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Estimating trends in quartz exposure in Swedish iron foundries: predicting past and present exposures
Department of Occupational and Environmental Medicine, Örebro University Hospital, Örebro, Sweden; Örebro University, Örebro, Sweden. (Man-Technology-Environment Research Center (MTM))
Department of Public Health, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands.
Department of Occupational and Environmental Medicine, Örebro University Hospital, Örebro, Sweden.
Örebro University, School of Science and Technology. Department of Occupational and Environmental Medicine, Örebro University Hospital, Örebro, Sweden. (Department of Science, Man-Technology-Environment Research Center (MTM))
2012 (English)In: Annals of Occupational Hygiene, ISSN 0003-4878, E-ISSN 1475-3162, Vol. 56, no 3, p. 362-372Article in journal (Refereed) Published
Abstract [en]

Background: Swedish foundries have a long tradition of legally required surveys in the work place that, from the late 1960s onwards, included measurements of quartz. The availability of exposure data spanning almost 40 years presents a unique opportunity to study trends over that time and to evaluate the validity of exposure models based on data from shorter time spans. The aims of this study were (i) to investigate long term trends in quartz exposure over time, (ii) using routinely collected quartz exposure measurements to develop a mathematical model that could predict both historical and current exposure patterns, and (iii) to validate this exposure model with up-to-date measurements from a targeted survey of the industry.

Methods: Eleven foundries, representative of the Swedish iron foundry industry, were divided into three groups based on the size of the companies, i.e. the number of employees. A database containing 2333 quartz exposure measurements for 11 different job descriptionswas used to create three models that covered time periods which reflected different work conditions and production processes: a historical model (1968– 1989), a development model (1990–2004), and a validation model (2005–2006). A linear mixed model for repeated measurements was used to investigate trends over time. In all mixed models, time period, company size, and job title were included as fixed (categorical) determinants of exposure. The within- and between-worker variances were considered to be random effects. A linear regression analysis was erformed to investigate agreement between the models. The average exposure was estimated for each combination of job title and company size.

Results: A large reduction in exposure (51%) was seen between 1968 and 1974 and between 1975 and 1979 (28%). In later periods, quartz exposure was reduced by 8% per 5 years at best. In the first period, employees at smaller companies experienced ~50%higher exposure levels than those at large companies, but these differences became much smaller in later years. The furnace and ladle repair job were associated with the highest exposure, with 3.9–8.0 times the average exposure compared to the lowest exposed group. Without adjusting for this autonomous trend over time, predicting early historical exposures using our development model resulted in a statistically significant regression coefficient of 2.42 (R2 5 0.81), indicating an underestimation of historical exposure levels. Similar patterns were seen for other historical time periods. Comparing our development model with our validation model resulted in a statistically significant regression coefficient of 0.31, indicating an overestimation of current exposure levels.

Conclusion: To investigate long-term trends in quartz exposure over time, overall linear trends can be determined by using mixed model analysis. To create individual exposure measures to predict historical exposures, it is necessary to consider factors such as the time period, type of job, type of company, and company size. The mixed model analysis showed systematic changes in concentration levels, implying that extrapolation of exposure estimates outside the range of years covered by measurements may result in underestimation or overestimation of exposure.

Place, publisher, year, edition, pages
Oxford, United Kingdom: Oxford University Press, 2012. Vol. 56, no 3, p. 362-372
Keywords [en]
Iron foundry, predicting exposures, quartz, time trends
National Category
Medical and Health Sciences Occupational Health and Environmental Health
Research subject
Occupational and Environmental Medicine
Identifiers
URN: urn:nbn:se:oru:diva-21296DOI: 10.1093/annhyg/mer106ISI: 000302015600011PubMedID: 22104319Scopus ID: 2-s2.0-84858671192OAI: oai:DiVA.org:oru-21296DiVA, id: diva2:482657
Available from: 2012-01-24 Created: 2012-01-24 Last updated: 2018-05-08Bibliographically approved
In thesis
1. Quartz in Swedish iron foundries: exposure and cancer risk
Open this publication in new window or tab >>Quartz in Swedish iron foundries: exposure and cancer risk
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aims of the studies underlying this thesis were to assess the exposure to quartz in Swedish iron foundries and to determine the cancer morbidity for Swedish foundry workers. A cohort of 3,045 foundry workers and a final measurement database of 2,333 number of samples was established.

The exposure measurements showed high levels of respirable quartz, in particular for fettlers and furnace and ladle repair workers with individual 8 hr TWA (GM=0.041 and 0.052 mg/m3; range 0.004-2.1 and 0.0098-0.83 mg/m3). In our database, the quartz concentrations as 8hr TWAs of current and historical data varied between 0.0018 and 4.9 mg/m3, averaging 0.083 mg/m3, with the highest exposures for fettlers (0.087 mg/m3) and furnace and ladle repair workers (0.42 mg/m3). The exposure for workers using respirators assuming full effect when used were assessed quantitatively, revealing workers with actual exposure exceeding the occupational exposure limits.

Overall cancer morbidity was not increased, but the incidence of lung cancer was significantly elevated (SIR 1.61; 95 % CI 1.20-2.12). In the cohort study, significant associations between lung cancer and cumulative quartz exposure were detected for quartz doses of 1-2 mg/m3 * year (SIR 2.88; 95 % CI 1.44-5.16) and >2 mg/m3 * year (SIR 1.68; 95 % CI 1.07- 2.52). These findings were not confirmed in the case-control analysis.

The agreement between the estimated exposure in our early historical model and the development model showed a regression coefficient of 2.42, implying an underestimation of the historical exposure when using the development model data. The corresponding comparison between the development and the validation model based on our survey data showed a B of 0.31, implying an overestimation of present exposures when using data from the validation model.

The main conclusions of the thesis are that certain foundry workers are still exposed to high levels of quartz, and the overall excess lung cancer could not be confirmed in the exposure-response analysis.

Place, publisher, year, edition, pages
Örebro: Örebro universitet, 2012. p. 78
Series
Örebro Studies in Environmental Science, ISSN 1650-6278 ; 16
Keywords
Case-control study, crystalline silica, exposure assessment, iron foundry, lung cancer, morbidity, occupational hygiene, respirable quartz
National Category
Earth and Related Environmental Sciences
Research subject
Enviromental Science
Identifiers
urn:nbn:se:oru:diva-20620 (URN)978-91-7668-837-3 (ISBN)
Public defence
2012-02-10, Bohmanssonsalen, B-huset, Universitetssjukhuset, Örebro, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2011-12-22 Created: 2011-12-22 Last updated: 2017-10-17Bibliographically approved

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