavior of technetium in the environment (soil) mainly depends on its chemical form. The pertechnetate form (TcO 4 , Tc(VII)) is highly soluble and mobile in the environment. Moreover, this chemical form is readily available to TABLE 5.5 239+240 Pu Activity Concentration, Amount of Humic Acid (HA) and Fulvic Acid (FA) Extracted from Soil Samples (100 g) at Different Depths [17] Depth (cm) 239+240 Pu (Bq/kg) Humic Acid (g/100g soil) Fulvic Acid (g/100 g soil) FA/HA (g/g) 0–5 5.1 2.14 1.04 0.49 5–10 6.2 1.50 0.99 0.66 10–15 2.8 1.72 1.10 0.64 15–20 1.3 1.39 0.95 0.68 20–25 0.2 0.57 0.63 1.11 DK594X_book.fm Page 122 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC [...]... from the activity concentration (in Bq/kg) of the radioactive series and the 40K in soils [51 ] The research was based on the possible increase in the concentration of some natural radionuclides in soil, water, and even in the airborne dust in the State of Chihuahua, Mexico, due to human activities The mining of uranium in this region started in the early 1970s and lasted until 1983, while the processing... cm The concentrations of radionuclides in the soil samples were determined by γ spectrometry employing a coaxial HPGe crystal of 59 % efficiency In total, more than 150 0 in situ” and in lab” measurements were made and the results are shown in Table 5. 13 The conditions of the fieldwork experiments are essential in order to obtain good agreement, as in Table 5. 13 The main reason to take into account the. .. 2006 9 :53 AM Radionuclide Concentrations in Soils 1 45 TABLE 5. 14 × Estimated Age (×103 Years) of Soils on the Raised Coral Reef Terraces of Kikai Island [55 ] Soil Age Soil Core Age of Coral Topographic Position 1 2 3 4 5 6 3 .5 5. 2 35 45 50–60 80 100 1 25 3 .5 3.9 35 40 50 55 70–80 95 100 120–1 25 10 Be No Erosion Erosion >8 >18 >56 >127 >136 >102 >8 >20 >68 >143 > 158 >119 deposition rate of 10Be (in atoms/cm2/year)... performed in 1998–1999 The study area’s geology is principally granitic A map is shown in Figure 5. 13 The characteristics of the contamination in this area can be described by the mean activity concentration values (in Bq/kg) in the affected area: 10,924, 10,900, 10,0 75, and 5, 289 for 238U, 234U, 230Th, and 226Ra, respectively, in soil samples, and 1, 050 , 1,060, 768, and 1,141 for the same radionuclides in. .. and strongly fixed by the surface soil [60] The short half-life of 7Be (T½ = 53 .3 days) and the similar behavior to 137Cs create the potential for its use in tracing the short-term behavior of sediment in marine and lacustrine systems However, there have been a few attempts to use 7Be as a tracer in soil erosion investigations The principles involved in using 7Be to document rates and patterns of soil... FIGURE 5. 14 Map of the sand dune study area [36] generally low level of transfer of radionuclides from the rooting substrate to the plant and the dominant in uence of external contamination adhering to the plant foliage The study of the bioavailability of radionuclides in agricultural soils was developed from another point of view by El-Mrabet et al [37] The objective of this work was the radionuclide enrichment... of the study area and soil sampling sites of Kikai Island Modified from [62] 5. 4.3 DATING Maejima et al [55 ] worked on the application of 10Be to date soils Soil samples were taken from six soil profiles (Figure 5. 18) consisting of Initial Rendzina-like soil (core 1), Rendzina-like soil (core 2), Brown Rendzina-like soil (core 3), Terra fusca-like soil (core 4), Terra rossa-like soil (core 5) , and intergraded... the ratio of the activity of this radionuclide in the fruiting bodies and that in the soil [46] Alternatively, Baeza et al [47] suggest the use of an available transfer factor, where the activity of a radionuclide in the soil is corrected by its available fraction Table 5. 12 lists the results obtained by Baeza et al [47] in species of mushrooms collected in Extremadura According to these results, the. .. DK594X_book.fm Page 131 Tuesday, June 6, 2006 9 :53 AM Radionuclide Concentrations in Soils 131 To prepare soil tailings mixtures, the tailings were thoroughly mixed with the soil in a ratio of 1:10 (soil I) and 1 :5 (soil II) according to the weight Nine plant species, including local vegetables, were selected for this investigation, including broad bean (Vicia faba), Chinese mustard (Brassica chinensis),... 0. 05 0.38 0.43 0.042 0. 35 0.46 0.043 DK594X_book.fm Page 142 Tuesday, June 6, 2006 9 :53 AM 142 Radionuclide Concentrations in Food and the Environment and almost 80% from the first 25 cm Soil moisture, the presence of radon, and ground roughness are the most important factors that in uence exposure rates [49] The main conclusion of Quindos et al [49] is that the estimation of exposure rates obtained . the behavior of long-lived radionuclides in soil. Factors in uencing the behavior of radionuclides in soils are mainly the chemical properties of the radioelement and the characteristics of the. temperature, and soil management. Finally, the pH value is an important parameter controlling the kinetics of elements in soil and consequently the kinet- ics of radionuclides. In order to understand the. placed in a 5 cm × 1 cm cylindrical box and subjected to γ spectrometry. K d is expressed as the ratio of the radioactivity in the soil (in Bq/g) and in the extracted solution (in Bq/ml). The new