The emerging use of wood chips as an alternative energy source has led to an increase in the number of wood chip piles in domestic and institutional environments. The presence of these piles may have an adverse effect on the quality of the air around them because of microorganisms surviving or growing on the wood. Depending on the type of wood used and the harvesting, handling and storage conditions, fuel wood chips have been found to support growth of a wide range of microorganisms, particularly fungi. In indoor storage areas of wood chips, spores, cells and cell particles can become airborne and be inhaled by persons working in these areas. A number of methods exist to sample and monitor airborne microbial particles. These methods, particularly if two or more are combined, are suitable to detect and quantify viable and non-viable airborne microbial particles, to determine particle sizes and, in most cases, to identify to the species level the microorganisms collected. Many of the fungi, actinomycetes and other bacteria which have been reported to occur on wood chips are potentially pathogenic or toxigenic. Inhalation of microbial spores, cells or fragments, especially at high concentrations and small particle sizes, can lead to serious allergic reactions or pulmonary diseases. There is evidence that even low concentrations of microbial aerosols may have sub-acute long-term health effects. Some microorganisms appear to produce toxins in sufficient concentration that toxicoses can be caused by them via the inhalation route. Microbially produced volatiles have also been suspected to cause adverse health effects. Proper harvesting, storage and handling procedures can minimize the contamination of wood chips by microorganisms and subsequent contamination of the air. However, it appears that wood chips are almost never free of potentially harmful microbial species for which acceptable levels still need to be established.
