Review of the Formaldehyde Assessment in the National Toxicology Program 12th Report on Carcinogens (2014) / Chapter Skim
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Appendix C: Exposure Assessment in Epidemiologic Carcinogenicity Studies
Appendix C: Exposure Assessment in Epidemiologic Carcinogenicity Studies
Pages 185-198
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From page 185... ...
The committee then discusses components of an exposure assessment, including defining job titles; measuring exposures using time-weighted averages (TWAs) , cumulative exposures, and peak exposures; strategies for exposure sampling; choosing an appropriate summary measure of exposure; and creating a job–exposure matrices (JEM)
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From page 186... ...
showed that improved quantitation of formaldehyde exposure tended to increase exposure gradients and sharpen estimates of relative risk. Exposure assignments that are imprecise can result in individuals being categorized into the wrong category of the exposure gradient and the epidemiologic study analysis table.
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From page 187... ...
In some cases those work activities may have close links with exposure, but the job titles may or may not be associated with exposures depending on how the work activities were distributed across the job titles. The 1 Typical summary measures of exposure include average exposure, duration of exposure, cumulative exposure, and various measures of peak exposure.
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From page 188... ...
Low exposure Jobs, tasks, or activities with only brief periods when formaldehyde vapors are present, and the work location is distant from the sources. Physical separation of work areas from areas with emission sources.
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From page 189... ...
Industrial hygiene expertise and data from long-term workers is required to translate job and work location information into exposure assignments. A widely used set of standardized job descriptions -- the International Standard Industrial Classification -- has been developed by the United Nations (UN 2008)
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From page 190... ...
The methods have been standardized to measure allowable exposures or emissions for regulatory purposes and they are used by the US Environmental Protection Agency for measuring formaldehyde vapor.2 The numbers of samples collected have also increased because of concern about exposure variability. In many cases, few or no historical exposure data have been available for long-term health studies.
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From page 191... ...
Some of the formaldehyde cancer studies reviewed by the committee used cumulative exposure to summarize occupational exposures across each study subject's entire work history. If Haber's rule holds for the carcinogenic effects of formaldehyde, then summarizing exposure histories using cumulative exposure will not introduce any exposure misclassification.
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From page 192... ...
Only large, extensive studies have collected the necessary data and measurements to estimate the intensity, frequency, and duration of situations with peak exposures, such as the National Cancer Institute cohort studies of the US chemical industries and the funeral industry (Beane Freeman et al. 2009; Hauptmann et al.
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From page 193... ...
1. Job titles and plant or worksites associated with jobs are abstracted from company work histories, or cases and controls or their proxies are interviewed.
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From page 194... ...
The plant-history documentation and exposure estimates are sent to participating plants for technical review by company engineers and industrial hygienists to verify their accuracy. EXPOSURE ASSESSMENT FOR CASE-CONTROL STUDIES Exposure assessment for case–control studies that draw their subjects from the general population is difficult because they generally rely on recalled job titles and industries.
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From page 195... ...
INFORMATION USED TO EVALUATE EXPOSURE ASSESSMENTS The committee evaluated five aspects of each epidemiologic study reviewed in Chapters 2 and 3 to determine the quality of discrimination and the utility of an exposure assessment. Those aspects are the expertise of the investigators, the assessment type (such as, personal monitoring or JEM methods)
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From page 196... ...
196 TABLE C-2 Information Used to Evaluate Exposure Assessment Components of Epidemiologic Studies in Chapters 2 and 3 Exposure-Assessment Components Site Data and Industrial- Discrimination of Exposure Hygiene Extrapolation of Exposure Differences Between Overall Method Job-History Data Evaluation Sampling Data Past Exposures Assignments Categories Qualitative -- None None None None Yes–qualitative Low -- few exposed in broad occupational broad job groups; strong groups and industries tendency to overestimate in a region number exposed; likely large misclassification Semiquantitative -- Yes -- job None -- many None or very None or maybe Yes– Moderate -- specific job specific jobs in one descriptions, worksites or no limited for the some data on time Semiquantitative titles and work site data; industry interviews, data on specific industry trends; industrial in years of limited measurements; questionnaires, and sites hygienist uses exposure likely much overlap proxies; industrial professional between categories hygienist uses judgment to High -- specific jobs with professional assess past defined exposures and judgment to assess exposures limited overlap of low and exposures high categories Quantitative -- Yes -- detailed Yes -- extensive Yes -- extensive Yes -- detailed Quantitative Moderate -- if specific job, specific jobs or areas company records data on for high- strategies and by substance, job area, or sampling data are in a company operations, sites, exposure jobs modeling; or area, and period limited; likely overlap and job activities or areas over industrial according to dose between groups time hygienist uses metrics High -- limited overlap professional between low- and high judgment to exposure categories assess past exposures
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From page 197... ...
2002. Sinonasal cancer and occupational exposures: A pooled analysis of 12 case-control studies.
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From page 198... ...
2000. Comparison of industrial hygienists' exposure evaluations for an epidemiologic study.
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