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Metalworking fluids provide an excellent environment for the growth and proliferation of a variety of bacteria and fungi. Historically, the incidence of infectious disease outbreaks at metalworking facilities has been rare. Consequently the primary focus of microbial contamination control efforts has been to prevent fluid biodeterioration. Research conducted over the past decade increasingly supports an argument for reevaluating microbial contamination control strategies. Although communicable disease risk remains low, there is likely to be an increased risk of toxin and allergen exposure for metalworking facility personnel routinely exposed to metalworking fluid aerosols. This paper summarizes current knowledge and suggests direction for further research on health risks associated with exposure to the biological constituents of metalworking fluid aerosols.


All recirculating metalworking fluid (MWF) systems provide aeration and surface area, both of which are conducive to microbial colonization and proliferation (Passman, (1988)).

As discussed by Rossmoore (Rossmoore, (1979)), some of the earliest reports on metalworking fluid microbiology (Bennett, et al., (1954), Tant, et al., (1956), Samuel-Maharajah, et al., (1956)) list potentially pathogenic bacteria that have been recovered from used emulsifiable oils. In 1956, Tant and Bennett (Bennett, et al., (1954)) reported their survey of metalworking fluids for potential pathogens. They defined potential pathogens as isolates representative of microbial genera that included bacteria known to cause disease, even if the isolated species were not known pathogens. Table 1, taken from the Tant and Bennett (Bennett, et al., (1954)) report illustrates the taxonomic diversity of MWF isolates. Many of the microbes listed in Table 1 are recovered rarely. Significantly, MWF taxonomic diversity is similar to that of public water supplies.

Tant and Bennett made no attempt to link MWF isolates with any disease reports, nor did they attempt to determine which isolates were able to proliferate and which were more likely to be incidental contaminants unlikely to persist. However, Wheeler (Bennett, et al., (1954)) did contract typhoid fever while working with the Salmonella typhosa (typhi) culture he isolated from a MWF sample.

Table 2 lists fungi that have been recovered from MWF. Acremonium, Aspergillus, Candida, Fusarium, Penicillium and Saccharomyces species are relatively common fungal isolates. The other fungi listed in Table 2 have been recovered infrequently.

There's no debate regarding the potential pathogenicity of some of microbes recovered from MWF. Despite considerable speculative and circumstantial evidence (Holden, (1977), Hill, et al., (1979), Cox-Ganser, et al., (1998)) that has been presented since 1956, there is little evidence for any direct cause and effect relationship between MWF exposure and infectious disease. However, there is a growing body of literature supporting hypotheses of toxic and allergic effects from MWF microbe exposure (Bernstein, et al., (1998), Robbins, et al., (1996)).

This paper summarizes the potential health risks associated with employee exposure to MWF microbes, and then describes the challenges confounding attempts to assess the actual risks.


With the exception of two conditions discussed below, a review of the various diseases caused by pathogens recovered from MWF is beyond the scope of this paper. For more information about diseases caused by specific microbes, the reader is referred to a manual of communicable disease (Chin, (2000)).

Microbes proliferating in MWF can cause three general types of health problems: disease, toxemia and allergy. Infectious disease occurs when a pathogenic microbe enters a susceptible host, proliferates and induces a body response. Examples of infectious disease include: salmonellosis, bacterial pneumonia and tuberculosis. Microbes that produce poisonous extracelluar substances cause toxemias. Microbe molecules and products can stimulate histamine responses in exposed individuals. This type of response is called an allergy.

Infectious Disease

Theoretically, a single pathogenic cell entering the body and settling at a suitable site can proliferate and lead to a disease state. In reality, a number of factors contribute to a microbe's ability to cause disease. These factors fall into two primary categories: pathogenicity and host susceptibility. A microbe's pathogenicity depends on its ability to cause damage to its host. Virulence is a semi-quantitative measure of a microbe's pathogenicity, and depends on the pathogen's biochemical, genetic and structural features. Host susceptibility reflects the host's inability to ward off infection. Generally speaking, healthy individuals are less susceptible to infection than are unhealthy individuals. The American Museum of Natural History has an excellent web site tutorial describing infectious disease (American Museum of Natural History (2001)). Kenneth Todar (Todar, (1998)) provides a detailed discussion of pathogenicity and susceptibility.

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Dr. Frederick Passman, PhD is a Certified Metalworking Fluids Specialist with over 35 years experience in Environmental & Industrial Microbiology. His company, Biodeterioration Control Associates, Inc. (BCA) provides clients with unparalleled expertise in Microbial Contamination Control.

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