Exposure to airborne microbial components in autumn and spring during work at Danish biofuel plants

Exposure to microbial components can cause respiratory problems. The exposure levels to microbial components at biofuel plants are not known. Therefore, exposure to inhalable airborne fungi, bacteria, actinomycetes, endotoxin and NAGase was measured using personal and stationary samplers at five Danish biofuel plants in autumn and spring. The personal exposure levels to endotoxin (median = 55 EU m(-3)), thermophilic actinomycetes (median = 1.3 x 10(4) colony forming units (cfu) m(-3)), total bacteria (median = 48 x 10(4) cells m(-3)) and total fungi (median = 21 x 10(4) spores m(-3)) were, in general, high at the five biofuel plants. At straw reception areas, higher exposure to most microbial components was found in spring than in autumn. Endotoxin was found in higher concentrations at straw plants than at wood-chip plants, while the opposite was measured for Aspergillus fumigatus. Some tasks were associated with exposures to microorganisms and endotoxins at much higher levels than the suggested occupational exposure limits. For example, people working with a straw shredder for at least 30 min during a working day were exposed to a median endotoxin exposure of 23 775 endotoxin units (EU) m(-3). People working with estimating the water content in wood chips and repairing the chips cranes for at least 30 min during a working day were exposed to a median value of A. fumigatus of 6.7 x 10(4) cfu m(-3) and a median value of fungi of 70 x 10(4) spores m(-3). Consequently, this working environment may cause respiratory disorders in the people working at the plant. Differences in exposure levels were seen between the plants and this may partly be due to differences of the process equipment, tasks and the biofuel handled.