Transcript 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
• 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.):
-
I
Linear dose-response.
Little credible evidence for a threshold effect.
Increased risk for nonsmokers confirmed.
Higher risk associated with exposure received
at low rates.
NAS BEIR VI Report
Update 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 neversmokers).
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-sinceexposure.
- 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
U.S.
Existing Dwellings
New Construction
4
-----------------------------------------------------------Germany
Ireland
Luxembourg
Sweden
Switzerland
6.75
5.4
6.75
5.4
5.4
U.K.
5.4
1.9
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
0/+
Re-analysis in ’96 showed
non-sig pos results
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 subanalyses
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.
4
8
12
16
20
Increased Risk
[Compared to outside Rn levels]
14%
28%
42%
56%
70%
NCI 1997 Meta-Analysis
of Residential Studies
• EPA’s Position on Lubin/Boice MetaAnalysis:
-
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 Highexposure 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),
554-64, 2002
p.
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.