Characterization of microbial particle release from biomass and building material surfaces for inhalation exposure risk assessment.

A conceptual approach including measurements of materials at rest (step 1), measurements using a large rotating drum (step 2) or a Particle-FLEC (step 2) and measurements at a workplace (step 4) has been used to characterize the release of microbial components (bacteria, fungi, actinomycetes, endotoxin or enzymes) and particles from straw, wood chips or fungal cultures of different ages on gypsum boards. Repeated agitation or handling periods were included in step 2 and step 4. There was a low similarity between the amount of microbial components measured in step 1 and the aerosolized amount (step 2) from gypsum boards, wood chips and straw. Ratios between some microbial components measured at the workplace (step 4) and measured in step 2, showed similarities. Less than 1.3% of the total amount of microorganisms and endotoxin becomes airborne during 5 min of agitation of straw or wood chips. Most microbial components were released at higher rates during the first agitation period than during the following periods. However, differences were seen between different microbial components, and endotoxin from straw was released at the same rate in two successive agitation periods. Fungal particles smaller than spores were released from fungal colonized gypsum boards at amounts that were up to 30 times higher in the first agitation period compared with that in the following period, while fungal spores were released at amounts that were five times as high in the first period compared with that in the following period. In addition to differences between microbial components, the release patterns of microbial components were different for wood chips and straw. The time for maximum particle release to half particle release was longer for straw than for wood chips. The observation that some components, e.g. endotoxin, are released at the same rate in two successive handling steps, and that others (e.g. fungi) are mainly released initially, shows that the exposure period to different components from the same material differs in duration. The observed differences in the release patterns of different components and the differences between materials are important when preventive steps are to be taken, and it stresses the importance of applying a relevant sampling time and period in exposure assessments.