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further determination. Therefore, when lapel breathing zone air samplers are
properly used, representative air sampling is not considered a shortfall. Urinalysis
Note: This section is reserved pending development of a relevant protocol. Fecal Analysis
Note: This section is reserved pending development of a relevant protocol. In-Vivo Analyses
As noted in section 4.3.3, in- vivo analyses depend on the detection of radiation
emitted by radioactive materials within the body by radiation detectors external to
the body. Because tritium decays by emission of low energy beta particles that will
not penetrate through the body to the external detector, in- vivo analysis is not
considered to be a viable means of assessing tritium intakes, including STC
Dose Conversion Factor for Insoluble Tritiated Particulates
Following the intake assessment, the intake amount may be converted to internal
dose using a DCF. Determination of internal dose from a tritiated particulate is
mainly dependent on two factors: particle size distribution, and dissolution rates of
tritium from the particulate into lung fluid. The impact of these factors on DCF or
intake determination, as derived from either bioassay or air concentration data, is
discussed below. Particle Size Distribution
For any given exposure scenario, the particle size distribution will affect both the
dissolution rates (discussed below) and the deposition fractions (i.e., the fractions of
the material that are deposited into each compartment of the lung). Smaller particle
sizes tend to deposit deeper into the lung, causing a greater dose than particles
that are physically larger, but otherwise similar (e.g., chemical characteristics,
quantity of infused tritium). Uncertainty in the particle size distribution causes
uncertainty in the DCF, regardless of the method used (e.g., bioassay or air
monitoring) to determine activity intake. Therefore, the particle size distribution
factor cannot be used to choose a preferred data collection method (urine bioassay
vs. fecal bioassay vs. air concentration values).
Fortunately, errors in determining the particle size distribution tend to result in self-
canceling errors in the dose assessment. If particle sizes are smaller than
assumed, the particles will deposit deeper in the lungs, resulting in the use of a
larger DCF and calculation of a larger dose. However, because the dissolution rate
for the smaller particles will be higher than assumed, intake will be overestimated.
Because intake is overestimated while DCF is under-estimated, the effects of
particle size uncertainty on assigned dose tend to cancel. These effects are
explored later in this Chapter.

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