Slides for a lecture for the University fo Cambridge, MPhil Epidemiology/Public Health course: Environmental Module

1. Occupational Epidemiology
and Exposure Estimation
John Cherrie

2. 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
• occupational exposure limits
• a case study - asbestos in the city

3. Scope of this session...
• Mostly occupational (and some environmental)
• Chronic exposure
• To hazardous substances
• By inhalation
• Occupational epidemiology
• Non-occupational epidemiology / risk assessment

4. 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

5. Asbestos lung cancer epidemiology…

6. 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

7. Changes…

8. Technological phase…

9. 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

10. Case-control study…

11. 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)

12. 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

13. The exposome is composed of every exposure to
which an individual is subjected from conception
to death.
Chris Wild

14. 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.

15. 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

16. From source to dose

17. 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

18. 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

19. 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

20. 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

21. Modern measurement…
• Personal sampling is
straightforward
• More relevant to personal
exposure
• Are more biologically
relevant
• Can provide information on
temporal variation
Cherrie. The beginning of the science underpinning occupational hygiene. The Annals of Occupational Hygiene
(2003) vol. 47 (3) pp. 179-85

22. Information sources for
assessing exposure in epi...
• Personnel records
• Other company records
• Subject
• Relatives or friends
• Co-workers
• Community records
• Environmental monitoring records

23. Strategies for assessment...
• Industry
• Job title
• Job-Exposure matrices
• Individual “expert” evaluation
• Exposure measurements
• Biological monitoring

27. 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

28. Coke works…

30. Work area determines exposure
level…

31. Structured assessment
based on theory…
Where...
ei = intrinsic emission
h = handling
hlv = local controls
etc.
C=f(ei , ℎ, hlv…)

32. 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
EstimatedB[a]P(mg/m3)
Measured B[a]P (mg/m3)

33. Estimates made using a
spreadsheet…

34. Exposure estimation...
Change in
technology
Ventilation
introduced

35. 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]P
Exposure
(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

36. 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

37. 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.

38. Some problems with OELs…
• As an example, respirable crystalline silica
– Silica causes silicosis, COPD and lung cancer
– We currently have an OEL of 0.1 mg/m3
– Many workplaces don’t comply with this limit but
few are prosecuted
– The cancer risks associated with long-term
exposure at the OEL are high
– Surely we should reduce the limit…
... but we’re not

39. 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?

40. 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

41. A serious public health risk...

42. 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

43. Mesothelioma risk for a child...
Age 10, exposed to 1fibre/ml for one day

44. So what should we do?

45. Some useful information...

46. What are your conclusions?

47. 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