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as a pulmonary cancer. The latent period varies from less than ten years up to over fifty years, depending e.g. on smoking characteristics. ( R a r t ...
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Chapter 31 The Validity of Risk Assessments for Lung Cancer Induced by Radon Daughters F. Steinhäusler Division of Biophysics, University of Salzburg, A-5020 Salzburg, Austria Available input data for the risk assessment from low level radon daughter (Rn-d)exposure are mostly either of low quality, partially contradicting or simply "guesstimates". Therefore at present only the upper limit of this risk can be estimated. Results of epi­ demiological studies amongst miners are associated with large uncertainties with regard to the assess­ ment of past radiation exposure, lung cancer diagnos­ tic and/or classification and synergistic effects due to smoking and dust exposure. An alternative approach uses dosimetric modelling for Rn-d inhalation to ob­ tain Rn-d exposure-dose conversion factors. Large un­ certainty is caused by individual variability due the influence of life style, physical and biological pa­ rameters. It is concluded that for "normal" indoor Rn-d exposure the resulting risk is neglegible compa­ red to other risks "accepted" by society. Lung cancer due to inhalation of radon decay products (Rn-d) represents the single most significant risk from all natural and non-made radiation sources. There is growing concern about its impact on society for occupationally and non-occupationally exposed persons. Increased lung cancer incidence amongst miners has already led to the request by labour unions for a lowering of the presently recommended Rn-d exposure limits (Williams, 1985). Trends in energy conservation efforts and recycling of unsuitable industrial wastes as construction material (Steinhàusler and Pohl, 1983) indicate an increase of a Rn-d induced lung cancer risk for members of the public. In view of the significant socio-economic consequences of these issues it is important to ensure that any input data used for risk assessments are subjected to stringent quality control. Such data can be derived from epidemiological studies, experimental animal inhalation research and theroretical dosimetric modelling. All three data pools are associated with considerable uncertainties. In this paper the following aspects are critically reviewed with 0097-6156/87/0331-0430$06.00/0 © 1987 American Chemical Society

31.

regard Rn-d

to

the

431

The Validity of Risk Assessments

STEINHÀUSLER

applicability

to

the

risk

estimation

for

low-level

exposure: -

limitations gical

-

suitability from

Data

of

Risk

Epidemiology.

related

have

extrapolating

inhalation

from

studies

uncertainties

epidemiolo-

of

to

results

obtained

man

presently

used

lung

models.

Assessment

Using

preconditions

of

animal

inherent

Needed f o r

Rn-d

studies

the

to

be

epidemiological

approach

the

met

establish

a

in

order

to

following dose-effect

relationship: a)

individual have

to

doses

be

due

determined

to

Rn-d inhalation

with

a

high

degree

in of

the

exposed

group

r e l i a b i l i t y

("dose-

data"); b)

in

order

gens

to

discriminate

other

should

than

Rn-d,

be

identified

control

population

from

lung

ideally which

is

a

cancer

cases

specific

induced

by

type Rn-d

due of

to

carcino-

lung

only

cancer ("effect-

data"); c)

a the

exposed

except

for

Individual

and

occupational of

as

its

dose

external is

of

risk

from

period

this

between

up

to

over

period

f i f t y and

is

continous latent

about low

using

even

(e.g. of

inhaled from

10

(occupational

mSv/WLM

C r i t i c a l important free. cancer the

diagnosis

population

assessment gens

in

the

of

of and

on

a

exposure

well

the

latent cellular

expression than

as

ten

a

years

characteristics As

the

latent

lifetime

risk,

lengthening

are

converted The

choice

physiological as

a l l

lifetime

of

the

to

dose

of

the

lifetime.

1983).

on

by

less

the

to

This

exposure,

through

1984). to

1983).

the

smoking

lead

particle

physical

size).

parameters

characteristics

Mean

(non-occupational

values

exposure)

range

to

about

exposure). of

the

data

overlooked

c l a s s i f i c a t i o n , under

on

and

lung

cancer

assumed as

comprises

medical

or

and

exposure

is

equally

largely

demographical

investigation

characteristics

atmosphere.

from

a l l non-

resulting

inducing

individual

"effect-data"

group

smoking

the

as

levels The

a l . ,

on and

Rn-d

influenced

on

et

depends

5 mSv/WLM

to

aspects,

data

Pohl,

level

macroscopic

(OECD/NEA,

(e.g.

frequently

group

is

may

data

volume)

analysis

but

This

about

work.

e.g.

exposure

and

varying

proportional of

comparable a l l

occupational

low

varies

Radford

value

minute

of

or

period

factors

aerosol

to

Rn-d exposure

individual

typically

at

home

exposure

excess

numerical

respiratory

the

in

case

depending

Rn-d

conversion

appropriate

Rn-d

inversely

Subsequently, by

to

1879;

level

period,

the

subsequent

years,

Hesse,

is

in

radiological

(Steinhausler

in

latent

which

exposure.

contributing

school,

the The

defined

requires

i n i t i a l

and

cancer.

(Rarting

Rn-d

chronic the

transformation pulmonary

at

be

investigation

exposure

exposed

e.g.

to

sources

importance

always

l i f e ,

of

assessment

radiation

is

stages

has under

lack

internal

particular

man

group

erroron

information

the to

data

lung on

quantitative

other

carcino-

432

RADON AND ITS DECAY PRODUCTS

A l l of

Members Rn-d a

this

has to

"spontaneous" of

this

be seen a g a i n s t

lung

cancer

population

levels

which

varies

relatively

small

city

Animal

Inhalation

partially logical

Although

exposure

i . e .

the

can occur

laboratory

conditions.

possibility

of

either

at

carcinogens

dust.

In

this

different

lung

carcinogens

achieving

true

randomization

epidemiology dence

data.

least lung

Since

However, studies for

for

humans

a)

i n

even

to

the following of

levels human

should to

should human

diesel

controlled to

the atmos-

fumes

or

ore

superposition

of

possibility

of

The

a further

advantage

lung

over

cancer

Rn-d exposed

i n c i -

animals

i s

constraints,

s t a t i s t i c a l l y to

conditions

significant

use the information studies

should

and

at such

numbers

associated with

similar other

studies,

magnitude

than

physiologically

from

risk

animal

assessments

be met:

and non-occupational

carcinogens

be

control to Rn-d,

offers

exposure

financial

dose-effect

a

least

low Rn-d levels.

be able

be o f

i n

at

under

study

unbiased

of

radiobiological

occupational

exposure

at

the uncertainties i n

of

synergistic

by

can provide

order

extrapolations

b)

only

of

even

Rn-d epidemio-

exposed

levels

type

represents

range

a homogenous

s t i l l

e . g . smoke,

obtaining number

Rn-d related

view

of

overcome

alternative

of

a wide

magnitude

human

can be a d d r e s s e d .

the

induction i n

Rn-d,

limited

experiments

cancer

than

this

or

the question

respect

theoretically

inhalation on

with

of

i s

population.

1983).

to

low environmental

pheric

to

of

experiments

i t s e l f

Furthermore

other

a l . ,

inherent

background

general

exposed

identification group

simultaneous

manner

et

Such

problems

control

increasing

the

by an order

(Steinhàusler

Experiments.

the

i n

are themselves typically

the major

studies,

group. this

one o f

a mostly

cases

high

animal

to

low

dose

Rn-d exposure

as those

occuring

i n

conditions;

Rn-d (e.g.

r e a l i s t i c ,

tobacco

simulating

smoke) those

of

exposure

conditions; c)

dosimetric

models

developed

should

adapted

for

into d)

be

account

radiation animals

Dosimetric enable the

should

atmosphere.

As

describe

bronchial (e.g.

or

for

methods cellular

hits

dosimetric needed

also

to

c e l l

Rn-d risk

to

and

of

Rn-d from

concepts values

for

particles. the

i n

test

dosimetry

i s

Rn-d deposited Rn-d

have

i n the

deposition developed

for

tracheo-

dose

calculations

Carlo

t h e random The r e s u l t s

following

i n

to

been

(e.g.

U s i n g Monte

provide

-geometry;

Rn-d concentration

microdosimetric

assessment:

taking

humans.

dose

account

tract

used,

mechanisms

an inhomogeneous

alpha

should

i n

measured

or

respiratory

animal

induction

objective observed

layer).

possible

by deposited

that

of

test

physiology

mean d o s e

region)

calculations

for

t h e human

dosimetric

regional

basal

lung

from

consequence

pulmonary i s

the

different

either the

i t

of

tract a

the lung,

i n

The main

assessment

for

specific

and cancer

be s i m i l a r

respiratory

within to

differences

sensitivity

Studies.

the

the

calculation nature of

of such

information

31.

The Validity of Risk Assessments

STEINHÀUSLER

a)

which

biological

within by b)

the

alpha

which

have

dose

the

Available

of

Risk

mining

studies

shortcomings individual

have

of

of

" . . . t h i s

a

analysis

estimate

was

cause is

present

not

about

a)

of

the et

activity,

Rn-d

exposure-

a l . .

the

individual ments

and

high

effect

the

a

been of

carried

out

the

later

to

to

the

inherent

unavailable

caveats

stage,

concerning

e.g.

for

the

relationship: not

offered

demonstrate in

States, period

of

severe

due

stated

many

as

a

basis

the

that

lung

for

1976)

low

levels

cancer

of

incidence

1967)

of

to

extrapolate

observation

to

at

lifetime

1983) to

draw

the

any

about

dose

uncertainty

in

and

effect

exposure

and

1973) associated with

into

three with

exposure,

job

conclusions

considerable

grouped

of

of

considered appropriate

associated

uncertainties

at

increase

uncertainties

Rn-d

unattached

dose..."(Royal Commission,

United

not

authors

mostly

emphatically

unit

truncated

can be

size,

significantly

they

dose-effect

error..."(Snihs,

general

particle

aware

data

designed...

possible

studies

f u l l y

their

the

uncertainties

b)

physical

The

detectable

1 0 0 WLM d u e

s t a t i s t i c a l In

age,

research has

most

therefore

r i s k . . . " ( M u l l e r

gical

cells)

probability

dose.

Therefore

per

not

any

from is

(e.g.

investigations,

of

is

risk

rate..."(Congress

below

hit

individual

epidemiologic

quantitative

of

study

exposure

" . . . i t

the

populations.

data.

misuse

deduction

" . . . i t

epithelial

highest

(e.g.

on

factor)

to

been

their

exposure

potential

"...the

the

Assessment

Hitherto,

amongst

original

parameters

exposure

for

Epidemiology.

any

influence

disequilibrium

conversion

the

parameters

most

physical

fraction,

mainly

bifurcations, have

conversion;

which

Data

(e.g. tract

particles.

physiological

sex) c)

targets

respiratory

433

these

epidemiolo-

categories: the

mostly

due

reconstruction

of

to

measure-

the

lack

of

past

mobility diagnosis

and

c l a s s i f i c a t i o n

of

lung

cancer

data c)

uncertainty other

In

order

to

Rn-d

between

"lung

since

these

years

ago,

this

available

have

to

using

e.g. Low

exposure

i s

the

on

indirect

level

from

most

important

not

carried

studies

exposure

concerned,

are

with of

ore

Rn-d exposure-effect

indoor

a in

for

of

than

past

the

a l l

a

the

individual

sufficient Rn-d

studies:

to

provided

press).

pure

induced

these

fifteen be

and

thirty

by

any

degree

Therefore

exposure

of of

they

levels,

content.

studies

situation, available

know

out

cannot

(Steinhausler, estimation

to

Rn-d

atmosphere.

rather

weakness

information

uranium

between

inhaled

carcinogen Rn-d and

particular were

essential

inference

i s

it

accuracy

effects

the

causal relationship

retrospective

and

rely

general

" is

in

suspected

measurements

r e l i a b i l i t y

the

This

a

the

cancer

exposure.

the

synergistic present

establish

association effect

about

carcinogens

at

that

least

miners

may as

in

be

far CSSR,

relevant as US,

to

lifetime Canada,

434

RADON AND ITS DECAY PRODUCTS

Newfoundland can

be

study miners

significant

due

to

As

only

for

these

compared

to lung

exposure

to to

derived Rn-d

cytological

regarded

since

observed

as

of

non-miners

as

In

the

cases

noted

s t a t i s t i c a l l y

associated

period.

members

the

Rn-d exposure

number

than

amongst

male

study,

i t

Norwegian

incidence

non-mining

uncertainties

expected

i s

of

the public,

methods i s

quality

It

with

the

assessments

case

even

of

the US-

exceeded

controls since

higher

i . e .

have

there

the

that

i s

an

frequency

of

by a factor

a l l

a

these

strong

lung

quantification

there

this i n

i s

lung

large

2

to

3

assumed

Rn-d

association

with

of

i s

lung

any other cancer

initiated

argued

with of

and c l a s s i f i c a t i o n

like

the

this

small

medical

Rn-d

for

the

Rn-d induced

type

frequency

However,

procedures

supposedly

questionable

c e l l

low

carcinogens,

that

c e l l .

by

h i s t o l o g i c a l -

by other

repeatedly

an unusual of

induced

with

are

s c i e n t i f i -

a

review

and data

used

induced

"effect"

following

reasons

press):

a high

cancer

degree

tissue

differences

cancer

cancer

frequency

aspects

just

distinguished

has been

high

control

that

diagnosis

present, be

associated

i . e .

(Steinhàusler,

At

cannot

from

cancer

distribution,

of

intra-

and interobserver

classification

i n

t h e numbers

by

variability

pathologists,

classified

as

a

causing particular

type;

the

source

term,

the

result

of

artifacts

biopsy

i n

post-mortem

or

as

examinations

primary

lung

autopsy,

misclassified

are categorized

biopsies; of

i . e .

potentially

a l l 4-0%

also cancer

information.

lung

revealed

margin, generally

cases

exposure smoke.

the

used

on lung

tobacco

c)

for

be

and uncertainties

e.g.

b)

cannot

"safety"

cancer data

level

in

data

were

cancer

the Newfoundland

large

miners

errors

cally

a)

In

levels,

smoke.

Medical

for

relevant

low exposure

cases

lung

the post-1960

studies

members

related

of

these

Czechoslovakian and

cancer

cases

estimates,

the

inherent

amongst

subject

At

the

observed.

additional smokers

the

the

Canadian miners

actually

lung

increase to

1). of

both

exposure

available

case

population.

small

retrospective and

i n

was compared

relatively

(Figure

the more

However,

the general

are

i n

significantly

expected. of

and Norway

seen that

cancer

i s

"small

c e l l

compared

to

are

of

lung

significance

tumors,

e . g .

carcinomas"

i n

anti-mortem

missed

for

crush 25% o f

diagnosis

altogether,

30%

are

false-positive. d)

histo-cytological ciple

because

intermixing carcinoma In

view

of

these

cancer

task,

resulting

Dosimetry. advances to

i s

lung are

fundamental

adeno-,

d i f f i c u l t i e s

and c l a s s i f i c a t i o n

for

the past

cancer

i s

generally

d i f f i c u l t

i n

heterogeneous,

large-

and

small

prini . e . c e l l

frequent.

frequently

extent

of

tumors

squameous,

diagnosis

Dosimetry

over

a large

of

cells

lung

typing

these

i n

data

inhaled

twenty

of

i s

on the WEIBEL A'

Lung

understandable

represents

a

that

d i f f i f u l t

r e l i a b i l i t y .

Rn-d particles

years. 1

low

i t

h a s made

modelling,

-symmetrical

lung

significant

based

i n i t i a l l y

model,

has

been

***)

URANIUM MINERS

(1 - 19)

NON-URANIUM MINERS

(0 - 9 )

[WLM]

POPULATION/ CUMULATIVE EXPOSURE

NO. OF LUNG CANCER CASES

NORWAY

>

Figure 1. Observed vs. expected number of lung cancer cases f o r miners exposed to low-levels of radon daughters.

ALL SMOKING MINERS

.EXPECTED

.OBSERVED

NEWFOUNDLAND

URANIUM MINERS WITH NO PRIOR GOLD MINING EXPERIENCE

n3 URANIUM MINERS FREQUENCY PER 10"

NUMBER OF LUNG CANCER CASES

436

RADON AND ITS DECAY PRODUCTS

refined lungs

to

present

(Weibel,

artefacts

are

dimensional tion)

i s

for a)

results of

Schum,

made

1980).

the information

(e.g. branching

target be

from

Thereby on

angles,

i n

human

potential

vivo

three-

bronchial

i n c l i n a -

for

from

the

lung

dose

conversion

modelling

of

s t i l l

Rn-d exposure

show

to

a

dose

reasons:

geometry: cells

the

below

i n

the bronchial

sensitive

deposited dose

obtained

values

following

basal

i n

the

target

received

region

for

the airways. bronchial

information b)

and

geometry

on thorax-casts

and

maintained.

range

the

based

Yen

minimized

lung

However, large

models

1963;

lung

c e l l s

on the depth

determines from

to

inhaled

distribution

considered

induction

The assumed depth

surface

by these

are generally

cancer

of

this

a large Rn-d.

i s

due to

to

Rn-d

c e l l

layer

extent

the

Physiological

scarce.

unattached/attached Rn-d: The

nature

attached of

and behavior to

controversy,

environmental presence are

of

exposure

particularly gases

t h e most

conversion.

"free"

This

with

(Busigin

can

regard

be o f

with

et

or atoms,

nuclei,

conditions,

c r i t i c a l

situations

Rn-d ions

condensation

atmospheric

other

one o f

of

atmospheric

i s

to

such

a l .

the

influence humidity

Free

parameters

for

particular

importance

a

large

the

ratio

not

subject

as

1981).

t

i . e .

s t i l l

of and

R n - d atoms

exposure-dose

of

i n

indoor

unattached

to

attached Rn-d. Figure and is

2

shows

the

dosimetric assumed Due

gical

(OECD/NEA,

to

the

and a

situations

Animal have

extensive using

and

studies. out

and

respectively. relevant

to

lifetime

of

Only the

a member

of

from

these

can

be

that

the

the

100 WLM.

lifespan

Rn-d. man lung

as

However, i t

has to

cancer

i s

These the i n

biological,

physiolo-

2 to

indicated effects

the

published

1 2 0 mGy

that

for

can reduce

per

WLM.

most

this

situations

hamsters, from

6^0 to

2

exposure

indoor

range

to

occurring

tumor data

have

order

to

most

exposure

for

up to

rats

out

et about

3

shows

i s

of

between

corrected

for

extrapolate

these

findings

susceptibility species.

and

1984), WLM

during

tumor

to

It

4%

at

shortening

lung

cancer from

Rn-d

Furthermore,

i s the

lung

2% a n d

than

two

100

the

other

the

rats,

Rn-d exposure.

causes

the

most

on

a l . .

experienced

Figure

for

studies

The two

8 0 0 0 WLM ( C h a m e a u d

situation

not been of

be assumed t h a t similar

carried

as a function

rate

result

were

20 to

inhalation

and mice.

5 6 0 WLM ( C r o s s

the public. studies

Rn-d

rats

investigations

the low-level

indoor

obtained

about

from

indoor

levels

from

rate

seen

situation

modelling,

Experimental

on dogs,

comparable

1984)

physiological

exposure

1983).

mean R n - d e x p o s u r e

Lafuma,

the

other

i n

range

compensatory

(OECD/NEA,

carried

two d i f f e r e n t

standardized

various

analysis

10 mGy/WLM f o r

inhalation

been

for

a

used

factors

sensitivity

to

of

parameters

conversion

about

frequently

results though

superposition

exposure 5

of

even 1983).

physical

exposure-dose However,

spread

models,

of

from

rat

to

induced i t

i s

31.

STEINHÀUSLER

437

The Validity of Risk Assessments CALCULATIONS BASED ON: YEH-SCHUM PHYSIOLOGICAL MODEL AND

JACOBI-EISFELD

DOSIMETRIC MODEL WEIBEL - A - PHYSIOLOGICAL MODEL AND JAMES-BIRCHALL

DOSE [mGy/WLMj

DOSIMETRIC MODEL 200

150

100

50

BREATHING RATE RESTING

LIGHT ACTIVITY

jrn3 /hj

H Figure

2.

Mean b r o n c h i a l

1 WLM e x p o s u r e physical librium

1

to

free

a c t i v i t i e s factor

dose

radon

to

basal

cells,

222 daughter

(assuming t y p i c a l

atoms

indoor

standardized f o r

for

different

exposure

with

equi-

F = 0.4)·

TUMOR RATE

%

15

10

100

200

Figure

3.

tion

Rn-d exposure.

of

Primary

300

e p i t h e l i a l

400

lung

500

tumor

600 700 MEAN EXPOSURE |WLMJ

rate

i n rats

as a

func-

RADON AND ITS DECAY PRODUCTS

438

questionable applies far

i t

of

a

Rn-d

i n

whether animals

has been similar

(Cross

models

a l . .

(Hofmann

and doses

tive

Animal influence

i n

cancer

to

on the lung

results

where

the

(Cross

et

Assessment

Rn-d

risk i s

latent Rn-d

period,

low

phase

up to

The

from

i n

with

more,

in

The studies

of

i s

animal following

compare

other

only

cocarcino-

to

the

i s

effec-

to

i t s

over

do n o t

relative

w i l l i n

with

i s

of

be

the

lung

of

This

to the

necesa l l

epidemiological this

occurs the

important

at

typically

latent

period

20 y e a r s

their

i s

observed

Rn-d exposures

during

used risk

input

the

early

to

assess

model,

i s

often

are

asso-

data

used

uncertainties.

to i n

(BEIR-II,

assess

the

the wide

an order

of

Rn-d exposure

population 1980).

range

of

The

cancer values

(Figure

dosimetry c a n be

the

Further-

lung

magnitude

by epidemiology,

indoor

to

include

the Rn-d exposed

used

i n Rn-d

exposure

to

a l l

model

the

reflected than

and

press).

same r e s u l t

the data

provided to

the

long

10 t o

absolute

follow-up

b y more

regard

i n

after i s

length

f u l f i l l

the

a

fumes

found

lifetime

a few years

risk

because

this

expression.

received

of

v s .

smoke

on the

that

unquantifiable

give

Rn-d inhalation

information

to

probably

mathematical

to

rate; was

on

1982).

exposure

l i k e l y

(Steinhâusler,

complete

differing

i s

diesel

The assessment of

tumor

smoke

indicate

smoke

rate a l . ,

Therefore

a period

importance

models

exposure cancer

low-level

as compared

and often

of

i t

and

alternating

of

which

clearly

ore dust

be s u f f i c i e n t l y

cases.

who most

of

not

induction

simultaneous

and cigarette

do

rate,

from

study

by the assumption

Therefore

uncertainties

from

to

a l l

region

the lung

chronic

studies

i . e .

case

published,

Whilst

by a period

mining

large

both

multiple

so

inhaling

the

c r i t i c a l

fumes

Exposure.

period

rates

choice

ciated groups,

the used

cancer

a

cancer

miners,

risk,

overrated

j u s t i f i e d

results

cancer

Indoor

4-0 y e a r s

uranium

lifetime

risk

lung

exposure

of

the relevance

1 9 7 8 ; Chameaud e t

t

determined

rates.

uranium

high

i n

Non-occupational Rn-d indoor

increased at

for

are truncated

exposure

with

lung

followed

induced

criterion.

i s

diesel

increases

a l .

the follow-up

studies

and animals

neglecting

been

obtained

resulting

largely

sitates

also

effect.

exposure

exposure,

cancer

of

out

( L C ) p e r WLM

demonstrated

i t

i . e .

However,

synergistic

decreasing Risk

man

the dose

have

induction.

Rn-d

contrast

risk

cancer

and dose

carried

induction.

no e f f e c t

i n i t i a l

only

lung

i f

cases,

Rn-d and ore dust,

potentially showed

i n

exposure

study

An a n a l y s i s

1983):

both

between

the animals

Rn-d exposed miners

1982).

studies

of

for

the

inhalation

then

tumor

From

that

Daschil,

effects, i n

lung

concluded

Rn-d

radiation genic

same r e l a t i o n s h i p

magnitude

et

for

the

and man.

and

4 ) ·

animal

summarized

as

follows : 1)

Physical

Rn-d),

parameters

(e.g.

the with

the

most of

Cigarette induction.

of

breathing

smoking

5

of

rate)

conversion

frequently

about

the a i r

ventilation

exposure-dose

exposure 2)

characteristics

unattached

for

inhaled t h e room

(e.g. and

can influence the

occurring

individual

fraction

of

physiological significantly inhabitant,

value

for

indoor

promotor

for

lung

Rn-d

mSv/WLM. may

act

as a

cancer

31.

STEINHÀUSLER

439

The Validity of Risk Assessments

RISK FACTOR CANCER/PERSON* WLM -4 x 10 V Ί I 1

Figure cancer

4. risk.

Published lifetime

risk

factors

for

Rn-d related

lung

440

RADON AND ITS DECAY PRODUCTS

3)

Up to 100 WLM of cumulative exposure, lung cancer risk shows linear dependence on Rn-d exposure; this is followed by a plateau region up to about 500 WLM. Due to the various sources of uncertainties associated with both groups of input data (dose and effect) needed for risk assessment, at present it is only possible to give an upper limit for the pure Rn-d related cancer risk. Using the miner data for this purpose may be overestimating the risk due to indoor exposure, since it includes risks from simulta­ neous exposure to external gamma radiation, long lived alpha emitters. This effect, however, may be outweighed by the fact that smokers amongst miners are generally twice as frequent as the number of smokers among members of the public. Therefore risk estimates derived from miners may only reflect the risk of male smokers exposed to Rn-d but may not be valid for children and women. Altogether it can be assumed that such a risk factor obtained from miners represents an upper limit for the risk associated with indoor exposure. Another possibility is the use of lung cancer incidence amongst non-smoking members of the public, representing the maximum value that can be attributable to Rn-d only. Because of statistical problems with a rare event, such as lung cancer amongst non-smokers, estimates of annual rates range from about 20 to 300 cases per 10 men depending on the age (Steinhàusler, in press). A third possibility consists of comparing the theoretically calculated lung cancer rate based on risk coefficients derived from miners with the actual cancer occurrence among non-miners, derived from Rn-d exposure assessment in dwellings and using appro­ priate exposure-dose conversion factors (Steinhàusler et al. 1983; Edling, 1983). From the above it can be concluded that the risk for lung cancer induction from chronic indoor exposure to Rn-d is unlikely to be higher than 1.10~4/mSv. i order to understand the magnitude of this risk it has to be emphasized that man can be exposed to a multitude of different hazardous materials in the indoor atmosphere besides Rn-d, such as formaldehyde, nitrogen dioxide, carbon monoxide, nitrosamines, polyaromatic hydrocarbons, volatile organic compounds, asbestos and pesticides (Gammage and Kaye, 1985). t

n

Literature Cited Busigin,A., Van der Vooren,A.W., Babcoock, J.C. and C.R. Phillips, The Nature of Unattached RaA (Po 218) Particles, Health Phys.40: pp 333-344 (1981). Chameaud,J., Perraud,R., Lafuma,J. and R. Masse, Cancers Induced by Rn-222 in the Rat, In: Proc. of Spec.Meet. on Ass, of Radon and Radon Daughter Exposure and Related Biological Effects (G.F. Clemen­ te, A.V. Nero, F. Steinhäusler and M. R. Wrenn, eds) p. 198, R.D. Press, Salt Lake City (1982). Chameaud,J., and J. Lafuma, Experimental Study of Cancer Induction with Rn 222. Daughters, Rad.Prot.Dosimetry 7: 385 (1984).

31. STEINHÀUSLER

The Validity of Risk Assessments

441

Congress of the United States,Joint Committee on Atomic Energy, Part I and II (1967). Cross,F.T., Palmer,R.F., Filipy,R.E., Busch,R.H. and B.O. Stuart, Study on the Combined Effects of Smoking and Inhalation of Uranium Ore Dust, Radon Daughters and Diesel Oil Exhaust Fumes in Hamsters and Dogs, Pacific Northwest Laboratory Rep. No. PNL-2744, Richland, National Technical Information Service, Springfield, VA., USA (1978). Cross,F.T., Palmer,R.F., Dagle,G.E., Busch,R.H., and R.L. Buschbom, Influence of Radon Daughter Exposure Rate, Unattached Fraction and Disequilibrium on Occurrence of Lung Tumors, Rad.Prot.Dosimetry 7: 381 (1984). Cross,F.T., Palmer,R.F., Busch,R.H., Filipy,R.E., Dagle,G.E. and B.O. Stuart, Carcinogenic Effects of Radon Daughters, Uranium Ore Dust and Cigarette Smoke in Beagle Dogs, Health Phys. 42: 33 (1982). Edling,C., Lung Cancer and Radon Daughter Exposure in Mines and Dwellings: study no. V. Linköping University, Medical Dissertation No. 157, Dept. of Occup. Med., Linköping, Sweden (1983). Evans,R.D., Harley,J.H., Jacobi,W., McLean,A.S., Mills,W.A. and C.G. Stewart, Estimate of Risk from Environmental Exposure to Radon-222 and its Decay Products, Nature 290: 98 (1981). Gammage,R.B.and S.V. Kaye (eds), Indoor Air and Human Health, Lewis Publ. Inc., Chelsea, MI., USA (1985). Härting,F.H., und W. Hesse, Der Lungenkrebs, die Bergkrankheit in den Schneeberger Gruben, Teil I, Eulenbergs Vierteljahrschriftf., Gerichtliche Medizin und öffentliches Gesundheitswesen, neue Folge 30: 296 (1879). Hofmann,W., and F. Daschil, The Relevance of Animal Models for Radionuclide Inhalation in Man, in Current Concepts in Lung Dosime­ try, Proc. of the 30th Annual Meeting of the Radiation Research Society at Salt Lake City 1982 (D.R. Fisher, ed) pp 95-102, Utah (1983). International Commission on Radiological Protection, Limits for Inhalation of Radon Daughters by Workers, ICRP Publication, No.32, Pergamon Press (1981). Lundin,F.E., Wagoner,J.K. and V.E. Archer, Radon Daughter Exposure and Respiratory Cancer, Quantitative and Temporal Aspects, Nat. Inst. Occup. Safety and Health/Nat. Inst. Env.Sciences, Joint Monograph No.1, US Dept. of Health, Education and Welfare, Public Health Service (NTIS, No. PB 204871), Washington, D.C. (1971). Masse,R., Histiogenesis of Lung Tumors Induced in Rats by Inhalation of Alpha Emitters: an Overview, in Pulmonary Toxicology of Respirable Particles (C.L. Sanders et al., eds) p. 498, CONF - 791002, National Technical Information Service, Springfield, USA (1980).

442

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Snihs,J.O., The Approach to Radon Problems in Non-Uranium Mines in Sweden, in Proc. Third Int. Congr. Prot. Assoc. p 909, (IRPA), U.S.A.E.C. Conf. 73097-P.2. (1973). Steinhäusler,F. and Ε. Pohl, Lung Cancer Risk for Miners and Atomic Bomb Survivors and its Relevance to Indoor Radon Exposure, Radiation Protection Dosimetry: Vol.7, No.1-4: 389-394 (1983). Steinhäusler,F., and Pohl,Ε., Lung Cancer as a Result of Energy Conservation and Waste Recycling, Proc. XI. Regional Congress of IRPA, Vol.1: pp 258-262, Vienna, Austria (1983). Steinhäusler,F., Hofmann,W., Pohl,Ε. and J. Pohl-Rüling, Radiation Exposure of the Respiratory Tract and Associated Carcinogenic Risk due to Inhaled Radon Daughters, Health Physics Vol.45, No.2: 331-337 (1983). Steinhäusler,F., The Epidemiological Evidence for Health Risks, in Radon and its progeny in indoor air, (A. Nero et al., eds), CRC­ -Press, (in press). United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), Sources and Effects of Ionizing Radiation, Report to the General Assembly with Annexes, United Nations, N.Y., USA, (1977). US-Environmental Protection Agency, Draft Environmental Impact Statement for Remedial Action Standards for Inactive Uranium Proces­ sing Sites (40 CFR 192), US-EPA Rep. No. EPA 520/4-80-011 (1980). US-National Academy of Sciences, National Research Council BEIRII, The Effects on Populations of Exposure to Low Levels of Ionizing Radiation, Washington, DC, USA (1980). US-National Academy of Sciences, National Research Council BEIR-II: Biological Effects of Ionizing Radiation, Washington, D.C., USA (1972).

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443

Weibel E.R., Morphometry of the Human Lung, Springer Verlag, Berlin (1963). Williams, L. R., Labour viewpoint, in Proc.Int.Conf. on Occupat. Rad. Safety in Mining (H. Stocker, ed) 29, Canadian Nucl. Assoc., Toronto, Canada (1985). Yeh,H.C., Schum, G.M., Models of the Human Lung Airways and their Application to Inhaled Particle Deposition, Bull.Math.Biol. 42: pp 461-480 (1980). RECEIVED September 9, 1986