Introduction: Objectives were to give an overview of endotoxin exposure and
its determinants in sewage treatment workers, and to study exposure to culturable and
non-culturable microorganisms and the applicability of the LAL assay in this work environment.
Material and methods: In 43 Dutch sewage treatment plants 470 full-shift,
123 task-based personal and 54 stationary inhalable dust samples were collected. Endotoxin
concentration was determined with the LAL-assay. Mixed effects models were
used to investigate possible determinants of exposure. Simultaneous parallel fi lter samples,
impinger samples and viable total bacteria and Gram-negative bacterial samples
were taken to compare analytical techniques. Filter and impinger samples were analyzed
with the LAL-assay, gas chromatography-mass spectrometry (GC-MS) and fl uorescence
microscopy. Results: Endotoxin exposure levels were moderate to low (geometric mean
personal exposure 27 EU/m³, stationary 33 EU/m³, task-based 64 EU/m³), yet differences
between jobs and sources and some determinants of exposure were identifi ed. Exposure
varied more from day to day than between workers. Concentrations in fi lter samples were
higher and more consistent than in impinger samples. Fungi and Gram-positive bacteria
were found in higher levels than Gram-negative bacteria. The LAL assay and GC-MS
showed comparable endotoxin levels. Discussion and conclusion: Endotoxin exposure in
Dutch sewage treatment workers was relatively low. Comparison of sampling and analytical
techniques suggests that the LAL-assay did not result in much exposure misclassifi
cation. It thus seems justifi ed to perform fi lter measurements in combination with the
LAL-assay to measure endotoxin exposure in sewage treatment plants.