Biokinetic models intake rates

The lEUBK model in its intake, uptake, and biokinetic components attempts to take some cognizance of interindividual variability of Pb in children s blood. Overall, this variability derives from both Pb exposure variation across children in a population as well as differences internally (bioki-netically) in the form of differing Pb retention and excretion rates. Comparatively speaking, it is exposure variability that ranges more widely. Pb intake rates and subsequent uptake rates, for example, can differ by orders of magnitude across Pb-contaminated environmental media... 

Indirect measurements generally interfere less with worker assignments, but require access to a radiochemical analytical laboratory such a laboratory may also be used for measttring environmental samples, but high level (e g. reactor water chemistry) and low level (e g. bioassay or environmental samples) measurements should be performed in separate laboratories. Excreta measurements determine the rate of loss of radioactive materials from the body by a particular route, and must be related to the body content and intake by a biokinetic model. Because of the ability of radiochemical analyses to detect low levels of activity, measrrrements of excreta usually give sensitive detection of activity in the body. 

Even if all of the assumptions in the reference biokinetic models are appropriate for a given workplace, there will still be differences between individuals in excretion rates and other biokinetic parameters for the same intake of a radionuclide. The... 

The most accurate assessments of internal dose can be made when the distribution and total body content of an incorporated radionuclide can be determined reliably by direct in vivo counting of emissions from the body. Nevertheless, biokinetic modelling of retention and biophysical modelling of energy deposition may still be needed to calculate the intake and the committed effective dose, so direct methods can also depend on the interpretation of rates of excretion, which often vary markedly over time and between individuals. 

Direct or indirect measurements provide information about the amount(s) of radionuclides present in the body, in parts of the body such as specific organs or tissues, in a biological sample or in a sample from the working enviromnent. The first use of these data is likely to be an estimation of the intake of the radionuclide by the worker. Biokinetic models which describe body and organ contents, and activity in excreta, as a function of time following intake, and exposure models which relate intake to workplace conditions, are used for this purpose. Alternatively, measurements of activity in the body can be used to estimate dose rates directly. The calculation of committed doses from direct measurements still involves the assumption of a biokinetic model if sufficient measurements are not available to determine retention functions. 

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