An intriguing question on Reddit from /u/wolframite was right up my alley. It went something like this:
What is the likelihood that my wine is contaminated with lead (Pb)?
I discovered a 1973 magnum of a Californian wine on its side in a wooden gift box. Water had gotten all around it so the top of the bottle looked like it had a mushroom on top; in fact, it was the foil, which I decided to remove after I realized it wasn't really corroded (which made me remember that before the 80's, they would often use lead in wine foils). The big surprise was that the cork had disintegrated and was submerged in the wine and it had been the foil that had been protecting the wine from oxidation etc. I was about to chuck it all when curiosity got the better of me, and I took a sip, found out it was actually pretty good…then spat it out just in case....
Now decanted and on my dining room table, I'm wondering --can I drink it or am I asking for a case of heavy metal poisoning?
At first blush, the Pb-Cl-O-H Pourbaix diagram shows that at, pH~3.5 (the pH of wine, more or less), PbCl+ is the equilibrium phase. This is a soluble species, which means lead is probably in solution, and it would not be physically separated by decanting. That is, unless a component of the wine is capable of reducing the lead or otherwise chemically combining or complexing with it and forming a solid. This is a possibility, as potassium is commonly removed in the course of bitartrate crystal (Weinstein/“wine diamond”) precipitation.
However, it is important to note that there are no other competing species, and concentration control is quite unlikely that far away from the equilibrium line at pH~7. Therefore, the wine should have eaten through the lead foil by now, and he would have had a very wet, wine-stained wooden box. This has not yet happened. This could be a coincidence, and he happened to find the bottle immediately after the cork dislodged. However, it also begs the question: are there other components in the wine that inhibited corrosion? Strong corrosion inhibition is common behavior in all metal species, especially in the presence of carbonate/bicarbonate, phosphate, etc. It seems to be particularly pronounced in the heavy metals like Zn, Pb, Cd, etc.
In the case of lead and wine, it is possible that sulfur actually came to the rescue and kept the capsule from corroding through. The Pb-S-O-H Pourbaix diagram shows a region of exceptionally strong passivation in equilibrium with the hydrogen reduction reaction (the dotted, diagonal line), as well as at most other potentials and pH values except for pH<2. Note that this diagram does not take into account the influence of chloride anions. Even so, lead does not appear to be strongly corroded in the presence of sulfur-bearing ion species in water.
What does this mean? First of all, I don't know the concentration of sulfide/sulfite/sulfate in this particular wine or its pH, so I can't very well calculate an accurate Pourbaix diagram. Second of all, even if the capsule didn't corrode through, there is still an acidic liquid in contact with lead. This is basically never good. I would really like to get my hands on a sample of a lead foil that has been exposed to wine so I can see what is going on at the wine-lead interface.
Basically, I wouldn't drink it, but there is a slim chance that wine in contact with the lead foil wouldn't kill you.*
*I take no responsibility if you are stupid enough to drink wine with dissolved lead or lead compounds and hurt yourself in the process.