Stable activable tracers rare earth

The rare earth tracers, especially those with short-lived activation products, are cost-competitive with other t) es of tracers. Tables I and II show typical rare earth stable activable tracers and the total cost of using them in tracing water pollutants. These cost estimates are, of course, rough approximations and are intended to demonstrate that the costs associated with different tracer technologies are similar. Also note, as shown in Table I, the small amounts of tracer that can be easily detected (give 10 counts). These detection sensitivities are emphasized further when one notes that the natural concentrations of the rare earths in fresh water are (17) in the ppt-ppb range and the atmospheric concentrations (19) are around 10" ng/m . 

Stable activable tracers are powerful tools for the study of many environmental problems. Compared with fluorescent dyes or radiotracers, they offer many advantages that are reviewed herein. Our research group has emphasized the use of rare earth nuclides with short-lived activation products as stable activable tracers. Use of rare earth nuclides is cost-competitive with conventional tracers and allows rare earth "fingerprints to mark individual sources with subsequent simultaneous tracing of effluents from several sources. We present results from the application of these tracers to monitor pollutant dispersal from multiple industrial stacks, monitor fluid-bound pollutant dispersal in estuarine and fresh-water systems, monitor herbicide dispersal, and trace toxic organic chemicals in the marine environment. 

Non Rare Earth SATs. Several candidates that meet these criteria have been found, and some of their applications are discussed by Kruger (5). Krugers discussion also contains an excellent accoimt of the early history of this field. In a series of experiments at the Pennsylvania State University, Jester and coworkers (6,7) have used Br" and I" to mimic the movement of soluble species in natural waters. In-EDTA complexes have been used by Behrens et al. (8) to monitor groundwater movement, while Dahl (9) has shown that In(N03)2 could be used to trace water stream patterns and pollutant dispersal in and around the harbor of a Norwegian town. Indium and scandium were used as stable activable tracers for monitoring in-plant movements of water in waste water treatment plants by Craft and Eicholz (10). The entire subject of industrial uses of activable tracers has been reviewed recently by Van Dalen and Wijkstra (II). 

Rare Earth SATs. One class of elements that are especially appealing as stable activable tracers is the class of rare earth elements. They admirably fulfill the criteria for stable activable tracers, especially those of low environmental concentration and ease of detection. These qualities were first recognized by Channell and Kruger (12), who used the lanthanides as estuarine tracers. 

In is not a member of the rare-earth family. It is a well known stable activable tracer and is therefore included here for comparison. 

Hydrospheric Applications. Most applications of stable activable tracers have been to trace pollutant movement in water systems. In one example of such an application, Loveland (17) used DTPA anionic complexes of the rare earth elements to trace the movement of fluid-bound pollutants in fresh waters. Figure 3 shows a comparison of the dispersal pattern of a Dy tracer injected into a municipal sewage outfall and the dispersal pattern of Zn, a naturally occurring trace element in... 

Activation with 14 MeV neutrons has been used to determine the oxygen content of various metals such as beryllium 20>, Cl, F, O, Na, Si, and various rare earths in complex molten salt electrolytes 45>, the protein content of food products by means of the nitrogen content 46>, i60/180 and 14N/15N isotopic ratios in stable isotope tracer experiments 47,48), and in a wide variety of other applications. One application we... 

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