Effects of Radiation on Biota Tom Hinton IRSN
Effects of Radiation on Biota Tom Hinton (IRSN)
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
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
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)
Different kinds of DNA damage induced by γ-radiation per 0. 01 Gy base loss base change H OH single stand break double stand break interstrand crosslinks www. ceh. ac. uk/PROTECT Feinendegen, Pollycove. J. Nucl. Medicine. 2001. V. 42. p. 17 N-27 N
Free Radicals (unstable molecule that loses one of its electrons) www. ceh. ac. uk/PROTECT
DNA damage and repair www. ceh. ac. uk/PROTECT
Fate of Mutations Somatic Cells Cell Death Cancer www. ceh. ac. uk/PROTECT Germ Cells Decrease in number and quality of gametes Increased embryo lethality Alteration to offspring
Fate of mutations in non-human biota For humans, risk of hereditary effects in offspring of exposed v individuals is about 10% of the cancer risk to the exposed parents (UNSCEAR, 2001) v For non-human biota the risk of hereditary effects is unknown Cell Confer a selective advantage Spread in the population Deleterious mutations Remove from the population Mutation Neutral mutations www. ceh. ac. uk/PROTECT Persist over many generations
Knowledge of ionising radiation’s effect on wildlife is the basis for the derivation of radiological risk benchmarks www. ceh. ac. uk/PROTECT
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
FREDERICA Database effects data; per ecosystem per exposure pathway (external or internal irradiation) per duration (acute or chronic) Chronic - external Acute-internal Chronic - internal Acute-external Chronic-internal Chronic-external www. ceh. ac. uk/PROTECT Acute-internal Acute-external 73% of all data
Radiation Effects on Non. Human Biota Early Mortality premature death of organism Morbidity reduced physical well being including effects on growth and behavior Reproduction is thought to be a more sensitive effect than mortality www. ceh. ac. uk/PROTECT Reproductive Success reduced fertility and fecundity 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
Fundamental Differences In Human and Ecological Risk Analyses Type Human Ecological Unit of Observation individual varies population, community, ecosystem www. ceh. ac. uk/PROTECT Endpoint lifetime cancer risk Dose-Response relationships established varies not established > mortality, < fecundity, sublethal effects for chronic, low level exposure to radiation, alone, or mixed with other contaminants
Predicting radiological effects to wildlife is complicated because: Populations are resilient Compensating mechanisms exist Indirect effects often occur that are unpredictable Blaylock (1969) studies at Oak Ridge DIRECT EFFECT: Increased mortality of fish embryos exposed to 4 m. Gy / d INDIRECT EFFECT: Fish produced larger brood sizes NET RESULT: No effect to population www. ceh. ac. uk/PROTECT
CHERNOBYL 26 April 1986 Radioactive releases for 10 days Contaminated 200, 000 km 2 350, 000 people relocated
Wildlife Defies Chernobyl Radiation By Stephen Mulvey BBC News 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
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
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
CHERNOBYL FORUM World Health Organization International Atomic Energy Agency United Nations Development Programme Food and Agriculture Organization The World Bank Belarus United Nations Environment Programme Russian Federation United Nations Office for the Coordination of Humanitarian Affairs Ukraine United Nations Scientific Committee on the Effects of Atomic Radiation
• Before Chernobyl • Chernobyl overview • temporal aspects • general effects to major classes of organisms • indirect effects – confounding variables • Possible reasons for controversy
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
Factors Influencing the Sensitivity of Plants to Radiation Increasing Sensitivity Decreasing Sensitivity Large nucleus Large chromosomes Acrocentric chromosomes Small nucleus Small chromosomes Metacentric chromosomes Low chromosome number Diploid or haploid Sexual reproduction Long intermitotic time Long dormant period High chromosome number High polypolid Asexual reproduction Short intermitotic time Short or no dormant period (Sparrow, 1961)
Pre-Chernobyl… Lethal Acute Dose Ranges (Whicker and Schultz, 1982)
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)
DOSE (Gy) to DOSE RATE (Gy / d) CONVERSION (5 to 60 d) x/10 Gy / d
Within Chernobyl’s 30 -km zone • Environmental effects were specific to 3 distinct time periods • Biota were exposed to a diverse group of radioisotopes • Tremendous heterogeneity and variability (in all parameters) • Accident occurred at a period of peak sensitivity for many biota I II III
First 20 to 30 days • Severe effects to biota • Gamma exposure dose rates were > 20 Gy / d • Dominated by short-lived isotopes 99 Mo; 132 Te/I; 133 Xe; 131 I; 140 Ba/La • High dose to thyroids from iodine I
Air Exposure Rates on 26 April 1986 0. 02 Gy /d 0. 2 Gy /d 20 Gy /d (1 R / h ~ 0. 2 Gy / d; UNSCEAR 2000)
• Dose rates from gamma exposures ranged from 0. 02 to 20 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 Gy / d
Second Phase • Decay of short-lived isotopes • Radionuclide migration • β to δ ~ 6: 1 to 30: 1 with > 90 % of dose from β II
Third and Continuing Phase • Dose rates are chronic, < 1% of initial • Beta to gamma contributions more comparable, depends on bioaccumulation of Cs • 137 Cs and 90 Sr dominate dose III • Indirect effects dominate • Genetic effects persist; although some results are controversial
General Effects to Plants • Morphological mutations 1 to 15 Gy (e. g. leaf gigantism) • Hardwoods more radioresistant • 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 • Evidence of adaptive response controls
General Effects to Plants 0. 3 Gy / d • Growth and developmental problems • Inhibition of photosynthesis, transpiration • Chromosome aberrations in meristem cells • Short term sterility • High mutation rates in wheat due to nontargeted mechanisms Twisted needles Gy / d
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 • Increased mortality of embryos • Dose-rate dependent increase in reciprocal translocations • Numbers of mice recovered within 3 years (immigration), but cytogenetic effects persisted Gy / d
Effects Data from Rodents Collected in Phase III Are Ambiguous and Controversial From virtually no effect…. … to significantly elevated mutation rates • ~ 30 to 40 generations post-accident • lower dose rates • chronic exposures • inadequate dosimetry III • sample size and technique sensitivity • indirect effects (immigration) • interpretation of results from new methods (microsatellites)
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
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
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.
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
Wormwood Forest: A Natural History of Chernobyl Mary Mycio
Barn Swallows at Chernobyl • partial albinism as a phenotypic marker for mutations ( ↑ 10 x) • 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 albinism correlated to reduced mating success • clutch size, brood size and hatching success reduced
IAEA Guidelines 1 & 10 m. Gy / d 0. 000001 Gy / d
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
Data on radiation effects for non-human species Chronic effects and γ external irradiation Morbidity Mortality Reproductive capacity Amphibians Aquatic invertebrates Aquatic plants Bacteria Birds Crustaceans Fish Fungi Insects Mammals Molluscs Moss/Lichens Plants Reptiles Soil fauna Zooplankton No data To few to draw conclusions Some data www. ceh. ac. uk/PROTECT Mutation
Most research is not directly relevant to responses in nature Data Plentiful Data Scarce but Least Relevant but Most Relevant Individual response Mortality Acute exposure External gamma Laboratory Short-term Population response Reproduction Chronic exposure Multiple exposure route Field Long-term
Alternative Paradigms in Radiation Biology are Gaining Acceptance • Bystander Effects • Genomic Instability • Epigenetic Damage
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?
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