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

• Scientific Basis

• Best Available Technology

• Cost-Benefit

• Legislation

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.

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.

Source of Radon Risk

Alpha Radiation

Alpha Radiation Compared to Gamma Radiation [X-rays]

• Bigger wallop

• Less penetration

Alpha Radiation Contacts Cell

• Possible Results:- Cell killed.

- Cell survives, unable to divide.

- Cell survives with damage, transmits damage to its progeny.

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.

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.

History of Risk Assessment

Based on Occupational

[Miner] Studies

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

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

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

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.

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.

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).

Strengths of the Radon Risk Assessment

Numerous

and

Extensive

Strength #1

• Classified as a known human carcinogen by:

- World Health Organization's IARC

- US DHHS

- US EPA

Strength #2

• Extensive epidemiologic studies:

- Large numbers

(68,000 miners, 2,700 deaths).

- Consistency in magnitude of risk.

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.

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

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.

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.

Strength #5

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

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

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

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.

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

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.

Strength #11

• Animal studies confirm the carcinogenicity of radon.

Strength #12

• International consensus on risk.

• U.S. action level in line with many developed countries.

INTERNATIONAL RADON ACTION LEVELS SIMILAR TO U.S.

Country Existing Dwellings New 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

Radon Residential Studies

Not Currently Helpful for Risk

Assessment

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

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.

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.

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.

Completed Residential Case Control Studies

Study # Cases Result SMC rating

N.J. 411 Sig trend of incr. risk with incr. exp.

++

Stockholm 210 Trend incr. risk with incr. exp.

+

Finnish 291 No obs. relationship

Re-analysis in ’96 showed non-sig pos results

0/+

Shenyang, China

308 No obs relationship 0

Swedish National

1360 Sig dose response obs +++

Canadian/

Winnepeg

738 No obs relationship 0

Completed Residential Case Control Studies [Cont.]

Study # Cases Result SMC rating

Missouri 538 No obs relationship overall

sig trends in sub-analyses

0/+

Finnish Nested

1055 No obs relationship 0

U.K. 982 Sig increase in risk @ UK action level of 5.4 pCi/L versus UK aver of less than 1 pCi/L

++

Iowa 413 Sig trend of incr. risk with incr. exp.

++

Gansu Province,

China

886 Sig trend of incr. risk with incr. exp.

+++

NCI 1997 Meta-Analysis

of Residential Studies • Studies Included:

Finnish I and II, Swedish National, Stockholm, Shenyang, Winnipeg,Missouri, N.J.

• Included 4,263 cases.

NCI 1997 Meta-Analysis

of 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%

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

NONE OF THE

COMPLETED RESIDENTIAL STUDIES

HAVE RESULTS WHICH ARE

INCONSISTENT WITH

THE MINER DATA

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.

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.

Gansu Province, China

Residential Radon Study

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

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.

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

Radon Measurements

• Two 1-year alpha-track detectors in each house the subject occupied for 2 or more years during the previous 30 years.

• one in the living area.• one in the sleeping area.• For quality assurance, duplicate detectors

were placed in 20% of the houses.

Results

• Odds ratios increased significantly with increasing concentration.

• No significant departure from linearity was found.

• Estimated excess risk at 100 Bq/m3 [approx 3 pCi/L] was 19%.

Quotable Radon Quotes

• “Indoor radon gas is a national health problem. Radon causes thousands of deaths each year. Millions of homes have elevated radon levels. Most homes should be tested for radon. When elevated levels are confirmed, the problem should be corrected.”

Office of the U.S. Surgeon General, 1988

• “There is strong epidemiologic evidence of the link between radon exposure and lung cancer in the studies of underground miners at exposures only one or two orders of magnitude greater than typical lifetime exposure from indoor radon.”

Jonathan M. Samet, 1994

• “Consider the danger of radon gas. If there is one environmental problem that is real, it is radon. ...there is no hysteria over radon...because it's natural…”

Rush Limbaugh, 1992

EPA’s Current Radon Action Level

• 4 pCi/L.• Supported by the risk estimate

(risk higher than accepted agency policy).• At limits of best available technology.• Supported by cost-effectiveness analysis.• Generally in line with the international

community and the trend toward lower levels.

EPA Policy Position on Radon

• Because radon: - Constitutes substantial risk - Is largely preventable - Is easy to control

• Reduction of risk from radon exposure is prudent public policy.