A Quantitative Retrospective Exposure Assessment for Former Chrysotile Asbestos Miners and Millers from Baie Verte, NL, Canada

Our plain-English summary of A Quantitative Retrospective Exposure Assessment for Former Chrysotile Asbestos Miners and Millers from Baie Verte, NL, Canada, by T. Giles Murphy, S. Bornstein, J. Oudyk, et al (Annals of Work Exposures and Health, 2021).

The study

• Authors: T. Giles Murphy, S. Bornstein, J. Oudyk, P.A. Demers
• Journal: Annals of Work Exposures and Health
• Published: 2021;65(1):113-126
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Despite numerous studies of asbestos workers in the epidemiologic literature, there are very few cohort studies of chrysotile asbestos miners/millers that include high-quality retrospective exposure assessments. As part of the creation of the Baie Verte Miners' Registry in 2008, a two-dimensional job exposure matrix (JEM) was developed for estimating asbestos exposures for former chrysotile asbestos miners/millers. Industrial hygiene data collected between 1963 and 1994 were analysed to assess validity for use in a retrospective exposure assessment and epidemiologic study. Registered former employees were divided into 52 exposure groups (EGs) based on job title and department and mean asbestos concentrations were calculated for each EG. The resulting exposure estimates were linked to individual registrants' work histories allowing for the calculation of cumulative asbestos exposure for each registrant. The distribution of exposure for most EGs (82.6%) could be described as fitting a log-normal distribution, although variability within some EGs (55%) exceeded a geometric standard deviation (GSD) of 2.5. Overall, the data used to create EGs in the development of the JEM were deemed to be of adequate quality for estimating cumulative asbestos exposures for the former employees of the Baie Verte asbestos mine/mill. The variability between workers in the same job was often high and is an important factor to be considered when using estimates of cumulative asbestos exposure to adjudicate compensation claims. The exposures experienced in this cohort were comparable to those of other chrysotile asbestos miners/millers cohorts, specifically Italian and Québec cohorts.

© The Author(s) 2020. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.

In plain English

The authors built a job exposure matrix, a table of estimated airborne asbestos levels by job and time period, for former workers of the chrysotile asbestos mine and mill at Baie Verte, Newfoundland, Canada, which operated from 1963 to 1994. For 1963 to 1975 they used older stationary dust samples converted to fibre counts. For 1976 to 1994 they used about 7000 samples. They sorted jobs into 52 exposure groups and combined these with each registrant's work history to estimate cumulative exposure. Early exposures were very high, averaging 6 to 42 fibres per ml across areas, and fell over time. From 1976 to 1994, the highest group, Dry Rock Storage Attendant, averaged 3.19 fibres per ml. Of 98 matrix cells for 1976 to 1994, 89.8% had enough samples to rate as good or very good. The authors judged the 1976 to 1994 estimates valid. They cautioned that earlier estimates are less certain. They also cautioned that in jobs where exposure varied widely between workers, the matrix value may not reflect everyone's exposure when used for compensation claims. Baie Verte levels fell between those reported for Italian and Québec chrysotile miners.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Retrospective exposure assessment: development and statistical evaluation of a two-dimensional job exposure matrix (exposure groups by calendar period) from historical industrial hygiene data
• Who was studied: Former employees registered in the Baie Verte Miners' Registry, set up in 2008, who worked at the Baie Verte chrysotile asbestos mine/mill, Newfoundland, Canada. The mine operated commercially from 1963 until it closed in 1994 and employed about 500 people at a time. The article does not state the number of registrants.
• Exposure: Airborne chrysotile asbestos fibres at a mine and mill. For 1963 to 1975, stationary midget impinger samples were converted to fibres per ml using area-specific conversion factors (from the Edstrom study). For 1976 to 1994, approximately 7000 personal and stationary samples were taken by the NIOSH 7400 membrane filter method. Jobs were grouped into 52 exposure groups across nine year categories, and cumulative exposure was expressed in fibre-years per ml.
• Main results:
  • There were 52 exposure groups. The data for 43 fit a log-normal distribution, 6 fit a normal distribution and 3 were bimodal.
  • Geometric standard deviations (a measure of spread within an exposure group) ranged from 1.74 (Forklift Operator-Warehouse) to 5.61 (Senior Tester). Of these, 45% were below 2.5, 35% were between 2.5 and 3.0, 16% were between 3.0 and 4.0, and 4% were over 4.0.
  • Exposure varied more within groups in the Pit than in the Mill. In the Mill, 92% of geometric standard deviations were below 3.0. In the Pit, 35% were between 3.0 and 4.0.
  • Judged by number of samples, 89.8% of the 98 matrix cells for 1976 to 1994 rated as 'good' or 'very good' quality, and 1% rated as 'poor'.
  • In the 1980 government full-shift sampling, 87 of 964 individual 1 to 2 hour samples (9.0%) differed from the shift mean by more than the error range of the NIOSH 7400 method.
  • In 1963 to 1975, the highest-exposed mill jobs (Shuttle Operator, Primary Crusher Operator, Dryer Operator, Secondary Crusher Operator, Dry Rock Storage Attendant) averaged 66.55 fibres per ml at their peak in 1968. By department, exposure in this period was highest in the Pit and lowest in Employee Relations.
  • Exposures in the early years averaged 6 to 42 fibres per ml across areas of the mine and mill and gradually decreased over time.
  • In 1976 to 1994, the highest-exposed group was Dry Rock Storage Attendant, with an overall average of 3.19 fibres per ml and a maximum of 18.8 fibres per ml in 1980. The lowest was Backhoe Operator in the Pit, averaging 0.08 fibres per ml with a maximum of 0.26 fibres per ml in 1982.
  • Between-worker variability was below 20% (the authors' threshold for a group value to represent all members) in 11 of 20 Mill groups, 7 of 13 Erection & Repair groups and 2 of 7 Pit groups.
  • Compared with published data, Baie Verte exposure estimates fell between those of Italian (Balangero) and Québec chrysotile miners. Québec levels were generally higher.
• The authors' conclusion: The authors concluded that their analysis of the 1976 to 1994 data allowed them to be confident in the validity of the matrix estimates for those years. They said possible misclassification in the earlier data must be considered. They also said care is needed when using matrix values to adjudicate compensation claims for groups with high variability, because the value may not represent everyone in the group.
• Limitations the authors state:
  • Raw sampling data were not available before 1976. The earlier estimates relied on stationary samples and may have underestimated exposure in 1963 to 1975.
  • Converting historical midget impinger dust and fibre counts to fibres per ml can introduce systematic bias.
  • Many 1976 to 1994 samples lasted only 1 to 2 hours rather than a full shift.
  • The sampling strategies of the union, government or company may have biased results toward worst-case or best-case conditions.
  • High between-worker variance in some groups may partly reflect small numbers of samples.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Chrysotile, Asbestos Exposure, Industrial Hygiene.

Related studies

• Lung mineral fibers of former miners and millers from Thetford-Mines and asbestos regions: a comparative study of fiber concentration and dimension — A. Nayebzadeh, A. Dufresne, et al. (2001)
• Development of an exposure measurement database on five lung carcinogens (ExpoSYN) for quantitative retrospective occupational exposure assessment — S. Peters, R. Vermeulen, et al. (2012)
• Mortality of former crocidolite (blue asbestos) miners and millers at Wittenoom — A.W. Musk, N.H. de Klerk, et al. (2008)
• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: development from 1904 and mortality to 1992 — F.D. Liddell, A.D. McDonald, et al. (1997)
• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: mortality 1976-88 — J.C. McDonald, F.D. Liddell, et al. (1993)
• Fiber burden and patterns of asbestos-related disease in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1993)

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