Verena Liebers

Endotoxins are ubiquitous in the environment and represent important components of bioaerosols. High exposure occurs in rural environment and at several workplaces (e.g. waste collecting, textile industry etc.). Adverse effects on human health induced by inhalation of endotoxin are described in several studies. Up to now the endotoxin levels are mainly measured using the Limulus amoebocyte-lysate (LAL) assay. This assay is well established, but for a suitable characterization of bioaerosols more parameters are necessary. Additional information, e.g. concerning the pyrogenic activity of organic dust samples may be delivered by whole blood assay. Whereas on the one hand protection measures at workplaces are demanded to avoid lung function impairment due to endotoxin exposure, on the other hand a protective effect of exposure to microbial agents like endotoxins with regard to allergy development has been observed. On the cellular level toll-like receptor 4 (TLR4) and IL-1 receptor as well as surface molecules like CD14 have been shown to play a pivotal role in the endotoxin activation cascade. In this review we summarize the mechanism of endotoxin recognition and its manifold effects on human health.

Endotoxin has been identified as important component of organic-dust exposure and is suspected as main cause of work-related adverse health effects in dusty areas. Although the determination of endotoxin levels by using the Limulus amoebocyte lysate (LAL) assay is internationally accepted, reliability and variation of values measured with this test remain a point of discussion. Therefore, the purpose of the study was to determine the influence of different parameters on endotoxin activity measured in airborne samples. This study thus analyzed: (a) dust filter extraction procedures, (b) storage of samples, (c) usage of different commercially available LAL assays, and (d) results of the whole blood assay (WBA) compared to the LAL test. Using a parallel sampler, 120 filters were loaded with dust at 4 different occupational settings and extracted in 2 labs using a standardized protocol. Parameters like Tween in the extraction medium, extraction volume, centrifugation speed, and material of tubes used for extraction were tested. The LAL test and the WBA were able to determine the differences in dust load of filters obtained from the settings investigated. In addition, results varied significantly with modifications in extraction procedures. Using Tween for filter extraction mainly influenced the resulting endotoxin activity. In addition, LAL test differences according to manufacturer of LAL test, extraction volume, and whether the samples are freshly processed or frozen also resulted in significant variations in the endotoxin levels. In conclusion, a reliable assessment of exposure to endotoxin activity is only possible if standard operation procedures (SOPs) for sampling and determination are established.

Background: Endotoxins are commonly found at workplaces where large amounts of bioaerosols are generated. In Germany, especially since the Ordinance on Safety and Health Protection related to work involving biological agents (Biostoff‐Verordnung) became effective (1999), threshold limit values are widely discussed. Up to the present, endotoxin values are measured with non‐uniform methods and therefore values are of limited benefit for classification of exposure groups. In Germany there is no threshold limit value for endotoxin.Methods: Relevant literature of the last 20 years was selected from Medline and discussed.Results: In this review we focused on the impact of endotoxin exposure on human health with special respect to the measurements on workplace and methodological aspects of endotoxin determination. Methods for sampling and endotoxin determination have to be validated, optimized, and standardized first.Conclusion: The adverse health effects of endotoxins are known, standardization of measurements is a necessary goal and protection measures should be established immediately. Am. J. Ind. Med. 2006.