Abstract
Bioaerosol monitoring was undertaken in a 185,000 m2 engine plant employing 900 production workers and 300 in the skilled trades. Sampling was performed across four seasons in nine locations: four sites were on an older (1970s) engine line, four sites on a new engine line with improved engineering controls, and one site was in assembly. The machining sites represented areas supplied with three different metal-working fluid (MWF) formulations from eight separate sump systems. Bulk in-use MWF samples were collected at the machining sites and compared with air measurements at the same sites. Gravimetric concentration of aerosol averaged 1.24 mg/m3 on the older engine line and 0.74 mg/m3 on the new line. The inhalable fraction was 87% of the aerosol and 57% was respirable. Formaldehyde yielded from biocides averaged 0.22 mg/m3 and was as high as 0.62 mg/m3. Endotoxin concentration ranged from 39 to 166,000 endotoxin units (EU)/mL in the bulk MWF and from below detection (<4 EU/m3) to 790 EU/m3 in air. Airborne viable fungi was generally low (<470 colony-forming units [CFU]/m3) to while viable mesophilic bacteria ranged from 40 to 4000 CFU/m3. Airborne total bacteria (culturable+nonculturable) ranged from 5560 org/m3 to 468,000 org/m3. Concentrations of endotoxin in the MWF were significantly correlated with bulk viable mesophilic bacteria (p<0.0001, r=0.62) and Gram-negative bacteria (p=0.014, r=0.54). Airborne endotoxin concentrations demonstrated significant associations with bulk endotoxin (p=0.022, r=0.44) and bulk total organisms (p=0.016, r=0.80), but correlations with airborne organisms were weak. Airborne endotoxin was strongly correlated with the gravimetric aerosol concentration (p<0.0001, r=0.83), suggesting that a standard based on gravimetric aerosol concentration is a reasonable surrogate for endotoxin in this environment. Perhaps most striking about the measured bioaerosol concentrations was the tremendous temporal and spatial variability and the dependence on adjustments of MWF constituents. The dynamics of the microorganisms in the MWF and the biocides added to control them suggested that close monitoring of MWF and early intervention when microbiota increase can help prevent excessive concentrations of airborne endotoxin.