Exposure Determinants of Wood Dust, Microbial Components, Resin Acids and Terpenes in the Saw- and Planer Mill Industry

Abstract

Objectives: Sawmill workers have an increased risk of adverse respiratory outcomes, but knowledge about exposure-response relationships is incomplete. The objective of this study was to assess exposure determinants of dust, microbial components, resin acids, and terpenes in sawmills processing pine and spruce, to guide the development of department and task-based exposure prediction models.

Methods: 2474 full-shift repeated personal airborne measurements of dust, resin acids, fungal spores and fragments, endotoxins, mono-, and sesquiterpenes were conducted in 10 departments of 11 saw- and planer mills in Norway in 2013-2016. Department and task-based exposure determinants were identified and geometric mean ratios (GMRs) estimated using mixed model regression. The effects of season and wood type were also studied.

Results: The exposure ratio of individual components was similar in many of the departments. Nonetheless, the highest microbial and monoterpene exposure (expressed per hour) were estimated in the green part of the sawmills: endotoxins [GMR (95% confidence interval) 1.2 (1.0-1.3)], fungal spores [1.1 (1.0-1.2)], and monoterpenes [1.3 (1.1-1.4)]. The highest resin acid GMR was estimated in the dry part of the sawmills [1.4 (1.2-1.5)]. Season and wood type had a large effect on the estimated exposure. In particular, summer and spruce were strong determinants of increased exposure to endotoxin (GMRs [4.6 (3.5-6.2)] and [2.0 (1.4-3.0)], respectively) and fungal spores (GMRs [2.2 (1.7-2.8)] and [1.5 (1.0-2.1)], respectively). Pine was a strong determinant for increased exposure to both resin acid and monoterpenes. Work as a boilerman was associated with moderate to relatively high exposure to all components [1.0-1.4 (0.8-2.0)], although the estimates were based on 13-15 samples only. Cleaning in the saw, planer, and sorting of dry timber departments was associated with high exposure estimates for several components, whereas work with transportation and stock/finished goods were associated with low exposure estimates for all components. The department-based models explained 21-61% of the total exposure variances, 0-90% of the between worker (BW) variance, and 1-36% of the within worker (WW) variances. The task-based models explained 22-62% of the total variance, 0-91% of the BW variance, and 0-33% of the WW variance.

Conclusions: Exposure determinants in sawmills including department, task, season, and wood type differed for individual components, and explained a relatively large proportion of the total variances. Application of department/task-based exposure prediction models for specific exposures will therefore likely improve the assessment of exposure-response associations.

Keywords: BW and WW variance; endotoxin; exposure prediction model; fungal fragments; fungal spores; mixed model; season; task-based and department-based.