Comparison of Sampling Media for Endotoxin-Contaminated Aerosols

In this study the influence of collection media and sampling method on endotoxin extraction for a variety of endotoxin-contaminated aerosols was examined. A first set of experiments compared endotoxin concentrations on eight different filter media after sampling from a chamber containing a saline endotoxin aerosol. Glass fiber (GF) and cellulose acetate (CA) filters were equivalent and showed significantly higher amounts of extractable endotoxin than any other filter type. Polysulfone, polyvinyl chloride (PVC), and polytetrafluoroethylene (PTFE) filters indicated two-thirds of the endotoxin concentration of GF and CA filters; concentrations on nylon, polycarbonate, and silver membrane filters were significantly lower (one-tenth that of GF and CA filters). The presence of chloride anion was comparable for all filter media from which significant amounts of endotoxin could be extracted, suggesting that extraction of endotoxin, but not chloride anion, was dependent on filter type. In subsequent experiments, GF, CA, and PVC filters were used to measure endotoxin concentrations in cotton dust and machining oil aerosol atmospheres. For cotton dust aerosols, CA and PVC filters showed approximately equal amounts of extractable endotoxin and were superior to GF filters. Significantly greater amounts of endotoxin were extracted from CA than either PVC or GF filters when sampling machining oil aerosols. Cascade impactors equipped with Mylar substrates demonstrated levels of endotoxin equivalent to the best filters for endotoxin/saline and cotton dust aerosols; no endotoxin was found when sampling machining oil mists. It was concluded that the extraction efficiency of endotoxin from different filter media was dependent on aerosol type, and that cascade impactors could not be employed successfully for the oil aerosols.