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Microbial Contaminations in Metalworking Fluids

Occupational Exposure To Metalworking Fluids and Microbial Testing

By Dr. Michael Berg, EMLab P&K Senior Molecular Biologist

Metalworking fluids (MWFs) are used in industrial machining and grinding operations to reduce heat and friction and to improve product quality. They are categorized into straight or neat oils, soluble oils, semi-synthetic and synthetic fluids. Generally, MWFs are complex mixtures containing a number of additives to improve performance and stability including emulsifiers, anti-weld agents, corrosion inhibitors, extreme pressure additives, buffers, dyes, odorants and biocides. In use, the fluid complexity is compounded by contamination with substances from the manufacturing process such as tramp oils, hydraulic fluids and particulates from grinding or machine operations. Furthermore, water-based MWFs may support microbial growth adding biological contaminants in the form of bacterial and fungal cells and their related byproducts such as endotoxins, exotoxins and mycotoxins. Each component of the complex mixture can contribute to health effects and pose a risk to workers handling machines and metalwork.

It is estimated that over a million workers in approximately 185,000 workplaces are potentially exposed to MWFs in the US. The majority of those workplaces (>85%) are establishments with less than 500 employees. Exposure to MWFs occurs via breathing aerosols generated in the machining process, or through skin contact while handling parts, tools, and equipment covered with the fluids. The National Institute of Occupational Safety and Health (NIOSH) recommends that exposures to MWF aerosols be limited to 0.4 milligrams per cubic meter of air.

A variety of health effects have been linked to occupational exposure to MWFs including hypersensitivity pneumonitis (HP), chronic bronchitis, impaired lung function and work-related asthma. Skin exposures are most commonly associated with allergic and irritant dermatitis (skin rash). In addition, there is substantial evidence suggesting that past exposure to some MWFs lead to cancer. To reduce the risk of unnecessary exposure, proper management of the MWFs is essential. This includes but is not limited to the use of personal protective equipment (PPE) and splash guards, employee training, proper choice of MWFs and additives, optimization of the delivery system and ventilation, and testing of the fluids for microbial contamination.

Testing for microbial contamination in MWFs typically entails endotoxin analysis and detection of Mycobacteria. Endotoxins are a component of the lipopolysaccharide complexes that make up a part of the outer layer of the cell wall of most gram-negative bacteria and some cyanobacteria. Symptoms of endotoxin exposure in humans include coughing, wheezing, fever, chills and decreased FEV (forced expiratory volume). Endotoxins may also potentiate reactions and exacerbate illness caused by other agents. Simpson et al. (2003) propose the following categories for endotoxin concentrations in MWFs and report their findings of endotoxin concentrations in a number of machine sumps.

Sump Endotoxin Levels

Figure 1: Sump Endotoxin Levels.
Copyright © 2010 EMLab P&K

Environmental mycobacteria are frequently isolated from MWFs and have been increasingly recognized as opportunistic pathogens. The most common manifestation of disease associated with environmental mycobacteria is HP, an inflammation of the alveoli in the lung. There is substantial evidence for an association of HP with exposure to mycobacteria-conatminated MWFs. Fast growing (less than 7 days to form visible colonies), non-pigmented, environmental mycobacteria, such as Mycobacterium immunogenum and M. chelonae, have been isolated in MWFs from engine plants reporting cases of HP. Due to their thick cell wall and slow growth, environmental mycobacteria are more resistant to biocide and heat treatments compared to many other bacteria. In the laboratory, environmental mycobacteria can be isolated and characterized via culture on selective media and acid-alcohol fast stain.

1. CDC: Metalworking Fluids

2. OSHA: Metalworking Fluids

3. NIOSH. (1998). Criteria for a recommended standard: occupational exposure to metalworking fluids. DHHS (NIOSH) pub. 98-102. Cincinnati, OH: National Institute for Occupational Safety and Health.

4. Simpson AT, Stear M, Groves JA, Piney M, Bradley SD, Stagg S, Crook B. (2003) Occupational exposure to metalworking fluid mist and sump fluid contaminants. Ann Occup Hyg; 44: 17-30.

5. Park D, Byungsoon C, Shinbum K, Hyunseok K, Kuidon J, Jongdeuk J (2005) Exposure assessment to suggest the cause of sinusitis developed in grinding operations utilizing soluble metalworking fluids. J Occup Health 47: 319-326.

6. Shelton BG, Flanders WD, Morris GK (1999) Mycobacterium sp. as a possible cause of hypersensitivity pneumonitis in machine workers. Emerging Infectious Diseases 5(2): 270-273.


This article was originally published on January 2011.