Epistemology of radiation protection

Transcription

1 United Nations Scientific Committee on the Effects of Atomic Radiation Epistemology of radiation protection Status of levels and effects of ionizing radiation Malcolm Crick, Secretary of UNSCEAR Presentation at IRPA-12, Buenos Aires, 20 October 2008

2 Content Introductory remarks Levels of exposure Effects of exposure Concluding remarks United Nations Scientific Committee on the Effects of Atomic Radiation 2

3 Introductory remarks United Nations Scientific Committee on the Effects of Atomic Radiation 3

4 Mandate Scientific Committee of UN General Assembly Assess levels, effects & risks of ionizing radiation identify emerging issues evaluate levels and effects improve knowledge for General Assembly, scientific community & public United Nations Scientific Committee on the Effects of Atomic Radiation 4

5 mjc8 International radiation safety regime UNSCEAR Scientific basis issues effects issues levels trends ICRP Protection philosophy, principles and units IAEA, WHO, ILO, FAO etc. recommendations ILO convention 115: occupational radiation protection -Safety standards -Protection programmes FAO/WHO Codex Alimentarius Commission (food contamination) implemented by Member States UN transport regulations United Nations Scientific Committee on the Effects of Atomic Radiation 5

6 UNSCEAR reports and 2001 reports 2006 and 2008 reports United Nations Scientific Committee on the Effects of Atomic Radiation 6

7 Levels of exposure United Nations Scientific Committee on the Effects of Atomic Radiation 7

8 Dose evaluation conventions Conversion factor (Sv Bq 1 ) Activity (Bq) w R w T Absorbed dose (Gy) Equivalent dose (Sv) Effective dose (Sv) Fluence (cm -2 ) Conversion factor (Sv cm 2) United Nations Scientific Committee on the Effects of Atomic Radiation 8

9 Reviews of levels Sources natural man-made Exposures general public workers patients Effects United Nations Scientific Committee on the Effects of Atomic Radiation 9

10 Natural sources Cosmic rays Terrestrial sources Primordial radionuclides Uranium-238 (4.5 billion years) Potassium-40 (1.3 billion years) Thorium-232 (14 billion years) Exposures External Inhalation (radon) Ingestion United Nations Scientific Committee on the Effects of Atomic Radiation 10

11 Exposure to natural sources Source Global average dose Typical range (msv per year) (msv per year) External exposure Cosmic rays to 1.0 Terrestrial gamma rays to 1.0 Internal exposure Inhalation (mainly radon) to 10 Ingestion to 1.0 Total to 13 Source: UNSCEAR 2008 Report United Nations Scientific Committee on the Effects of Atomic Radiation 11

12 Annual natural background dose millisieverts (msv) Few people in few areas ~100 VERY HIGH Many people in many areas ~10 HIGH Majority of people around the world ~2.4 AVERAGE ~1 MINIMUM United Nations Scientific Committee on the Effects of Atomic Radiation 12

13 Artificial sources of exposure Medical uses Military activities Civil nuclear power Occupational exposures Accidents United Nations Scientific Committee on the Effects of Atomic Radiation 13

14 Medical sources United Nations Scientific Committee on the Effects of Atomic Radiation 14

15 Medical exposures Largest artificial source - by far Last 15 years, annual examinations increased ~50% to 3.6 billion Major country differences For some, doses from diagnostic medicine exceed natural sources Computerized tomography (CT) high growth Per caput dose (msv) I II III & IV Global Health care level United Nations Scientific Committee on the Effects of Atomic Radiation 15

16 mjc procedures by year (millions) CT scans by year in US (millions Computerized tomography (CT) Annual growth > 10%/yr Annual growth of >10% per yea U.S. population < 1%/yr No. of procedures (millions) Source: Private communication, F. Mettler United Nations Scientific Committee on the Effects of Atomic Radiation 16

17 mjc3 10-fold variation Multiple Scan in Average CT scan Dosedoses 30% Frequency 25% 20% (n = 203) 15% 10% 5% 0% >100 MSAD (mgy) 1990 (n = 249) S. Stern, USFDA United Nations Scientific Committee on the Effects of Atomic Radiation 17

18 Era of digital radiology new risks Underexposed: cannot be fixed Overexposed: simply adjust computer United Nations Scientific Committee on the Effects of Atomic Radiation 18

19 Medical overexposures Brain damage from radiotherapy overexposure Whole body of baby exposed instead of chest only Overheated X-ray tube stopped cardiac procedure 18 months after cardiac catheterization and stent placement United Nations Scientific Committee on the Effects of Atomic Radiation 19

20 Military activities United Nations Scientific Committee on the Effects of Atomic Radiation 20

21 Nuclear weapons tests >540 atmospheric Atmospheric tests Underground tests NU M BER >1800 underground Source: UNSCEAR 2000 Report United Nations Scientific Committee on the Effects of Atomic Radiation 21

22 Atmospheric nuclear testing 0.12 Annual effective dose (msv) Year Largest environmental release Maximum world dose (1963) = 0.11 msv Present world average = msv Individuals near some sites - high exposures Underground tests exposures little concern United Nations Scientific Committee on the Effects of Atomic Radiation 22

23 e.g. Semipalatinsk nuclear test site 19,000 km nuclear tests 113 atmospheric 348 underground Total yield 17.4 Mt Doses Sv Thyroid: up to 8 Gy Population 30/40,000 (outside) 5 United Nations Scientific Committee on the Effects of Atomic Radiation 23

24 Production of nuclear weapons When arsenals in development ( ), controls over discharges often lacking. Significant exposures of local residents near largest installations: e.g. 131 I from Hanford plant (USA) several radionuclides from Chelyabinsk United Nations Scientific Committee on the Effects of Atomic Radiation 24

25 Civil nuclear power United Nations Scientific Committee on the Effects of Atomic Radiation 25

26 Civil nuclear power As of 2007, 439 nuclear power reactors in 31 countries Approximately 15% of world s electricity Global average dose = msv up to 0.02 msv near plant 400 Installed capacity (GWe) Year United Nations Scientific Committee on the Effects of Atomic Radiation 26

27 Normalized collective doses to the public 14 Local and regional components Normalized collective dose (man Sv/Gw a) Reprocessing Reactors Rest Period United Nations Scientific Committee on the Effects of Atomic Radiation 27

28 Occupational exposures United Nations Scientific Committee on the Effects of Atomic Radiation 28

29 Normalized occupational exposures at reactors Collective effective dose per unit electrical energy (man Sv per GW(e) a) UNSCEAR survey United Nations Scientific Committee on the Effects of Atomic Radiation 29

30 Occupational exposures Past focus - artificial sources Annual effective dose (msv) 6 Man-made sources Very many workers - natural sources Millions 2 exposed 1 Natural sources Artificial Natural 0 Nuclear industry Defence Medicine Coal mining Other mining Aircrew Other workplaces United Nations Scientific Committee on the Effects of Atomic Radiation 30

31 Orphan source, Goiania, 1987 Exposures resulting from accidents Industrial facility, San Salvador, 1989 Nuclear power plant, Harrisburg, 1979 Transportation Medical overexposures United Nations Scientific Committee on the Effects of Atomic Radiation 31

32 Chernobyl accident (1986) Worst nuclear accident Emergency workers Exposion killed acute radiation syndrome 28 died since (mostly not radiation) skin injuries; cataracts 600,000+ recovery workers Leukaemia; cataracts rates higher among for higher doses General public: Belarus, Ukraine, Russia Thyroid cancer incidence increased among then-children 6,000+ cases (15 deaths) primarily I-131 in milk Effective doses (20 years) in contaminated areas: 9mSv average up to few hundred millisieverts Other radiation health effects no consistent evidence Crude annual incidence rate (per 100,000) Radioactive deposits Large areas USSR and Europe Contaminating land, water, biota Socio-economic disruption Important radionuclides Iodine-131: high thyroid doses in few weeks Caesium-137: low chronic whole body doses over many years Reconfirm essential conclusions on nature and magnitude of consequences Calendar period Females Males United Nations Scientific Committee on the Effects of Atomic Radiation 32

33 mjc7 Illustrative comparison of collective doses Year Accident Chernobyl Kyshtym SNAP 9A Windscale fire Ciudad Juarez Goiânia TMI Cosmos 954 Palomares Tokai-mura Tomsk man Sv < Atmospheric weapons testing: 22 million man Sv United Nations Scientific Committee on the Effects of Atomic Radiation 33

34 mjc5 Early effects surely underreported Number of cases likely underreported Injuries Deaths Nuclear facilities Industry Research Orphan sources Medical United Nations Scientific Committee on the Effects of Atomic Radiation 34

35 Global average exposures Medical examinations 20% Weapons fallout <0.2% Natural sources 80% Chernobyl accident <0.1% Nuclear power <0.01% Source: UNSCEAR 2000 Report United Nations Scientific Committee on the Effects of Atomic Radiation 35

36 Effects of exposure United Nations Scientific Committee on the Effects of Atomic Radiation 36

37 UNSCEAR s paths to knowledge Clinical diagnosis Epidemiology Animal experiments Knowledge Molecular/cellular biology United Nations Scientific Committee on the Effects of Atomic Radiation 37

38 Radiation health effects Certain (100%) Likelihood Statistical limit of epidemiology Limit of pathology Burns, radiation sickness & death Disease statistics for populations (epidemiology) Clinically observable in individuals Biologically plausible Increasing risk of cancer 100 Natural background, occupational doses, radioactive waste Chernobyl child thyroid doses 1000 Chernobyl firemen Dose (msv) United Nations Scientific Committee on the Effects of Atomic Radiation 38

39 United Nations Scientific Committee on the Effects of Atomic Radiation 39

40 Base alteration Abasic site Single-strand break United Nations Scientific Committee on the Effects of Atomic Radiation 40

41 Simple doublestrand break Complex lesion United Nations WNU, Scientific ISNL; Montpellier, Committee France; on August the Effects 2008, of July Atomic 2008 Radiation 41

42 radiation hits cell nucleus No change DNA mutation United Nations Scientific Committee on the Effects of Atomic Radiation 42

43 Likelihood of mutation Probability, p p = a D + b D 2 p D (a D + b D 2 ) e -cd p = a D Dose 1mSv 10mSv 100 msv 1000mSv United Nations Scientific Committee on the Effects of Atomic Radiation 43

44 No effect Repaired Deterministic effect Dies Stochastic effect DNA mutation p D a D Survives but mutated United Nations Scientific Committee on the Effects of Atomic Radiation 44

45 Normal process United Nations Scientific Committee BARCon the Effects of Atomic Radiation 45

46 Altered process United Nations Scientific Committee BARCon the Effects of Atomic Radiation 46

47 Prevalent opinion on radiation-induced cancer Radiation mutates DNA Tumour promotion Failure to repair DNA Malignant conversion Viable cell with carcinogenes Immune system Metastasis of malignancy United Nations Scientific Committee on the Effects of Atomic Radiation 47

48 Radioepidemiology United Nations Scientific Committee on the Effects of Atomic Radiation 48

49 Numbers to detect increasing trend of risk with dose United Nations Scientific Committee on the Effects of Atomic Radiation 49

50 UNSCEAR reviewed many epidemiological studies Survivors of atomic bombings in Japan and many others United Nations Scientific Committee on the Effects of Atomic Radiation 50

51 mjc9 Cohort of Hiroshima and Nagasaki: Life Span Study (LSS) 86,611 individuals both sexes, all ages wide dose range (maximum >4 Sv, average 0.1 Sv) 2000: 45% still alive Solid cancer Leukaemia Total deaths 10, Number associated with exposure United Nations Scientific Committee on the Effects of Atomic Radiation 51

52 Risks for specific cancer sites Salivary gland Oesophagus Stomach Small intestine (inc. duodenum) Colon Rectum Liver Pancreas Lung Bone and connective tissue Female breast Uterus Ovary Prostate Urinary bladder Kidney Brain and central nervous system Thyroid Cutaneous melanoma Non-melanoma skin cancer Non-Hodgkin s lymphoma Hodgkin s disease Multiple myeloma Leukaemia Organs marked in yellow and underlined were not considered in 2000 Report United Nations Scientific Committee on the Effects of Atomic Radiation 52

53 Site-specific solid cancer mortality (ERR with 90% confidence intervals) Preston et al. Radiat Res 162(4), 2004 United Nations Scientific Committee on the Effects of Atomic Radiation 53

54 Excess risks of all solid cancers Age at exposure Preston et al. Radiat Res 162(4), 2004 United Nations Scientific Committee on the Effects of Atomic Radiation 54

55 Lifetime risk estimates Average: five populations; all ages; both sexes acute 1 Sv acute 0.1 Sv Risk (%/Sv) Present Previous Present Previous (DDREF=2) Solid cancer Leukaemia New dosimetry: 10% lower Increased follow-up: 3 7% lower Risk projection and transfer models: 35 40% Non-linear extrapolation to low doses (no need for DDREF) Children: 2 3 times higher UNSCEAR 2006 Report United Nations Scientific Committee on the Effects of Atomic Radiation 55

56 2006 report, Annex A: Cancer epidemiology M.Little, J. Boice, E. Gilbert, D. Hoel, P. Inskip, C. Land, J. Lubin, C. Muirhead, D. Preston, E. Ron, R. Shore, L. Travis and R. Wakeford Certain (100%) Likelihood Statistical limit of epidemiology All new relevant studies Longer follow-ups Particularly Hiroshima and Nagasaki survivors Risks slightly lower Conclusion: No major change Burns, radiation sickness & death Increasing risk of cancer Dose (msv) United Nations Scientific Committee on the Effects of Atomic Radiation 56

57 United Nations Scientific Committee on the Effects of Atomic Radiation Hereditable Effects

58 Prevalent opinion on induction of hereditable effects from radiation exposure Radiation alters DNA of germ cell Failure to repair Viable sperm or ovum containing defective genes United Nations Scientific Committee on the Effects of Atomic Radiation 58

59 Hereditable Effects Total risk to first generation from parental exposure: ~ % per msv 1/10 risk of fatal cancer United Nations Scientific Committee on the Effects of Atomic Radiation 59

60 2006 Report, Annex C: Non-targeted effects Certain (100%) Likelihood W. Morgan Statistical limit of epidemiology Much new information Important Unclear as yet, but probably not simple extrapolation Further surveillance needed Burns, radiation sickness & death Biologically plausible Increasing risk of cancer Dose (msv) United Nations Scientific Committee on the Effects of Atomic Radiation 60

61 Non-targeted effects Genomic instability Bystander effects Abscopal effects Clastogenic plasma effects United Nations Scientific Committee on the Effects of Atomic Radiation 61

62 Basic paradigms of radiobiology Damage fixed in DNA of irradiated cell, if not lethal, transmitted to descendant Effects occur in cells whose nucleus crossed by radiation United Nations Scientific Committee on the Effects of Atomic Radiation 62

63 Challenge to the paradigm Genomic instability Cellular death Micronucleus Mutation Chromosomal aberration Mitotic failure: aneuploid United Nations Scientific Committee on the Effects of Atomic Radiation 63

64 Bystander effect Signals via medium/plasma (Lehnert 1997) Signals via intercellular unions (Azamm 2001) United Nations Scientific Committee on the Effects of Atomic Radiation 64

65 Adaptive response conditioning dose response challenging dose response conditioning dose + challenging dose response United Nations Scientific Committee on the Effects of Atomic Radiation 65

66 Abscopal effects Effects in marrow Irradiation of liver United Nations Scientific Committee on the Effects of Atomic Radiation 66

67 Clastogenic plasma factors irradiated blood plasma seems capable of inducing chromosomal damage in unexposed cells United Nations Scientific Committee on the Effects of Atomic Radiation 67

68 UNSCEAR conclusion on non-targeted and delayed effects Dominate at low doses Debate - causal relationships between effects and health impact Unclear as yet, but probably not simple extrapolation Epidemiology implicitly encompasses effects United Nations Scientific Committee on the Effects of Atomic Radiation 68

69 Certain (100%) Likelihood 2006 Report, Annex B: Cardiovascular disease K. Mabuchi Statistical limit of epidemiology Increased cardiovascular disease at high doses seen in survivors of A-bombs Radiation-induced heart disease long known at therapeutic doses Burns, radiation sickness & death No clear evidence at lower doses Mechanisms unclear Major confounding factors Increasing risk of cancer Dose (msv) United Nations Scientific Committee on the Effects of Atomic Radiation 69

70 Radiation epidemiology of cardiovascular diseases LSS cohort United Nations Scientific Committee on the Effects of Atomic Radiation 70

71 2006 Report, Annex D: Effects on the immune system M.Perez, M.Bourguignon Infections Cancer Reviewed exposed groups, animal and cellular studies Depressive effect at high doses Uncertain at low doses both stimulatory and suppressive effects found United Nations Scientific Committee on the Effects of Atomic Radiation 71

72 Annex E: Risks from radon D.Chambers Lung cancer principal risk New miner and residential data consistent More work to account for time since exposure, attained age, dose rate, smoking Given uncertainty, no change to UNSCEAR 2000 estimates ERR at 100 Bq/m 3 = 0.16 (90% of population risk occurs in smokers) UNSCEAR converts radon exposure to effective dose using convention of 9 nsv per Bq.h/m 3 United Nations Scientific Committee on the Effects of Atomic Radiation 72

73 Plants and animals 1996 Report derived radiation levels below which effects on populations of plants and animals were unlikely Reproductive changes more important indicator than mortality Mammals most sensitive Reviewed new studies from follow-up of Chernobyl accident No need to change overall 1996 conclusions Red forest Eagle chick United Nations Scientific Committee on the Effects of Atomic Radiation 73

74 Overall conclusions Wide-ranging review of health effects New cellular, genetic, microbiological studies Longer follow-up from epidemiology Differences at detailed level, but overall risk factors remain essentially unchanged United Nations Scientific Committee on the Effects of Atomic Radiation 74

75 Concluding remarks United Nations Scientific Committee on the Effects of Atomic Radiation 75

76 Arthur Schopenhauer All truth passes through three stages. First, it is ridiculed, Second, it is violently opposed, Third, it is accepted as being self-evident. United Nations Scientific Committee on the Effects of Atomic Radiation 76

77 Contact details Malcolm Crick Secretary of UNSCEAR Vienna International Centre Wagramerstrasse 5 P O Box 500 A-1400 Wien, AUSTRIA Tel: Fax: malcolm.crick@unscear.org Web: United Nations Scientific Committee on the Effects of Atomic Radiation 77