Historical Asbestos Measurements in Denmark-A National Database

Abstract

Objectives: Due to the long lag-time for health outcomes, historical asbestos exposure measurements are valuable to support assessments of associated occupational health effects, and also to assess time trends and effects of preventive measures.

Methods: Different sources of stored data were collated, assessed and refined to create a harmonized database on historical asbestos fibre concentrations measured in specific work tasks and different industries. The final database contains 9236 asbestos measurements from Danish workplaces collected from 1971 to 1997.

Results: The geometric mean of asbestos concentrations in different occupations and tasks ranged from 0.003 to 35 fibres cm^-3. Highest concentrations were registered during handling of asbestos products in the construction services during the period 1981-1997. Although all the measured asbestos exposures without the use of respiratory equipment by the worker in the period of 1971-1997 exceeded the current 8-h time-weighted average exposure limit of 0.1 fibres cm^-3, the majority of samples collected in the earlier period of 1971 to 1980 did not exceed the exposure limit of 2 fibres cm^-3, which was in place at the time. All exposure data obtained from 1980 and onwards were found to be one seventh of the mean fibre concentrations in the previous measurement period. The impact of time shows a clear exponentially decreasing trend-line.

Conclusions: Despite limitations in coverage of different occupations and tasks associated with the inventoried historical asbestos measurements, the data are helpful to identify specific work scenarios within an industry, where relatively high asbestos exposure levels may still occur or have occurred from 1971 to 1997.

Keywords: asbestos fibres; database; historical exposure measurements; occupational exposure; personal sampling; phase contrast microscope.

Figure 1

Vertical box plots for the measured personal exposure asbestos concentrations (with N ≥ 4) without respiratory protective equipment being used by the worker (unless specified) for each industry code for the period 1971–1980 and 1981–1997: (a) Manufacturing of asbestos products; (b) Transport, storage and package; (c) Maintenance jobs; (d) General supervision and inspection tasks; and (e) Cleaning activities. The lower and upper limits of the box plots represent the 25th and 75th percentiles, and the line within the box marks the median. Whiskers (error bars) above and below the box indicate the maximum and the minimum fibre concentration excluding high values (marked as *), respectively. N: total number of measurements available; Manuf: manufacturing; Auto: Automotive.

Figure 2

Vertical box plots for the measured personal exposure asbestos concentrations (with N ≥ 4) without respiratory protective equipment being used by the worker (unless specified) during active handling of asbestos products in each industry code for the period 1981–1997. The lower and upper limits of the box plots represent the 25th and 75th percentiles, and the line within the box marks the median. Whiskers (error bars) above and below the box indicate the maximum and the minimum fibre concentration, respectively. N: total number of measurements available.

Figure 3

Personal exposure asbestos exposure concentrations against sampled year. The grey and blue lines stand for the log-linear gamma model fit applied for industry sector 36993 and 38439, respectively. All the personal measurements at the asbestos cement plant correspond to exposures without use of RPE, while at the automotive industry it is unknown if RPE was used. Horizontal red lines show the different health guideline values over time. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).

Figure 4

Personal exposure asbestos concentrations in each occupational category for the period 1971–1980 or 1981–1997 compared to the current 8-h TWA health guideline value (horizontal dashed line). The white, grey and black dots correspond to minimum, geometric mean (GM) and maximum asbestos concentration, respectively. Concentrations = 0 fibres cm⁻³ are represented in y = 0.01 with an arrow towards down. All the personal measurements which workers used respiratory protective equipment were taken outside the mask unless specified; *: Mechanical ventilation used from 1977 onwards; ^a Measurements taken inside the respiratory protective equipment; Manuf.: manufacturer; Const.: construction.