I encountered a new case this morning of what I suspect is occupational asthma related to Cobalt exposure. I have never met someone known to be exposed to this heavy metal before, and never had cause to evaluate the literature regarding respiratory disease caused by Cobalt.
A brief literature search yields an array of clinical case reports, lab-rat studies and OH&S documents. Cobalt, it turns out, has been reported to be associated with interstitial lung disease and asthma. The latter is more commonly associated – and, I suspect, underdiagnosed.
Interestingly, the mechanism by which Cobalt causes asthma may be entirely allergic (ie the same mechanism by which grasses and pollens cause asthma). Cases have reported evidence of sensitivity on skin-prick testing to solutions of cobalt chloride, and nasal inhalation of the same mixture has been reported to be followed by increased markers of allergic inflammation in the blood – all of which might be consistent with IgE mediated allergy.
An OH&S report from British Columbia, Canada in 1999 makes interesting reading. This paper refers specifically to people in the occupation which my patient pursues; saw doctors (or saw filers) in timber mills. Saw tips are often made of tungsten carbide.
This paper quotes estimates of up to 5% of cobalt-exposed workers as developing sensitivity to cobalt resulting in asthma. Far fewer develop interstitial lung disease. The authors conducted a study in the filing rooms of eight sawmills, seven of which used tungsten carbide saw tips, and seven of which used stellite tips (some used both). Cobalt was present in both sorts of saw tip – at concentrations of up to 30% and up to 50% respectively. Employees working in the filing rooms at the mills wore, for the purpose of the study, filter cassettes and personal sampling pumps to catch airborn metals. Lung function tests were performed before and after work, and questionnaires were also filled out. The results were interesting, and pertinent to my patient.
1. Levels of airborne metals were low. Only 62 of 278 air samples had measurable cobalt levels. Measurable levels actually occurred more often if the saw blade was tungsten carbide than if it was stellite. Wet grinding (running water over the blade while grinding) made no difference, and in fact may have made things worse. (Because wet grinding was thought to fix the problem of airborne exposure, ventilation was usually worse in rooms where wet grinding was used, and cobalt got from the grinder coolant into the air. Cobalt levels in coolant from the wet grinders were higher for TC grinders then satellite grinders).
2. No current workers in the mills (118 in total) were diagnosed as having current lung disease related to cobalt. They were, however, twice as likely to report coughing up phlegm, and three times s likely to report coughing, phlegm and wheezing which was worse at work than industrial workers from different environments. (Sounds a bit like asthma to me). TC filers doing wet grinding had significantly higher rate of abnormally low lung function.
The study recommended that automated saw-grinding machines should be fitted in complete enclosures and vented to outside air. They also recommended that any hard-metal tool grinder with respiratory symptoms should be carefully evaluated by their family doctor, and should have respiratory function tests and a chest xray.
My patient has a long history of asthma, predating his current employment. In my opinion he should not, unfortunately, have been employed in an environment where he was exposed to a substance known to cause occupational asthma. I trust the recent advent of visiting OH&S specialists in his work environment signals that mill operators are waking up to their responsibility to their workers in this regard.
Andrew
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