Radiation Dose Reconstruction for Epidemiologic Uses (1995) / Chapter Skim
Currently Skimming:
4 Environmental Pathways
4 Environmental Pathways
Pages 27-39
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 27... ...
The environmental pathway analysis, which in most cases uses the source term assessment as an input, may involve an iterative procedure for making estimates of exposure rates and of environmental concentrations of radionuclides. In the scoping study, which is carried out to determine if there is a need for a full-scale dose reconstruction study, only the most important environmental pathways and radionuclides are considered, and readily available information on the characteristics of the site and on the population distribution is used to estimate the exposure rates and environmental concentrations at a limited number of locations of interest.
|
From page 28... ...
Direct Releases to the Atmosphere Analysis of the environmental pathways from atmospheric releases to humans requires study in four areas. First, the meteorologic processes that govern atmospheric dispersion and the precipitation processes that deposit gaseous and particulate emissions must be considered.
|
From page 29... ...
The presence of radionuclides in air may lead to two modes of radiation exposure inhalation and external irradiation. If the individual considered is outdoors, the measured or calculated radionuclide concentration in outdoor air at that location is used without modification in the estimation of the radiation dose, using an appropriate model for the inhalation dose.
|
From page 30... ...
In the absence of precipitation, effluent material also can be removed from the atmosphere through gravitational settling onto the ground, vegetation, or other ground cover, such as buildings. The transfer of airborne contaminants from ground-level air to the ground surface, including vegetation, is usually modeled through the use of the deposition velocity concept, which is the quotient of the deposition of radioactivity (in becquerel, Bq)
|
From page 31... ...
The alternative is to depend on atmospheric transport and deposition models, which are much less reliable than are direct measurements. The use of soil-monitoring data is particularly valuable when the longer lived contaminant has the same chemical and physical properties as do the shorter lived components.
|
From page 32... ...
Radionuclides can enter the terrestrial food chain by direct deposition onto forage and food crops or by plant uptake from soil or from irrigation water. Contaminated plants can then be consumed directly by humans or ingested by animals with transfer of the radioactivity to human food products (meat, milk, or eggs)
|
From page 33... ...
For example, leafy vegetables contaminated by direct deposition of radionuclides exhibit greater concentrations on the outer leaves, and removing those leaves as well as washing the vegetables will eliminate a substantial fraction of the contamination. Boiling or frying food also can reduce radionuclide concentrations.
|
From page 34... ...
Radionuclides can become less soluble because of chemical changes and precipitate onto bottom sediments. Physical changes in the receiving waterway may also affect radionuclide sedimentation.
|
From page 35... ...
The potential pitfalls in reconstructing doses associated with the discharge of radionuclides to the aquatic environment depend on whether the discharges were to the freshwater or marine environment and whether they were chronic or episodic. The factors that introduce large uncertainties into an aquatic dose reconstruction include retention or delay of groundwater migration in unsaturated subsurface flow, the removal of radionuclides by sedimentation processes and their resuspension during floods, and the bioavailability of radionuclides in solution and in the bottom sediment.
|
From page 36... ...
The parameters require fairly precise numerical estimates if the model is to be more than heuristic. Appropriate Use of Mathematical Models When actual measurement data are either absent or incomplete, mathematical models are needed to estimate concentrations of radionuclides in air, water, soil, food, fodder, and human organs.
|
From page 37... ...
Some investigators have used a geometric mean and geometric standard deviation; others have used an 80% to 95% probability interval based on expert judgment; still others use the entire joint pdf of the model result. The one most appropriate for dose reconstruction depends on the type of decision that is to be made with the exposure information.
|
From page 38... ...
The environmental releases most frequently encountered are those directly to the atmosphere or to the hydrosphere. Conceptually, the steps involved in the analysis of the environmental pathways from releases into the atmosphere or the hydrosphere to humans are similar.
|
From page 39... ...
Insofar as possible, measurements of environmental radiation or of radionuclides should be used in the environmental pathway analysis. For example, if a single contaminating event has taken place and if measurements have been made (such as external gamma exposure rate or deposition of one or more radionuclides or stable materials)
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.