59 4 Radionuclide Concentrations in Water José Luis Mas, Manuel García-León, Rafael García-Tenorio, and Juan Pedro Bolívar CONTENTS 4.1 Introduction 60 4.2 Radionuclides in Rivers and Lakes: Levels and Behavior 60 4.3 Radionuclides in the Sea and Ocean 68 4.3.1 System Overview 68 4.3.2 Sources and Sinks of Natural Radionuclides in the Ocean 70 4.3.3 TENORM-Related Pollution Cases 75 4.3.4 Artificial Radionuclides in the Oceanic Ecosystem 76 4.3.4.1 Fissile Materials and Transuranide Activation Products 77 4.3.4.2 Fission Fragments and Other Activation Products 79 4.4 Radioactivity in Rainwater 83 4.4.1 Introduction 83 4.4.2 The Presence of Radioactivity in Rainwater: Sources and Pathways 84 4.4.2.1 Natural Radioactivity 84 4.4.2.2 Man-Made Radioactivity 84 4.4.3 Levels and Distribution 85 4.4.3.1 Natural Radioactivity 85 4.4.3.2 Man-Made Radioactivity 86 4.5 Radionuclides in Groundwater 91 4.5.1 Introduction 91 4.5.2 Radionuclide Fractionation in Groundwater 92 4.5.3 Some Application Cases 95 4.6 Radioactivity in Drinking Water 98 4.6.1 Introduction 98 4.6.2 The Presence of Radioactivity in Drinking Water 99 DK594X_book.fm Page 59 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 60 Radionuclide Concentrations in Food and the Environment 4.6.2.1 Natural Radioactivity 99 4.6.2.2 Man-Made Radioactivity 99 4.6.2.3 Levels 99 4.6.3 Dose Assessment 101 References 102 4.1 INTRODUCTION Different kinds of water cover more than two thirds of the Earth’s surface. This resource is extremely important for human life: water is used for direct consump- tion, it is used in the production of food, it is used for many industrial activities, etc. Thus radioactivity present in water can reach humans and the environment through many different mechanisms. Water is a medium for the transport and interaction of radionuclides with and within different compartments of the troposphere: soils, sediments, crustal rocks, biota, and even air are continuously exchanging their radioactive contents with water. The nature of the compartment determines the nature of the dominant interaction mechanisms. The properties of the compartments depend, of course, on the nature of the ecosystem where the compartment is located. Therefore, a systematic categorization can be established according to the possible scenarios where water is considered an important medium for the exchange, supply, or storing of radioactivity. In this chapter, four different compartments are considered. In Section 4.2, rivers and lakes, which act as a water supply source to the sea, are described in detail. An overview of radioactivity in the oceans is presented in Section 4.3. Rainwater is discussed in Section 4.4. Underground reservoirs are intensively used for different human activities; these are discussed in Section 4.5. Finally, drinking water is analyzed in Section 4.6. 4.2 RADIONUCLIDES IN RIVERS AND LAKES: LEVELS AND BEHAVIOR The natural compartment analyzed in this section could first be characterized by the fact that it does not contain any intrinsic radionuclides in its composition. The presence of natural and artificial radionuclides at different levels in surface waters is clearly correlated with the existence of some coupling between the different compartments. In fact, surface waters are coupled to subsurface aquifers, to soils, and to the atmosphere, allowing incorporation of several radionuclides following different routes. Indeed, some radionuclides previously dissolved in deep underground aquifers may reach surface waters, other radionuclides may be directly incorporated in surface waters by deposition from the atmosphere, and a large fraction of the radionuclides in aquatic systems have their origins in the underlying soils, from where they can be transported to surface waters through runoff or leaching into the groundwater. The first and last routes are the most DK594X_book.fm Page 60 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Radionuclide Concentrations in Water 61 important ones explaining the presence of natural radionuclides in rivers and lakes, while the second and third routes, together with direct discharges from nuclear facilities, are the main ways artificial radionuclides are deposited in aquatic ecosystems. Once radionuclides are incorporated in a body of water, their dispersion and behavior is hard to predict in a general or straightforward way. Each stream, river, lake, etc., has its own mixing characteristics that vary from place to place and time to time [1], the rate of mixing being dependent on the depth of the water, the type of bottom, the shoreline configuration, wind, etc., and on the different chemical, physicochemical, and biological processes. Modeling of the hydrologic behavior of a water body requires site-specific parameters that limit its general applicability in water dispersion studies. Furthermore, the fate of a radionuclide can be complicated by its physicochemical behavior. If the radionuclide is present in the water body as a suspended solid, it can be deposited to the bottom or can pass to solution via desorption. On the other hand, if the radionuclide is incorpo- rated in the solution phase, it can be adsorbed on suspended organic and inorganic solids, and then settle to the bottom. This physicochemical behavior is obviously element dependent; in addition, it depends on other factors such as pH, redox conditions, the total amount of solids, etc., as is shown later in this chapter [1]. All these facts make it quite difficult to predict, especially in rivers, the behavior and dispersion of radionuclides. However, if sufficient information can be obtained about their physical characteristics, it is possible to estimate with some degree of certainty the dispersion of some specific radionuclides. More advances have been made in the prediction of radionuclide behavior in lakes. Models for predicting the migration of radionuclides through the biotic and abiotic components of lacustrine environments have been clearly identified and are widely accepted by the scientific community [2]. For some radionuclides, such as 137 Cs and 90 Sr, a quantitative evaluation of the most important transfer parameters through lacustrine ecosystems has been performed. To do that, experimental studies following the most significant nuclear accidents (Chernobyl, Kysthym) were developed. Today, it is possible to obtain levels of uncertainty of a factor of two to three when models for these nuclides are applied as generic tools for predicting their behavior in the abiotic components of the lacustrine environment. These uncertainties can be decreased if a detailed study of site-specific values of the model’s parameters is performed. Nevertheless, for several important radionuclides, the parameters are not yet available with enough uncertainty, and further assessments are necessary, mainly in relation to the evaluation of model uncertainties [2]. In surface water bodies such as rivers and lakes, an understanding of the role of bottom sediments is essential to understanding the behavior and fluxes of radionuclides incorporated from the coupled ecosystems (atmosphere, soils, groundwater, etc.). On a long time scale, the bottom sediments can be considered, at least temporally, as sinks for a fraction of the material in the different chemical and biological aquatic cycles. Radionuclides adsorbed onto organic or inorganic material in the water or forming part of the crystalline structure of suspended DK594X_book.fm Page 61 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 62 Radionuclide Concentrations in Food and the Environment inorganic material can be incorporated into the sediments. Once a radionuclide has been incorporated to the sediment phase, its future depends on a great number of complex factors. In fact, radionuclides can either be permanently linked to a sediment component or can be liberated and take part in different biogeochemical reactions. Consequently the ability to predict the future behavior of a radionuclide initially incorporated in the sediment is one of the key factors in evaluating its effect on the environment. For this reason, it is insufficient to determine its total content in the sediment in order to understand its behavior. It is necessary, in addition, to obtain information about the path or mechanism followed by the radionuclide in its linking to the sediment. In order to do this, it is necessary to distinguish between the residual and nonresidual fractions in the sediment. This separation is very important in relation to the possible liberation of radionuclides (both natural and artificial) incorporated in the sediment. The radionuclides forming part of the residual phase can be considered immobile (i.e., not reactive in the environment), while the radionuclides associated with the nonresidual fraction can be considered potentially mobile. Consequently this mobile phase can be considered as reactive in the different chemical and biological processes that occur in the water–sediment interface. Among the different natural radionuclides that can be found in nature, there are the radionuclides belonging to the uranium and thorium series and 40 K, the isotopes that may be present at higher levels in water. Both uranium and thorium are initially in the valence state +4 in igneous rocks and primary minerals, but uranium, in contrast to thorium, can experience oxidation in the valence states of +5 and +6. In oxidized environments, uranium will be in the state +6, forming the quite soluble uranyl ion (UO 2 2+ ), which plays an essential role in the transport of uranium in the environment. For this reason, uranium can be found in disso- lution in most surface water systems. In contrast, thorium is quite insoluble in the majority of natural waters, being present or transported in the suspended matter of water bodies. Even in the case when thorium is generated as a daughter of uranium in dissolution, it is quickly hydrolyzed and adsorbed to the surfaces of the particulate matter fraction. Few studies have been conducted on riverine uranium. A global survey of uranium concentrations in dissolution from 43 rivers ranging in flow from less than 1 km 3 /year to 6930 km 3 /year was published by Palmer and Edmond [3], estimating the average concentration of uranium in river water at 2.3 mBq/l. Recently this database was extended to include smaller watersheds (an additional 29 rivers with flow rates ranging from less than 1 km 3 /year to 100 km 3 /year); the result when the two datasets are combined does not change the previously indi- cated average concentration of dissolved uranium in rivers [4]. Nevertheless, the authors of these studies pointed out (1) the difficulty in obtaining representative samples from rivers, which show large fluctuations in runoff and dissolved load, and (2) the scatter of the uranium concentrations in the different rivers that can vary considerably in relation to the worldwide average value. Values 10 times higher than the average have been determined, for example, in the upper parts of the Ganges River, while concentrations two to three times higher have been DK594X_book.fm Page 62 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Radionuclide Concentrations in Water 63 determined in the Guadalquivir (Spain) and Seine (France) rivers. Values one order of magnitude lower than the average worldwide uranium concentration have been found in the Amazon River system. The higher or lower values of uranium in dissolution in rivers and lakes can be associated with the characteristics and relative influence of the different sources terms of this element. The bedrock type of the aquifers feeding their waters into the analyzed river as well as the soil types in the river basins and their drainage area are important factors in the levels of uranium in dissolution in the waters incorporated into the river. As explained by Schmidt [4], the high values of uranium in dissolution in the Seine River are associated with the main charac- teristics of its drainage basin, which is rather homogeneous with sedimentary rocks, mainly carbonate rocks, such as limestone. This explanation follows the suggestion of Broecker [5], indicating that uranium variations in river water may be due to variations in the carbonate concentrations in dissolution, because the uranium in carbonate form is quite stable and soluble. It is also well known that high levels of uranium can be found in water from granitic aquifers, while lower values are found in water from sandy ones. A high positive correlation has been observed between the level of uranium in dissolution in river water and the concentration of NO 3 [6] and the total amounts of solids in dissolution [7]. In several rivers, an inverse correlation between the uranium in dissolution and silicon/total anions has been found. This indicates that the dominant control on uranium in dissolution is probably the chemical weathering of nonsilicate minerals [8]. At this point it is necessary to remark about what is meant by uranium in dissolution: this term is applied to the uranium activity (or mass) that is associated with the fraction passing filters with a pore size of 0.45 µm. It has been observed in several rivers, and associated to the filtered fraction, that a large proportion (30 to 90%) of the uranium is carried by colloids, a fact that is compatible with a possible uranium complexation with humic acids [9]. In addition to natural uranium inputs, the presence of uranium with an anthro- pogenic origin should be considered. It has been suggested [10] that some high values in specific rivers may be due to the extensive use of phosphate fertilizers in agriculture, which have uranium contents up to 1 Bq/g. In contrast, Mangini and Dominik [6] conclude that the uranium from phosphate fertilizers is mainly adsorbed to the surface layers of the sediment. However, phosphate fertilizers may also affect the uranium in dissolution via a more indirect route, because high phosphate levels can lead to eutrophication and to an increase in the biological breakdown of organic matter, which may result in enhanced uranium in dissolution. A number of investigations have been performed in the mouths of the rivers, studying the influence of dissolved uranium in the complex interactions between fresh- and saltwater. In estuarine zones, where a pronounced gradient of salinity can be observed, the iron and manganese dissolved in river water can precipitate as oxihydroxides, provoking the coprecipitation of uranium and its incorporation in the sediment together with the organic matter in dissolution [11]. Nevertheless, this process is not general. A good number of studies show the conservative DK594X_book.fm Page 63 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 64 Radionuclide Concentrations in Food and the Environment behavior of uranium in estuaries, with a positive correlation between uranium concentrations and water salinity. This correlation is due to the higher levels of uranium in seawater in relation to freshwater. This conservative behavior has been observed, for example, in the estuary of the Seine River [4], and can be correlated with the proportion of uranium present in the water in colloidal form. Studies performed by Porcelli et al. [9], in a river discharging in the Baltic Sea, suggest that while solute uranium behaves conservatively during estuarine mixing, colloid-bound uranium is lost due to rapid flocculation of colloidal material. Thus the association of uranium with colloids may play an important role in determin- ing uranium estuarine behavior. Regarding the characteristics of the main source terms and the routes followed by the natural radionuclides for their incorporation in water bodies, it can be seen in rivers and lakes that there is a clear fractionation or disequilibrium between radionuclides belonging to the same natural series. The water passes through the solid grain either in the bedrock of the aquifers or in the soils from the drainage area. The rate of this weathering is not the same for the different radionuclides, some elements being more soluble than their parents or daughters under different redox and pH conditions. The result is a liquid phase enriched in radionuclides of one natural series and depleted in others. Later, the soluble radionuclides can even decay into daughters with less solubility than their progenitors. It is possible to observe other fractionation processes through precipitation and adsorption onto the surface of the particulate matter of some radionuclides. The processes indicated below can explain, for example, the high level of disequilibrium observed in river and lake daughters between 234 U and its daughter 230 Th. 230 Th/ 234 U activity ratios are clearly lower than those observed in the studied water bodies because (1) the uranium under oxidized conditions is clearly more soluble than thorium, and for that reason the groundwater and the leached soil waters are enriched in 234 U in relation to 230 Th; and (2) even when the 230 Th is formed inside the surface water body due to the decay of its progenitor, 238 U, it tends to incorporate to the solid phase by precipitation or adsorption. These processes also explain the very low levels of 210 Pb and 210 Po in dissolution in river and lake waters due to their low solubility and tendency to be associated with particulate matter. In the river and lake waters, a clear disequilibrium has also been observed between two radionuclides that belong to the same natural series and are isotopes of the same element ( 238 U and 234 U). Studies have been carried out in a number of rivers distributed all over the world and with quite a broad range of flow rates. A general consensus has been reached indicating that 234 U/ 238 U activity ratios are in the range of 1.20 to 1.30 [12]. This fractionation cannot be explained simply by a combination of dissolution/precipitation processes in the previously explained way, because both radionuclides are isotopes of the same chemical element. It is necessary to explain the observed disequilibrium on the basis of other type of processes. The preferential presence of 234 U in relation to 238 U in dissolution can be explained by a process called the Szilard-Chalmers effect. This process is based DK594X_book.fm Page 64 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Radionuclide Concentrations in Water 65 on the increased vulnerability of the daughter nuclide to the dissolution process. In solid grains, and due to the decay of 238 U by emitting an α particle, the crystalline structure is destroyed in the route followed by the recoil daughter. The daughter can end up hosted in an inhospitable place in the crystalline structure and can present, as a result of the nuclear transformation, an unstable electronic configuration. As a consequence, this nuclide can be more vulnerable to dissolution than the neighboring atoms, including other members of the same series with long half-lives or even other isotopes of the same chemical species. This process is especially significant in the activity isotope ratios 234 U/ 238 U and 228 Th/ 232 Th. Relatively few studies exist about 226 Ra investigations in riverine systems. Several authors concluded their investigations by indicating that the concentra- tions of 226 Ra in dissolution in freshwater ecosystems are generally low (although higher than the thorium concentrations) because of the tendency of this radionu- clide to be associated by adsorption to the surface of the suspended particulate matter in water. But they also found, in general, a noticeable increase in the concentrations of this radionuclide in dissolution in estuarine environments. This increase is clearly correlated with the increase in the gradient of salinity due to the mixture of fresh- and saltwater. In this case, and because of the low concentrations of 226 Ra in the marine environment, the 226 Ra concentration in estuaries cannot be associated with inputs from the oceans, as in the case of uranium. In the case of radium, the explanation is related to a change in its chemical behavior, with a noticeable increase in the desorption of this radionuclide initially bound to particle surfaces as the particles transported by the rivers enter the high ionic strength estuarine water. The increments in the concentrations of competing ions in the processes of adsorption to the surface particles induce a clear decrease in the radium adsorption coefficients, as was proved by Li et al. [13]. These authors concluded that the release of radium from river-borne particles is the main mechanism that explains the increments of radium in dissolution in estuarine environments. In addition to the modern inputs of uranium and other natural radionuclides related to increased agriculture, some specific rivers around the world have not been free of anthropogenic inputs of natural radionuclides due to releases pro- duced by nuclear and nonnuclear industries or activities. Indeed, the contamina- tion is clearly evident in uranium and its daughters in some rivers due to uranium mining activities in the drainage area. But even so, anthropogenic inputs of uranium associated with other mineral mining activities have been observed, such as the ones related with pyrite extraction. In this last case, the mining of heavy metal sulfates and the use of river water for mineral washing induces the pro- duction of sulfuric acid, the consequent acidification of the water, and an increase in uranium dissolved from the river bed. Also, saline water from underground coal mines contains natural radioisotopes, mainly 226 Ra from the uranium decay series and 228 Ra from the thorium series, and this water is sometimes released into surrounding rivers. Furthermore, several industrial activities exist that, in their production processes, form by-products and wastes that are radionuclide enriched (techno- logically enhanced naturally occurring radioactive material [TENORM]). Such DK594X_book.fm Page 65 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 66 Radionuclide Concentrations in Food and the Environment industries release, or have released in the past, a fraction of these radionuclides to freshwater or estuarine aquatic systems. This is the case, for example, in the production of phosphoric acid for phosphate fertilizers, which use as a primary mineral sedimentary phosphate rocks and release, or have released, into riverine or estuarine environments large amounts of phosphogypsum, which contains 226 Ra (up to 1 Bq/g) and 210 Pb (up to 1 Bq/g) [14]. This is also the case in the production of titanium bioxide pigments. These wastes produce a clear radioactive impact in relatively local zones of the aquatic systems that receive the releases. These zones have been used as natural laboratories to obtain information about the behavior of several natural radionuclides [14]. At the beginning of the 21st century, the levels of artificial radionuclides in rivers and lakes are fairly low, with the exception of limited rivers affected by the releases of some nuclear facilities. The main historical source of artificial radionuclides on a global scale, the fallout from nuclear weapons tests, affected water bodies worldwide mainly in the middle of the 20th century. The great majority of these artificial radionuclides that were incorporated in surface waters have either been transported to the oceans or have been accumulated and fixed in the sediment. This is even true for some European rivers contaminated by the Chernobyl accident; only small amounts of radionuclides are present today. Aarkrog [15] estimated that historically about 9% of the 90 Sr inventory on land would be removed by runoff and incorporated in surface waters, while this percentage is about 2% for 137 Cs and even lower for plutonium isotopes. The amount of radionuclides that can be mobilized through runoff depends on the tendency of the chemical species considered to be fixed or associated to particulate matter. For example, the quite soluble behavior of 90 Sr and the more reactive character of plutonium isotopes are well known. Today, the concentrations of artificial radionuclides in dissolution are gener- ally below the detection limit in most rivers and lakes. This is the case observed in some artic lakes, where the concentrations of 241 Am and 137 Cs were less than 1 µBq/l and less than 0.3 mBq/l, respectively, while the 239+240 Pu concentrations in filtered water ranged between 3 and 6 µBq/l [16]. This clearly indicates that these radionuclides are effectively scavenged from the water column. The same effect was observed in the four largest rivers in Slovenia, where the concentration of 137 Cs could only be found in traces up to a maximum of 0.5 mBq/l. As an aside, in these Slovenian rivers, it is possible to find higher concentrations of 131 I released from nuclear medicine centers than 137 Cs. Levels of 131 I in the studied Slovenian rivers range from 10 to 21 mBq/l. Authorized releases from nuclear power plants introduce into surface waters only small amounts of 3 H, with a negligible radiological impact, as well as very small amounts (so small they are difficult to be detected) of other artificial radionuclides. Water concentrations of 3 H of several tens of becquerels per liter can be found in some rivers where authorized releases from nuclear power plants occur. Due to the conservative behavior of this nuclide in water, 3 H routinely released by nuclear power plants has been used as a radiotracer to determine the longitudinal dispersion coefficient and velocity of the river water [17]. DK594X_book.fm Page 66 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC Radionuclide Concentrations in Water 67 Higher concentrations of artificial radionuclides can be found in water bodies affected by releases from other nuclear facilities, such as reprocessing plants and reactors for plutonium production. This is the case in the Rhone River (France), which was affected by releases from the Marcoule fuel reprocessing plant. This plant was shut down some years ago and is now being dismantled. Nevertheless, this has not reduced, until now, the discharge activities of plutonium isotopes, as washing effluents continue to be produced and released [18]. The authors reported that the annual amount of 239+240 Pu carried toward the Mediterranean Sea by the Rhone River is about 1 GBq/year. They state that the 239+240 Pu, 241 Am, and 137 Cs concentrations in the Rhone River due to Marcoule releases are about 0.025, 0.041, and 2 mBq/l, respectively. These values are clearly higher than those found in rivers not affected by local sources of artificial radioactivity. The radioactivity released by nuclear reprocessing plants and reactors may be incorporated in water bodies, eventually reaching the sediments. The magni- tude of this effect is variable and depends on (1) the composition of the particulate matter (its capacity for sorption and ion exchange), which can vary from place to place in the same river, (2) the salinity of the overlying water, and (3) the radionuclide considered. In studies carried out in the Clinch River (Tennessee; below the Oak Ridge nuclear facility), it was estimated that from the total amount of radioactive material released during a 20-year period, the sediments contained 21% of the 137 Cs and only about 0.2% of the 90 Sr, reflecting the behavior of both radionuclides in freshwater aquatic systems [1]. One of the freshwater systems most contaminated historically by artificial radionuclides is the Techa River, in the former Soviet Union. The main source of contamination on this river is the Mayak Nuclear Complex, which began operations in 1948. It includes reactors for plutonium production, radiochemical facilities for plutonium separation, and reprocessing plants. A historical overview of contamination of the Techa River can be found in Kryshev et al. [19]. They indicate that in the period 1949 to 1952, about 10 17 Bq of liquid radioactive waste were discharged into this river system. Radionuclide transport was reduced through the construction of a system of bypasses and industrial reservoirs for the storage of low-activity liquid wastes. They also indicate that at the present time, the main source of radionuclide intake in the Techa River is the transport of 90 Sr through the bypasses. About 6 × 10 11 Bq/year of 90 Sr, on average, entered the Techa River through the bypasses in the period 1981 to 1995. Finally, they report that the highest radionuclide concentrations in the river were observed in the period 1950 to 1951, at a distance of 78 km from the discharge site: there the amount of 90 Sr in the water was 27,000 Bq/l and that of 137 Cs was 7500 Bq/l. Thereafter a decrease in radionuclide concentrations in the water was observed (by a factor of approximately 1000). In the period 1991 to 1994, the annual average amount of 90 Sr ranged from 6 to 20 Bq/l, while the annual average amount of 137 Cs ranged from 0.06 to 0.23 Bq/l. The concentration of 239+240 Pu in the water during this time ranged from 0.004 to 0.019 Bq/l. The contamination of freshwater bodies due to the release of artificial radio- nuclides produced by nuclear facilities has affected very limited or local zones. DK594X_book.fm Page 67 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC 68 Radionuclide Concentrations in Food and the Environment But this fact should not cause us to underestimate its importance both in the environment and in humans. In fact, in most cases these contaminated water bodies play an essential role in the development and life of the people who use these waters, as in the case of the Techa River, where the water is used extensively in agriculture and as a drinking water supply [19]. 4.3 RADIONUCLIDES IN THE SEA AND OCEAN 4.3.1 S YSTEM O VERVIEW Ocean waters are continuously interacting with different substrates, which act either as sources or sinks for radionuclides. A summary of the interaction mech- anisms of radionuclides is shown in Figure 4.1. The three major mechanisms for radionuclide incorporation in the ocean system are (1) atmospheric input, (2) riverine input, and (3) radionuclide input associated with the interaction of ocean water and the crustal oceanic basalts. These input mechanisms are in competition with radionuclide removal processes. First, the radionuclides can be removed from the water column to the sediment thorough adsorption onto sinking particles, so-called particles scavenging. Second, they can be incorporated in biota thorough direct uptake mechanisms, thereafter FIGURE 4.1 A simplified schematic diagram of radionuclide exchange paths within a sea compartment model. Biota Suspended matter Uptake Excretion Redissolution Adsorption Close scavenging Sorption Excretion Bioturbation Turbulent resuspension Bottom sediment Rock substrate Water column dissolved Lateral scavenging Rain water Atmospheric nuclear tests Stratospheric input General air circulation Tropospheric input Evaporation, marine aerosol resuspension Global fallout Local/mesoescale deposition River stream Underground water Uptake Industrial activities Water mass circulation Detritus DK594X_book.fm Page 68 Tuesday, June 6, 2006 9:53 AM © 2007 by Taylor & Francis Group, LLC [...]... contamination event Such are the cases of the Kysthym accident in 1957 in the former Soviet Union, Palomares (Spain) in 1966, and Thule (Greenland) in 1968 The accident at Windscale, in the U.K., can also be included in this group, although a portion of the released radioactivity was detected in western Europe Nevertheless, the majority of the pollution was deposited in the U.K The contamination from other... radionuclides and therefore shows very well the level of radioactivity in the environment Thus the study of radioactivity concentrations in rainwater should be included in all surveillance programs In most cases they include weekly or monthly sampling, which is enough to estimate the level of radioactivity contamination in the environment In the case of a nuclear accident, the periodicity of sample collecting must... determination © 2007 by Taylor & Francis Group, LLC DK594X_book.fm Page 87 Tuesday, June 6, 2006 9:53 AM Radionuclide Concentrations in Water 87 There is very little data in the current literature on the content of 99Tc in rainwater In García-León et al [1 04] , levels are measured in rainwater in southern Spain from 19 84 to 1988 Activity concentrations ranging from 0.009 to 0.18 mBq/l were found and the. .. AM Radionuclide Concentrations in Water 81 Two important iodine radioactive isotopes have been released to the environment since the beginning of the nuclear era 131I is very significant from the radiological point of view, although exposure through the marine environment is not very significant because of its short half-life In contrast, 129I has both a long half-life and persistence in the marine environment, ... example is the U.S satellite SNAP-9, powered by a 238Pu generator, which suffered an accident in 19 64 while entering the atmosphere, disseminating about 0 .4 PBq of 238Pu in the Southern Hemisphere and about 0.2 PBq in the Northern Hemisphere, changing the expected plutonium isotopic ratio in the environment The Soviet Cosmos 9 54 satellite, powered by a nuclear reactor, suffered a similar accident in 1978... follow the global transport pattern taking place in the atmosphere Rainwater helps to remove radioactivity from the troposphere and transport it to the Earth’s surface Rainwater is neither a source nor a sink of radionuclides, but rather a connection between two different environmental compartments: the atmosphere and the surface of the Earth Rainwater helps to transport and disseminate radionuclides and. .. summarized in the following diffusion equation [43 ]: dA ∂2 A ∂A =K −ϖ −λA dt ∂x ∂ x2 © 2007 by Taylor & Francis Group, LLC (4. 1) DK594X_book.fm Page 74 Tuesday, June 6, 2006 9:53 AM 74 Radionuclide Concentrations in Food and the Environment where A is the nuclide concentration, K is the eddy diffusivity coefficient, x is the distance from the shoreline, ω is the advection velocity, and λ is the corresponding... the species and locations, CF values are in the range of 2200 to 61,000 l/kg for mussels, 241 0 to 31,590 l/kg for winkles, and 70 to 2585 l/kg for seaweed The distribution of the nuclide within the organism depends on the organ Hence, muscle tissue accumulates it in mussels and the digestive gland accumulates it in winkles The transport and distribution of 210Po in the aquatic environment and seafood... some 40 EBq are present in ocean water In any case, this amount still masks the cosmogenic 3H The decline of 3H in the environment can be seen in the measurements of concentrations in rainwater A very interesting example of this is presented in Rank et al [113], where the concentration of 3H in rainwater taken in Vienna, Austria, is presented In 1961 some 500 Bq/kg were observed, compared with the concentration... presence within the sediment should mark deposition after the beginning of the nuclear era 241 Am has also been released with nuclear tests, with inventories of 25 Bq/m2 in sediments within the band 40 ˚N to 50˚N latitude [73] Direct releases from Sellafield have been determined to be about 940 TBq, and approximately 360 TBq more following the β decay of 241 Pu [ 74] Usual levels in surface water are in the range . Radioactivity in Rainwater 83 4. 4.1 Introduction 83 4. 4.2 The Presence of Radioactivity in Rainwater: Sources and Pathways 84 4 .4. 2.1 Natural Radioactivity 84 4 .4. 2.2 Man-Made Radioactivity 84 4 .4. 3 Levels. Levels and Behavior 60 4. 3 Radionuclides in the Sea and Ocean 68 4. 3.1 System Overview 68 4. 3.2 Sources and Sinks of Natural Radionuclides in the Ocean 70 4. 3.3 TENORM-Related Pollution Cases 75 4. 3 .4. important role in determin- ing uranium estuarine behavior. Regarding the characteristics of the main source terms and the routes followed by the natural radionuclides for their incorporation in water