A model for predicting endotoxin concentrations in metalworking fluid sumps in small machine shops

Methods: In British Columbia, Canada, nineteen small machine shops which us ed waterbased metalworking fluids (MWF) were examined. One bulk MWF sample was taken from each independent sump (N=140) and tested for endotoxin using the Limulus Amoebocyte Lysate assay. Factors that might influence the MWF sump endotoxin concentration were investigated using mixed effect multiple regression modelling to control for repeated measures within shops. Results: The geometric mean (GM) endotoxin concentration was 6791 EU/ml. Co ntamination of MWF with tramp oil, MWF pH, MWF temperature, and MWF type we re significant predictors of sump fluid endotoxin concentration (model P=0. 0001, ordinary least squares R-2 =0.36). Concentrations of endotoxin in sum p fluids were increased by MWF contamination with tramp oils such as hydrau lic oils, preservative oils, spindle oils, slidway lubricants, gear lubrica nts, and greases (model predicted GM=17 400 EU/ml vs. 1600 EU/ml without tr amp oil). Concentrations were also elevated where pH was lower than 8.5 (pr edicted GM=10 600, vs 3600 EU/ml for pH 8.5 to 9.5), where soluble fluids w ere used (predicted GM=11 800 vs. 2800 EU/ml for synthetic fluids), and whe re sump fluid temperatures were higher (predicted GM=2600 EU/ml at 11 degre esC vs. 21500 EU/ml at 32 degreesC). The within-shop correlation of sump bu lk fluid endotoxin concentrations was 38%. Conclusions: Minimizing tramp oil contamination, using synthetic fluids, an d monitoring pH and temperature would be valuable tools for controlling end otoxin contamination in MWF sumps. In addition, since there was correlation within-shop, contamination of one sump in a shop may suggest changing the fluids in all. (C) 2001 British Occupational Hygiene Society. Published by Elsevier Science Ltd. All rights reserved.