Metalworking Fluids Bacteria and Fungi

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What are Metalworking Fluids?

Metalworking fluids (MWF) is the name given to a range of oils (mineral -petroleum, animal, marine, vegetable or synthetic oils) and other liquids that are used to cool and/or lubricate metal works during machining, grinding, cutting, milling, etc. There are four basic classes of Metalworking Fluids:

  • Straight Oils: Also called "cutting" or "neat" oils.
  • Soluble Oils: This category contains 30 to 85% severely refined petroleum oils, as well as emulsifiers to disperse the oil in water.
  • Semi-synthetic fluids: These contain 5 to 30% severely refined petroleum oils, 30 to 50% water and a number of additives.
  • Synthetic fluids: These do not contain petroleum oils. Instead, they use detergent-like components and other additives

Although each class will vary greatly in composition, each may contain additives such as sulphurized or chlorinated compounds, corrosion inhibitors, extreme pressure additives, emulsifiers, biocides, stabilizers, dispersants, defoamers, colorants, dyes, odorants and fragrances.

Why test for bacterial or fungal contamination of Metalworking fluids?

Although metalworking fluids are used throughout the industry by hundreds of thousands of workers safely, problems can develop when good hygiene practices are not followed or when fluids are not properly managed or maintained.

Bacterial and fungal contamination of metalworking Fluids (MWFs) is a major concern in the industries which use these fluids. It may cause equipment malfunction, off-odors, degradation in the fluid quality, economic losses and finally, they pose as a major health hazard. Several Gram +ve and Gram -ve bacteria are found as contaminants. These include Staphylococcus sp., Bacillus sp., Pseudomonas sp., Proteus sp. and Coliforms. Amongst the fungi, Aspergillus sp., Penicillium sp., Fusarium sp. and Cephalosporium sp. are found to be prevalent.

What are the health concerns?

Major health concerns of improperly managed Metalworking fluids include skin irritation, allergic contact dermatitis, irritation of the eyes, nose and throat, and, occasionally, breathing difficulties such as bronchitis and asthma. There is also evidence that some MWFs are associated with an increase in risk of certain cancers such as larynx, rectum, pancreas and skin.

What are the possible sources of contamination?

Most bacteria and fungi enter the system through the water supply, debris and build up in any equipment like hoppers, conveyors and sump pump. Therefore, it is highly recommended by experts to perform monitoring of metalworking fluids, associated machinery and pipe work, periodically, to ensure quality and safety.

What can MBL do for you?

At MBL, we perform total mould and bacterial counts of the samples to help you monitor quality standards of MWFs. MBL provides you with a Report of Analysis that indicates levels of mold and/or bacterial contamination and what can be regarded as good, reasonable or poor standards of fluid management.

Following are the acceptable indicator levels used to determine the standard of the fluids and required action:

  • < 103 CFU/mL: Good control. Bacteria are being maintained at low levels. No further action is required;
  • 103 to < 106 CFU/mL: Reasonable control. Review control measures to ensure levels of bacteria remain under control. Risk assessment should specify action to be taken. Biocides and or cleaning may be indicated. If biocides are used, expert advice should be obtained, and the concentration of biocides should be monitored
  • > 106 CFU/mL: Poor control. Immediate action should be taken in line with the risk assessment. Normally at very high levels draining and cleaning, should take place.

Comparing your counts with these levels will help you decide the quality of your metal working fluid. It will also help you select the treatment method if contamination is detected and economize performance.

Should you have a question concerning contamination of metalworking fluids or our services contact us via email, or fill out our Question Form and submit for priority attention. Your questions will be answered within 48-72 hours. For immediate assistance call 905-290-9101.

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Dr Jackson Kung'u
Dr. Jackson Kung’u is a Microbiologist who has specialized in the field of mycology (the study of moulds and yeasts). He is a member of the Mycological Society of America. He graduated from the University of Kent at Canterbury, UK, with a Masters degree in Fungal Technology and a PhD in Microbiology. He has published several research papers in international scientific journals. Jackson has analyzed thousands of mould samples from across Canada. He also regularly teaches a course on how to recognize mould, perform effective sampling and interpret laboratory results. Jackson provides how-to advice on mould and bacteria issues. Get more information about indoor mould and bacteria at
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