Will the most widely used biocide, formaldehyde, disappear completely from metalworking fluids? Will newer technologies replace this tried-and-true additive? Formaldehyde, a relatively small molecule (CH2O), performs important protective roles as an effective disinfectant, bactericide, fungicide and preservative in metalworking fluids. However, it also can be corrosive and highly toxic, and is classified as a probable human carcinogen. Its use, therefore, is heavily regulated, including strict standards for workplace exposure.
Consultant Fred Passman, Ph.D., president of BCA Inc. in Princeton, New Jersey, explained in an interview with LubesnGreases that a safer alternative is formaldehyde-releasing or formaldehyde-condensate compounds. These synthetic chemicals are the result of reacting formaldehyde with other molecules. Formaldehyde releasers such as HTHT (hexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine, the most widely used biocide for metalworking fluids) are stable in alkaline fluids (pH 9.0 to 9.5). But when formaldehyde releasers are near cell walls where the pH is acidic (pH 6.8 to 7.0), they can release formaldehyde that destroys bacteria and fungi. Passman emphasized that formaldehyde releasers are stable in properly formulated and maintained metalworking fluids, and they do not spontaneously release free formaldehyde.
Biocides are essential additives for emulsifiable oils, semi-synthetic and synthetic formulations, all of which contain water and make up an estimated 80 percent of the metalworking fluids market. (Straight oils, which do not contain water, do not need preservatives.) A metalworking fluid formulation of water, hydrocarbons, minerals and phosphorus-, nitrogen- and sulfur-containing additives provides a complete nutritional diet for microbes. Rapid growth of bacteria and fungi causes biodeterioration of metalworking fluids as supplied, during storage and in metalworking applications.
Biodeterioration does more than simply alter the composition and performance of metalworking fluids. Microbes proliferate rapidly and form biofilms and bioaerosols. A biofilm is a slimy layer of microbes embedded in a polymeric matrix. Biofilms form on solid surfaces and plug filters, cause corrosion, restrict fluid flow, and lead to other problems. Bioaerosols are airborne particles that contain microbes or materials that microbes release, which pose an inhalation hazard to workers. Only a small, select group of chemicals can control the rapid growth of the hundreds of species of bacteria and fungi that can be present in metalworking fluids, bioareosols and biofilms.
Chemical control of bacteria and fungi in metalworking fluids presents a paradox: the need to balance benefits of microbial contaminant control versus risks associated with improper handling of biocides. The federal Centers for Disease Control and Prevention advises that occupational exposures to metalworking fluids can cause respiratory (allergic rhinitis, industrial asthma, hypersensitivity pneumonia) and dermatological (skin rash) conditions.
Passman explained, A recirculating metalworking fluid provides an environment which, if uncontrolled, is conducive to microbe growth and aerosol formation. He continued, Biocides protect metalworking fluids from biodeterioration during blending, storage and end-use operations. They limit growth of bacteria and fungi and production of toxins. And they extend service life of fluids, which helps metalworking facilities comply with the 1977 Clean Water Act.
The Federal Insecticide, Fungicide and Rodenticide Act authorized the U.S. Environmental Protection Agency to regulate biocides. EPAs Office of Pesticide Programs approves biocides for target pests and specific sites, for example, metalworking fluids. Registration requires toxicity and environmental testing and expires after 15 years. While EPA classified formaldehyde as a probable human carcinogen, it did not extend this designation to formaldehyde releasers. Even so, uncertainty over possible future carcinogenicity testing of formaldehyde releasers and costly registration testing fees have motivated some chemical companies to discontinue formaldehyde-releasing biocide sales.
However, Passman noted that formaldehyde releasers are the least expensive microbicides, in both cost per pound and cost to use, that can control microbes in the broadest range of metalworking fluids. While formulators are reluctant to abandon tried-and-true formaldehyde releasers, they are concerned about possible limitations on their end-use by North American and European regulators. To learn more, a large audience of formulators, engineers and managers crowded into conference rooms in Chicago for the 5th International Conference on Metal Removal Fluids, sponsored in late September by the Independent Lubricant Manufacturers Association.
During the conference, Stefan Baumgartel, Ph.D., gave a presentation about new European legislation on behalf of Verband Schmierstoffe-Industrie, a Hamburg-headquartered organization that represents 74 companies that distribute and manufacture lubricants and additives in Germany. He informed the audience that the number of substances classified as dangerous was around 600 in 1967. That number passed 3,000 substances in 2010, and may exceed 50,000 in 2018 under Europes Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) program. However, classification as dangerous depends upon test data, he emphasized, and does not necessarily correspond to actual experience in commercial applications.
Baumgartel reviewed serious implications for biocides used in metalworking fluids. There were around 100 active substances (biocides) in 1999, but only 27 registered biocides in 2015. Eleven of these are formaldehyde releasers. Some customers started to hesitate to use formaldehyde releasers, even at concentrations below regulatory threshold values, after formaldehyde was re-classified as a carcinogen. He predicted that outcomes of REACH will include standardization of products (decrease in number and variety of chemicals), price increases, less innovation and registration of fewer new substances.
Another conference presenter, Michelle Rioux of Lonza Group, revealed that formaldehyde-releasing compounds comprise over 30 percent of the biocides used worldwide for metal removal fluids. As she pointed out, a metalworking fluid system is at its optimum state when a fresh charge of fluid is first installed. Over months of use, though, the physical and chemical properties of a coolant bath vary dynamically; water evaporates and is replaced, the sump is topped up with coolant concentrate, and biocides are added tank-side to counter microbial growth.
The Alpharetta, Georgia-based technical service manager recommended combining different classes of biocides that have different modes of action, but this requires a deep knowledge of the available biocides and of the bio-burdens in coolant systems. The concept of using more than one biocide and using biocides with different modes of action makes sense, she said. For example, formaldehyde-releasing compounds react with amino and sulfhydryl groups on proteins and deactivate microbes, while pyrithiones alter the membranes of bacteria and block respiratory enzymes. Caution must be taken in formulating these cocktails, she stressed: Not all biocides work well together; in fact, some are antagonistic.
Rioux also noted that some new technologies are on the horizon: adjuvants (non-biocidal additives) and synergistic amines that may boost biocide performance. Ominously, she cautioned that for biocide manufacturers, metalworking fluids are becoming an orphan industry, with daunting barriers to entry, high data requirements and discouraging regulatory hurdles.
Attendees also heard Matthias Hentz of Schulke & Mayr GmbH describe how quickly microbes can cause biodeterioration of metalworking fluids, if left uncontrolled. An initial bacterial count of 100 microbes per gram or milliliter of fluid, in the presence of water and nutrients, can soar to 800 in the first hour; 6,400 in the second hour; 51,200 in the third hour; 409,600 in the fourth hour; and more than 3×106 (3 million microbes!) in just five hours.
The EU countries plus Switzerland, Iceland and Norway have adopted the Biocidal Product Regulation, which requires the review of dossiers of test data and accepts or rejects active substances for the Annex I list. Individual member-states may review dossiers of listed substances and authorize or reject their use. He confirmed that only 27 chemicals (including 11 formaldehyde releasers) are listed now in Annex I for Product Type 13 – Working or cutting fluid preservatives (metalworking fluid preservatives). At the time this issue went to press, 24 chemicals were under review and three were approved. Moving forward, no additional biocides will be permitted, Hentz stated.
Hentz, who is based in Norderstedt, Germany, added that EU authorities classified formaldehyde as a Category 1B carcinogen. Effective Jan. 1, 2016, all EU suppliers must include the exploding man symbol on labels for all products that contain more than 0.1 percent or 1,000 ppm of free formaldehyde. Signal words are required on labels for products with higher levels. Companies that sell or use biocidal products in the EU will need to ensure that those containing formaldehyde releasers are compliant. Carcinogens such as formaldehyde may be used, provided that employers guarantee the protection of their workers. At this time, individual countries define Occupational Exposure Levels; a new EU-wide OEL of 0.4 ppm will be published in the REACH dossier.
New methods for identifying biohazards in metalworking fluids and mists (bioaerosols) were the topic of a presentation by Jodi Brookes, a graduate student at Sheffield Hallam University, U.K. She explained that more accurate methods are needed to identify toxins and enzymes (proteases) released by bacteria in metalworking fluids and investigate whether they cause respiratory conditions. Proteases are associated with allergic respiratory irritation and disease in other occupational settings that involve detergents, cleaners and baking products.
In her research, Brookes collected samples of metalworking fluids and analyzed them with two experimental techniques. First, she used zymography, a form of electrophoresis, to detect proteases and identify classes of enzymes. She observed proteolytic activity – the rapid breaking down of proteins into amino acids, spurred by enzymes – in 76 percent of the samples. Second, she used fluorescence substrate assay techniques to quantify amounts of protease in the samples. Looking ahead, her next step will be to apply these test methods to monitor microbial growth in metalworking fluids. She also plans to evaluate samples of metalworking fluid mists and compare proteases in mists and sumps. There is potential for bacterial proteases to be used as a marker to monitor microbial growth, Brookes believes.
Thus, while chemistry and engineering fields traditionally have dominated the development and use of metalworking fluids, biology is on the cusp of making critical new contributions to the industry.
Mary Moon, Ph.D., is a physical chemist with hands-on R&D and management experience in the lubricating oil and grease and specialty chemicals industries. She volunteers as Treasurer of the Philadelphia Section of STLE. Contact her at email@example.com or (267) 567-7234.