Tuesday, September 23, 2014

My wine was exposed to lead foil from the capsule…will it kill me?

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?

Turns out, this is a really interesting chemistry question.

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.

Tuesday, September 09, 2014

Why supporting wine bottles by the neck for long-term aging is a bad idea

A relatively recent trend in short-term wine storage are cute holders that use the neck of the bottle as the holding point and counter-balance themselves against the weight of the lower portion of the bottle.  Some hobbyists have even taken to crafting racks like this themselves (not unlike riddling racks).  One well-built example (borrowed from Reddit user “ILovePooch”) is shown here:

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This is a nice design, very attractive, with a wide base that should prevent any tipping of the rack, and good points on the top that can be wall-anchored.  However, there are concerns about using this for long-term bottle aging.

The short explanation: This is a bad idea for long-term storage. The fundamental reason for this are inherent flaws in the glass that may propagate in high-stress regions (i.e. in the neck and shoulder, in this case) when exposed to wine.

The long explanation: The fracture mechanics of glass are dominated by largest flaw in a stressed region...this is why scoring and breaking works on glass and ceramics, but not on metals. In materials science, we quantify this by calculating a Weibull modulus by testing many hundreds of test specimens. In general, a single pore or surface scratch will not be enough to allow a relatively thick bottle to fracture under a constant minor load. Hence, this design is OK for the short term.

Over time, though, a small (read: tens of microns/< 0.001 inches) crack exposed to an aqueous environment - especially an acidic environment - will grow. The mechanism for this is still debated, but it is usually thought that the atoms at a sharp crack tip in a ceramic tend to react quickly with the water. This makes sense to some extent; the atoms at the crack tip are in a state of triaxial tension when the crack is under a tensile load, meaning they are "higher energy" and more likely to react. Over months, large starting cracks could propagate quickly and cause failure of the bottle. Over years, even small flaws could react with the aqueous environment.

The worst part is that this is not a sure thing. It is a purely statistical process. It may happen to thin-walled bottles, thick-walled bottles, expensive bottles, or bottles of two-buck-chuck. It may never happen if one happens to buy bottles without significant flaws facing the wine (as external (air-facing) and internal cracks in a ceramic are very unlikely to grow under a constant applied stress). For long-term cellaring, it really will be playing the odds.

Freely available further reading: Cicotti, M., “Stress-corrosion mechanisms in silicate glasses,” http://arxiv.org/abs/0901.2809

Thursday, March 20, 2014

Zinc phosphate “arrowheads” in the SEM

Imaging some zinc that had been soaked in a phosphate buffered saline-based solution last week, I ran across lots of little zinc phosphate crystals.  Two really stood out, and are shaped almost exactly like arrowheads.  Far out!

Zinc phosphate arrowhead (1)

Zinc phosphate arrowhead (2)

The instrument used was Michigan Tech’s Hitachi S-4700 FE-SEM.  Both of these images were captured in “low magnification” mode because the salt crystals are so darn big.  They measure a little less than 0.1 mm, and so they are a little smaller than you can see with the naked eye.

Thursday, March 13, 2014

ResearchGate introduces new “open review” feature

ResearchGate, a peer networking site for research professionals, is introducing an "open review" feature that allows users to comment on published studies and characterize them as "reproducible" or "non-reproducible," among other things. This could evolve into a very important tool for disseminating post-publication validation studies, and would be a welcome alternative to the current expensive, centralized validation efforts.

image

The statement that “peer review isn’t working” might be a little harsh, but there is at least anecdotal evidence to back it up. 

They seem to zero in on the current controversy surrounding the article “Stiumuls-triggered fate conversion of somatic cells into pluripotency,” using that as an example publication.  It is marked “non-reproducible” on the announcement page:

image

There are still some questions to be answered here. 

Could there be opportunity for abuse of this systems?  

Will it be an issue for novice ResearchGate users, who might tend to clutter the "reviews" area with unrelated questions and criticisms? 

The latter seems more likely, as ResearchGate does not easily allow for anonymity, and the “questions” feature is already cluttered with easily answered questions from undergraduate and graduate students.  Hopefully the helpful “open reviews” on ResearchGate will not be in the minority, as is currently the case with the questions feature.

Monday, June 17, 2013

Degradable zinc stent research featured in the June 2013 MRS Bulletin

Exciting news!  Our research on bioabsorbable zinc stents has been featured in the June 2013 edition of the Materials Research Society (MRS) Bulletin.  The article discusses our recent article in Advanced Materials titled “Zinc Exhibits Ideal Physiological Corrosion Behavior for Bioabsorbable Stents” (read it on Scribd).  They interview my advisor, Prof. Drelich, about our research program and discovery.

Bio Focus: Is zinc the perfect material for bioabsorbable stents?

I believe this article is free-to-read, but I could be wrong about that.  Feel free to contact me if you would like a copy!