Radium transport

The final output for the atmospheric model is the radon concentration at a defined distance from the source, in each wind direction and in the dominant wind direction, where is considered to be located the receptor. For the hydrological model the final outputs are the radium concentration in the well water and the corresponding cumulative rate of radium transported to the well after the time considered. Local meteorological data, namely wind velocity and frequency, was used for simulating the dispersion in each octant direction. These data was obtained from a local automatic meteorological station (INAG 2004). The dominant wind direction is NW. The unknown parameters were estimated from available data. 

A less common entry mechanism is the outgassing of radon from well water. A well supplied by groundwater that is in contact with a radium-bearing formation can transport the dissolved radon into the home. It is estimated that the health risks associated with breathing radon gas released from the water are 10 times higher than the risks associated with ingesting water containing radon.9... 

Charette, M.A., K.O. Buesseler, and J.E. Andrews. 2001. Utility of radium isotopes for evaluating the input and transport of groundwater-derived nitrogen to a Cape Cod estuary. Limnology and Oceanography 46 465-470. 

In the environment, thorium and its compounds do not degrade or mineralize like many organic compounds, but instead speciate into different chemical compounds and form radioactive decay products. Analytical methods for the quantification of radioactive decay products, such as radium, radon, polonium and lead are available. However, the decay products of thorium are rarely analyzed in environmental samples. Since radon-220 (thoron, a decay product of thorium-232) is a gas, determination of thoron decay products in some environmental samples may be simpler, and their concentrations may be used as an indirect measure of the parent compound in the environment if a secular equilibrium is reached between thorium-232 and all its decay products. There are few analytical methods that will allow quantification of the speciation products formed as a result of environmental interactions of thorium (e.g., formation of complex). A knowledge of the environmental transformation processes of thorium and the compounds formed as a result is important in the understanding of their transport in environmental media. For example, in aquatic media, formation of soluble complexes will increase thorium mobility, whereas formation of insoluble species will enhance its incorporation into the sediment and limit its mobility. 

Another procedure is based on the measurement of the radioactive isotope radon-222 (half-life 3.8 days), the decay product of natural radium-226. At the bottom of lakes and oceans, radon diffuses from the sediment to the overlying water where it is transported upward by turbulence. Broecker (1965) was among the first to use the vertical profile of 222Rn in the deep sea to determine vertical turbulent diffusivity in the ocean. 

It is assumed that radium that has been deposited in the lung as a radium salt enters the systemic circulation either as that salt or as individual radium atoms at a rate dependent upon the solubility and chemical characteristics of the specific radium salt involved. Subsequently, these salts or radium atoms would be systemically transported in the same manner as radium acquired by oral or parenteral administration. However, some of the radium in the lung could be retained for a long time before this process is completed. The ultimate distribution, many years after an inhalation exposure, would probably be very similar to that of other routes of administration that is, most of the radium that was retained in the body would eventually be deposited in the skeleton (Marinelli et al. 1953). 

Radium may be transported in the atmosphere in association with particulate matter. It exists primarily as a divalent ion in water, and its concentration is usually controlled by adsorption-desorption mechanisms at solid-liquid interfaces and by the solubility of radium-containing minerals. Radium does not degrade in water other than by radioactive decay at rates that are specific to each isotope. Radium may be readily adsorbed by earth materials consequently, it is usually not a mobile constituent in the environment. It may be bioconcentrated and bioaccumulated by plants and animals, and it is transferred in food chains from lower trophic levels to humans. 

Radium may be transported in the atmosphere by the movement of particulate matter derived from uranium and coal utilization (see Section 5.2.1). These fugitive emissions would be subject to atmospheric dispersion, gravitational settling and wash-out by rain. 

No data were located on the residence time of radium in the atmosphere or its deposition rate. However, data for other elements adsorbed to particulate matter indicate that the residence time for fine particles is about 1 to 10 days (EPA 1982b Keitz 1980). Radium may, therefore, be subject to long-range transport in the atmosphere. 

Marinelli LD, Norris WP, Gustafson PF, et al. 1953. Transport of radium sulfate from the lung and its elimination from the human body following single accidental exposures. Radiology 61 903- 914. 

Marie Curie worked tirelessly to develop radioactivity as a new discipline in physics. With the help of five assistants, she studied the effects of radioactivity and developed the atomic theory of its origin. In 1911, Marie was awarded her second Nobel Prize— this time in chemistry, for the chemical processes discovered in the identification of radium and polonium and for the subsequent characterization of these elements. During World War I, she trained doctors in the new methods of radiology and, after learning to drive, personally transported medical equipment to hospitals. After the war, Madame Curie assumed leadership of the newly built Radium Institute in Paris. In 1920, a campaign was mounted in the United States to produce 1 gram of radium for Marie to support her research. She traveled to the United States to receive the precious vial of radium at the White House in 1921. 

Be, with its 1.5 Ma half-life, adds a longer-lived subduction tracer to the arsenal, one that will decay away in the mantle on a time frame of several million years. The data for the SVZ of S Chile (Figure 6(a)) illustrate the power of the combined approach. The very well correlated U-Th, Ra-Th, and Be/ Be data indicate that uranium, radium, and Be, but not thorium, were transported from slab to mantle to produce the nearly horizontal arrays on the disequilibria diagrams (right panel) and the strong correlations between Be addition and uranium and radium excesses (left panel). Taken at face value, these results suggest that a slab/sediment-derived fluid was added to the... 

Dynamic melting models produce all correlated excesses at the bottom of the melting regime and require melt transport rates sufficient to transport radium from the bottom of the melting regime on timescales short compared to the half-life of radium (1,600 yr). 

Equilibrium transport models produce excesses throughout the melting column. In particular, thorium excesses are produced at depth in the presence of garnet and high-pressure pyroxenes, while potentially observable radium excesses are produced near the top of the melting column. These models still require rapid melt transport near the top so that the porosity in the radium production zone is comparable to Dxh-... 

Analogous to the process releasing Ra to seawater, decay of Th in sediments releases dissolved Ra which is then mixed into the ocean interior. Radium-226 decays through a series of short-lived nuclides to Pb (half-life 22.3 yr) which, like thorium and protactinium, is insoluble and readily sorbs to particles. Radioactive decay of gaseous Rn in the atmosphere also produces Pb, which is then deposited on the sea surface with aerosols and in precipitation. Although Pb and, to a lesser extent, Pa have found many applications as tracers of particle transport, by far the greatest use has been made of thorium isotopes, which form the focus of this review. 

The ground level air concentrations of lead-210 have been measured at numerous locations all over the world (Rangarajan et al., 1976). The vertical distribution of this nuclide in the atmosphere was determined by Burton and Steward (1960), Rama and Honda (1961), Feely et al. (1965) and Peirson et al. (1966). The results of these measurements were used for the study of the air mass transport and the residence time of aerosols in the atmosphere (Machta, 1965 Karol, 1970 Moore et al., 1973, 1980 Martell and Moore, 1974 Rangarajan et al., 1975). Air concentrations of radium-226, lead-210 and uranium near ground level at different locations are shown in Table 9.9. 

In water and sediments, the time to chemical steady-states is controlled by the magnitude of transport mechanisms (diffusion, advection), transport distances, and reaction rates of chemical species. When advection (water flow, rate of sedimentation) is weak, diffusion controls the solute dispersal and, hence, the time to steady-state. Models of transient and stationary states include transport of conservative chemical species in two- and three-layer lakes, transport of salt between brine layers in the Dead Sea, oxygen and radium-226 in the oceanic water column, and reacting and conservative species in sediment. 

Groundwater discharge of the short-lived radium isotopes 223Ra and 224Ra from coastal wetlands has actually proven useful to scientists who model flow rates through sediments. Measurements of isotopic ratios can provide information on vertical transport of the groundwater in shallow bays and other marshy wetlands. 

---