Tamiko Iwasaki

Second analysis of mortality of nuclear industry workers in Japan, 1986-1997.

Abstract Iwasaki, T., Murata, M., Ohshima, S., Miyake, T., Kudo, S., Inoue, Y., Narita, M., Yoshimura, T., Akiba, S., Tango, T., Yoshimoto, Y., Shimizu, Y., Sobue, T., Kusumi, S., Yamagishi, C. and Matsudaira, H. Second Analysis of Mortality of Nuclear Industry Workers in Japan, 1986–1997. Radiat. Res. 159, 228–238 (2003). A cohort study of nuclear industry workers was initiated in 1990 to determine the possible health effects of low-level radiation. A total of 5,527 deaths were ascertained among 176,000 male workers who had been retrospectively and/or prospectively followed for an average of 7.9 years during the observation period 1986–1997. Statistical analyses were made mainly on the prospective follow-up outcome of 120,000 workers followed for an average of 4.5 years. The standardized mortality ratio (and its 95% confidence interval) was 0.94 (0.90, 0.97) for 2,934 cases of all causes combined and 0.86 (0.82, 0.91) for 1,305 cases of non-malignant diseases combined, which suggested a healthy worker effect. For 1,191 cases of all cancers combined, it was 0.98 (0.93, 1.04), indicating no difference in mortality from that of the general population. In tests for trend of death rate with increasing radiation dose, no significant correlation was found for all cancers combined. For site-specific cancers, most cancers including leukemia showed no positive correlation with dose, except for cancers of the esophagus, stomach and rectum and multiple myeloma. External causes showed a significant correlation with dose. A separate questionnaire study indicated that these positive findings could be ascribed in part to lifestyle characteristics of the workers. For leukemia only, we attempted to estimate the excess relative risk per unit dose of radiation, which, with reservations because of its wide confidence interval, was within the range of variation of the risks reported in other radiation epidemiological studies. This population must be studied for a longer time and with a consideration of the possible effects of confounding factors.

Effects of fast neutrons and 60Co gamma-rays on Artemia.

The effects of a single exposure to 2-MeV fast neutrons were compared with the effects of exposure to60 Co γ-ray irradiation on dry eggs of Artemia. Comparison of the survival data showed that neutrons were 2.1, 2.8, and 4.8 times as effective as γ-irradiation in producing mortality of nauplii at 1, 2, and 3 days after hatching. Irradiation with fast neutrons produces severe chromosomal abnormalities and leads to a depression in mitotic activity. On the basis of the cytological observations, the relative biological effectiveness of fast neutrons was about 2 with reference to γ-rays.

Sensitivity of Artemia eggs to gamma-irradiation. VII. Relationship between the degree of biological damage and the decay of free radicals in irradiated eggs.

SummaryThe present experiments pertain to the relationship between radical amount measured by E.S.R. and biological damage of dried Artemia eggs irradiated with γ-rays.(1) The amount of free radicals increased with the increase of the dose of irradiation; however, the relation was not linear. At the same time, the hatchability rate of the eggs decreased with the exposure dose, producing a sigmoid curve.(2) The amount of free radicals produced by irradiation in the intact eggs was similar to that in the denuded eggs.(3) The radical decay was very rapid, immediately after irradiation, then retarded. However, hatchability decreased continuously with time after irradiation.(4) The hatchability and radical-decay rate of the irradiated eggs stored at 25°c decreased much more rapidly than those at dry-ice temperature.From these results, it is concluded that decay of free radicals does not imply recover from radiation damage but continues to the point of fixation of the damage.

Sensitivity of Artemia Eggs to γ-irradiation

SummaryThe effects of heat or hydration treatment after irradiation on hatchability of, and the decay of free radicals in dry eggs of Artemia were examined. Immediately after irradiation with 480 kr of 60Co γ-rays, the eggs were heated at 100°c for 5 min, or hydrated at 4°c for 30 min, and re-desiccated with the aid of a vacuum pump for 2 hours. After these treatments, the hatchability of eggs did not change if they were examined just after treatment, but the amount of free radicals produced by irradiation instantly decreased as measured by E.S.R.In the irradiated eggs, the hatchability decreased during storage for one week under dried conditions. After post-irradiation heat treatment, the decrease in hatchability was reduced. If the irradiated eggs were hydrated, re-desiccated and stored for a few weeks, the hatchability did not decrease during the storage period. Free radicals in the irradiated eggs decayed rapidly after heat or hydration treatment. The possible role of the decay of free radicals in bio...

Sensitivity of Artemia Eggs to γ-irradiation IX. A Correlation between Radiation-induced Free Radicals and Hatchability in Eggs Exposed to β-mercaptoethylamine

SummaryBoth free-radical and hatchability measurements were made on the same samples of Artemia eggs treated with MEA. MEA present at the time of irradiation protected eggs under both dry and wet conditions, but was not effective when administered after irradiation. Radiation protection was accompanied by a reduction in the number of free radicals. The effect of MEA was to increase the rate of decay of radiation-induced radicals. However, transfer of unpaired electrons to the sulphur nucleus in MEA was not found.The protective mechanism of MEA is discussed in the light of current hypotheses.

A Study of the Biological Effectiveness of High-Energy Electrons at Ultra-High Dose Rates using Dry Eggs of Artemia

Dry Artemia eggs were used to determine the biological effectiveness of a 29-MeV electron beam at depths of 2.3 cm (2 x 10/sup 8/ rads/second), 11.3 cm (1 x 10/sup 8/ rads/second), and 13.0 cm (5 x 10/sup 7/ rads/second) in a water phantom. It appears that a significant difference in effectiveness exists at these three depths as measured by the hatchability and hatching delay of the eggs. The effect at the 11.3- and 13-cm depths is 1.16 and 1.32 times greater than at the 2.3-cm depth. Experiments to determine the effect of dose rates ranging from 1 x 10/sup 7/ to 2 x 10/sup 8/ rads/second at the same depth demonstrated an apparent lower effectiveness of radiation exposure when delivered at extremely high dose rates. From the results of these experiments, it was concluded that the difference in biological effectiveness of 29-MeV electrons at various depths is the result of a dose-rate effect. (auth)

The Effect of Oxygen on the Radiation Sensitivity of Artemia Eggs: A Preliminary Result of OER on Dry Eggs

The effects of oxygen on the radiation response of Artemia eggs in a dried state was examined by using a high-vacuum system. As a procedure to measure the oxygen effect, eggs were dried at 5× 10-5 Torr for 7 hr, exposed to gases, and left overnight. Under these conditions, an oxygen enhancement ratio of 17 was found for the reduction of hatchability to 50%.