Objectives To study asthma, respiratory symptoms and lung function among energy plant employees working with woodchip, straw or conventional fuel.

Methods Respiratory symptoms in 138 woodchip workers, 94 straw workers and 107 control workers from 85 heating- or combined heating and power plants were collected by questionnaire. Spirometry, metacholine provocation tests and skin prick tests were performed on 310 workers. The work area concentrations of ‘total dust’ (n=181), airborne endotoxin (n=179), cultivable Aspergillus fumigatus (n=373) and cultivable fungi (n=406) were measured at each plant. Personal exposure was calculated from the time spent on different tasks and average work area exposures.

Results Median (range) average personal exposures in biofuel plants were 0.05 (0 to 0.33) mg/m³ for ‘total’ dust and 3.5 (0 to 294) endotoxin units/m³ for endotoxin. Fungi were cultivated from filters (straw plants) or slit samplers (woodchip plants); the average personal exposures were 5.230×10³ (118 to 1.85×10⁴) and 1.03×10³ (364 to 5.01×10³) colony-forming units/m³ respectively. Exposure levels were increased in biofuel plants compared with conventional plants. The prevalence of respiratory symptoms among conventional plant and biofuel plant workers was comparable, except for asthma symptoms among non-smokers, which were higher among straw workers compared with controls (9.4 vs 0%, p<0.05). A trend for increasing respiratory symptoms with increasing endotoxin exposure was seen with ORs between 3.1 (1.1 to 8.8) (work-related nose symptoms) and 8.1 (1.5 to 44.4) (asthma symptoms) for the most exposed group. Associations between fungal exposure and respiratory symptoms were less clear but suggested cultivable fungi to be associated with asthma symptoms and work-related respiratory symptoms. No associations were seen between lung function and the level of endotoxin or fungal exposure.

Conclusions Working with biofuel at an energy plant does not generally enhance the prevalence of respiratory symptoms. However, the exposure level to micro-organisms has an impact on the occurrence of respiratory symptoms among biofuel workers.