4.2.2
Results and Discussion
(a) Food. A summaryof the alpha and beta activity on the surface of representative food
samples from Rongelap at 43 days. postdetonation is presented in Table 4.2. The beta activity
was relatively high, the alpha activity fairly low. The surface contamination found on Utirik
samples was considerably lower than that found on samples from Rongelap.
After the surface contamination of the foodstuffs was measured, decontamination measures were studied. Coconuts, papayas, and pandanus were decontaminated by scrubbing with
TABLE 4.2—External Contamination on Representative Rongelap Food Samples
(Day 42 postdetonation)
Alpha activity of
Beta activity
Food sample
fissile material
(ug x 104)
(Sr® equivalent)
(uc)
Coconuts (3)
Papayas (2)
Pandanus (surface)
Pandanus (peel)
Pandanus (leaves)
Pandanus (stem)
2.2—-3.3
0.6-1.0
22—56
3.5
8
4
0.9-—1.3
0.2—-0.4
8.9-—22.7
0.76
1.71
0.40
tap water and detergent. Approximately 90 per cent of the activity was removed from the
papayas and the coconuts (Table 4.3). Decontamination of the pandanus was moredifficult than
that of the other foodstuffs because of their rough surface. Only 50 per cent of the contamination of the pandanus could be removed. In general, effectiveness of decontamination was
inversely proportional to the roughness of the surface of the fruit.
After the surface was washed, the edible portions of the food were surveyed with an ionization chamber. Beta activity of individual fruits ranges from 0.001 uc for a papaya to 0.2 uc for
a pandanus (Table 4.4). The relatively high levels of activity detected in the pandanus were
probably the result of contamination from the rough external surface of the fruit. It is possible
that active material was transported through the root system of the plant and deposited in the
fruit during the two-month period that the fruits were growing in the contaminated area. The
arrowroot may very likely have been contaminated in this manner since it is a tuber growing
underground.
The likelihood of the incorporation of radioactive contaminants into plants is supported by
the very high levels of activity found in the Rongelap coconut tree sap at two months (1.4 pc/
liter) and in the Utirik specimens, which showed about '/, of this activity (Table 4.4). The
presence of this activity in the tree sap appears to be the result of uptake of contaminated
water by the root system since both the water and the tree sap had approximately the same
isotopic composition.
Larsen'* has shown that small amounts of fission products are immediately taken up by
plants growing on soils contaminated from fallout material. This early uptake of fission products seems to be a function of the solubility of the material. The predominant fission product
incorporated into the plants in Larsen’s studies as well as in the present studies is Sr®. This
high strontium concentration is probably a function of the relatively high solubility of the element in water. Thus sr®, because of its abundance and long half life, is the radionuclide of
greatest potential hazard associated with ingestion of the contaminated food.
The radiochemical analysis for alkaline-~earth and rare-earth activity of the material found
on pandanus, grass, and thatch, as well as in water and coconut tree sap, is listed in Table 4.5.
The highest levels of beta activity found on thatch, grass, and pandanus atthis time appeared
in the rare-earth fraction. The alkaline earths, strontium and barium, contributed a small
fraction of the total beta activity. There was a marked variation in the ratio of the strontium,
42