Endotoxin exposure in sewage treatment workers: investigation of exposure variability and comparison of analytical techniques.
BACKGROUND
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.


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 filter 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 fluorescence microscopy.


RESULTS
Endotoxin exposure levels were moderate to low (geometric mean personal exposure 27 EU/m(3), stationary 33 EU/m(3), task-based 64 EU/m(3)), yet differences between jobs and sources and some determinants of exposure were identified. Exposure varied more from day to day than between workers. Concentrations in filter 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.


CONCLUSIONS
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 misclassification. It thus seems justified to perform filter measurements in combination with the LAL-assay to measure endotoxin exposure in sewage treatment plants.
Spaan
Suzanne
S
Institute for Risk Assessment Sciences, division of Environmental Epidemiology, Utrecht University, Utrecht, The Netherlands. suzanne.spaan@tno.nl
Smit
Lidwien A M
LA
Eduard
Wijnand
W
Larsson
Lennart
L
Arts
Huib J J M
HJ
Wouters
Inge M
IM
Heederik
Dick J J
DJ
D000395:Air Pollutants, Occupational / Q000032:analysis*; D004391:Dust / Q000032:analysis; D004731:Endotoxins / Q000009:adverse effects / Q000032:analysis*; D004784:Environmental Monitoring; D062665:Epidemiological Monitoring; D005374:Filtration / Q000379:methods; D005658:Fungi / Q000302:isolation & purification; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods; D006094:Gram-Positive Bacteria / Q000302:isolation & purification; D006801:Humans; D019570:Inhalation Exposure / Q000032:analysis*; D009426:Netherlands / Q000453:epidemiology; D016273:Occupational Exposure / Q000032:analysis*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012722:Sewage / Q000009:adverse effects / Q000737:chemistry / Q000382:microbiology
D000395:Air Pollutants, Occupational; D004391:Dust; D004731:Endotoxins; D012722:Sewage