Airbags and poisoned tea: a mystery story

Yes, I know, I said I would be closing up shop for a few months. But I saw a paper just today that was kinda intriguing, so I couldn’t resist the temptation to share it here. Aside from this my blog will remain out of action for now…

It was April in Dallas when a string of unusual cases started to turn up at the ER. Four patients in four hours, all of them fainting from low blood pressure. All four had eaten at the same restaurant, and all four had ordered iced tea.

The police stopped by the restaurant to halt further sales of iced tea and take samples. But chemical testing for over a hundred possible poisons/drugs turned up negative. It wasn’t until five months later that an FBI laboratory identified the mystery poison: sodium azide.

Ordinarily you find nitrogen in our atmosphere in the form of N2, two nitrogen atoms joined by an exceptionally strong triple bond. If you give them the opportunity, the nitrogen atoms in the azide ion would really like to regroup and form N2, which is much more stable than this miserable-looking azide ion will ever be. The resulting reaction releases a lot of energy and (of course) nitrogen gas.

What do you call a reaction that releases a lot of heat and gas? An explosionof course. And if it’s heated to high temperatures or brought in contact with certain metals (lead, copper), sodium azide can become lively indeed. Mixing sodium azide with acid makes hydrazoic acid (HN3), which is not only volatile and highly toxic but even more prone to violent misbehavior.

In labs like the one where I work, we sometimes use dilute solutions of sodium azide as a preservative, and although these don’t pose a serious explosion risk they can be hazardous for a different reason. The azide is lethal not only to bacteria but to humans as well, and yes, you can absorb it through your skin. The mechanism by which sodium azide kills you is very similar to the way cyanide works. Both compounds latch onto cytochrome c oxidase, a key enzyme in the electron transport chain in your mitochondria, the cellular powerplants that do most of the work in extracting chemical energy from glucose. And that’s especially dangerous for cells that rely heavily on aerobic respiration — the cells in your heart and central nervous system.

Sodium azide might sound like a rather unpleasant character, but it has its redeeming virtues. Car airbags work by zapping a mixture of sodium azide and a couple other compounds with an electric current. The sodium azide quite literally blows up, releasing a large amount of nitrogen in a split second, and the airbag inflates so fast you don’t even have time to hit the dash.

So there are several places you might expect to find sodium azide — in an auto airbag or a research lab. An urn of iced tea at a Dallas area restaurant, however, would not be one of them. All of the patients who drank iced tea on that April 2010 day survived; the dose they ingested was too small to be lethal. But the mystery remains. How the hell did sodium azide get into the iced tea? It’s not like it’s a compound you find just lying around everywhere.

If you ask me, I reckon somebody’s got some explaining to do…

[1] Sodium Azide Poisoning at a Restaurant — Dallas County, TX, 2010. Morbitidy and Mortality Weekly Report. June 29, 2012 / 61(25);457-460 

7 thoughts on “Airbags and poisoned tea: a mystery story

  1. Doesn’t it take a rather large dose of sodium azide to kill someone? I have heard about several poisoning with it now (The ice tea one above, and a instance a few years ago where a lab coffee maker was spiked with it) yet no deaths. Despite this, I’m hearing a lot of comparisons with cyanide in terms of LD50. Care to elaborate? Are the poisoners just incompetent?

    • MSDS says the LD50 in rat for sodium cyanide is 27 mg/kg. (The LD50 for sodium cyanide per MSDS in rat is 6.44 mg/kg for your calibration.) As to whether they’re incompetent, well…your guess is as good as mine. Was this really a poisoning attempt? or was it some sort of bizarre accident? I dunno. Clearly there was sodium azide in the iced tea, but as to how it got there and why it was put there (if it was), I don’t think anybody knows.

      • You gave both numbers as for sodium cyanide, I’m guessing the first one is Sodium azide. So, if humans are the same as rats (Good or bad assumption?) it would take 1.7 g to have a 50% chance of killing me within 1 hour with sodium azide (Do I have that right?)

        Whereas it would take 0.412 g of sodium cyanide to get the same effect.

      • Ja, sorry, the first number is for the azide. But I don’t know that humans and rats are necessarily that similar, so the LD50 number for rats doesn’t necessarily tell you what the lethal dose would be in humans. Toxicologists use rats because it would be both impossible and hideously unethical to do that kind of experiment with humans. But at the end of the day the rat data isn’t always a good proxy. It’s just the best we can do.

        What LD50 actually means is the dose it takes to kill 50% of a given population. Whether that would be within an hour or not I don’t know…but yeah, that IS how you would calculate that.

  2. That amount of sodium azide (1.7g) would leave a nasty taste in the tea. It would have to be added and covered up with copious amounts of sugar. I’m guessing someone replaced some artificial sweetener packets with azide.

    • Unlikely, as only people who drank from one of the two pitchers were hit, making it likely it was in the liquid. I think they also tested the pitcher for it, though I could be misremebering. How do you know what a toxic chemical tastes like? I didn’t think we’d done identification by taste for 100 years or so!

  3. I used sodium azide to study uptake of trace metals in algae. I would pretreat cells with azide and see how uptake of radiolabeled metals was affected compared to untreated cells to find out whether transport was an active process. It turns out that azide is toxic to algae, but way less toxic than some other respiratory inhibitors!

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