except for concentration of zirconium in an octopus gill and of rare earths by plankton and by
a surgeonfish and a butterfly fish. Results of these analyses are shown in Table 4.21.
In the method used, 20- to 50-g portions of sand or soil samples were ashed at 700°C to
destroy organic matter, and the ash was dissolved in dilute nitric acid. Filtering the solutions
and counting the filters showed that solution of the active material was complete. Biological
samples were also ashed and dissolved in dilute nitric acid. Filtering the solutions and counting the filters for these samples showed that in most cases the small insoluble residue contained less than 10 per cent of the activity of the sample. Duplicate portions of the filtrates
were taken and analyzed by the following methods.
Rare earths and zirconium were separated as hydroxides by precipitation with ammonium
hydroxide. The resulting precipitate was dissolved in nitric acid, and rare earths were separated from zirconium by precipitation as fluorides. Cerium was separated from trivalent rare
earths by precipitation as ceric iodate. In the analysis of Rojoa dredged sand, an attempt was
made to separate trivalent rare earths {rom yttrium by precipitating them on lanthanum car‘bonate, but an absorption-curve study showed that this separation was not complete. A large
fraction of other trivalent rare-earth isotopes had carried on yttrium instead of on lanthanum.
The two results were added together and reported as trivalent rare earths. This separation
was not attempted in other analyses. Trivalent rare earths were counted together on yttrium
carrier. The rare earths were weighed as oxalates. Zirconium was recovered from the fluoride
supernatant by precipitation first as barium fluozirconate and then as zirconium mandelate,
which was ignited and weighed as zirconium oxide. The supernatant from the hydroxide precipitation contained barium, strontium, and calcium, which were precipitated as carbonates,
Barium was separated as barium chromate, and strontium and calcium precipitated together as
oxalates. Chemical separation of strontium and calcium was not attempted. A separate aliquot
of Rojoa dredged-sand solution was analyzed for cesium by the standard cesium perchlorate
method, and no detectable radiocesium was found. Since rubidium also is carried on this
precipitate, it is evident that rubidium was also absent. In most samples the absence of ce~
sium was indicated by the absence of activity in the solution remaining after precipitation of
rare-earth hydroxides and alkaline-earth carbonates. Ruthenium: was determined in separate
aliquots by the standard perchloric acid distillation method and oy subsequent reduction to
ruthenium metal by magnesium powder.
Chemical-yield factors were determined and applied to the results of all analyses except
barium and strontium-calcium. Spiked samples prepared by mixing appropriate carriers and
corresponding radioisotopes were run concurrently with samples. Tne results are shown in
Table 4.21 as percentage of total recovered activity. Total activity recovered varied from 60 to
100 per cent of total activity in the aliquot of the sample solution used, as determined by plating
and counting triplicate 1-ml aliquots of the solution.
Absorption curves were made of each fraction separated from the Rojoa dredged sand and
in each case showed the energy characteristic of the particular isotope separated. The curve of
calcium-strontium shows that about three-fourths of the activity has the energy corresponding
to Ca‘. The remaining one-fourth may be Sr*®, y**, and Sr™, These mass-absorption curves
and decay curves for the samefractions are presented in Figs. 4.11 and 4.12.
4.9
ABSORBED AND SURFACE CONTAMINATION
In a discussion of results the path of the radioactive materials to the tissue and the source
from which they are taken into the organism are important considerations. If injury to the individual organism is being considered, the proximity of the radioactive material to sensitive
cells and the potential duration of contamination are important and are, in part, dependent on
the source of the contamination. If biological cycling is considered, the nature of the contami-
nation of each organism in the food chain affects the availability of the radioactive materials
ta
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