Soil that is contaminated with radioactive elements poses an exposure hazard
to those whom may take up temporary or permanent residence on such a site. Of
particular interest is the internal exposure from ingestion of this radioactive soil.
Although most ingestion of soil is inadvertent, usually being attached to foodstuffs
that are not properly cleaned, it is possible that a person might consume a larger
quantity. Childhood soil ingestion from simple hand-to-mouth activities is one
explanation for this larger intake, as well as geophagia (eating dirt) or pica (craving
and eating non-food items). The assumption that any person might consume a
"mouthful" of dirt is a rare but possible occurrence that, when analyzed, will help with
decisions about safe contamination levels of soil.
Samples of soils contaminated with radium-226 were sent from an engineering
and environmental firm to Oregon State University's Department of Nuclear
Engineering and Radiation Health Physics for assessment. The analysis of the
samples was aimed at the determination of bioavailability and bioaccessibility of the
radioactive species found in the soils. Subsequent site remediation actions for the
New Jersey-based project would be partially dictated by the results of Oregon State
University's testing.
Initially, the soils were tested for the presence of carbonates, for leachability of
radioactivity in water and in acid, and for particle size distribution, i.e., soil type.
Each of the eight samples was then subjected to a stomach/intestinal analogue to
determine how much of the radioactivity would be transferred to solution upon human
ingestion, (bioaccessibility). Mass balance and gamma spectrometry outputs for the
soil samples before and after the digestion was one way the loss to solution was
assessed. Another method to determine the loss of radioactivity to solution was to
count aliquots of the digestive fluids in a high purity germanium detector, using a
library of only radium isotopes and their progeny to locate peaks. The combination of
results from mass balance and gamma spectrometry outputs allowed for OSU's
researchers to determine the bioaccessibility of each soil's radioactive components.
Using the determined bioaccessibility and previous animal models, the determination
of bioavailability varied between the samples, from zero to 28% of the total initial
radioactivity in the samples.
A hot particle estimation of the dose from the non-bioavailable portion of the
samples yielded a high dose to a small number of cells. Assuming ingestion of the
most radioactive sample, (Sum-03a), the amount of damaged (killed) tissue in each
section of the gastrointestinal tract was estimated to be less than 0.0407 cm³. This
small volume of tissue is not likely to result in evident damage as the healthy human
gastrointestinal tract regenerates all surface cells approximately every six days and
most items are resident in the digestive system for less than 48 hours. / Graduation date: 2006
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/22651 |
| Date | 01 March 2006 |
| Creators | Tack, Krystina M. |
| Contributors | Higley, Kathryn A. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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