IOM Exposure Assessment Guide
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The aim of this lecture is to provide an introduction to occupational exposures and the strategies used in epidemiological studies to assess exposure of subjects.
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IOM Exposure Assessment Guide
- 1. INSTITUTE OF OCCUPATIONAL MEDICINE . Edinburgh . UK www.iom-world.org Exposure assessment 2 John Cherrie
- 2. Summary… • General approaches to exposure estimation • Linkage to the individual – the central role of job title • Examples from synthetic mineral fibre studies • JEMs • Use of exposure data • Lenters et al and asbestos
- 5. The essence of exposure assessment… • Identify a theoretical framework for exposure and select the most appropriate exposure metric • Identify the maximum amount of information you can collect about the subjects • Identify an algorithm to translate the available information to an exposure estimate
- 6. Types of exposure metric… • Quantified personal exposure measurements • Quantified job or area data • Ordinally ranked jobs or tasks • Duration of employment in industry • Job title unranked • Ever employed in industry Best Worst
- 7. Information sources... • Personnel records • Other company records • Subject • Relatives or friends • Co-workers • Community records • Environmental monitoring records
- 9. Linkage to individual… • Industry or work area • Job title • Grouped job titles • Task lists by job • Task lists by individual • Obtained retrospectively by interview or collected prospectively • From the subject or other informant source
- 10. 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
- 11. Changes…
- 12. Descriptive exposure data… Cherrie et al (1986). Environmental surveys in the European man-made mineral fiber production industry, 12(SUPPL. 1), 18–25.
- 13. Technological history… Cherrie, J., & Dodgson, J. (1986). Past exposures to airborne fibers and other potential risk factors in the European man-made mineral fiber production industry, 12 Suppl 1(SUPPL. 1), 26–33. • Early phase • Intermediate • Late phase
- 15. 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
- 16. Exposure assessment for a nested case- control study… • Use of an algorithm based on source-receptor paradigm • Near-field and far-field 𝐶 𝑁𝐹 = 𝜀𝑖,𝑁𝐹. ℎ 𝑁𝐹. 1 − 𝜂𝑙𝑣,𝑁𝐹 . 𝑡 𝑎,𝑁𝐹 + 𝜀 𝑝 . 1 − 𝜂 𝑝𝑝𝑒 . 𝑑 𝑔𝑣,𝑁𝐹 𝐶 𝐹𝐹 = 𝜀𝑖,𝐹𝐹. ℎ 𝐹𝐹. 1 − 𝜂𝑙𝑣,𝐹𝐹 . 𝑡 𝑎,𝑁𝐹 + 𝜀 𝑝 . 1 − 𝜂 𝑝𝑝𝑒 . 𝑑 𝑔𝑣,𝐹𝐹 𝐶 = 𝐶 𝑁𝐹 + 𝐶 𝐹𝐹 Cherrie, J., & Schneider, T. (1999). Validation of a new method for structured subjective assessment of past concentrations. The Annals of Occupational Hygiene, 43(4), 235–245.
- 18. Job-exposure matrices… • Job axis, generally coded to an appropriate standardised coding scheme • Exposure axis, defined by the purpose of the authors • Matrix cells, categorical exposure level (and probability) • Sometimes includes a time dimension • May be extended to include tasks or aspects of exposure algorithms • Exposure assignment generally carried out by ”expert” review FINJEM… NOCCA-JEM… Syn-JEM…
- 20. Geoparkinson study… • 959 cases of parkinsonism and 1989 controls • Exposure assessed for solvents, pesticides and metals • Questionnaire administered to subjects • Significantly increased risk with pesticide exposure and ever knocked unconscious • Tobacco smoking was protective Dick, et al. (2007). Environmental risk factors for Parkinson's disease and parkinsonism: the Geoparkinson study. Occupational and Environmental Medicine, 64(10), 666–672.
- 21. Exposure assessment methods… • JEM produced base estimate • 4 categories of intensity (inhalation, skin contact and ingestion) • High = 100 (equivalent to the occupational exposure limit) • Medium = 40 • Low = 5 • None • Base values adjusted based on questionnaire response by expert evaluation Semple, S. E., Cherrie, J., Seaton, A., Dick, F., Haites, N., Osborne, A., et al. (2004). Exposure assessment for a population-based case-control study combining a job-exposure matrix with interview data, 30(3), 241–248.
- 23. Coke workers mortality study… • 6,600 workers from 13 coke works operated by NSF and 14 BSC plants in 1967 • 20-year follow-up resulted in 300 lung cancer deaths and SMRs of around 1.25 • Annual geometric mean concentrations of inhalable dust, BSM and B[a]P for jobs at NSF plant from 1971 to 1983 • Much more limited data for BSC plants – modelled concentrations • Early measurements probably biased • Time trend in BSM but not B(a)P data Miller, B. G., Doust, E., Cherrie, J. W., & Hurley, J. F. (2013). Lung cancer mortality and exposure to polycyclic aromatic hydrocarbons in British coke oven workers. BMC Public Health, 13(1), 962–1. http://doi.org/10.1186/1471-2458-13-962
- 24. 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
- 25. Results from coke study… • No evidence for a relationship of lung cancer risk with exposure to either BSM or B[a]P • There was a statistically significant increase in risk in men with more than 5 years spent working in Ovens Tops jobs at BSC • The estimated relative risk for this was 1.81, • Overall, there was little evidence of an effect of coke oven exposures on lung cancer risk
- 26. Lenters et al… • Classified quality of exposure assessments • Documentation • CE ratio, i.e. the ratio of the average exposure in the highest and lowest CE categories • Conversion factor used • Coverage of exposure data • Job histories
- 27. Summary… • Many strategies open to estimate exposure • Understand the theory behind the exposures and select an appropriate metric • What information about the subjects is available? • Translate the available information to an exposure estimate
Editor's Notes
- Nellie Kershaw was born in Rochdale in 1891. She left school, aged 12, to take up employment and began working in an asbestos mill – later Turner Brothers Asbestos. She was a rover, spinning raw asbestos fibre into yarn. She died aged 33 from asbestosis. 113 men who worked in an asbestos factory. 39 dead.
- Nested case-control study. Cohort 31k men – data from pension fund. Job information and limited info about industry only. OR for engine crew for mesothelioma was 9.75, 20 year latency Lymphoma OR = 2.78 amongst Deck personnel on tankers and leukaemia OR = 2.26 to 6.86 depending on duration of employment Example of job-title approach
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- Earliest JEMs originate in the 1980s Most often used for population-based case-control studies.
- OR = 1.13 for low vs no exposure = 1.41 for high vs no exposure
- Adjustment rules provided… Symptoms reported while working with solvents Ventilation and engineering controls Use of respiratory protective equipment (RPE) Work location Quantity of solvent used
- Complex mixture What to use as a marker of risk?
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- Armstrong review and meta-analysis: 100 μg/m3 years benzo[a]pyrene was 1.20 [95% confidence interval (CI), 1.11–1.29]