Determinants of microbial exposure in grain farming.

OBJECTIVES: Exposure to organic dust containing high concentrations of microorganisms is common in grain farming, although the farmers have practices to counteract microbial growth to obtain optimal grain yields. We investigated the influence of weather and production practices on personal microbial exposure during grain work.

METHODS: Airborne dust was collected by personal sampling during threshing and storage work on 92 Norwegian farms. The personal exposure for bacteria, endotoxin, fungal spores and hyphae, beta-(1-->3)-glucans and actinomycetes was quantified and compared with climatic data expressed as fungal forecasts from the grain growth season and production practices as reported by farmers.

RESULTS: Farmers were exposed to a geometrical mean of 4.4 mg m(-3) inhalable dust [geometrical standard deviation (GSD) = 4.0], 4 x 10(6) m(-3) bacteria and fungal spores (GSD = 5.2 and 5.9, respectively), 5.9 x 10(3) EU m(-3) of endotoxins (GSD = 8.6), 2 x 10(5) m(-3) actinomycetes (GSD = 15.3), 120 mug m(-3) beta-(1-->3)-glucans (GSD = 4.7) and 5 x 10(5) AU m(-3) of hyphae (GSD = 4.4). Univariate associations were found between one or several of these microbial factors and work operation, visible fungal damage, grain species, lodging of grain, storage technology or harvester type. As assessed by general linear models, storage work was the main predictive determinant for microbial exposure, although grain species and visible fungal damage also were also important. Wet and warm weather throughout the grain growth season were associated with elevated exposure for inhalable dust, beta-(1-->3)-glucans, endotoxins and hyphae during threshing. The beta-(1-->3)-glucan exposure could biologically be explained by the fungal spore and hyphal exposure, both variables contributing equally. However, spores were most important during storage work, whereas only hyphae were predictive during threshing.

CONCLUSIONS: Farmers were exposed to high levels of microorganisms and their components during dusty grain work. Dust prevention and protection may reduce microbial exposure, and may be particularly important in areas with frequent fungal forecasts, when fungal damage has been observed, during storage work or when handling barley.