Are you among the believers that formaldehyde condensates are not effective antimicrobials in metalworking fluids because they are ineffective against mycobacteria? Do you ascribe to the commonly held perception that exposure to formaldehyde is a real health concern in the metalworking environment?
Both of these issues contain elements of truth as well as elements of myth. Well debunk the myths and demonstrate why formaldehyde condensates are useful, and why they can be the right choice to enhance the performance properties of your metalworking fluids.
Myth #1: Formaldehyde condensates are not effective against mycobacteria.
Lubrizol tested several formaldehyde condensates against two mycobacteria strains: a lab strain (mycobacterium immunogenum, ATCC 700505) and a field-isolated strain. In general, we learned that it is difficult to grow mycobacteria in metalworking fluids in the laboratory, especially above log 4 cfu/ml. (That is, above 104 colony-forming units per milliliter, which is the basic unit of measurement for these organisms.) Mycobacteria is a slow-growing bacteria, even when special nutrients are used in the cultures.
Formaldehyde condensates are produced by a reaction between formaldehyde (CH2O) and an active hydrogen-containing organic, most commonly amines and alcohols. The most common CH2O condensate is triazine, also known as hexahydrotriazine or HHT. There are also atypical condensates such as methyl-enebismorpholine (MBM), methylenebisoxazolidine (MBO) and ethylenedimethanol (EDM).
The conventional wisdom is that it is easier to kill the ATCC lab strains than the field-isolated strain of mycobacteria. Yet nearly equivalent results were obtained when using these atypical formaldehyde condensates (see Figures 1 and 2). However, we obtained inconsistent results when we used the conventional formaldehyde condensates (triazine) against both the laboratory and field-isolate mycobacterium strains (see Figures 3 and 4).
The reason for the ineffectiveness? We believe that CH2O does not efficiently penetrate the hard, waxy cell wall of the mycobacteria when released from conventional condensates. On the other hand, we obtained good results when we tested new, atypical formaldehyde condensates manufactured by Lubrizol and currently in use in Europe. The reasons are unclear why these atypical CH2O condensates were more effective against mycobacteria. However, the hypothesis is that these new condensates, due to their lipophilic nature, penetrate the cell wall intact and then release CH2O within the bacteria cell, making them more effective against mycobacteria than the conventional condensates.
Myth #2: Formaldehyde exposure is a real health risk in the metalworking environment.
There has always been concern that exposure to formaldehyde from metalworking fluids poses a cancer risk. That concern has been heightened by IARCs June 2004 press release proposing to raise formaldehydes status from probably carcinogenic to humans to is carcinogenic to humans, stating that new information from studies of persons exposed to formaldehyde has increased the overall weight of the evidence. Add to that the fact that France is spearheading an effort in the European Union to ban formaldehyde use altogether – in all applications – and the concern has increased even more.
We all know that every chemical has some degree of risk associated with it, but risk is a function of both hazard and exposure. Controlling exposure to CH2O from its condensates used as antimicrobial agents in metalworking fluids is a key factor. However, accurately measuring free CH2O in metalworking fluids has been a significant analytical challenge. That is because most methods are destructive, and they measure the combination of free CH2O plus available CH2O from the hydrolysis of the condensate during the analysis.
Lubrizol has completed extensive analytical work on atypical condensates using high-pressure liquid chromatography (HPLC) coupled with post-column derivitization. This enables the differentiation of free CH2O from the condensate, indicating that prior metalworking studies may have overstated the exposure to free formaldehyde. And even those studies (e.g., Cohen, 1995) showed barely detectable amounts above background amounts in plant atmospheres.
The federal Occupational Safety & Health Administration (OSHA) estimates that approximately 500,000 workers in 40,000 U.S. establishments are potentially exposed to formaldehyde over the course of an eight-hour work day at levels from 0.5 to 1.0 parts per million (ppm). Many studies have been completed in environments where exposure to CH2O would be reasonably expected, from manufacturing to medical facilities. This table shows some of the findings:
|Environment||Exposure in ppm|
Medical autopsy facility
Funeral home embalming
Kidney dialysis clinics
|0.8 to 5.0
0.6 to 1.3
0.2 to 1.3
0.02 to 0.75
0.2 to 0.5
Chronic exposure of rats to formaldehyde via the inhalation route showed they were prone to get malignant tumors in the nasal epithelium. Tumors occurred only under exposure conditions that resulted in marked, chronic inflammation (irritation) of the upper respiratory tract.
When rats were exposed to less than 2 ppm formaldehyde, less inflammation was observed and no tumors were formed. The risk of nasopharyngeal cancer in rats was more likely to increase when peak exposures to formaldehyde were above 2 ppm, as opposed to when duration or cumulative exposure was considered.
At equivalent exposure levels, there was a lower incidence of tumors in mice, and there was no effect in hamsters.
Over 50 epidemiological investigations of cancer in formaldehyde-exposed workers have been conducted. Among those studies were Hauptmann et al., 2004; Coggon et al., 2003; and Marsh et al., 2002. Overall, these investigations have fallen short of proving a clear and causal association with formaldehyde exposure and tumor formation, and we need to keep in mind that nasopharyngeal cancer in humans is rare.
One study (Coggon) concluded that there were no cases of nasopharyngeal cancer in 14,000 workers from six plants in the United Kingdom who were exposed to 2 ppm levels of formaldehyde. Another 25,000-worker study, by Hauptmann et al. in 2004, reported nine cases of nasopharyngeal cancer. In all nine cases, workers were exposed to 4 ppm or higher levels of formaldehyde, and data supporting causation was biased by a clustering phenomenon at a single facility.
Fortunately, sophisticated monitoring of the workplace environment may not be required to determine whether formaldehyde concentration in the metalworking shop atmosphere is approaching a high-risk level. Human sensory systems do a good job of that for us. The table (below) shows a composite of 10 different studies of various human responses to formaldehyde based on the level of exposure.
|Response||Exposure in ppm|
Upper airway irritation
Average sensory irritation
|0 to 0.24
0.24 to 1.2
0.24 to 1.2
0.24 to 2.1
When used properly, CH2O condensates have many benefits in metalworking fluids. These include the need to dispose of coolant less frequently, lower labor cost to clean out the system, less part rejection or failure, and longer tool life. In addition, when used at proper treat levels, CH2O condensates can reduce the incidence of adverse health effects caused by exposure to bacterial growth in metalworking fluids.
Based on this information, one should consider taking a practical approach to CH2O exposure. If formaldehyde cannot be smelled, and particularly if there is no eye or respiratory irritation, the risk is low for adverse health effects.
If nasal, eye or throat irritation is experienced, investigate further; there are other components of metalworking fluids that could be causing the irritation. We suggest limiting the use of odor-masking substances such as pine oil, citrus, sassafras and other scents in metalworking fluid formulations, so that CH2O can be detected and appropriate steps taken to reduce exposure.
And finally, using mist suppressants will reduce exposure to metalworking mists in general. So far, the metalworking industry has not widely adopted their use, but it would certainly appear to be the prudent course to take. Managing risk is the name of the game.