Immune modulating effects of continuous bioaerosol and terpene exposure over three years among sawmill workers in Norway.

Objectives: Exposure to wood dust, resin acids, microbial and volatile components among sawmill workers may impair respiratory health, with inflammation indicated as a key mechanism. Previous, mostly cross-sectional studies have shown mixed results, and a conclusive association between wood dust exposure and chronic respiratory inflammation has therefore not yet been established. This study assessed associations between exposure to bioaerosols and volatile terpenes and serum inflammatory marker levels over three years.

Methods: Serum biomarkers and blood cell counts were analyzed based on 702 observations from 450 exposed sawmill workers and 102 observations from 65 unexposed sawmill workers in Norway at baseline and after three years. Job-exposure-matrices, based on measurements among the same cohort, were used to assess exposures for wood dust, endotoxins, resin acid, monoterpenes, fungal spores, and fungal fragments. Changes in exposures, biomarkers and cell counts over the study period, as well as group differences and potential cause-and-effect associations were assessed using linear mixed regression.

Results: Exposures were relatively low and below occupational limits, although variances were relatively high (GSD_tot 2.1-8.3), largely driven by differences between workers (GSD_bw 1.9-7.8). Serum CC-16 and mCRP were slightly higher after three years, whereas IL-1β, TNF-α and IL-10 levels were significantly lower among exposed compared with unexposed workers. Exposures positively associated with increases in biomarker levels included endotoxin with mCRP, monoterpenes with IL-10, and fungal spores with TNF-α and IL-8. Exposed workers had higher counts of total leucocytes, neutrophils, lymphocytes and basophils after three years. Several of the increased leucocyte counts were associated with concurrent increase in mCRP and IL-6 concentrations, predominantly in the exposed group. Conversely, increased CC-16 levels were associated with lower leucocyte and neutrophil counts, mainly in the unexposed group.

Conclusion: Continuous exposure to wood dust and related components for three years appears to induce a chronic low-grade inflammatory response among sawmill workers with a shift in cytokine profiles towards a less regulated, potentially more muted immune state.