Fukushima NPP Disaster and Implica6ons for Human Health
Assessment of Low Dose Radia6on Exposure
James P. Seward, MD MPP FACOEM Clinical Professor of Medicine UCSF Presented at US-‐Japan Roundtable October 24, 2013
Risk Assessment Hazard Iden6fica6on Dose-‐Response Exposure Assessment Risk Characteriza6on
Risk Management Risk Evalua6on Op6on Assessment Op6on Implementa6on Monitoring and Review
Risk
Communica2on
The Risk Paradigm
Core Concepts in Radiation Exposure
• Equivalent Dose measures the biological damage potential and health risk from radiation
• Equivalent dose is measured in Sieverts (Sv) • “Low dose” is <0.1 Sv (100 mSv)
Natural Background Radia6on Natural background radia2on dose approx 2 mSv/year (range 1-‐10 mSv) without known health effects
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2.3 mSv 0.38 mSv
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Average Natural+ Man-‐made Background Dose (USA) 6 mSv Established Human Cancer Threshold 100 mSv Fatal Acute Dose (LD-‐50) 4000 mSv
____ Linear No Threshold ( High Energy) ._._._ Linear No Threshold (Low Energy) _ _ _ _ Linear Quadra2c
(leukemias) ………… Linear with Threshold
Uncertainty of dose response rela6onship for radia6on-‐induced cancers
Source: BEIR VII 7
Linear No-Threshold Hypothesis (LNT) for Cancer Causation
• US Na6onal Academy of Science (BEIR VII): • “Difficult to evaluate cancer risk at less than 100 mSv” • “Risk would con6nue at lower doses without threshold”
• “Smallest dose has poten6al to cause small increase in risk”
• Predicts 1 person in 100 gets cancer from dose> 100 mSV • Errs on safe side
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Concerns about the Linear No Threshold Approach
• Studies of areas with higher background radia6on show no increased cancer rates
• Biologic repair may reduce risk • UNSCEAR: “does not recommend mul6plying low dose by
large numbers of individuals to es6mate numbers of radia6on-‐induced health effects …”
• Example: 100 Sieverts: Effect of 1 Sv to 100 people ≠.001Sv to 100,000 people
“Es6mates of risk should be limited to individuals receiving a dose of
50 mSv in one year or a life6me dose of 100 mSv
in addi6on to natural background.”
The Health Physics Society
____ Linear No Threshold ( High Energy) ._._._ Linear No Threshold Low Energy) _ _ _ _ Linear Quadra2c
(leukemias) ………… Linear with Threshold
Human Epidemiology Shows Increased Cancer Risk Above 100 mSv
Modified from: BEIR VII
? ∧ ∧
100 mSv 11
Health Concerns for >20,000 Fukushima Workers
• No Rad-‐related fatali6es or determinis6c effects seen acutely
• Less than 1% receive doses> 100 mSv – Uncertainty of dose measurements – Small projected increased risk for leukemias and solid tumors – Psychological concerns
• Ongoing exposure poten6al • Health monitoring
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Radio-‐Iodine Exposures near Fukushima much lower than Chernobyl
WHO es6mates thyroid cancer risk of most highly exposed female infant increases by 0.5%
(from 0.75% to 1.25% life6me risk)
WHO Preliminary Dose Reconstruc6on Whole Body—All Key Radioisotopes
High Areas: 10-‐50 mSv effec6ve dose—mostly external Lower areas: 1-‐10 mSv effec6ve dose—mostly internal
Japanese Food Radioac6vity Standards Highly Protec6ve
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< 100 Bq/Kg
• ~0.075 mSv dose to Japanese consumer ea6ng fish for a year at maximal regulatory limit • Naturally occurring radia6on in fish (210Po , 40K ) a greater risk
Life6me Cancer Mortality Risk per Becquerel
(not adjusted for rela6ve amounts in different fish)
0.0E+00
5.0E-‐09
1.0E-‐08
1.5E-‐08
2.0E-‐08
2.5E-‐08
3.0E-‐08
3.5E-‐08
4.0E-‐08
4.5E-‐08
5.0E-‐08
HTO Cs-‐134 Cs-‐137 Sr-‐90 K-‐40 I-‐129 Po-‐210 U-‐238 Pu-‐239
Life6me CA Mortality Risk (per Bq)
For fish mee6ng Japanese food safety standards radia6on dose from Po-‐210 far exceeds Fukushima-‐related dose
Ongoing Water Leaks Are an Environmental Concern
Not a significant health risk to general popula6on as long as seafood safety standards are maintained
Mental Health Issues • Surveys show high levels of stress in adults and children • Fear of radioac6vity and health consequences • Long las6ng psychological health consequences in Chernobyl evacuees
• S6gma6za6on • Reluctance to discuss personal issues • Con6nued displacement
Summary of Health Implica6ons for people living near Fukushima Dai-‐ichi
• WHO es6mates small increased radia6on-‐related cancer risk that may be difficult to measure – greatest risk is thyroid cancer in infants
• Psychological distress in the local popula6on has been very high
• Leaks of contaminated water from the NPP are not likely to be significant health risk – Contribu6on to total radioac6ve material in ocean likely to be small
rela6ve to ini6al disaster – Current food safety standards are very protec6ve – Natural radia6on in seafood is higher than contribu6on from NPP
emissions in marketable fish