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Radon Risk Assessment How Strong Is The Science?

Radon Risk Assessment How Strong Is The Science?. EPA & Radon. EPA has no regulatory authority for controlling radon exposure. EPA has an active radon outreach effort to promote voluntary risk reduction. EPA relies on others for research/science development. Policy Setting Considerations.

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Radon Risk Assessment How Strong Is The Science?

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  1. Radon Risk AssessmentHow Strong Is The Science?

  2. EPA & Radon • EPA has no regulatory authority for controlling radon exposure. • EPA has an active radon outreach effort to promote voluntary risk reduction. • EPA relies on others for research/science development.

  3. Policy Setting Considerations • Scientific Basis • Best Available Technology • Cost-Benefit • Legislation

  4. Radon Risk in Perspective • Comparative risk assessments by EPA and its Science Advisory Board have consistently ranked radon among the top four environmental risks to the public.

  5. Radon Risk • Second leading cause of lung cancer, exceeded only by active cigarette smoking. • Radon (and indoor air) are leading environmental cancer risks to the public.

  6. Source of Radon Risk Alpha Radiation

  7. Alpha Radiation Compared to Gamma Radiation [X-rays] • Bigger wallop • Less penetration

  8. Alpha Radiation Contacts Cell • Possible Results: - Cell killed. - Cell survives, unable to divide. - Cell survives with damage, transmits damage to its progeny.

  9. Deadly is Good • Most cells are killed or damaged so they cannot divide. • Cells which survive and transmit their genetic damage to their progeny can result in cancer.

  10. Penetration • Gamma - penetrates skin & muscle. • Alpha - stopped by skin or a piece of paper. - the thin membrane in the air sac of the lung lets alpha radiation pass through.

  11. History of Risk Assessment Based on Occupational [Miner] Studies

  12. EPA's 1992 Radon Risk Assessment • Lifetime risk at 4 pCi/L action level: -1:100 (10-2) for smokers -1:1000 (10-3) for non-smokers • Central Risk Estimate: -14,000 lung cancer deaths/year • Uncertainty Range: -7,000 to 30,000 lung cancer deaths/year

  13. NCI-Led Joint Analysis of Miner Data (1994) • Conclusions: - Authors’ estimates for U.S.: 15,000 lung cancer deaths/year 10,000 in smokers 5,000 in never-smokers - Uncertainty range = 6,000-36,000/yr

  14. NCI-Led Joint Analysis of Miner Data (1994) • Conclusions (Cont.): • Linear dose-response. • Little credible evidence for a threshold effect. • Increased risk for nonsmokers confirmed. • Higher risk associated with exposure received at low rates. I

  15. NAS BEIR VI ReportUpdate of Radon Risk Estimate • Objectives: - Analyze data from existing miner, residential, and cellular studies. - Analyze possibility of pooling residential data - Reassess/re-examine/update: • Interaction between radon and smoking • Comparison of mine to home exposure • Exposure-rate effect - Propose risk model based on updated miner data. - Test/adjust model regarding residential data.

  16. NAS BEIR VI Conclusions[Released 2/19/98] • Radon is an important health risk. • Radon is the second leading cause of lung cancer. • Effects of smoking and radon are more powerful in combination.

  17. NAS BEIR VI Conclusions[Continued] • Radon contributed to 15,400 or 21,800 US lung cancer deaths in 1995. • 2,100 or 2,900 annual radon-related lung cancers are in never-smokers. • Reduction of residential radon levels to 4 pCi/L could prevent approximately 1/3 of the annual deaths (including ~1,000 never-smokers).

  18. Strengths of the Radon Risk Assessment Numerous and Extensive

  19. Strength #1 • Classified as a known human carcinogen by: - World Health Organization's IARC - US DHHS - US EPA

  20. Strength #2 • Extensive epidemiologic studies: - Large numbers (68,000 miners, 2,700 deaths). - Consistency in magnitude of risk.

  21. Consistency of Risk • Close correlation of risk estimates despite presence/absence of different environmental pollutants. • Increased lung cancer risk from radon: - Regardless of silica dust levels. - Regardless of arsenic levels. - In absence of arsenic, chromium, nickel, asbestos, diesel engine fumes, radioactive ore.

  22. Strength #3 • Extensive review by national/international groups: - The National Academy of Sciences - The International Commission on Radiological Protection (ICRP50) Committee - The National Council on Radiation Protection & Measurement - The World Health Organization - The NCI-led International Reassessment of Radon Miner Data

  23. Consensus of Expert Committees • Radon is a human carcinogen. • Linearity of risk with cumulative exposure is a reasonable assumption. • No evidence of a threshold. • Can extrapolate from miners to the general population. • Majority assume interaction with smoking.

  24. Strength #4 • Identified as a serious public health risk by organizations with scientific/medical expertise such as: - The Office of the Surgeon General - Centers for Disease Control and Prevention - American Medical Association - American Lung Association - and more.

  25. Strength #5 • Risk model derived from human data by National Academy of Sciences (NAS).

  26. Strength #6 • Well-characterized exposure of the general population. • Based on the National Residential Radon Survey: - Nation-wide - Statistically valid - U.S. national average = 1.25 pCi/L

  27. Strength #7 • Examined the differences in mines/homes - NAS Dosimetry Study Dose/unit exposure in homes= 70% of mine dose - NAS BEIR VI Report Dose/unit exposure in homes = 100% of mine dose

  28. Strength #8 • Extrapolation from miner risk is NOT large. • Home exposure@4 pCi/L for 70 yr. =54 WLM cumulative exposure. • Increased risk documented in miners down to 40 WLM cumulative exposure.

  29. Strength #9 • Extensive peer review: - EPA's Independent Science Advisory Board (SAB) - Centers for Disease Control and Prevention's (CDC) Center for Environmental Health - Peer Review Journal: Journal of Risk Analysis

  30. Strength #10 • Detailed uncertainty analysis: - Lack of definitive residential risk coefficient. - Differences in sex, age, & smoking status. - Differences between mines & homes. - Influence of other mine exposures. - Combined effect of radon & smoking. - Potential exposure-rate effect. - Effect of age at exposure & time-since- exposure. - Uncertainties in miner exposure data.

  31. Strength #11 • Animal studies confirm the carcinogenicity of radon.

  32. Strength #12 • International consensus on risk. • U.S. action level in line with many developed countries.

  33. INTERNATIONAL RADON ACTION LEVELS SIMILAR TO U.S. CountryExisting DwellingsNew Construction U.S. 4 ------------------------------------------------------------ Germany 6.75 Ireland 5.4 Luxembourg 6.75 Sweden 5.4 1.9 Switzerland 5.4 U.K.5.4

  34. Radon Residential Studies Not Currently Helpful for Risk Assessment

  35. Epidemiology Study Designs • Cohort: - Identify population based on exposure - Follow for disease occurrence • Ecological: - Compares level of disease and exposure in groups - Cannot correlate exposure to sick individuals • Case-Control: - Identify individuals with disease and individuals without disease - Look at and compare exposures

  36. Problems with Residential Studies • Lack of Statistical Power: - Many of the case-control studies [completed and in progress] do not have sufficient statistical power to detect an effect if it were present. - The easiest way to increase statistical power is to increase the number of cases in the study.

  37. Problems with Residential Studies • Confounders: - Other causes of lung cancer can obscure the radon/lung cancer relationship. - The most important confounder for the U.S. population is smoking. - Results from other countries may be fuel, influenced by different confounders, i.e. charcoal heredity, diet, etc.

  38. International Consensus on Residential Studies • Ecological Studies should be discouraged. • Any future studies should be case-control studies. • The results of completed and on-going studies should be pooled before any new studies are begun.

  39. Completed Residential Case Control Studies

  40. Completed Residential Case Control Studies [Cont.]

  41. NCI 1997 Meta-Analysisof Residential Studies • Studies Included: Finnish I and II, Swedish National, Stockholm, Shenyang, Winnipeg,Missouri, N.J. • Included 4,263 cases.

  42. NCI 1997 Meta-Analysisof Residential Studies Results: • Showed a 14% increase in lung cancer risk for each additional 150 Bq/m3 [approx. 4 pCi/L] of radon concentration • Real World Implications: Radon Conc. Increased Risk [Compared to outside Rn levels] 4 14% 8 28% 12 42% 16 56% 20 70%

  43. NCI 1997 Meta-Analysisof Residential Studies • EPA’s Position on Lubin/Boice Meta- Analysis: - Suggests a risk of excess lung cancer as a result of residential radon exposure - Validates EPA’s miner-based approach to radon risk assessment - Forges another link in the chain connecting residential radon exposure to increased lung cancer risk

  44. NONE OF THE • COMPLETED RESIDENTIAL STUDIES • HAVE RESULTS WHICH ARE • INCONSISTENT WITH • THE MINER DATA

  45. INTERNATIONAL POOLING EFFORTS • On-going since 1989. • Three international workshops held in 1989, 1991 and 1995. • The North American and European pooling efforts are proceeding independently.

  46. Problems with International Pooling Efforts • Different study designs. • Different measurement protocols. • Different ways of defining confounders [i.e. for smoking: pack yrs. vs cigs/day]. • Different timelines for completion. • Individual egos.

  47. Gansu Province, China Residential Radon Study

  48. Gansu Study • Funded by NCI & EPA • Publication Info: Title:Residential Radon and Lung Cancer Risk in a High-exposure Area of Gansu Province, China Authors: Zuoyuan Wang, Jay H. Lubin, Longde Wang, Shouzhi Zhang, John D. Boice, Jr., et al American Journal of Epidemiology, Vol 155 (No. 6), p. 554-64, 2002

  49. Gansu Province • Predominantly rural. • Low mobility. • High radon levels. • Prior to 1976, most residents lived in underground dwellings. • Since 1976, many have moved to aboveground houses. • 99% of study population had lived in an underground dwelling sometime during their lives.

  50. Study Subjects • All persons diagnosed with lung cancer from Jan 1994-Apr 1998. • Aged 30-75 • Lived in Pingliang or Qingyang rural prefectures in Gansu Province. • Excluded if: -insufficient supporting evidence - incorrect diagnosis - had moved from area • 768 cases (563 males, 205 females) • 1659 controls (1232 males, 427 females) • Surrogates provided information for 481 (54%) cases and 71 (4%) controls

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