Quality control of endotoxin measurement in dust samples/Qualitätskontrolle der Endotoxinmessung in Staubproben

Endotoxin activity determination is a common tool and a surrogate marker for bioaerosol assessment and is used at workplaces especially for this purpose. The reliability of the methods used for quantification in airborne dust samples is important for exposure estimation and thus for assessing the workplace situation. Within the scope of this study, the reproducibility of the endotoxin activity values determined with the two common methods, the LAL test and the rFC test, should be determined and compared. 21 water-based dust extracts from electrostatic dust collectors (EDC) were used for repeated endotoxin quantification using LAL and rFC test. As a result, twelve independent standard curves (0-50 EU/ml) were applied showing a median coefficient of variation (CV) of 9% for rFC and 12% for LAL test. The measured endotoxin activities of the samples could be reproduced within one test as well on three consecutive days. The CV of the 7- and 8-fold measured samples was below 20%. in 92% (LAL) and 93% (rFC) of the samples. Multiple measurements of the same sample showed that the results of LAL and rFC tests are highly reproducible. To eliminate interfering factors detected by recovery of spiked samples, dilutions of the samples are valuable methodological tools. This study demonstrates that quality-assured quantification of endotoxin activity is possible with both methods and is suitable for workplace measurements using the respective Standard Operation Procedure (SOP).