an
1364.
sicr.on 12
reduced the content of Cs-157 in the tissuc. Also reported aie the results of a field
experiment on Rongelap Island in which fertilization with KC] 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 commonpattern, K and Cs-137 coutents of the
upperfoliage were higher than those of the lowerIcaves, but one species con-
sistently showed higher K but lower Cs-187 in the upper foliage. Low K 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-137 by plants from soils of
Rongelap Atoll, Marshall Islands, with special reference tu fertilization of the
soil with N, P, and K. The report includes the results of greenhouse pot culture
tests using Rongelaptop soil, as well as foliar analyses of native vegetation grow-
ing 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-187, Radionuclides in the soil remain in the top few inches with
90% or moreof the radioactivityin the top two inchesorless.
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, 152 Mg, 4¢ Na, and 0.7% K; the soil is coarse, very friable, and highly
porous.
The pot culture technique wasessentially that of Jenny et 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 gamma rayspectroscopyusing a three-inch thallium-
activated sodium iodide crystal in conjunction with a multichannel analyzer.
Tissue was dry ashed and the acid solution analyzed for potassiumbytitration 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-driedin the ficld headquarters. and was subsequently
re-dried, ground, und analyzed in the same manner as the greenhouse samples.
Greenhouse Experiments
RESULTS
In a preliminary experiment with tomato, varietv Marglobe, the fertilizer treat-
ments and the Cs-137 in disintegrations per minute per gm drv tissue were:
unfertilized control. 490; N-P-k, 100; N-P, 190; N-K, 240: P-K. undetectable.
These results are particularly interesting becauseall fertilizer additions depressed
the uptake of cesium. There was marked response in vield to the nitrogen and