Endotoxin deposits on the inner surfaces of closed-face cassettes during bioaerosol sampling: a field investigation at composting facilities

Sampling on filters is the most widely used method in the literature for airborne endotoxins measurements (Duquenne et al., 2013). The protocols used involve the analysis of endotoxins collected only on the filters following elution. However, several studies have reported the presence of particle deposits on the inner surfaces of filter holders when sampling aerosols to perform gravimetric analyses of dust, analyses of organic compounds, metals and non-metals as well as silica (Harper and Demange, 2007). The deposits on the inner surfaces of samplers could account for a large fraction of the aerosol sampled and measurement protocols have been modified to include these deposits in the analysis of samples. The occurrence of endotoxin deposits on the inner surfaces of the closed-face filter cassette (CFC) has not been explored up to now and very few data are available on this issue. The objective was to measure the quantity of endotoxin deposits on the inner surfaces of the cassettes (sometimes referred to as “inner surfaces deposits”). More than a third of the samples presented a percentage of inner surface deposits higher than 40% of the total quantity of endotoxins collected (filter+inner surfaces). Omitting these inner surfaces deposits in the analytical process leads to measurement errors, resulting in underestimated exposures, and may affect the decision whether or not a result is acceptable in comparison to airborne concentration limits. The results of this study suggest including the endotoxins deposited on the inner surfaces of CFCs during analysis. However, additional research is needed in order to investigate the phenomenon in other occupational environments and to determine whether or not to consider the deposits for endotoxin exposure. The communication presents possible alternative technical solutions.