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Uptake of Plutonium and Americium by Barley from Two Contaminated Nevada Test Site Soils¹

ABSTRACT

Barley (Hordeum vulgare, Var. Atlas 68) plant uptake of ^239,240Pu and ²⁴¹Am was studied using two soil samples collected from widely separated areas of the Nevada Test Site. Each area had been previously contaminated with plutonium and americium as a result of a separate high explosive (nonnuclear) detonation of a device containing plutonium. The plants were grown on 3-kg soil samples in a controlled environment chamber. The plutonium concentration ratio (plutonium concentration in dry plant tissue/plutonium concentration in dry soil) was in the order of 10^–5 for plant vegetative material. The plutonium concentration ratio for the grain was 20–100 times lower than that in the vegetative material. Concentration ratios for americium were in the order of 10^–4 for vegetative growth and 25–75 times lower for the grain. These results imply that americium is more available to plants than plutonium.

Plutonium-bearing particles were identified in a soil sample using an autoradiographic technique and then separated from the soil samples. The ²³⁹Pu oxide equivalent diameters of plutonium-bearing particles could be described by a log-normal distribution function in the range of 0.2 to 0.7 µm. The actual diameters of the particles were 2 to 3 times the PuO₂ equivalent diameter. Microprobe analyses of the surface region of particles >2 µm showed the following order of abundance: U, Pu > O > Al > Si > Fe > Mg. Photographs obtained with a scanning electron microscope revealed that some of the particles are quite irregular and have large specific surface areas which might enhance solubility and plant uptake.

Key Words: plant uptake • concentration ratio • particles • availability

¹ Contribution from the Dep. of Soils and Plant Nutr., Univ. of California, Berkeley, CA 94720. Supported by the Energy Res. and Develop. Admin. under Contract No. AT(04-3)-34, PA 211.

² Associate Research Soil Chemist and Radiation Biologist, Univ. of California, Berkeley; Assistant Research Soil Scientist, Univ. of California, Berkeley; Senior Scientist, LFE Environmental, Richmond, Calif.; Professor of Soil Chemistry, Univ. of California, Berkeley, respecticely. The present address of the second author is Lawrence Livermore Lab., Livermore, Calif.

Received for publication May 17, 1976.