Biological Effects of Ionizing Radiation

1. Biological Effects of Ionizing Radiation Science Teacher Workshop University of Richmond Richmond, VA July 18, 2007 Science of Nuclear Energy and Radiation Carl A. Tarantino, CHP Corporate Health Physicist Dominion Generation

2. Radiation in Life Solar Radiation Cosmic Rays Nuclear Medicine X-Rays •  Radon Consumer Products Each Other Radioactive Waste Nuclear Power Food & Drink Terrestrial Radiation

3. Old UnitsSI UnitsWhat It Is Ionizing Radiation Units 1 C kg-1 = 3876 R rad Gray 1 Gy = 100 rad rem Sievert 1 Sv = 100 rem

4. Measuring Radiation Effects • How much radiation is produced • Activity: decays per time (Curie (Ci), Becquerel (Bq)) • How much energy absorbed by tissue • Dose • How much biological damage does the radiation do per energy absorbed • Dose equivalent

5. Ionizing Radiation Effects Absorption of Radiation Ionization Chemical Change Repair or Damage High Dose Effects Cell killing Tissue or organ effects Whole body effects Low Dose Effects Mutations Cancer Effects to unborn

6. Cellular Organization Cells Tissue Organ Organism

7. Potential Radiation Damage to DNA Most critical molecule within humans: DNA • Direct effect on molecule by ionization or excitation of the molecule and subsequent dissociation of the molecule

8. Other Damage to DNA • Many other entities cause breaks in DNA • Temperature, chemicals, etc. • Human DNA suffer millions of DNA breaks daily • Most repaired

9. Radiation Induced Decomposition of Water Within a Cell Most abundant molecule within humans: Water H2O H2O+ H2 e- H+ Incoming Radiation WATER OH- Ho HO2 H2O2 OHo Production of free radicals within the cell can result in indirect effects

10. Potential Outcomes of Radiation Damage to Parent Cells

11. Cell Repair after Chronic Dose Damage Radiation Dose Reparable Accumulated Irreparable Time

12. Cellular Radiosensitivity:Law of Bergonie and Tribondeau The basic law of Bergonie and Tribondeau is that young and rapidly dividing cells are more sensitive than cells with adult development. Cells tend to be radiosensitive if they have three properties: • Cells that have high division rate (the time between divisions) • Cells that have long dividing future (immature cells in early cellular life) • Cells that are unspecialized (cells which have a widely diverse future)

13. Relative Sensitivity of Cell and Tissue Types MOST SENSITIVE • Lymphocytes • Spermatogonia • Hematopoietic (Blood Forming) • Intestinal Epithelium • Skin • Nerve Cells • Muscle Tissue • Bone • Collagen LEAST SENSITIVE

14. Hematological Response 1 Sv (100 rems)

15. Hematological Response 3 Sv (300 rems)

16. 1- Linear (Non-Threshold) 2 - Linear-Quadratic 3 - Threshold 4 - Supralinear Effects Dose (rem) Possible Radiation Dose Response Curves • Most conservative model: An increase in dose results in a proportional increase in risk • At low doses there is only a slight increase in risk that becomes proportional to dose at higher doses • There is a threshold for dose response at which lower doses do not result in increased risk • At low doses there is a higher risk that becomes proportional to dose at higher doses • Hormesis model (not shown): Low doses of radiation have a positive effect and decrease risk

17. Hormesis • Some data indicate that low doses of radiation are beneficial • Not widely accepted • Conservative is better • But not impossible

18. Risk Terms A large dose of radiation in a short period of time Small doses of radiation protracted over a long period of time Health effects that occur randomly and for which the probability of the effect occurring, rather than its severity, is assumed to be a linear function of dose without threshold Health effects which do not appear until a threshold value is exceeded and for which the severity of the effect increases with dose beyond the threshold Effects which occur in the exposed individual Effects which occur in the progeny of the exposed individual due to chromosome aberrations in the parent Effects to the unborn fetus irradiated in-utero • Chronic • Acute • Stochastic • Non-stochastic • Somatic • Genetic • Teratogenic

19. Hereditary effects Cancer (leukemia, tumors) Erythema (skin reddening) Cataracts Sterility Epilation (hair loss) Hematological effects Genetic; stochastic Somatic; stochastic Somatic; non-stochastic Somatic; non-stochastic Somatic; non-stochastic Somatic; non-stochastic Somatic; non-stochastic Risk Examples

20. Biological Effects from Low Doses of Radiation Biological effects from low doses potentially occur due to chronic exposures. A chronic exposure occurs when a relatively small amount of radiation is absorbed by tissue over a long period of time. • Under 5 rad of exposure - No detectable health effects in exposed individual • Chronic exposures result in an increased risk in latent adverse health effects • Health effects could be genetic effects or somatic effects

21. Latency period is the time from time of exposure until the effect is exhibited Time radiation dose received Latent period Period at risk Risk curve Risk 0 4 30 Time (years) Latency Period • Radiation exposure does not produce cancer in every exposed person • Effects can be immediate or years later for acute, high-level exposures Leukemia latency and time at risk periods

22. Biological Effects from High Doses of Radiation Biological effects from high doses occur due to acute exposures. An acute exposure occurs when a relatively large amount of radiation is absorbed by tissue over a short period of time; effects can occur in the short term and long term. • Hematopoietic Syndrome: (100-200 rad or 1-2 Gray) Early symptoms are anorexia, nausea, and vomiting followed by a phase of bone marrow depression and subsequent susceptibility to infection. After several weeks, death may occur. • Gastrointestinal Syndrome: (700-1000 rad or 7-10 Gray) Early symptoms are anorexia, nausea, and vomiting followed by fever, diarrhea, and electrolyte imbalance due to ulceration of the intestinal wall. Once GI system ceases to function, death will occur. • Central Nervous System Syndrome: (2000-5000 rad or 20-50 Gray) Symptoms occur very quickly and the brain and muscles can no longer control bodily functions, including breathing and blood circulation. Death within hours or within several days.

23. Effects From Acute, High-level Radiation Doses

24. Median Lethal Dose Curve Dose (rad) LD50 - Median Lethal Dose LD50/30 - Lethal dose to 50% of exposed population within 30 days of irradiation, without medical attention Defined at approximately 450 rad

25. What is Safe? • Driving a car is “safe” • 1:6,000 • Living at home is “safe” • Falls -- 1:20,000 • Fires -- 1:50,000 • Poisoning -- 1:40,000 • Total -- 1:10,000 • Radiation (1 mSv) is safe • 1:20,000

26. Relative Risk:Years of Life Lost

27. Relative Risk:Days of Life Lost

28. Relative Risk:Hours of Life Lost Anti-nuclear activists Government

29. Summary of Ionizing Radiation Effects • All radiation may not be harmful • However, data does not contradict the linear, non-threshold theory for some effects (cancer, genetic effects) • Effects from high doses are known fairly well • Depending upon dose, radiation may affect various cells, tissues, and organs • Without medical treatment, about 50% of people exposed to approximately 450 rad of radiation are expected to die within 1-2 months • Acute (short-term) effects below 100 rad are relatively minor

30. Summary of Ionizing Radiation Effects • Effects from low doses occur less frequently and take longer to develop than high dose effects • Studies of populations chronically exposed to low levels of radiation have not shown conclusive evidence of increased cancer risk • The magnitude of the risk is inferred from data at higher doses • The lower the dose of radiation, the longer it takes for the cancer to develop • Some changes in blood have been detected down to several rad

31. Summary of Ionizing Radiation Effects • Genetic effects have not been detected in people • Genetic effects may occur, but at rates so low that they have not been detected over the rate that occurs in the absence of radiation • The unborn child and young children appear to be more sensitive to the effects of radiation than adults are • The rate that effects occur is very low

32. The End Questions or Comments?