OK, I restore old speakers. Recently I picked up a pair of Harman Kardon HK-40's with decent cabinets. Thought I'd tweak and refinish them and do OK fixing them up. Got inside and noticed some white powder on the outside of the potentiometers. These speakers are from the 60's.
I'm a curious sort and wondered what the powder was...kind of like the stuff you see around battery terminals on an old car battery. I have a PhD chemist friend who works for a famous company that's big on science. Who better to ask? So I shot him an email. He did some checking around and shot me back a reply a day or so later, after I'd buffed the powder off the pots and was preparing to do more.
His message said to stop everything that the white powder was likely oxidized cadmium which is a "heavy metal" and quite toxic. Unlike the stuff that's on car batteries that is simply another form of sulphuric acid, this stuff was really dangerous. I was to handle it with rubber gloves and then realize that those gloves had now become toxic waste. He recommended disposing of the speakers at a toxic waste reception facility.
He'd checked his info with another PhD scientist at this firm. This other scientist is also into electronics... including the vintage stuff. He said in the 60's they'd often coat potentiometers' iron parts with Cadmium to retard oxidation because it was highly resistant to corrosion, but have since discovered that it eventually does break down and becomes problematic.
I'll leave it to you to read the WEB about the dangers of cadmium, particularly if it is inhaled. [http://en.wikipedia....dmium_poisoning ] Well, in the intervening time I'd used a buffing wheel to remove the mystery substance from the outside of the potentiometers. That makes it airborne toxic waste. GREAT!
After getting his ominous warning, I scraped up the powder remains inside the speaker, and gave it to my friend who had the million dollar equipment to test it to see what it actually was. Yes it was loaded with cadmium. He recommended I call an "ask a nurse" who then referred me to poison control. I wasn't having any immediate symptoms, thankfully, and I'd done the brushing that stirred it up a couple of days earlier. Poison control said that if I wasn't suffering symptoms at this point I'd probably be fine, but cadmium is indeed nothing to mess with. I hope he's right. Forms of cadmium poisoning can be life-threatening, leading to pneumonia, kidney failure etc. etc. Who knows what the long term effects of this nasty substance might be now that it been inhaled even in small quantities that didn't cause immediate respiratory distress. One is not even supposed to touch it let-alone inhale it.
A word to the wise, my friends.