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

Abstract

Exposure to machining fluid aerosols in the automotive industry is associated with a variety of respiratory symptoms including cross-shift changes in pulmonary function, cough, asthma, and phlegm. Lubricating and cooling fluids used in machining operations are predominantly water and thus are susceptible to microbial growth. In the present study, the role of endotoxin in the acute pulmonary injury produced by machining fluid aerosols was examined in guinea pigs. Animals were exposed to nebulized water, unused machining fluid, or used machining fluid. At the end of a 3-hr exposure, specific airway conductance (SGaw) was not affected by exposure to the vehicle water, but was decreased in a dose-dependent manner by exposure to aerosols of the used machining fluid. SGaw decreased from preexposure baseline values by 0, 7, and 40% in animals exposed to 1, 10, and 100 mg/m3 used machining fluid, respectively. These exposure levels also produced acute lung injury as evidenced by changes in cellular and biochemical indices in lavage fluid. These adverse respiratory effects may have been due to microbial contamination of the used machining fluid as the aerosol exposures were associated with airborne endotoxin concentrations of 0.3, 1.9, and 5.3 μg/rn3, respectively. Animals exposed to aerosols of the endotoxin-free unused machining fluid had no statistically significant adverse functional, cellular, or biochemical effects except for a fourfold increase in neutrophils at 100 mg/m3. These results suggest that contamination of machining fluid during use or storage may lead to the adverse respiratory effects of aerosolized machining fluids. To examine whether contaminating endotoxin was responsible for these respiratory effects, animals were exposed to 10 or 100 mg/m3 unused machining fluid to which endotoxin was added to provide airborne endotoxin concentrations similar to those determined in the used machining fluid studies. Endotoxin-contaminated unused 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 biochemical parameters of acute lung injury in lavage fluid. Thus, endotoxin may play a significant role in the adverse respiratory effects of aerosolized machining fluids.