Occupational epidemiology and exposure assessment


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A lecture given at the University of Cambridge MPhil course in Public Health

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  • 02/24/10
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  • 02/24/10 Studies published between 1974 and 1998
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  • 02/24/10 First follow-up to 1979 produced small non-significant excesses of lung cancer. Increases in risk with time since first exposure. Studies continued with follow-up to early 1980s Only 2 mesothelioma deaths
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  • 02/24/10 133 cases, 513 controls No consistent risk for asbestos or silica, although exposures quite low. Risk for current smokers (>400kg) vs non or low smokers was OR=10 (people employed >1yr)
  • 02/24/10 Armstrong BK, White E, Saracci R. (1990) Principles of exposure measurement in epidemiology. Monographs on Epidemiology and Biostatistics 21. Oxford: Oxford University Press.
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  • 02/24/10 Cherrie JW and Aitken R. (in press) Measurement of human exposure to biologically relevant fractions of inhaled aerosols . Occupational and Environmental Medicine.
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  • 113 men who worked in an asbestos factory. 02/24/10
  • Nested case-control study. Cohort 31k men – data from pension fund. Job information only. OR for engine crew for mesothelioma was 9.75, 20 year latency 02/24/10
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  • 02/24/10 Cherrie JW. (in press) The effect of room size and general ventilation on the relationship between near and far-field concentrations. Applied Environmental and Occupational Hygiene. Cherrie JW, Schneider T. (in press) Validation of a new method for structured subjective assessment of past concentrations. Ann.occup.Hyg. Seaton A, Cherrie JW. (1998) Quartz exposures, hilar lymphadenopathy and severe silicosis. Occup Env.Med.; 55: 383-386.
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  • 02/24/10 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.
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  • Occupational epidemiology and exposure assessment

    1. 1. Occupational Epidemiology and Exposure Estimation John Cherrie www.OH-world.org
    2. 2. Summary… <ul><li>asbestos and man-made mineral fibres </li></ul><ul><li>a general definition of exposure </li></ul><ul><li>from the source to dose </li></ul><ul><li>the occupational history </li></ul><ul><li>strategies for estimating exposure </li></ul><ul><li>the consequences of inaccurate or imprecise exposure estimates </li></ul><ul><li>a case study - asbestos in the city </li></ul>
    3. 3. Scope of this session... <ul><li>occupational (and environmental) </li></ul><ul><li>chronic exposure </li></ul><ul><li>to hazardous substances </li></ul><ul><li>by inhalation </li></ul><ul><li>occupational epidemiology </li></ul><ul><li>non-occupational epidemiology / risk assessment </li></ul>
    4. 4. Asbestos… <ul><li>Doll (1955) lung cancer </li></ul><ul><li>Wagner et al (1960) mesothelioma </li></ul><ul><li>1964 New York conference </li></ul><ul><li>Stanton and Wrench(1972) and Pott and Friedrichs (1972) in vivo induction of mesothelioma </li></ul><ul><li>Mid-1970s glass and rockwool industries commission studies </li></ul>
    5. 5. Asbestos lung cancer epidemiology…
    6. 6. Epidemiology… <ul><li>Cohort studies </li></ul><ul><ul><li>start with a defined group of people </li></ul></ul><ul><ul><li>follow-up to date </li></ul></ul><ul><ul><li>classify exposure </li></ul></ul><ul><ul><li>enumerate causes of death </li></ul></ul><ul><ul><li>standardize mortality in relation to larger population group (SMR) </li></ul></ul><ul><li>Case-control study </li></ul><ul><ul><li>people with the disease being studied (cases) matched with controls </li></ul></ul><ul><ul><li>exposures estimated for each subject </li></ul></ul><ul><ul><li>risk of disease </li></ul></ul>
    7. 7. Strengths and weaknesses… <ul><li>Strengths </li></ul><ul><ul><li>Realistic exposures </li></ul></ul><ul><ul><li>In human populations </li></ul></ul><ul><li>Weaknesses </li></ul><ul><ul><li>It takes a long time before a cancer mortality study is practicable </li></ul></ul><ul><ul><li>You generally need a very large study population </li></ul></ul><ul><ul><li>Co-exposures and confounding (e.g. other occupational carcinogens or smoking) </li></ul></ul>
    8. 8. European MMMF studies… <ul><li>Five glasswool plants, seven rock/slagwool plants and two glass continuous filament plants </li></ul><ul><li>Total of 13,788 subjects </li></ul><ul><li>Employed between 1940 and 1978 </li></ul>Lung cancers SMR 95% CI Rock/slag 97 138 112 - 168 Glasswool 149 112 94 - 132 GCF 14 93 51 - 157
    9. 9. Changes…
    10. 10. Technological phase…
    11. 11. Co-exposures… <ul><li>Asbestos </li></ul><ul><ul><li>Used in some form or other in all of the plants </li></ul></ul><ul><ul><li>Four plants used cloth, yarn or cement products in production processes </li></ul></ul><ul><li>PAH </li></ul><ul><ul><li>Bitumen and tar used in some plants </li></ul></ul><ul><li>PCBs </li></ul><ul><li>Ionising radiation </li></ul><ul><li>Formaldehyde </li></ul><ul><li>Possible arsenic exposure </li></ul>
    12. 12. Case-control study…
    13. 13. Definition of exposure... <ul><li>“ 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.” </li></ul><ul><li>Armstrong, White and Saracci (1990) </li></ul>
    14. 14. From source to dose ambient concentration exposure internal exposure source dose disease
    15. 15. Routes of exposure... <ul><li>Inhalation </li></ul><ul><ul><li>exposure level, duration of exposure </li></ul></ul><ul><li>Dermal </li></ul><ul><ul><li>concentration on skin, area of skin exposed, duration of exposure </li></ul></ul><ul><li>Ingestion </li></ul><ul><ul><li>mass of chemical being swallowed </li></ul></ul>
    16. 16. Biological relevance... <ul><li>The chosen exposure metric should be biologically relevant </li></ul><ul><ul><li>what substance </li></ul></ul><ul><ul><li>what sub-fraction of an aerosol </li></ul></ul><ul><ul><li>what averaging time </li></ul></ul>
    17. 17. Fibre analysis criteria... <ul><li>Fibres are harmful because… </li></ul><ul><ul><li>they are thin (d < 3  m) </li></ul></ul><ul><ul><li>they are long (l > 5  m) and </li></ul></ul><ul><ul><li>because of their shape (l/d > 3) </li></ul></ul><ul><li>also because they are persistent in the lung </li></ul>
    18. 18. Information sources... <ul><li>subject </li></ul><ul><li>relatives or friends </li></ul><ul><li>personnel records </li></ul><ul><li>other company records </li></ul><ul><li>co-workers </li></ul><ul><li>community records </li></ul><ul><li>environmental monitoring </li></ul>
    19. 19. Strategies for assessment... <ul><li>Industry </li></ul><ul><li>Job title </li></ul><ul><li>Job-Exposure matrices </li></ul><ul><li>Individual “expert” evaluation </li></ul><ul><li>Exposure measurements </li></ul><ul><li>Biological monitoring </li></ul>
    20. 24. Historic monitoring data... <ul><li>Benefits… </li></ul><ul><ul><li>quantitative data </li></ul></ul><ul><li>Drawbacks… </li></ul><ul><ul><li>may be unbalanced or incomplete </li></ul></ul><ul><ul><li>changes in sampling or analytical methods </li></ul></ul><ul><ul><li>variations in sampling strategy </li></ul></ul><ul><ul><li>changes in process or control measures </li></ul></ul>
    21. 25. Structured subjective assessment Where...  i = intrinsic emission h = handling  lv = local controls etc.
    22. 26. Exposure estimation... Change in technology Ventilation introduced
    23. 27. Validity... 10 1 0.1 0.01 0.001 0.001 0.01 0.1 1 10
    24. 28. Problems with estimates... <ul><li>reporting bias </li></ul><ul><li>exposure misclassification </li></ul>
    25. 29. Asbestos in the city... <ul><li>asbestos roofing dumped near a school </li></ul><ul><li>children have broken into the bags and were playing with the asbestos </li></ul><ul><li>how do you advise the parents? </li></ul>
    26. 30. Asbestos <ul><li>a group of six naturally occurring fibrous silicate minerals which have been used commercially… </li></ul><ul><ul><li>chrysotile (white) </li></ul></ul><ul><ul><li>crocidolite ( blue ) </li></ul></ul><ul><ul><li>amosite ( brown ) </li></ul></ul><ul><li>can cause asbestosis, lung cancer and mesothelioma </li></ul>a WARNING CONTAINS ASBESTOS Breathing asbestos dust is dangerous to health Follow safety instructions
    27. 31. A serious public health risk...
    28. 32. The risks... <ul><li>for lung cancer </li></ul><ul><ul><li>risk is proportional to cumulative exposure </li></ul></ul><ul><ul><li>1% increase in risk for each year at 1 fibre/ml </li></ul></ul><ul><li>for mesothelioma </li></ul><ul><ul><li>risk is related to cumulative exposure and age at first exposure </li></ul></ul><ul><ul><li>where n = 3.2 and K M = 3.10 -8 </li></ul></ul>
    29. 33. Mesothelioma risk for a child... Age 10, exposed to 1fibre/ml for one day
    30. 34. So what should we do?
    31. 35. Some useful information...
    32. 36. What are your conclusions?
    33. 37. Summary... <ul><li>exposure estimation is central to reliable risk assessment </li></ul><ul><li>quantitative exposure assessment is more useful than categorical evaluations </li></ul><ul><li>even short-term exposure to asbestos may create important risks </li></ul>Useful information … 1. Human Exposure Assessment (IPCS EHC214) available at www.inchem.org/documents/ehc/ehc/ehc214.htm
    34. 38. Check out www.OH-world.org