UNSCEAR ANNEX E RADON: SOURCES TO EFFECTS ASSESSMENT FOR RADON IN HOMES AND WORKPLACES

Transcription

1 UNSCEAR ANNEX E RADON: SOURCES TO EFFECTS ASSESSMENT FOR RADON IN HOMES AND WORKPLACES FIRST OPEN MEETING OF THE ITALIAN NATIONAL RADON PROGRAM Rome - January 24-25, 2008 Douglas B. Chambers, Ph.D. 1

2 UNSCEAR Established by UN General Assembly resolution in 1955 Scientists from 21 UN Member States Other States & organizations provide relevant data Holds annual sessions Assess scientific information on levels and effects of ionizing radiation Disseminate findings to UN Assembly, UN agencies, scientific community & public 2

3 General Assembly, public & scientific community Findings UNSCEAR - Levels, effects, risks - Scientific independence Effects Risks ICRP - Protection - Philosophy - Principles & units Recommendations Data Scientific Literature, UN Member States & organizations Levels Development FAO, IAEA, ILO, WHO, UNEP - Protection - Standards Member States Implementation 3

4 Most Recent UNSCEAR Reports (available at SOURCES EFFECTS HEREDITARY EFFECTS were issued every 5-6 years 4

5 Average Radiation Dose From Natural Sources* Internal Exposure Inhalation (mainly radon) Ingestion Total Source External Exposure Cosmic rays Terrestrial gamma rays Worldwide Average Annual Effective Dose (msv) Typical Range (msv) a b c d 1-10 a Range from sea level to high ground elevation. b Depending on radionuclide composition of soil and building materials. c Depending on indoor accumulation of radon gas. d Depending on radionuclide composition of foods and drinking water. *UNSCEAR (2000) 5

6 Levels of Radon - Annex E Builds on UNSCEAR 2000 typical outdoors 10 Bq/m 3 (1-100 Bq/m 3 ) typical indoors 30 Bq/m 3 ( Bq/m 3 ) Considers: UNSCEAR surveys in 2001, 2004 & 2006 Reports of national authorities presented by delegates to UNSCEAR Scientific (Peer Review) literature Does not consider grey literature (e.g. conference proceedings) 6

7 Levels of Radon WHO GBD Current World Health Organization (WHO) project to assess Global Burden of Disease (GBD) associated with residential radon Builds on data from UNSEAR Annex E and additional information including grey literature of high quality Collaboration between Jan Zielinski (Health Canada), Doug Chambers (SENES), and Francesco Bochicchio (Italian National Institute of Health) 7

8 Levels of Radon WHO GBD continued Current database on indoor radon levels includes information from 67 countries representing nearly 80% of world s population However Extent and quality of data varies greatly from country to country and geographical area Anticipate (Hope?) that UNSCEAR will be able to improve survey approach and move to a web based database 8

9 List of Countries and Radon Data Availability by Continent* Note: Countries with red colour highlighted have mean radon data available and mapped as of December 2007 * Zielinski and Chambers 9

10 World Radon Map Based on Data to December, 2007 * Zielinski and Chambers 10

11 Annex E Dosimetry Annex E provides thorough overview of current dosimetry ICRP and others have attempted to use a dosimetric approach to assessing risk Dosimetry is complex and depends on many biological, physical and behavioral factors Annex E recommends continued use of 9 nsv (Bq hm -3 ) -1 for public dose conversion factor 11

12 Annex E Dosimetry contined Other than Lung Kendall and Smith (2002) estimate that doses to other organs are at least an order of magnitude smaller than dose to lung. Darby et al. (1995) studied 11 miner cohorts for non-lung endpoints and considered that exposure to high concentration of radon in air unlikely to result in increased risk of cancer mortality other than for lung cancer. 12

13 Experimental Studies UNSCEAR 2000 provides a detailed review of data in: Annex G - biological effects from low dose; Annex H - effects of exposure to radiation and other agents. Annex E summarizes results of experimental studies relevant to radon 13

14 Experimental Studies continued A separate Annex discusses non-targeted and delayed effects Provides a comprehensive review of current issues in radiation biology Traditional dosimetry assumes that dose must be to cell nucleus for an effect to occur Non-targeted effects refer to effects in cells whose nucleus did not receive a radiation dose Bystander effects appear limited to the irradiated organ, and since risk estimates are to an organ and not a cell, bystander effects are essentially encompassed in current radiation risk estimates for carcinogenesis 14

15 Annex E Epidemiological Studies of Miners Until recently, miner studies formed the only basis for risk estimation In the past, miners were exposed to very high and uncertain levels of radon Need to extrapolate from studies of miners at historical exposures in mines to residential exposures Uncertainty in exposure (and the effect of uncertainty) is a major consideration of both UNSCEAR and NCRP evaluations 15

16 Annex E Epidemiological Studies of Miners continued Colorado Plateau Ontario Czech Swedish Iron Beaverlodge Wismut Port Radium French Uranium Newfoundland Fluorspar Chinese (uranium and tin) Currently being updated Recently updated Dosimetry only updated 16

17 Uncertainty in Measured Exposures for Underground Uranium Mines 1000 in Colorado Average Exposure (WL) Year 17

18 Annual Exposure (WLM) in French Uranium Mines 18

19 Time Since Exposure (ERR per 100 WLM) WLM Window Ontario* Eldorado*** BEIR VI** 5 9 y y 5.23 (1.3, 14.5) y y 2.5 (0.63, 7.05) 5.99 > 15 y 0.3 > 25 y 1.37 (0.36, 3.99) 3.92 * Muller et al ** BEIR VI 1999 *** Howe et al

20 ERR for Miners from Annex E After Figure XVI UNSCEAR 2007 Annex E 20

21 Epidemiological Studies of Residential Radon Ecologic (e.g. Cohen) Useful for problem identification Limited use for dose-effect assessment Case control Suitable for effects assessment North American pooled European pooled Pooled North American and European (underway) 21

22 Risk Estimates from Residential Radon After Figure XVII UNSCEAR 2007 Annex E 22

23 Lifetime Risk From Residential Radon Study European (13 studies) N American (7 studies) Chinese (2 studies) Combined* Primary Analysis ( )` 0.11 ( ) ( ) 0.09 ( ) ERR per 100 Bq m -3 (95% CI) Restricted Analysis a ( ) 0.18 a ( ) b ( ) 0.11 ( ) Exposures Adjusted For Uncertainty 0.16 c ( ) * approx based on weighting by inverse variance (After UNSCEAR 2007 Annex E) 23

24 Smoking is Main Cause of Lung Cancer Darby et al (2005) in a study of 13 European residential case control studies looked at combined effect of smoking and residential radon on the absolute risk of lung cancer and found that for lifetime (75y) of exposure to 100 Bq m -3 and using the same relative risk factor of 0.16 per 100 Bq m -3 : 0.47% risk from radon to never smokers 11.6% risk from radon to smokers 24

25 Miner vs. Residential Assume exposure at home 100 Bq/m 3 Equilibrium factor of years of exposure ~22 WLM Annex E uncertainty analysis on miner ERR 0.59 x 10-2 per WLM 95% CI ( ) X 10-2 PER WLM 25

26 Miner vs. Residential continued ERR FROM 100 Bq/m 3 ~ 22 WLM x 0.59 ( ) x 10-2 per WLM ~ 0.12 ( ) This compares to ERR for residential studies (restricted analysis) of Europe: ( ) N. America: 0.18 ( ) Annex E: 0.11 ( ) 26

27 Overall Observations Additional effort needed to understand residential radon exposures Lung cancer is main risk from radon exposure Smoking is the main cause of lung cancer Miner studies provide historic basis for estimating risk (of lung cancer) from exposure to radon Miner studies continue to provide basis for investigating factors, TSE for example, that influence risk 27

28 Overall Observations continued Residential radon studies now provide reliable risk estimates Remarkable coherence between results from miner epidemiology and residential radon epidemiology 28