Effects of Radiation on Biota

1. Tom Hinton (IRSN) Effects of Radiation on Biota

2. OBJECTIVES To have a fundamental, introductory understanding of: • radioactive decay and ionization as it relates to effects of radiation • DNA’s role as the primary target for the induction of biological effects • the broad similarities in radiation responses among organisms • the wide variation in responses among organisms • free radicals and their role in the biological effects from radiation • repair of damage from radiation • mis-repair of damage and the fate of mutations within a population of organisms • fundamental differences in human versus ecological risk analyses from the perspective of radiation effects • a general idea of the state of knowledge about radiation effects and some of the major data gaps that need to be addressed

3. Ionization The radiation emitted from radioactive atoms can be of sufficient energy to cause ionization of other atoms. Ionization occurs when energy is sufficient to eject an electron

4. DNA is the primary target for the induction of biological effects from radiation in ALL living organisms Broad similarities in radiation responses for different organisms……and yet, wide differences in radiation sensitivity www.ceh.ac.uk/PROTECT (Whicker and Schultz, 1982)

5. Different kinds of DNA damage induced by γ-radiation per 0.01 Gy base loss base change H O OH single stand break H double stand break interstrand crosslinks www.ceh.ac.uk/PROTECT Feinendegen, Pollycove. J. Nucl. Medicine. 2001. V.42. p. 17N-27N

6. Free Radicals (unstable molecule that loses one of its electrons) www.ceh.ac.uk/PROTECT

7. DNA damage and repair www.ceh.ac.uk/PROTECT

8. Cell Death Cancer Fate of Mutations Germ Cells Somatic Cells Decrease in number and quality of gametes Alteration to offspring Increased embryo lethality www.ceh.ac.uk/PROTECT

9. Confer a selective advantage Spread in the population Cell Remove from the population Deleterious mutations Mutation Persist over many generations Neutral mutations Fate of mutations in non-human biota • For humans, risk of hereditary effects in offspring of exposed individuals is about 10% of the cancer risk to the exposed parents(UNSCEAR, 2001) • For non-human biota the risk of hereditary effects is unknown www.ceh.ac.uk/PROTECT

10. Knowledge of ionising radiation’s effect on wildlife is the basis for the derivation of radiological risk benchmarks www.ceh.ac.uk/PROTECT

11. Data Base of Knowledge on Effects of Radiation Exposure on Biota FREDERICA (www.frederica-online.org) • An online database of literature data to help summarise dose-effect relationships • FREDERICA can be used on its own; or in conjunction with the ERICA assessment tool (for conducting risk assessments of wildlife exposed to ionising radiation) (> 1500 references; 26 000 data entries) www.ceh.ac.uk/PROTECT

12. FREDERICA Database Chronic - external Acute-internal Chronic - internal Acute-external Chronic-internal Chronic-external Acute-external Acute-internal 73% of all data effects data; per ecosystem per exposure pathway (external or internal irradiation) per duration (acute or chronic) www.ceh.ac.uk/PROTECT

13. Radiation Effects on Non-Human Biota Early Mortality premature death of organism These categories of radiation effects are similar to the endpoints that are often used for risk assessments of other environmental stressors, and are relevant to the needs of nature conservation and other forms of environmental protection Morbidity reduced physical well being including effects on growth and behavior Reproduction is thought to be a more sensitive effect than mortality Reproductive Success reduced fertility and fecundity www.ceh.ac.uk/PROTECT

14. for chronic, low level exposure to radiation, alone, or mixed with other contaminants population, community, ecosystem > mortality, < fecundity, sublethal effects Fundamental Differences In Human and Ecological Risk Analyses TypeUnit of ObservationEndpoint Dose-Response Human individual lifetime cancer relationships risk established Ecological varies varies not established www.ceh.ac.uk/PROTECT

15. Predicting radiological effects to wildlife is complicated because: Populations are resilient Compensating mechanisms exist Indirect effectsoften occur that are unpredictable Blaylock (1969) studies at Oak Ridge DIRECT EFFECT: Increased mortality of fish embryos exposed to 4 mGy / d INDIRECT EFFECT: Fish produced larger brood sizes NET RESULT: No effect to population www.ceh.ac.uk/PROTECT

16. CHERNOBYL 26 April 1986 Radioactive releases for 10 days Contaminated 200,000 km2 350,000 people relocated

17. 20 April 2006 “It contains some of the most contaminated land in the world, yet it has become a haven for wildlife - a nature reserve in all but name”. Sergey Gaschak

18. Chernobyl ‘Shows Insect Decline' By Victoria Gill, Science Reporter, BBC NEWS 18 March 2009 “Two decades after the explosion at the Chernobyl nuclear power plant, radiation is still causing a reduction in the numbers of insects and spiders”. A. Moller and T. Mousseau

19. In 2004 – 2006, the IAEA established the CHERNOBYL FORUM Goal of reaching international consensus and eliminating the controversy about the effects of the Chernobyl accident

20. World Health Organization International Atomic Energy Agency The World Bank United Nations Development Programme Belarus Food and Agriculture Organization Russian Federation United Nations Environment Programme United Nations Office for the Coordination of Humanitarian Affairs Ukraine United Nations Scientific Committee on the Effects of Atomic Radiation CHERNOBYL FORUM

21. Before Chernobyl • Chernobyl overview • temporal aspects • general effects to major classes of organisms • indirect effects – confounding variables • Possible reasons for controversy

22. Pre-Chernobyl… • wealth of data about the biological effects of radiation on plants and animals • early data came from… • laboratory exposures • accidents (Kyshtym, 1957) • areas of naturally high background • nuclear weapons fallout • large-scale field irradiators

23. Factors Influencing the Sensitivity of Plants to Radiation (Sparrow, 1961)

24. Pre-Chernobyl… Lethal Acute Dose Ranges (Whicker and Schultz, 1982)

25. Pre-Chernobyl… Effects from Short Term Exposures (5 to 60 d) • minor effects(chromosomal damage; changes in reproduction and physiology) • intermediate effects(selective mortality of individuals within a population)

26. DOSE (Gy) to DOSE RATE (Gy / d) CONVERSION (5 to 60 d) x/10 Gy / d

27. Within Chernobyl’s 30-km zone • Environmental effects were specific to 3 distinct time periods I II III • Biota were exposed to a diverse group of radioisotopes • Tremendous heterogeneity and variability (in all parameters) • Accident occurred at a period of peaksensitivity for many biota

28. First 20 to 30 days • Gamma exposure dose rates were • > 20 Gy / d • Dominated by short-lived isotopes • 99Mo; 132Te/I; 133Xe; 131I; 140Ba/La I • Severe effects to biota • High dose to thyroids • from iodine

29. 0.02 Gy /d 0.2 Gy /d 2 Gy /d 20 Gy /d Air Exposure Rates on 26 April 1986 (1 R / h ~ 0.2 Gy / d; UNSCEAR 2000)

30. Gy / d • Dose rates from gamma • exposures ranged from • 0.02 to 20 Gy / d

31. Gy / d First Phase • Acute adverse effects within 10-km zone • Mortality to most sensitive plants and animals • Reproductive impacts to many species of biota

32. Second Phase • Decay of short-lived • isotopes • Radionuclide migration II • β to δ ~ 6:1 to 30:1 with • > 90 % of dose from β

33. III Third and Continuing Phase • Dose rates are chronic, < 1% of initial • Beta to gamma contributions more comparable, depends • on bioaccumulation of Cs • 137Cs and 90Sr dominate dose • Indirect effects dominate • Genetic effects persist; although some results are controversial

34. Hardwoods more radioresistant General Effects to Plants • Morphological mutations 1 to 15 Gy (e.g. leaf gigantism) • Shift in ecosystem structure: Deceased pine stands were replaced by grasses, with a slow invasion of hardwoods • Genetic effects extended in time • 1993, pines of 5 to 15 Gy had 8 X greater cytogentic damage than controls • Evidence of adaptive response

35. General Effects to Plants 0.3 Gy / d • Growth and developmental problems Gy / d Twisted needles • Inhibition of photosynthesis, transpiration • Chromosome aberrations in meristem cells • Short term sterility • High mutation rates in wheat due to non- targeted mechanisms

36. General Effects to Rodents • During Fall 1986, rodents population < 2- to 10-fold, dose rates 1 to 30 Gy/d (δ & β) • At ~ 0.1 Gy/d temporary infertility, reduced testes mass Gy / d • Increased mortality of embryos • Dose-rate dependent increase in reciprocal translocations • Numbers of mice recovered within 3 years(immigration), but cytogenetic effects persisted

37. Effects Data from Rodents Collected in Phase III Are Ambiguous and Controversial III From virtually no effect…. … to significantly elevated mutation rates • ~ 30 to 40 generations post-accident • lower dose rates • chronic exposures • inadequate dosimetry • sample size and technique sensitivity • indirect effects (immigration) • interpretation of results from new methods (microsatellites)

38. General Effects to Soil Invertebrates • 60 to 90% of initial contamination captured by plant canopies • Majority washed off to soil and litter within several weeks • Populations of soil invertebrates reduced 30-fold, reproduction strongly impacted

39. General Effects to Soil Invertebrates • Dose and effects to invertebrates in forest litter were 3- to 10- fold higher than those in agricultural soils • 30 Gy altered community structure (species diversity) for 2.5 years

40. Indirect Effects of Human Abandonment Pripyat Abandoned 4 km N of Reactor 50,000 people 135,000 people and 35,000 cattle evacuated Dozens of towns and villages deserted.

41. With the removal of humans, wildlife around Chernobyl are flourishing 48 endangered species listed in the international Red Book of protected animals and plants are now thriving in the Chernobyl Exclusion Zone Russian Boar Wolves Przewalski Horses

42. Wormwood Forest: A Natural History of Chernobyl Mary Mycio

43. Barn Swallows at Chernobyl • partial albinism as a phenotypic marker for mutations ( ↑ 10x) • carotenoids used for free-radical scavenging…rather than plumage coloration • reduced levels of antioxidants in blood • increase in abnormal sperm • elevated mutation rates in microsats • partial albinismcorrelated to reduced mating success • clutch size, brood size and hatching success reduced

45. Gy / d IAEA Guidelines 1 & 10 mGy / d 0.000001

46. Potential Causes for Controversial Data • Poor dosimetry can cause misinterpretation of data • Spatial heterogeneity of exposure; free-ranging wildlife • Confounding variables and indirect effects • Lack of analogous controls • Questionable statistical analyses • What constitutes a “significant effect”?? • Adaptation to generations of chronic exposure

47. Data on radiation effects for non-human species Chronic effects and γ external irradiation Reproductive capacity Morbidity Mortality Mutation Amphibians Aquatic invertebrates Aquatic plants Bacteria Birds Crustaceans Fish Fungi Insects Mammals Molluscs Moss/Lichens Plants Reptiles Soil fauna Zooplankton To few to draw conclusions No data Some data www.ceh.ac.uk/PROTECT

48. Most research is not directly relevant to responses in nature Data Plentiful but Least Relevant Data Scarce but Most Relevant Individual response Population response Mortality Reproduction Acute exposure Chronic exposure External gamma Multiple exposure route Laboratory Field Short-term Long-term

49. Alternative Paradigms in Radiation Biology are Gaining Acceptance • Bystander Effects • Genomic Instability • Epigenetic Damage

50. Questions remaining to be answered… • What is the extent of inherited, transgenerational effects from chronic, low-level irradiation? • What is the significance of molecular effects to individuals and populations? • Can definitive studies be conducted that eliminate • the controversy?