36 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



TABLE 16 Examples of Dose Rates Calculated from Measured Tissue Concentrations 

 of Plutonium in Environmentally Exposed Organisms 



* Includes dose from ^" ' Am. 



Opportunities to observe and quantify ecological changes resulting from transuranic 

 contamination of terrestrial environments have also been extremely limited. Terrestrial 

 ecosystems contaminated with plutonium at levels of 10 to 1000 ixC'ilm^ have been 

 examined carefully but without demonstrable effects (Whicker, this volume). Assays of 

 plutonium in plants and animal tissues from such contaminated areas reveal levels of 

 plutonium generally less than 10 pCi/g. Dose rates from such plutonium concentrations 

 are a few millirad per day. Chronic dose rates of at least a few rad per day are generally 

 required to cause detectable ecological changes (Whicker and Fraley, 1974; Turner, 

 1975). Calculations based on a substantial body of information suggest that man could 

 occupy and derive sustenance from land containing 20 to 200 juCi ^^^Pu/m" without 

 exceeding the nonoccupational maximum permissible dose to the lung or other critical 

 organs (Healy, 1974; Martin and Bloom, 1976). Other calculations suggest that ^^^Pu 

 levels of 1 to 1000 mCi/m'^ would be required to cause significant mortality in plant and 

 animal populations. Mammals would probably show mortality at lower levels than plants 

 (Whicker, this volume). 



Summary 



The preceding discussion leads to a number of generalizations that can be summarized as 

 follows: 



l.The nature of the source for release to the environment is important in the 

 initial deposition and distribution of transuranic elements. However, as environmental 

 factors, such as erosion, chemical weathering, and biological processes, proceed, tlie 

 original chemical and physical properties are altered and source influence diminishes. 



2. The major repositories of plutonium and americium are soils and sediments. 



3. Suspended particles in air and water act as vectors for the physical movement of 

 plutonium and americium, and erosional processes are the principal means of translational 

 movement in the environment. 



