Identifying the determinants of viable microorganisms in the air and bulk metalworking fluids

Exposure assessment was conducted for an epidemiologic study of the respira tory effects of exposure to metalworking fluids (MWF). As part of the study , airborne microorganisms were collected with a two-stage microbial impacto r, and a sample of the bulk soluble MWF was collected from each machine sum p, as well as information about the work environment. These data were then used to develop multivariate statistical models of the determinants bulk MW F and airborne microbial levels. Microbial concentrations in the bulk MWF r anged from 5 x 10(4) to 5 x 10(10) colony-forming units (CFU)/mL, with a ge ometric mean of 3.4 x 10(7) CFU/mL. The geometric mean airborne microbial l evel was 182 CFU/m(3) (for particles size <8 <mu>m) with a range of 1 to 83 08 CFU/m(3). In modeling the determinants of bulk microorganisms, fluid-rel ated factors were the most important characteristics associated with microb ial levels, followed by process-related and environmental factors. The fina l full multivariate model predicted a significant reduction in bulk microbi al levels by increasing pH of the fluid and reducing the amount of tramp oi l leaking into the fluid. For the airborne microbial models, process-relate d factors were the major characteristics associated with microbial levels, followed by factors related to worker activities and environmental factors. The final full multivariate model predicted a significant control of airbo rne microorganisms by increasing worker distance from the machine, reducing the number of machines within 10 feet of the worker, decreasing the bulk m icrobial levels, and adding machine enclosures. These models can be used to prioritize nonbiocidal interventions to control microbial contamination of the bulk MWF and the air.