WORKING FOR A HEALTHY FUTURE

INSTITUTE OF OCCUPATIONAL MEDICINE . Edinburgh . UK www.iom-world.org

Occupational Epidemiology and Exposure Estimation

John Cherrie

www.OH-world.org

Summary…

• asbestos and man-made mineral fibres• a general definition of exposure• from the source to dose• the occupational history• strategies for estimating exposure• the consequences of inaccurate or

imprecise exposure estimates• a case study - asbestos in the city

Scope of this session...

• occupational (and environmental)• chronic exposure • to hazardous substances• by inhalation

• occupational epidemiology • non-occupational epidemiology / risk

assessment

Asbestos…

• Doll (1955) lung cancer• Wagner et al (1960)

mesothelioma• 1964 New York conference• Stanton and Wrench(1972)

and Pott and Friedrichs (1972) in vivo induction of mesothelioma

• Mid-1970s glass and rockwool industries commission studies

Asbestos lung cancer epidemiology…

Epidemiology…

• Cohort studies• start with a defined group of people• follow-up to date• classify exposure• enumerate causes of death• standardize mortality in relation to larger population

group (SMR)

• Case-control study• people with the disease being studied (cases) matched

with controls • exposures estimated for each subject• risk of disease

Strengths and weaknesses…

• Strengths• Realistic exposures• In human populations

• Weaknesses• It takes a long time before a cancer mortality study is

practicable• You generally need a very large study population • Co-exposures and confounding (e.g. other occupational

carcinogens or smoking)

European MMMF studies…

• Five glasswool plants, seven rock/slagwool plants and two glass continuous filament plants

• Total of 13,788 subjects• Employed between 1940 and 1978

Lung cancers

SMR 95% CI

Rock/slag 97 138 112 - 168

Glasswool 149 112 94 - 132

GCF 14 93 51 - 157

Changes…

Technological phase…

Co-exposures…

• Asbestos• Used in some form or other in all of the plants• Four plants used cloth, yarn or cement products in

production processes

• PAH• Bitumen and tar used in some plants

• PCBs• Ionising radiation• Formaldehyde• Possible arsenic exposure

Case-control study…

Cases/controls OR 95% CI OR 95% CI95% CI

15-year lagged cumulative MMVF exposure within the MMVF industry Quartile 136/115 1.00 1.00Quartile 236/111 1.08 0.59-1.97 1.25 0.66-2.340.41-9.83Quartile 330/108 0.93 0.50-1.71 1.02 0.54-1.930.27-2.17Quartile 430/174 0.60 0.33-1.09 0.67 0.35-1.270.28-1.42

p-value for trend 0.07 0.170.19

Adj. to smokingAll workers

Unadj. to smoking

Definition of exposure...

“In epidemiology exposure denotes any of a subject’s

attributes or any agent with which he or she may come

into contact that may be relevant to his or her health.”

Armstrong, White and Saracci (1990)

From source to dose

source ambientconcentration exposure internal

exposure dose

disease

Routes of exposure...

• Inhalation• exposure level, duration of exposure

• Dermal• concentration on skin, area of skin exposed,

duration of exposure

• Ingestion• mass of chemical being swallowed

Biological relevance...

• The chosen exposure metric should be biologically relevant• what substance• what sub-fraction of an aerosol• what averaging time

Fibre analysis criteria...

Fibres are harmful because…•they are thin (d < 3m)•they are long (l > 5m) and •because of their shape (l/d > 3)

also because they are persistent in the lung

Information sources...

• subject• relatives or friends• personnel records• other company records• co-workers• community records• environmental monitoring

Strategies for assessment...

• Industry• Job title• Job-Exposure matrices• Individual “expert” evaluation• Exposure measurements• Biological monitoring

Historic monitoring data...

• Benefits…• quantitative data

• Drawbacks…• may be unbalanced or incomplete• changes in sampling or analytical methods• variations in sampling strategy• changes in process or control measures

Structured subjective assessment

,...),,( lvi hfC ηε= ,...),,( lvi hfC ηε=Where...

εi = intrinsic emissionh = handlingηlv = local controls etc.

Exposure estimation...

0

0.1

0.2

0.3

0.4

0.5

1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990

fibres/ml

∑=

=n

iii tCE

1

.

Change in technology

Ventilation introduced

Validity...

10

1

0.1

0.01

0.0010.001 0.01 0.1 1 10

Problems with estimates...

• reporting bias• exposure

misclassification

0

20

40

60

0 10 20 30 40 50 60 70 80 90 100

Exposure

Response

Asbestos in the city...

• asbestos roofing dumped near a school

• children have broken into the bags and were playing with the asbestos

• how do you advise the parents?

Asbestos

• a group of six naturally occurring fibrous silicate minerals which have been used commercially…• chrysotile (white)• crocidolite (blue)• amosite (brown)

• can cause asbestosis, lung cancer and mesothelioma

aWARNINGCONTAINSASBESTOS

Breathing asbestosdust is dangerous

to health

Follow safety instructions

A serious public health risk...

The risks...

• for lung cancer• risk is proportional to cumulative exposure• 1% increase in risk for each year at 1 fibre/ml

• for mesothelioma• risk is related to cumulative exposure and age at first

exposure

• where n = 3.2 and KM = 3.10-8

€

I =KM . f .tn

Mesothelioma risk for a child...

0

0.00002

0.00004

0.00006

0.00008

0.0001

0.00012

0.00014

0.00016

0.00018

1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090

Incidence

Age 10, exposed to 1fibre/ml for one day

So what should we do?

Some useful information...

Typical airborne fibre levels while working with asbestos insulation boards and tiles (normally brown and blue asbestos)

Activity Typical exposure level

(fibres/ml)

unscrewing and removing ceiling tiles with controlled wetting

up to 0.5

unscrewing and careful removal of ceiling tiles using local ventilation

up to 2

careful removal of whole asbestos boards up to 5

hand sawing tiles 5 to 10

breaking and ripping out boards 5 to 20

cutting tiles with a circular saw greater than 20

What are your conclusions?

Summary...

• exposure estimation is central to reliable risk assessment

• quantitative exposure assessment is more useful than categorical evaluations

• even short-term exposure to asbestos may create important risksUseful information… 1. Human Exposure Assessment (IPCS EHC214)

available at www.inchem.org/documents/ehc/ehc/ehc214.htm

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