Acute Respiratory Effects of Endotoxin-Contaminated Machining Fluid Aerosols in Guinea Pigs

Exposure to machining fluid aerosols in the automotive industryis associated with a variety of respiratory symptoms includingcross-shift changes in pulmonary function, cough, asthma, andphlegm. Lubricating and cooling fluids used in machining operationsare predominantly water and thus are susceptible to microbialgrowth. In the present study, the role of endotoxin in the acutepulmonary injury produced by machining fluid aerosols was examinedin guinea pigs. Animals were exposed to nebulized water, unusedmachining fluid, or used machining fluid. At the end of a 3-hrexposure, specific airway conductance (SGaw) was not affectedby exposure to the vehicle water, but was decreased in a dose-dependentmanner by exposure to aerosols of the used machining fluid.SGaw decreased from preexposure baseline values by 0, 7, and40% in animals exposed to 1, 10, and 100 mg/m³ used machiningfluid, respectively. These exposure levels also produced acutelung injury as evidenced by changes in cellular and biochemicalindices in lavage fluid. These adverse respiratory effects mayhave been due to microbial contamination of the used machiningfluid as the aerosol exposures were associated with airborneendotoxin concentrations of 0.3, 1.9, and 5.3 µg/rn³,respectively. Animals exposed to aerosols of the endotoxin-freeunused machining fluid had no statistically significant adversefunctional, cellular, or biochemical effects except for a fourfoldincrease in neutrophils at 100 mg/m³. These results suggestthat contamination of machining fluid during use or storagemay lead to the adverse respiratory effects of aerosolized machiningfluids. To examine whether contaminating endotoxin was responsiblefor these respiratory effects, animals were exposed to 10 or100 mg/m³ unused machining fluid to which endotoxin was addedto provide airborne endotoxin concentrations similar to thosedetermined in the used machining fluid studies. Endotoxin-contaminatedunused machining fluid produced significant decrements in SGaw(14 and 38% for 0.9 and 8.2 µg/m³ endotoxin, respectively)as well as significant increases in cellular and biochemicalparameters of acute lung injury in lavage fluid. Thus, endotoxinmay play a significant role in the adverse respiratory effectsof aerosolized machining fluids.