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reduced the content of Cs-187 in the tissue. Also reported are the results of a field
experiment on Rongelap Island in which fertilization with KCI at least temporarily reduced the content of Cs-137 in a native grass. Potassium and Cs-137
contents of foliar samples of several woody species collected on Rongelap Island
are also included. In the most common pattern, K and Cs-137 contents of the
upperfoliage were higher than those of the lower leaves, but one species consistently showed higher K but lower Cs-187 in the upperfoliage. Low status of
the soil and differences in mobility within the plant may explain these patterns.
INTRODUCTION AND METHODS
The data reported here concern the uptake of Cs-187 by plants from soils of
Rongelap Atoll, Marshall Islands, with special reference to fertilization of the
soil with N, P, and K. The report includes the results of greenhouse pot culture
tests using Rongelap top soil, as well as foliar analyses of native vegetation growing on the atoll. Rongelap Atoll was contaminated by radioactive fallout on
March 1, 1954. The principal radionuclide found in plant tissues in 1958 and
1959 was Cs-137. Radionuclides in the soil remain in the top few inches with
90% or more of the radioactivity in the top two inches orless.
In the current greenhouse studies, tomato and squash plants were grown in
Seattle on top soil (0 to 10 inches) collected in a coconut grove on Rongelap
Island. The soil (perhaps better called soil material) consists entirely of calcium
carbonate fragments derived from corals and foraminifera, into which is incor-
porated about 9% organic matter. In the rather coarse unsieved field soil the pH is
8.0; the cation exchange capacity is attributable entirely to the organic fraction
and is about 8 meq per 100 gm; among the exchangeable cations there are about
80% Ca, 15% Mg, 4% Na, and 0.7% K; the soil is coarse, very friable, and highly
porous.
The pot culture technique wasessentially that of Jenny e¢ al. (1950). Fertilizer
solutions were mixed with 667 gm portions of soil which were placed into 6-inch
plastic pots, uniform seedlings were transferred to the pots, and the plants were
watered with distilled water as needed. Plants were harvested after about 30
days, and the tissue oven-dried and ground. The Cs-137 content of the dry
material was determined by gammaray spectroscopy using a three-inch thalliumactivated sodium iodide crystal in conjunction with a multichannel analyzer.
Tissue was dry ashed and the acid solution analyzed for potassium bytitration of
the cobaltinitrite precipitate with permanganate. Samples collected in the field
usually included leaves from the upper (younger) and lower (older) foliage,
and were composite samples from several plants in the vicinity of a collecting
point. The tissue was oven-dried in the field headquarters, and was subsequently
re-dried, ground, and analyzed in the same manneras the greenhouse samples.
RESULTS
Greenhouse Experiments
e
In a preliminary experiment with tomato, variety Marglobe,thefertilizer treat-
ments and the Cs-137 in disintegrations per minute per gm dry tissue were:
unfertilized control, 490; N-P-K, 100; N-P, 190; N-K, 240; P-K, undetectable.
These results are particularly interesting because all fertilizer additions depressed
the uptake of cesium, There was marked response in yield to the nitrogen and