50 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



Pathways and Inhalation 



The inhalation pathways for a number of exposure modes for man have been identified 

 by ICRP. In addition to the direct inhalation of airborne transuranics released from an 

 operating facility, other secondary pathways are possible and have been discussed by 

 Healy (1974), These secondary pathways are the primary inhalation pathways from 

 existing areas of transuranics in the environment. Resuspension by wind is discussed in 

 another chapter. Other means of generating airborne transuranics, such as agricultural 

 activities (including home gardening), carriage into homes on clothes and pets, children's 

 play, and movement by vehicular activity, need further quantification. 



Estimates of the doses from inhalation of the different airborne transuranics use the 

 ICRP II lung model (International Commission on Radiological Protection, 1960), which 

 categorizes the inhaled material as soluble or insoluble. The Task Group on Lung 

 Dynamics model (International Commission on Radiological Protection, 1966) has three 

 categories- of solubiUty. Additionally, the deposition of particulates in three respiratory 

 regions is dependent on particle size in the Task Group model. Residence time in the lung 

 is dependent on solubihty classification in both models. After transuranics have resided in 

 the environment for months or years, the solubiUty and particle sizes may change. Data 

 are needed which evaluate the changes of solubility and particle-size distribution with 

 time and weathering. Although some work has been started for plutonium, more 

 long-term studies of the solubihty and particle-size changes are needed. Data for 

 neptunium, americium, and curium is sparse to nonexistent. The derivation or collection 

 of some of this information could be incorporated into the design of present 

 environmental monitoring programs. More detail about the association of the transuranics 

 with soil particles, particle-size distribution, and chemical changes with time and 

 weathering is gathered in separate projects that are usually beyond the scope and budget 

 of monitoring programs. 



Pathways and Ingestion 



Although inhalation is the primary pathway for human exposure, ingestion also plays an 

 important role. Transuranics can be ingested through numerous pathways. These 

 pathways are strongly influenced by local water-use practices, agricultural systems, sport 

 fisheries and wildlife use, and estuarine and marine fisheries, and by the amount of soil 

 directly ingested on contaminated plants and from the hands. The deliberate ingestion of 

 soil by children is a special pathway for evaluation identified by Healy (1974). Dose 

 assessments for transuranics have generally indicated that inhalation is the dominant 

 pathway. The hmited data available for such transuranics as neptunium, americium, and 

 curium, however, indicate that these elements are possibly more available than plutonium 

 for plant uptake, as indicated by an examination of the data available for plant uptake of 

 transuranics. Thomas and Healy (1976) concluded that current information is inadequate 

 for accurate dose assessments. The research needs discussed in the following chapters on 

 physical and biological transport mechanisms are many of those which would reduce the 

 great number of uncertainties contained in present dose assessments for transuranics from 

 ingestion. Pathways in particular that need further quantification are the contamination 

 of food plants by resuspension and the consequences of incorporation of transuranics 

 into organic molecules. 



The identification of local food webs is one of the more important aspects of dose 

 assessment and design of monitoring programs. Regional diets throughout the United 



