survival was lower for microorganisms irradiated before lift-off compared to survival for ground-based controls treated in the same way. It was noted that the difference in survival did not seem to be dose dependent. These results were interpreted as indicating that DNA repair was less efficient in microgravity. No experiments were carried out in space using a 1-g centrifuge for controls.

Recent ground-based experiments, summarized by Kronenberg, on radiation-induced DNA fragmentation, neoplastic transformation of cells plated 24 hours after irradiation, and the effects of a chemical radioprotector on mutation induction showed that DNA repair and cell recovery take place readily after low-LET radiation, but not following exposure to HZE particles.7 Since the only reported significant effect of microgravity may be on DNA repair and cell recovery following low-LET exposure and there seems to be no DNA repair/cell recovery following high-LET exposure, microgravity should not be important for HZE particle effects.

The above considerations indicate that HZE particles are a very important factor in the damage resulting from long space missions and that the effects of microgravity probably will not alter the cellular response to HZE particles but might actually increase the effect of low-LET radiation.

Hence, the task group concluded that the majority of the useful information on radiation effects and risks will come from ground-based experiments described in Chapter 4 and that radiation experiments in space, with all their logistical difficulties, will not be rewarding and may not be worth the effort.

Plants and Food Supply

Since any interplanetary spaceflight will be of long duration (up to 3 years), it will be necessary not only to have packaged food available, but also to grow additional plant food. The very high doses of radiation used to sterilize food do not significantly affect food quality. Hence, no significant effects of irradiation are plausible for packaged food, and given the predicted magnitude of exposure during spaceflight, no effect is likely on growing plants. In general, plants are relatively radiation resistant when growing and extremely resistant as dormant seeds. The most sensitive response of plants to irradiation would be overall growth, and this occurs at doses above those predicted during spaceflight.

References

1. National Council on Radiation Protection and Measurements (NCRP). 1995. Radiation Exposure and High Altitude Flight. NCRP Commentary No. 15. National Council on Radiation Protection and Measurements, Bethesda, Md.

2. Culotta, E., and Koshland, R.D.E. 1993. p53 sweeps through cancer research. Science 262:1958–1961.

3. Jones, L.A., Scott, D., Cowan, R., and Roberts, S.A. 1995. Abnormal radiosensitivity of lymphocyte from breast cancer patients with excessive normal tissue damage after radiotherapy: Chromosome aberrations after low-dose-rate irradiation. Int. J. Radiat. Biol. 67: 519–528.

4. Jones et al., 1995, Abnormal radiosensitivity of lymphocyte from breast cancer patients with excessive normal tissue damage after radiotherapy.

5. Horneck, G. 1992. Radiobiological experiments in space: A review. Int. J. Radiat. Appl. Instrum. 20: 82–205.

6. Nelson, G. 1995. Space-based radiation biology. Presentation to the Task Group on the Biological Effects of Space Radiation, November 13, 1995, Washington, D.C.

7. Kronenberg, A. 1995. NASA space radiation health program: Ground-based radiobiology research program. Presentation to the Task Group on the Biological Effects of Space Radiation, Washington, D.C.



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