METABOLISMS OF 13C IN CATTLE SEMITENDINOSUS MUSCLE AFTER ADMINISTRATION OF 13C LABELED ORCHARD GRASS.

14C released from nuclear facilities is transferred to cattle through their consumption of 14C contaminated grasses. To estimate the concentrations of 14C in their meat, we conducted two sets of experiments. In the first experiment, 230 mg of 13C per day was administered to cattle aged 10 months for 28 days in the form of 13C-labeled grass. The 13C concentration in the semitendinosus muscle decreased exponentially after reaching its peak value. The mean half-life was 76 ± 13 days. In the second experiment, 550 mg of 13C per day was administered to 24-month-old cattle. The change in the semitendinosus muscle was smaller than that recorded in the first experiment, even though the amount of 13C administered per body weight was slightly higher than that in the first experiment. Consequently, the half-life was not determined. Therefore, further studies are required to clarify the metabolism of carbon in 2-year-old cattle.

DEVELOPMENT OF IN-SITU SYSTEMS FOR 13CO2 EXPOSURE AND DETERMINATION OF 13C NET ASSIMILATION RATE OF FRUIT-BEARING SHOOTS AND WHOLE TREE AND CHAMBER FOR PRECISION 13CO2 EXPOSURE OF YOUNG POTTED TREES.

14C is the most important radionuclide for assessing exposure dose around the Rokkasho nuclear fuel reprocessing plant, Aomori Prefecture, Japan. A simplified model with ample margins has been used so far for the assessment of the dose derived from 14C. Realistic dose estimate of 14C using more realistic model is necessary for safety. Apple production is an important core industry in Aomori Prefecture. To construct the dynamic model for apple, using 13C as a tracer to substitute for 14C, we collected data on 13C abundance in organs including fruit after 13CO2 exposure at various fruit growth stages. We developed 13CO2 exposure systems for three intact fruit-bearing shoots (1), whole mature tree (2) and young potted trees (3). Systems (1) and (2) also can determine net amounts of carbon and 13C photoassimilated. System (3) is capable of precise feedback control of 13CO2 and 12CO2 concentrations based on on-time determination.

Investigation of ratio of carbon to hydrogen (C/H ratio) in agricultural plants for further estimation of their productivity of organically bound tritium.

The carbon to hydrogen ratio (C/H ratio, w/w) in plants is a key factor in estimating the amount of hydrogen in the photosynthetic product. The amount of hydrogen calculated from photosynthetic model estimation associated with the C/H ratio is an essential parameter of the estimation model of productivity of organically bound tritium (OBT) by plants. To propose a sophisticated estimation model of OBT by agricultural plants, temporal changes in the C/H ratio of six plant species (Japanese radish, cabbage, orchard grass, paddy field rice, apple, and radish) during their cultivation were investigated for each plant part. The C/H ratio in the plants cultivated in the field and growth chamber generally exceeded 6, which is the value for the primary photosynthetic monosaccharides, such as glucose and fructose (both chemical formulae, C6H12O6). In the vegetative parts (e.g. Japanese radish leaves, cabbage leaves and roots, rice leaves and roots, and radish leaves and fine roots) the C/H ratio fluctuated irregularly or remained constant within an approximate range of 6.6-7.3 during cultivation. The C/H ratio in enlarged organs (e.g. Japanese radish root, rice ear, apple fruit, and radish main root) decreased continuously, approaching 6. These results suggest that the C/H ratio can be generally set as approximately 6.9 except for enlarged organs, in which the ratio may change over time during cultivation, within an approximate range of 6-7.

A dynamic transfer model for the estimation of 14C radioactivity in Japanese radish (Daikon) plants.

A dynamic compartment model was developed to describe C accumulation in the Japanese radish plant, which is an important crop in the area around Japan's first commercial nuclear fuel reprocessing plant in Rokkasho, Aomori, Japan. Photosynthetically fixed carbon is distributed into the leaf and the root compartments, and a part of the carbon accumulated in the leaf compartment is redistributed to the root compartment. The model parameters were estimated by using data obtained from exposure of the plant to CO2. The model estimates were in good agreement with the experimental observations, showing that the newly developed compartment model is applicable to assessment of the accumulation of C in Japanese radish plants around the nuclear facility. In this study, respiration rate was set to be proportional to the carbon mass of the compartment, though the respiration rate has been assumed generally to be proportional to the growth rate of the compartment. While the estimates using both respiration rates differed only slightly from each other, the ratio of the respiratory rate of the root to that of the leaf was too high in the case of the respiratory rate proportional to the growth rate.

Development of a dynamic transfer model of (14)C from the atmosphere to rice plants.

A dynamic compartment model was investigated to describe (14)C accumulation in rice plants exposed to atmospheric (14)C with temporally changing concentrations. In the model, rice plants were regarded to consist of three compartments: the ear and the mobile and immobile carbon pools of the shoot. Photosynthetically fixed carbon moves into the ear and the mobile carbon pool, and these two compartments release a part of this carbon into the atmosphere by respiration. Carbon accumulated in the mobile carbon pool is redistributed to the ear, while carbon transferred into the immobile carbon pool from the mobile one is accumulated there until harvest. The model was examined by cultivation experiments using the stable isotope, (13)C, in which the ratios of carbon photosynthetically fixed at nine times during plant growth to the total carbon at the time of harvest were determined. The model estimates of the ratios were in relatively good agreement with the experimental observations, which implies that the newly developed compartment model is applicable to estimate properly the radiation dose to the neighboring population due to an accidental release of (14)C from nuclear facilities.