Occupational Epidemiology and Exposure Estimation

John Cherrie

www.OH-world.org

Summary…

asbestos and man-made mineral fibres

a general definition of exposure and the exposome

from the source to dose

the occupational history

strategies for estimating exposure

the consequences of inaccurate or imprecise

exposure estimates

limits on exposure

a case study - asbestos in the city

Scope of this session...

Mostly occupational (and some environmental)

Chronic exposure

To hazardous substances

By inhalation

Occupational epidemiology

Non-occupational epidemiology / risk assessment

Asbestos…

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

Mid-1970s glass and rockwool industries commission studies

Doll (1955) lung cancer

Wagner et al (1960) mesothelioma

1964 New York conference

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

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

Polycyclic Aromatic Hydrocarbons (PAH) Bitumen and tar used in some plants

Polychlorinated Biphenyls (PCBs)

Ionising radiation

Formaldehyde

Possible arsenic exposure

Case-control study…

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)

Two-thirds of the deaths in the world are

caused by noncommunicable diseases,

especially cancer and cardiovascular

disease

Only about 10% of this mortality attributed

to genetic variation

The exposome is composed of every

exposure to which an individual is

subjected from conception to death.

Chris Wild

The Exposome…

The exposome is composed of every exposure to

which an individual is subjected from conception

to death.

It comprises:

processes internal to the body such as metabolism, gut

microflora, inflammation…

external exposures including infectious agents,

chemical contaminants, diet…

social, economic and psychological influences.

Wild, C. P. (2012). The exposome: from concept to utility. International

Journal of Epidemiology, 41(1), 24–32.

Agnostic investigations…

Steve Rapport recommends searching for

potential causes without any prior hypothesis

Approach lends itself to “omics” technologies

Although other approaches can also adopt this

approach

Follow-up with more focused

epidemiological and mechanistic

studies

From source to dose

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 averaging time

what sub-fraction of an aerosol

Cherrie and Aitken. Measurement of human exposure to biologically relevant

fractions of inhaled aerosols. Occup Environ Med (1999) vol. 56 (11) pp. 747-52

Biological relevance…

Cherrie and Aitken. Measurement of human exposure to biologically relevant fractions

of inhaled aerosols. Occup Environ Med (1999) vol. 56 (11) pp. 747-52

Fibre analysis criteria...

Fibres are harmful because…

•they are thin (d < 3mm)

•they are long (l > 5mm) and

•because of their shape (l/d > 3)

also because they are persistent in

the lung

Information sources...

Personnel records

Other company records

Subject

Relatives or friends

Co-workers

Community records

Environmental monitoring records

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

Coke works…

Work area determines exposure level…

Structured assessment based on theory…

Where...

ei = intrinsic emission

h = handling

hlv = local controls

etc.

Validity...

R² = 0.96

0.0

20.0

40.0

60.0

80.0

100.0

0.0 10.0 20.0 30.0 40.0 50.0 60.0

Esti

mate

d B

[a]P

(mg

/m

3)

Measured B[a]P (mg/m3)

Estimates made using a spreadsheet…

Exposure estimation...

Change in

technology

Ventilation

introduced

Estimates…

Job B[a]P Inhalable dust

Yard Foreman 3 2

Oven top - Airstream 3 2

Wharf Man 5 5

Quench Car Operator 7 6

Foreman - HMAG 7 4

Suprintendent - all areas 9 13

Superintendent - Briquetting 9 14

Foreman - Briquetting 11 14

Oven Foreman 12 5

Process Foreman 12 5

Sampler 15 18

Backend man 16 21

Press Operator 16 13

Pug man 17 22

Screen Man 20 15

Oven Top 30 15

Oven tops - Pre 1970 31 16

Cleaning Bussettes 32 9

Cleaning tar tanks 42 42

Assistant Fitter 44 15

Pump Man 45 3

Shuttle 46 33

Plater - Rigger - Briquetting 47 36

Plater - Rigger - liquid pitch 55 34

Shift Fitter 64 23

Plater - Rigger 77 33

Pitch Man 101 7

Rough Brush Painter 204 157

Job No Start End Job Duration (yr)

Average % of job

B[a]PExposure (μg/m3)

Cumulative (μg/m3.yr)

1a J-52 J-54Pug 2.00 33% 13 10

1b J-52 J-54Press 2.00 33% 13 9

1c J-52 J-54Backend 2.00 33% 10 8

2 J-54 J-56Fitter 2.00 100% 66 149

3 J-56 J-61Shift Foreman 5.00 100% 32 178

4 J-61 J-71Shift Superintendant -Whole plant

10.00 100% 18 203

5 J-71 J-80Shift Superintendant -Briquetting plant

8.59 100% 17 160

Total J-52 J-80 31.58 23 716

Problems with estimates...

Watt M, Godden D, Cherrie J, Seaton A. (1995). Individual exposure to particulate air pollution and

its relevance to thresholds for health effects: a study of traffic wardens. Occupational and Environmental Medicine; 52: 790-792.

Occupational Exposure Limits (OELs)

Concentrations (e.g. mg/m3) averaged over either

8-hr or 15-min

Personal exposure

Each country sets

its own limits,

There can be up

to two orders of

magnitude difference

Health-based

OEL

OEL based

on socioeconomic

factors

Setting limits on exposure…

In Europe The Scientific Committee on Occupational

Exposure Limit Values (SCOEL) advises the EC on OELs

assemble all relevant data on the hazards of the substance

determine whether it is adequate for the setting of an OEL

identify the most important adverse effects that may arise

review the quality of key studies.

establish whether there is a non-threshold mechanism

establish a ‘no observed adverse effect levels’ (NO(A)ELs) or

‘lowest observed adverse effect levels’ (LO(A)Els)

establish a value for an 8-hr OEL, plus Uncertainty Factor

can the OEL be measured

Bolt, H.M. & Huici-Montagud, A., 2008. Strategy of the scientific committee on occupational

exposure limits (SCOEL) in the derivation of occupational exposure limits for carcinogens and

mutagens. Archives of Toxicology, 82(1), pp.61–64.

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

aWARNING

CONTAINS

ASBESTOS

Breathing asbestos

dust 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

Mesothelioma risk for a child...

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

So what should we do?

Some useful information...

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 risks

Useful information…

Human Exposure Assessment (IPCS EHC214) available at

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

Check out www.OH-world.org