effects of low doses probability of causation and implications for public policy lecture at uc...
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Effects of Low Doses Probability of Causation
and implications for Public Policy
Lecture at UC Berkeley
March 2nd 2001
by
Richard WilsonMallinckrodt Research Professor of Physics
Harvard University
The Future of Nuclear Power may depend upon a Rational Approach to
Risks of Radiation Exposure and their
regulation.What are they?
Do we compensate those exposed?
If not what?
LINEARITY AT LOW DOSES
IS USUAL!!
Walking blindfold across
University Avenue
is safe:
(Risk (R) = 0)
IF THERE ARE NO CARS!
The risk (R)
increases roughly in proportion
to the number of cars.
Alternate Dose-Response Models
Dose
Res
po
nse Super Linear
Linear
Hockey Stick
Hormesis
Datum
Datum
Threshold
Acute Effects
Characteristics• One dose or dose accumulated in a
short time KILLS
• 1/10 the dose repeated 10 times DOES NOT KILL
CHRONIC EFFECTS including CANCER
Characteristics
A dose just sub-acute can give effects if repeated.
Usually not all people affected - dose response is flatter
Typically an accumulated
Chronic Dose = Acute LD50
gives CANCER to 10% of the population.
E.g. LD50 for radiation is about 350 Rems.
At 350 Rems about 10% of exposed get cancer.
(more or less depending on rate of exposure)
Early Optimism Based on Poisons
There is a threshold below which nothing happens
__________
J.G. Crowther 1924
Probability of Ionizing a Cell
Linear with Dose
Repair Mechanisms
BUTDoes the Mechanism
Reject/Repair:
ALL DAMAGED CELLS UP TO XXXX?
(implying a threshold)
OR 99.999% of CELLS
INDEPENDENT OF DOSE
WE DON’T KNOW
CRITICAL ISSUES FOR LINEARITY
• The POLLUTANT ACTS
• in the same way as
• WHATEVER ELSEINFLUENCES THE
• CANCER RATE
• CANCERS CAUSED BY
• THE POLLUTANT
• ARE INDISTINGUISHABLE FROM OTHER CANCERS
Annual Death Rate By Daily Alcohol Consumption
0
500
1000
1500
2000
0 0.5 1 2 3 4 5 6
Average Number of Drinks Per Day
Dea
th R
ate
(Per
100
,000
)
Alcohol-augmentedconditionsCardiovasculardiseaseAll causes
Probability of Causation
Come let us Cast Lots to find out who is to blame
for this ordeal.
Jonah 1:7
Risk from all causes can be approximated as the Prevalence in a similar
Population.
If the cancer is rare, POC can be high even if
the risk is low.
E.gPOC for berylliosis is
unity for beryllium as a cause
POC for asbestos exposure as a cause of mesothelioma among
males is 80% and 20% among females
Administrative Uses of the POC concept.
Aluminum workers in Quebec
(compensate if POC > 50%)
Radiation Workers in UK (compensate if POC >20%)
Compensation for Radiation Exposures
1985 veteran “Downwinders”
(if upper 99th percentile of POC > 50%; effectively POC >5%)
1996 UK Workers(if POC >20%)
2000Old AEC employees
(if upper 99th percentile of POC > 50%; effectively POC >5%)
Medical CausationGeneral Causation:
the Postulated Cause is Known to Cause the Disease under some
conditions(POC>0)
Specific Causation, exposure and other circumstances make POC large enough (>50%)
General Causation needs a Risk Ratio that is
significant,statistically and otherwise
Usually RR>2 (POC >50%)
Rule to avoid frivolous lawsuits:
The postulated cause must be
“more likely than not” POC>50%
But Rutherford instructionIf total asbestos exposure is a
proven cause, it can be assigned to individual
suppliers even if POC < 50%.
RISK of respiratory ailments due to
LIFETIME exposure to
AIR POLLUTIONis
3 to 5%average in the
USA!POC varies from 30% to 80%
If I develop leukemia:The POC
from my Medical Exposures would be over 50%
Can I sue using the Rutherford case?
Minister of Health, UKUS State DepartmentHarvard University
Commonwealth of MassachussetsONR
DOE (AEC)
Assignment of a Cause does not mean that
Compensation is payable.
E.g.Chemotherapy agents are
often carcinogenic and increase risk of future
cancers even as they cure.