Hi MacLeod:
This topic comes up occasionally, usually from the anti-aluminum/pro-steel tank crowd as another reason to avoid "Satan's alloy". They talk about how aluminum dust from aluminum cyliders damages the lungs and brains of divers. There are a lot of good reasons for using steel tanks, but I don't believe that avoiding lung or brain damage from aluminum is one of them.
Aluminum can indeed be toxic to humans. I have reviewed the abstracts from numerous medical studies on Medline that look into this problem. It has long been known that workers in the aluminum processing industry (ore processors, alumina based chemical products, synthetic abrasives manufacturers, etc.) were prone to develop lung conditions similar to silicosis and asbestosis (sometimes called bauxite lung, aluminosis, or Shaver's disease) and it has long been assumed that this was due to inhalation of large amounts of aluminum oxide dust and aluminum crystals during processing. Indeed workers in these industries do have an increased incidence of similar lung diseases, but human and animal studies indicate that while exposure to aluminum or aluminum oxide dust can cause lung damage that you can see under the microscope, the lung damage is generally minimal and follows a benign course in the patient. The evidence that I have seen indicates that those aluminum workers with clinical diseases that look and act like silicosis actually have silicosis from the silica exposure in their work--not from the aluminum exposure (although not all the studies support this view.)
When aluminum builds up in the tissues it can cause nervous system problems that look similar to Alzheimer's disease (aluminum has been hypothesized to be a contributing factor to that disease), osteomalacia (weakening of bones), and other disorders. These problems are frequently found in people with poor kidney function and particularly in people with kidney failure on renal dialysis. This is because aluminum is excreted by the kidneys, and if you don't have normal kidney function, aluminum can build up in the body. Some people have taken this further and suggest that aluminum can be harmful in people with normal kidney function. Studies comparing "control" patients to kidney failure patients support the fact that in patients with healthy kidneys, aluminum is largely excluded from the body because it is excreted in the urine. The patients with normal kidney function (and typical every-day aluminum exposure) had low levels of aluminum in their blood and tissues.
I found one very interesting study. Apparently, miners in northern Ontario were treated with "McIntyre Powder" (finely ground aluminum and aluminum oxide dust) between 1944 and 1979 with the idea that if they were exposed to McIntyre Powder, they would have a lower incidence of silicotic lung diesease. In 1990 a study was published (in the journal Lancet) that looked at these miners to see if the practice of exposing them to large amounts of McIntyre Powder caused neurotoxic (nerve damaging) effects. There were no significant differences between exposed and non-exposed miners in reported diagnoses of neurological (nervous system) disorders. They did find that the exposed miners performed less well than the non-exposed workers on specific cognitive tests, but not uniformly so. Some of the exposed workers performed better than some of the non-exposed miners on the tests (but the study did indicate the non-exposed miners performed better in general.) Remember this study compared people with a long history of intentional exposure to large amounts of aluminum dust.
What do I think? With no hard data to prove my position (or data to disprove it either) I believe that exposure to aluminum when cooking in aluminum pans, drinking sodas in aluminum cans, taking reasonable amounts of aluminum based antacids should be of no significant concern to healthy individual (but it wouldn't hurt to limit excessive exposure.) I certainly don't believe that exposure to the minimal amounts of aluminum oxide that you could breath as a recreational scuba diver is of any concern whatsoever. I don't even know that you breathe any aluminum oxide from a scuba tank! Even if you do breathe some aluminum oxide dust, the risk that you face from the dive itself far outweighs the risk from the aluminum exposure. You are far more likely to have neurological damage from a diving accident (AGE, DCS, hitting your head on the bottom of the boat, etc.) than you are from breathing a minuscule amount of aluminum oxide dust from a scuba tank.
Just my 2¢, hope it helps,
Bill
