Radioecological behavior of ⁶⁰Co after a single administration was investigated in a nonflowing small-scale rice field ecosystem which consisted of natural pond water, rice seedlings, mud snails, loaches, earthworms and sandy soils. The radioactivity of 6oCo in water decreased rapidly for about ten days and gradually thereafter. Ten days after addition of ⁶⁰Co, the fraction, remained in aqueous phase, was about 0.1% of the initially administered radioactivity. The radioactive concentrations of both mud snails and earthworms reached maximums in two hours, while those of rice seedlings, loaches and sandy soils reached maximums in one day, and then decreased with time to an equilibrium level. The relative order for maximum concentration factors was:
rice seedling > mud snail > sandy soil > earthworm > loach.
In a mass balance analysis of the radionuclide in the system, ⁶⁰Co retained in the biomass including side wall algae grown during the experiment showed about 12%, although the proportion based on wet weight of the biomass was only about 2.3%.

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Adsorption of uranium on soils and its desorption from uranium-adsorbed soils in the presence of carbonate ion were examined by using three kinds of soils, alluvial soil, sandy soil and volcanic ash soil.
1) The adsorption ratio of uranium for each soil was approximately 100 per cent for the mixtures of uranyl (1—50 μgU/ml) and carbonate solutions (4.3—109 μgCO₃^--/ml).
2) In the uranium adsorbed soil (7.1—500 μgU/g air-dried soil) with carbonate ion (4.3, 43.4 μg/ml), the desorption ratio of uranium for each soil was low (0.09—1.2%).
The adsorption of uranium on soils and the desorption from uranium adsorbed soils with stream water were probably similar to those with carbonate solution.

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Since 1961 through 1971, this study was conducted to determine the distribution of the replaceable ⁹⁰Sr in loam surface soil originated from volcanic ash under three kinds of soil management, i. e. clean, mulch and sod systems at a citrus orchard.
The level of the replaceable ⁹⁰Sr in the surface soil measured in 1963 was in the order of clean(41) ÷ sod(40) > mulch (31 nCi/m²·(0—30 cm)) and decreased exponentially with a half-time of approximately 5.9, 12.3 and 10.2 years for clean, mulch and sod systems, respectively. It was observed that the distribution coefficient of ⁹⁰Sr calculated for these soils depended largely on the replaceable ⁹⁰Sr content in surface soil and that the level of the coefficient in the soil under each soil management system in 1971 was nearly equal to that in 1961. The distribution coefficient of three systems are in order of clean < sod < mulch.

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Since 1961 through 1971, the replaceable ¹³⁷Cs content in the same surface soil of the same area under clean, mulch and sod systems of soil management at a citrus orchard with that described in the previous paper¹⁾ was determined in order to compare its annual change with that of replaceable ⁹⁰Sr.
The relation of humus content in surface soils classified as clean < sod < mulch closely related to half-time for an exponential decrease of replaceable ¹³⁷Cs from 1963 through 1971 and with distribution coefficient¹⁾ for the downward distribution of replaceable ¹³⁷Cs in, surface soil. Both half-times of approximately 8.5, 45.2 and 30.7 years and distribution coefficient of 0.094—0.111, 0.142—0.165 and 0.129—0.140 for clean, mulch and sod, respectively, are larger than those of ⁹⁰Sr. The ratios of replaceable ¹³⁷Cs to ⁹⁰Sr of 0.92—1.13 in surface soil found for the year from 1961 through 1967 followed by a slight increase afterwards and reached 1.24—1.36 in 1971. It was found that ¹³⁷Cs is fixed much more strongly than ⁹⁰Sr in the surface soil of a citrus orchard.

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The x-ray survival curve of Ehrlich ascites tumor cells and its modification by iodoacetamide were determined by the TD₅₀, assay. Survival curves for tumor cells of 1, 6 and 12-days after transplantation were examined in the presenc or in the absence of the agent. The D₀ was 130, 350 or 230 rads for 1-, 6 and 12-day-old tumor cells, respectively. The response to x-rays of 1 and 6-day-old tumor cells was enhanced by iodoacetamide, while that of 12-day-old or stationary phase tumor cells was hardly enhanced. The increased radiosensitivity and the lowered sensitization by iodoacetamide of 12-day-old tumor cells might be attributed to an increased proportron of the stationary phase cells.

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Pedigrees of HeLa S 3 cells irradiated with 300 rads of X-rays were studied by time-lapse photography. The pedigrees were analyzed by classifying the cells as surviving and nonsurviving groups. In both groups, high degree of synchrony in division was observed after a division delay. In the nonsurviving group, loss of cells occurred in a synchronous fashion. Generation time was restored to nearly normal in the 1st postirradiation generation, but prolonged in succeeding ones. Division probability in the surviving group approached unity (0.9-1.0) except for a slightly reduced value (0.74) at the 3rd generation. In the nonsurviving group, the division probability was relatively high in the irradiated and the 1st generations (0.76), but declined from the 2nd to 4th generations with a progressive increase in cell damage, such as fusion and death.

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In the present study, we have established the optimum conditions for a combination of colcemid (0.025 μg/ml for 6 hours) and harvesting techniques in order to obtain a large highly purified population of mitotic HeLa S 3 cells. This method does not cause any visible biological or cytological damage to cells. The mitotic phase and the late G₁ to the early S phase of HeLa S 3 cells synchronized by this method were found to be more sensitive to X-irradiation of 400 R than were the other phases in the cell cycle. Sensitivity to UV-irradiation of 100 ergs/mm² increased late in the G₁ phase, reached a maximum in the middle of the S phase, and decreased through the remainder of the S and G₂ phases. In addition, the mitotic phase was as sensitive to UV-irradiation as the middle of the S phase. On the other hand, sensitivity to 4-NQO-treatment with 5 × 10^-9M for 20 minutes decreased from the late S to the early G₂ phase. All other phases were relatively sensitive to 4-NQO. These findings may indicate that the effects of X-, UV-irradiation and 4-NQO on HeLa S 3 cells differ qualitatively from each other.

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Six wrokers were accidentally exposed to a 5.3 Ci ¹⁹²Ir source. One case showed severe pancytopenia associated with marked bone marrow hypoplasia. Although no significant signs of infection and of hemorrhage were observed, he was isolated in a bio-clean room and was administered with antibiotics prophylactically. He was recovered without any further measures, such as blood transfusion and bone marrow transplantation. In three cases, radiation dermatitis were observed. The ulcers developed on the buttocks of one patient were corrected surgically. Azoospermia was noted in one case and oligospermia in five other cases.

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Among six persons (male, age 20-30) exposed accidentally to ¹⁹²Ir gamma-rays, five cases showd hematopoietic disorders of various degrees. One case (S. H. 25 Yr.) showed a severe hematopoietic injury such as pancytopenia between the 3rd and 7th week after the initial exposure. On the 4th and 5th week, thrombelastogram showed an earliest and significant improvement, followed by increase of leukocyte and platelet counts. This clinical test was useful for diagnosis and prognostic evaluation in this crucial pancytopenic period during which some treatments or cares were needed. He was treated only with a prophylactic administration of antibiotics in an isolated clean aseptic room. Since 5th week, the hematopoietic disorders were rapidly improved although the leukocyte counts still remained at a subnormal level for more than 18 months. The other 4 cases showed various degrees of temporal leukopenia and hypoplasia of bone marrow, while neither anemia nor thrombocytopenia was observed.
From the severity of hematopoietic disorders, a dose delivered to hematopoietic organs of S. H. was estimated to be somewhat between 200 and 400 rad. This was different from a cytogenetically estimated dose of 124 rad. The difference may mainly reflect a difference of doses received between hematopoietic cells and of peripheral circulating lymphocytes, which might be resulted from a different distribution of these cells in the body and from a non-uniform gammarays irradiation of ¹⁹²Ir source.

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Serum levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were determined by radioimmunoassay in 6 subjects who had been exposed accidentally to ¹⁹²Ir gamma rays. All subjects showed normal levels of LH and FSH shortly after the irradiation. From 100 to 150 days post-irradiation, however, serum FSH levels increased in subjects who received 12.2 rad or more, a finding in agreement with the decrease in sperm concentration below 10 millions/ml, while in the other 2 subjects who received 9.8 and 10.9 rad, it remained within normal range. The elevation in serum FSH levels in one of the severely exposed subjects (Y. S.) was noted as late as 413 days after the exposure, while the hormone levels in the all other cases declined toward normal level.

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Eleven biochemical indicators (5-hydroxyindoleacetic acid, xanthurenic acid, creatine, creatinine, β-aminoisobutyric acid, taurine, 11-deoxy-17-ketosteroid, total estrogens and Dische reaction-positive substance(s) in urine; 5-hydroxytryptamine in whole blood; and cortisol in blood plasma) of the ‘radiation injury’ were analyzed in 6 cases which were accidentally exposed to a gamma ray source of ¹⁹²Ir. Among them, 4 indicators including 5-hydroxyindoleacetic acid, taurine and Dische reaction-positive substance(s) in urine and 5-hydroxytryptamine in whole blood reflected the severity of the injury to some extent for long period far after the exposure :
(1) Urinary excretion of 5-hydroxyindoleacetic acid was less than that of non-irradiated persons from days 11 to 17 after the exposure and increased to several times more than those of the non-irradiated in the subsequent week (days 17 to 25).
(2) Blood levels of 5-hydroxytryptamine were minimal at the day 24th after the exposeure in the 2 cases (S. H. and Y. S.) which were exposed to higher doses.
(3) The ratio of urinary taurine over alanine remained high in the two higher dose cases for several weeks of the post-irradiation period and returned to normal level thereafter.
(4) The ratio of Dische reaction-positive substance(s) to creatinine in urine was high in the same two cases during 8 to 13 weeks of the post-irradiation.

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Six persons were accidentally exposed to gamma-rays from an ¹⁹²Ir source. Since they were non-occupational persons, a means to estimate the absorbed dose was needed to be established. As three of them wore wrist watches when they were exposed to gamma-rays from the ¹⁹²Ir source, cumulative doses of three persons were able to be estimated by measuring a thermoluminescence from jewels(ruby) of their watches.
The absorbed doses of the six persons were also estimated through reconstructing timetables of the six persons in relation to the ¹⁹²Ir source. The doses estimated with reference to the thermoluminescence for three persons were in good agreement with those obtained only through reconstruction of their movements without refering to the thermoluminescence data. This indicates that the absorbed doses of the three others without the use of the thermoluminescence data were probably close to what they received.
The newly developed thermoluminescence method was proved to be a very useful one for dose estimation of persons accidentally exposed, if they wear wrist watches and to be far quicker in estimating the absorbed dose than the meticulous reconstruction of timetables of them.

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Chromosome examinations were made both in cultured peripheral lymphocytes and in freshly aspirated bone marrow cells of 6 persons accidentally exposed to gamma rays from an ¹⁹²Ir. Samplings of peripheral blood for the chromosome analysis were repeated mostly at weekly intervals during the hospitalization beginning on 10-11 days after the initial exposure, and at more prolonged intervals after that period. The average yield of dicentrics plus rings in peripheral lymphocytes ranged from 0.0015 to 0.1367 per cell. The chromosome abnormalities, mostly of the stable-type rearrangements of chromosomes, were observed in bone marrow from two of the 6 cases. Based on the aberration yield in peripheral lymphocytes, the average total body absorbed dose was estimated to be equivalent to 9.8 to 124 rad of ⁶⁰Co gamma rays and 15.6 to 152 rad of high energy X-rays. When the dose estimate was made with the Q_dr value, the average total body absorbed doses were higher than those obtained by direct extrapolation of the aberration yield. This seemed to be resulted from non-uniformity of the exposure.

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