Have I rendered my aluminum baking sheet pan unusable?

Aluminum is a neuro-toxin and is suspected of leaching small amounts of toxins into the foods cooked in it. I’d just replace it anyway.

@incendiary_dan – Do you mean just flat out get rid of it because it may be dangerous? Or do you mean because of this incident?

In general, I don’t ever cook on aluminum.

Yes, avoid aluminum as much as you can. There are medical studies that have found that aluminum is a neurotoxin:

http://www.ncbi.nlm.nih.gov/pubmed/2198876
http://www.drpepi.com/aluminum-poisoning.php
http://www.med.nyu.edu/content?ChunkIID=164929

Don’t cook or eat off aluminum any more than you’d cook or eat off lead.

The discoloration is probably oxidation… IMO if you use it with parchment or somesuch, it will be fine since the food won’t actually contact the metal.
@HungryGuy , your sources seem to indicate that OTC meds and processed foods are more of a concern than cookware.

@ccrow – Well, be concerned and avoid it, but don’t go screaming in terror or become a hermit from everything post stone-age. From what else I’ve read, children and the elderly are most at risk from exposure to it. I definitely wouldn’t store food in it or eat off it (don’t buy pop and beer in aluminum cans, for instance, or wrap food in aluminum foil). But don’t be paranoid either. Aluminum is one of the most abundant elements on earth, so we have evolved with it as part of the natural environment, although it doesn’t occur naturally as a pure element. See this for a casual scientific overview of aluminum.

I usually use parchment when I bake. But maybe I’ll save this pan to use with a Silpat.

Any ideas on how to get rid of the discoloration?

600 grit sandpaper?