Endotoxin deposits on the inner cassette walls during bioaerosol sampling: a field investigation in composting facilities

A set of 270 bioaerosol samples was collected among 15 composting facilities using 37 mm closed-face sampling cassettes. The aim of the study was to investigate the endotoxin deposits on the inner cassette walls during sampling and to the issue is a relevant one for the assessment of exposure to endotoxins. The results show that deposition of endotoxin may occur during sampling and sample transport. Wall losses may represent a large and variable amount of the sampled endotoxins. More than 33 % of samples exhibited inner cassette walls deposits over 40 % of the total (filter+walls) endotoxins sampled. Wall deposits induce measurement bias and the underestimation of real exposure levels when not taken into account in the analytical process; this may affect the interpretation of results. The new data suggest that endotoxin deposits on the inner cassette walls should be taken into account in the analytical process. Our study also recommends further researches to determine whether endotoxin deposits are a relevant issue in other occupational environments and to imagine technical alternatives to overcome them.