In 1971, the Occupational Safety and Health Administration set a permissible exposure limit (PEL) for metalworking fluids, requiring that no worker be exposed to more than 5 milligrams of mineral oil-based metalworking fluids per cubic meter of air (5 mg/m3) over an eight-hour period. The United Auto Workers petitioned OSHA in 1993 to lower that mist standard to 0.5 mg/m3, a drastic reduction of 90 percent. The petition eventually was rejected, and almost four decades after that PEL first went into effect the standard still stands.
Metalworking fluids have moved on to new chemistries since the 1970s – U.S. metalworking fluids today are water-based, wholly synthetic or made with safer, highly refined mineral oils. And automakers and other large industries agreed in the mid-1990s to reduce mist levels in their plants well below what OSHA allows. But that doesnt mean the issue has been put to rest.
Fluid suppliers are still haunted by older formulations which were associated with cancers in workers. Occupational respiratory and dermatological issues are still with us as well, as are issues of poor industrial hygiene. According to Eugene White, author of Investigations of Contaminated MWF and Respiratory Ill Health: An American Experience, some 1.2 million U.S. workers are exposed to metalworking fluids each year. So its important to educate industry and provide it specific tools to further minimize fluid exposures and enhance worker health and safety.
Many research projects are seeking to understand more about the microbiology of metalworking fluids and how to minimize the impact of spent fluids, said White, environmental manager at Milacron in Cincinnati. One significant area of progress has been in the R&D and manufacture of metalworking fluids that have minimal impacts on health, especially dermal and respiratory.
[In recent years] there have been significant publications on metalworking fluids, and what we are seeing is not revolutionary but evolutionary change, agreed John Howell, a safety, health and environmental specialist at D.A. Stuart in Warrenville, Ill. He told LubesnGreases that researchers are exploring issues such as how to effectively determine mist levels, battle microbial contamination, and accurately pinpoint substances and practices which may hurt workers.
In a presentation in May to the Society of Tribologists & Lubrication Engineers meeting in Cleveland, Howell reviewed some of the most recent findings. He noted that microbiological contamination issues are high on the list of concerns, and new test methods may help determine what agents are involved.
The Right Stuff
One ongoing project has sought a way to analyze the content of fluid mists, which often mingle with other airborne matter in the plant environment. It might then be possible to isolate which specific components in the mist are causing occupational diseases.
After 10 years of development, this effort seems to be bearing fruit, Howell said. A 2007 report, published in the Journal of Occupational and Environmental Hygiene, found that a method adopted by the National Institute for Occupational Safety and Health in Cincinnati (NIOSH Method 5524/ASTM D 7049-04) can be used to determine the content of metalworking fluid mists.
The method recently completed a round robin performance test to see how well it could be used to characterize metalworking fluid samples gathered from industrial-type filters. The six-laboratory round robin got good results with the NIOSH test, and most participants were able to analyze the test fluid quantitatively and precisely.
This standardized test method, Howell explained, may help answer many questions, such as how much mist in industrial workplaces is generated by metalworking fluid, and how much is due to general activities such as dust, concrete, jackhammering and welding.
Mycobacteria and More
Another recent study Howell described focused on the contamination of metalworking fluids by Mycobacterium immunogenum, a pathogen that some studies have linked to hypersensitivity pneumonitis – an inflammation of the lungs that can be fatal – in exposed workers. That link is still unclear, and a method to quickly detect the organism could help settle the question.
Recently such a method was unveiled by the U.K-based Center of Ecology and Hydrology (an environmental science research center), in collaboration with Swiss lubricant manufacturer Blaser Swisslube. They developed a low-cost and rapid test called real-time quantitative Taqman PCR. Costing as little as $10 per assay, the test uses a specific Polymerase Chain Reaction to amplify and high-light the pathogens DNA, so it can be spotted quickly if it is present in a sample of metalworking fluid.
Glenn Rhodes, one of the studys authors, explained to LubesnGreases that the assay is a two-hour procedure that centrifuges 1 milliliter of metalworking fluid sample, and then uses an illuminating fluorogenic probe to monitor the progress of the PCR as it occurs in real time. Fluorescence emission data is collected at every cycle when the Taqman probe is in the presence of target DNA, rather than after a fixed number of cycles. This is much faster than other methods, such as culturing the M. immunogenum.
One of our aims was to develop a method that was applicable to industry, said Roger Pickup, a visiting professor of molecular microbial ecology at CEH Lancaster who worked to develop the method. The method is transferable from the research environment to industrial laboratories for routine use. Data generated by screening fluids with this method will allow a more robust assessment of whether there is a positive or negative association between M. immunogenum and HP.
Another study published earlier this year (by Katrin Steinhauer and Peter Goroncy-Bermes) also explored the issue of mycobacteria, asking which biocides used in water-based metalworking fluids would best prevent their growth. Using three biocide chemistries – triazine, formaldehyde and methyloxa-zolidine – the study sought to establish the minimum inhibitory concentrations (MIC) needed for both M. chelonae and M. immunogenum. (The MIC is the dosage rate required to inhibit or kill a certain strain of mycobacteria.)
The results indicated that methyloxazolidine-based biocidal preparations were most effective in preventing microbial contamination, including rapidly growing mycobacteria. If there is a causal link between mycobacteria and HP, the two researchers suggested, this shows that biocides can play a protective role and help prevent outbreaks.
Ten years ago we could not verify if HP was brought on by just bacteria of this class or another, Howell said. Ten years later, we are able to detect it and do more.
He pointed to another encouraging report, pooling the results of cohort studies published through February 2007, which asked whether industry workers exposed to formaldehyde faced a higher risk of cancer. Formaldehyde is often used to inhibit microbial growth in metalworking fluids, but this comprehensive review found no link with oral and pharyngeal, sino-nasal or lung cancers in exposed workers.
This debate has been going on for 30 years, Howell added, and the general consensus is that there is no appreciable excess risk.
Three Bad Actors?
Howell also outlined a presentation by Fred Passman of Biodeterioration Control Associates and consultant Alan Eachus, given in January to the 16th International Colloquium Tribology in Germany. They observed that debate in the United States is intensifying around bad actors when it comes to metalworking fluid microbes and worker health. Three hypotheses have emerged and need to be addressed, they said.
1. Endotoxin exposure presents a significant risk to machinists exposed to metalworking fluid mists and their associated bioaerosols. Endotoxins – the outer cell envelopes of Gram-negative bacteria – are known to be harmful to humans, so there is a large body of evidence to suggest this hypothesis may be true. Therefore, the authors urged industry to use fluid management, housekeeping and good engineeering practices to minimize endotoxin exposure in metalworking plants.
2. Mycobacterium immunogenum is the cause of hypersensitivity pneumonitis in metalworking plants. This hypothesis is on shakier ground, felt Passman and Eachus, because the scientific data to prove it hasnt been generated. While M. immunogenum may be one cause of the disease, they believe its unlikely to be the only cause or even the primary agent responsible for HP. The two researchers again advised that the most prudent course is to minimize worker exposure to these organisms, through better fluid system engineering, condition monitoring and plant ventilation.
3. Mycotoxin exposure presents a significant health risk to workers exposed to metalworking fluid mist and mist-associated bioaerosols. Mycotoxins are the harmful excretions of spores and fungi such as Aspergillus, Fusarium and Penicillium; Legionnaires disease and sick building syndrome are well-known examples of respiratory diseases attributed to mycotoxins. This particular hypothesis may be the toughest to validate, because theres no industry-specific data that addresses mycotoxins in metalworking fluids and worker exposures. Much more study is going to be needed, the authors said, and they urged industry to develop a consensus and begin gathering the data needed to get this work under way.
The final research report Howell covered was an intriguing study of the link between synthetic metalworking fluids and the risk of developing rhinitis-related symptoms. Led by Dong-Uk Park, a group of Korean researchers surveyed workers in an automotive piston-ring manufacturing plant where synthetic metalworking fluids were heavily used – some 18 to 30 tons a year.
Rhinitis has not been studied much in relation to metalworking fluid exposure, perhaps because the symptoms – stuffiness, nasal itching, runny nose and post-nasal drip – are considered minor and are common in every workplace.
Using questionnaires and interviews, Parks research team asked operators of grinding equipment and finishing equipment in the plant to describe their symptoms. For those most heavily exposed to the synthetic fluids – grinders – the frequency of complaints was 66.7 percent for nasal stuffiness, 77.8 percent for anosmia (loss of smell), 77.8 percent for runny nose and 50 percent for headache. By comparison, office workers at the auto plant who had no exposure to fluids suffered these symptoms at rates of 22.5 percent, 7.5 percent, 17.5 percent and 15 percent, respectively.
Whats more, 82.4 percent of the grinding workers sampled were exposed to total metalworking mist levels of less than 0.2 mg/m3, and 17.6 percent sampled were exposed to 0.5 mg/m3. NIOSH has been contending that nonmalignant respiratory diseases like rhinitis may occur in mist exposures below 0.5 mg/m3, and these findings confirm that stance, Park and his colleagues said.
Although not malignant, rhinitis may be followed by more serious illnesses, such as allergies and asthma, and is a daily nuisance to large numbers of metalworking industry workers. So while endotoxins may deservedly draw a large share of the research, there are other culprits in metalworking fluids that also deserve attention.
Much to Be Done
This survey of recent developments in MWF was not meant to be exhaustive, Howell said, but by spotlighting some of the major papers he hoped to show that knowledge is advancing, and action can be taken to safe-guard workers.
There are ongoing research efforts, and a wealth of information coming out of trade groups, concurred Milacrons White. Industries are also working with federal agencies such as OSHA Alliances to share and discuss ideas.
White also noted the level of safety measures and precautions taking place in plants. Todays metalworking fluid health and safety specialists are better equipped to prevent and control potential hazards in the workplace. There are improved surveillance and monitoring techniques to assess conditions in machine shops, he said.
Another positive sign is the upcoming symposium on the Assessment and Control of Metal Removal Fluids, Oct. 5 to 8 in Dearborn, Mich. (See www.mrf2008.org) Sponsored by a coalition of manufacturers and industry groups, the symposium is being chaired by John Burke of Houghton International. Some 60 abstracts already have been submitted for presentation, from national and international presenters, so the metalworking industry is about to get a fresh injection of research to debate.
The best progress we can make is for a cooperative agreement between the industry, various trade associations and OSHA, Burke said. Today we have education, STLE with its courses, and peer-reviewed materials. There is just such a higher level of knowledge than in the past.