ENVIRONMENTAL ASSESSMENT OF AEROSOLS, BIOAEROSOLS, AND AIRBORNE ENDOTOXINS IN A MACHINING PLANT

Bioaerosol monitoring was undertaken in a 185,000 m(2) engine plant em ploying 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 machi ning sites represented areas supplied with three different meta[workin g fluid (MWF) formulations from eight separate sump systems. Bulk in - use MWF samples were collected at the machining sites and compared wit h air measurements at the same sites. Gravimetric concentration of aer osol averaged 1.24 mg/m(3) on the older engine line and 0.74 mg/m(3) o n the new ine. The inhalable fraction was 87% of the aerosol and 57% w as respirable. Formaldehyde yielded from biocides averaged 0.22 mg/m(3 ) and was as high as 0.62 mg/m(3). Endotoxin concentration ranged from 39 to 166,000 endotoxin units (EU)/mL in the bulk MWF and from below detection (<4 EU/m(3)) to 790 EU/m(3) in air. airborne viable fungi wa s generally low (<470 colony-forming units [CFU]/m(3)) while viable me sophilic bacteria ranged from 40 to 4000 CFU/m(3). Airborne total bact eria (culturable + nonculturable) ranged from 5560 org/m(3) to 468,000 org/m(3). Concentrations of endotoxin in the MWF were significantly c orrelated with bulk viable mesophilic bacteria (p<0.0001,r=0.62) and G ram-negative bacteria (p=0.014, r=0.54). Airborne endotoxin concentrat ions demonstrated significant associations with bulk endotoxin (p=0.02 2, r=0.44) and bulk total organisms (p=0.016, r=0.80),but correlations with airborne organisms were weak. Airborne endotoxin was strongly co rrelated 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 tre mendous temporal and spatial variability and the dependence on adjustm ents of MWF constituents. The dynamics of the microorganisms in the MW F and the biocides added to control them suggested that close monitori ng of MWF and early intervention when microbiota increase can help pre vent excessive concentrations of airborne endotoxin.