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

DATA

• HIROSHIMA - NAGASAKI

(RERF)

• RADON

COHEN

OTHERS

• NUCLEAR INDUSTRY

IARC

• MEDICAL

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

Probability of Causation

equals

Risk from Substance

divided by

Risk from all Causes

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%)

What do the Courts say?

US Supreme Court

DaubertJoiner

Kumho Tire

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.

Go back to the beginning: Does it make sense?

Can we study those cohorts where NIH calculate POC

near 50%?Risk Ratio of 2?

Those x-rayed just post world war II?