Benzene in soft drinks

I was involved in an argument at work today about the horrible, horrible poison I was ingesting – namely, diet soda. You see, apparently potassium benzoate is just another name for benzene, and we all know that benzene causes cancer! Right, so, obviously I’m not a total moron and I didn’t fall for it. But in poking around, there may be a nugget of truth in the mountain of horseshit.

Here’s what I’ve been able to figure out might be going on:

  1. Potassium/sodium benzoate, by itself, becomes benzene when exposed to heat and light. The amounts used in soft drinks are negligible and pose no threat.

  2. Potassium/sodium benzoate becomes benzene when exposed to heat and light in the presence of vitamin C (citric or ascorbic acid). Again, negligible in soft drinks, no threat.

  3. It’s the end of the world, don’t drink soft drinks! THEY are out to KILL YOU ALL!
    I’m curious from a chemistry point of view which is accurate. I know my idiot coworker is wrong – if nothing else, I can rely on the fact that she thinks iodized salt will poison your thyroid as evidence of her stupidity – but I don’t know exactly what happens. And the stuff on the net is just varied enough that I can’t quite filter it for myself. (I’m ignoring the obviously biased sites, but even sticking to reasonable-sounding ones, I’m not sure what’s actually going on here.)

Can the Dope straighten me out?

previous thread

Thanks, Rick. That partially answers it, but there’s still something missing that got me going on this in the first place.

To wit: does the benzoate -> benzene reaction require citric or ascorbic acid, or not? What about the heat and light?

I can provide a three-weeks-past expiration, left-in-the-sun bottle of Diet Pepsi if anyone has the stuff to do a real test… :wink:

There are such things as goiters from too much iodine.

But that would be the saltiest dish ever.

And I once at a big bowl of salt.

What i remember from my previous research was that it does require the asorbic acid as well as time/heat.

While im too lazy to find the research I previously read, it was a .gov study that said yes there IS benzene in some soft drink samples. But, the levels were very small.
All the same I avoid drinks w/ both asorbic and benzoate especially if i think they might have been there a while. I’m pretty sure that the USRDA of benzene is zilch.

sorry for the lack of cites
get mad if you like

My first thought as an organic chemist was that the breakdown of benzoic acid is not bloody likely except in possibly minute amounts. Benzoic acid is a pretty stable beast by itself. Some digging found me this (from a reference in the wiki article about benzoic acid):

I’d love to see actual literature references to the studies that found the conditions for the benzene formation.

Yes, I have the stuff to do a real test on your Diet Pepsi, but not the inclination. :slight_smile:

I think you have that backwards. Iodine deficiency is the cause.
Survey of benzene in foods by using headspace concentration techniques and capillary gas chromatography.
McNeal TP, Nyman PJ, Diachenko GW, Hollifield HC.
U.S. Food and Drug Administration, Division of Food and Chemical Technology, Washington, DC 20204.
Recently, the combination of sodium or potassium benzoate with ascorbic acid was shown to produce low levels (ng/g) of benzene in fruit-flavored soft drinks. The presence of benzene also was reported in butter, eggs, meat, and certain fruits; levels of these findings ranged from 0.5 ng/g in butter to 500-1900 ng/g in eggs. Because benzoates are widely used as food preservatives, a limited survey of other foods containing added benzoate salts was conducted to investigate the potential for benzene formation. Selected foods that did not contain added benzoates but were previously reported to contain benzene were analyzed for comparison. More than 50 foods were analyzed by purge-and-trap or static headspace concentration and capillary gas chromatography. Benzene was quantitated by using the method of standard additions, and its identity was confirmed by mass selective detection. Results of this limited survey show that foods without added benzoates (including eggs) contained benzene at levels equal to or less than 2 ng/g. Slightly higher levels were present in some foods and beverages containing both ascorbic acid and sodium benzoate.
PMID: 8286958 [PubMed - indexed for MEDLINE]

Data on Benzene in Soft Drinks and Other Beverages
Data through May 16, 2007

In November 2005, the Food and Drug Administration (FDA) received private laboratory results reporting low levels of benzene in a small number of soft drinks that contained benzoate salts (an antimicrobial) and ascorbic acid (vitamin C). FDA has no standard for benzene in beverages other than bottled water, for which FDA has adopted the US Environmental Protection Agency (EPA) maximum contaminant level (MCL) of 5 ppb for drinking water, as a quality standard.

As follow-up to the November 2005 benzene findings, FDA’s Center for Food Safety and Applied Nutrition (CFSAN) initiated a limited survey of beverages with a focus on soft drinks that contain both benzoate salts and ascorbic or erythorbic acid. The vast majority of beverages sampled to date (including those containing both benzoate preservative and ascorbic acid) contain either no detectable benzene or levels below the 5 ppb EPA MCL for drinking water.
In May 2006, FDA posted results obtained between November 2005 through April 20, 2006, from CFSAN’s survey of benzene in beverages (Table 1). Over 100 soft drinks and other beverage samples were collected from retail stores in Maryland, Virginia, and Michigan. Only four beverage products containing both added benzoates and ascorbic acid contained benzene levels above the 5 ppb EPA MCL for drinking water. One cranberry juice beverage product with added ascorbic acid and only natural levels of benzoic acid (i.e., no added benzoates) also contained benzene above 5 ppb. All five products have been reformulated by the manufacturers. CFSAN tested samples of these reformulated products and found that benzene levels were less than 1 ppb.
FDA is now updating the survey data with results from 86 additional samples that were analyzed from April 21, 2006, through May 16, 2007 (Table 2). These additional samples were collected from retail stores in Maryland, Maine, and Massachusetts. Only five products containing both added benzoates and ascorbic acid contained benzene levels above 5 ppb. Four of these products have been reformulated. CFSAN tested samples of these reformulated products and found that benzene levels were less than 1.5 ppb. The fifth product is no longer manufactured. We are presenting these data to inform the public of FDA’s progress.

Table #1

Table #2

What I’m curious about and not seeing in the above references (and thanks for them, PatriotX) is any situation where someone has caused any benzoates to convert to benzene under conditions found in common soft drinks. For all we know the benzene may have been present in either the water used to prepare the drinks or in one of the ingredients.

Energetically, the conversion is not favorable (to the best of my knowlege, without digging up actual numbers).

The conversion of benzoate to benzene is not favorable, but the conversion of benzoic acid to benzene and CO[sub]2[/sub] is very favorable both entropicly and enthalpicly. It’s the transition state that is a problem because they ultimately go through a very unstable C[sub]6[/sub]H[sub]5[/sub] anion, cation or anion. If this transformation is to occur, it is most likely to occur by a radical process, since that is the least stable of the three.

Ascorbic acid is a very good antioxidant because it has several stable oxidation states each differing by one electron. In otherwords, it is the ultimate radical sink. Given all of the resonance structures available to both ascorbic acid (of any oxidation/protonation state) and benzoate, it would not suprise me the two could form a cage complex where occasionaly enough energy is provided that CO[sub]2[/sub] is released while a hydrogen atom is provided to the benzene from ascorbic acid. Once the system loses CO[sub]2[/sub] there would be no going back.

You have to remember, this is not the type of reaction you would draw a mechanism for in class. It is likely to be a rare reaction, that is not well understood. I don’t search the literature on benzene in diet soda regularly, as it is of little interest to me. It seems as if some literature presented here has come around to say that it doesn’t happen at all. I’ll consider the jury to be out.

Either way, there is nothing to worry about. Benzene is used in labs all over the place as a solvent, and while caution is taken, it is not treated as deadly. My wife likes the smell, but I’m more of a cyclohexene man. Old time chemists used to use it to wash their hands, and it absorbs readily through the skin. I’m not saying throw caution to the wind when it comes to benzene, but most of the worrying about benzene is media hysteria. You encounter much worse carcinogens in your daily life.

I mentioned polyaromatic hydrocarbons in the previous thread. These things are just nano-sized portions of graphite that are formed anytime you burn something. I’ve never worried to much about benzene in the lab, but a bottle of pyrene is treated like the ebola virus. The media has reported on this many times. The biggest offenders are barbeque, well done meat, and anything smoked. I love the stuff, but if your going to worry about benzene in your soft drinks you may as well worry about things that we know count.

I love the Dope.

This is the sort of information I was curious about, but unable to figure out or find on my own. I studied just enough chemistry that I can (sorta) follow what was said.

My concern wasn’t that my Diet Pepsi was poisonous, I just was wondering about the possibility of benzene formation. That question has been answered superbly; thanks, folks!

I ran across a different compound that I have to wonder about. Is Bisphenol A from the liners in canned goods as toxic as this article says it is

Probably needs its own thread

Exactly - a perfect storm of conditions to create a minute amount of benzene from a tiny amount of preservative.
All the above reference studies do not prove the conversion is taking place. Just because there is benzene and benzoate based preservatives in some soft drinks does not automatically mean that the benzene came from the benzoate. I want to see someone make benzene from sodium/potassium benzoate under soft-drink like conditions. (Heck if I hadn’t sold my soul to the corporate world, I’d try it myself.)
Oh, and I’m not toucing the bisphenol A issue with a 10’ pole.

Maybe someone w/ access to the whole study can shed some more light.
I note the language of my first cite:
“Recently, the combination of sodium or potassium benzoate with ascorbic acid was shown to produce low levels (ng/g) of benzene in fruit-flavored soft drinks.”

I find it interesting that you say that, given that my previous employer (a multi-national contract pharmaceutical company) and my… well, more recently previous employer (a multi-national generic pharmaceutical company) both made efforts to remove benzene from the lab, citing heath reasons. Methods using it, but which didn’t require it, were redeveloped and validated without it, and most raw materials were, as much as possible, removing benzene from their synthesis, unless it was absolutely required. The entire building basically had a tiny bottle of benzene left, to do residual solvent GC assays, and that was it. The second company I worked for was trying to see if it were possible for them to take the same steps.

In looking at some MSDSs, the OELs are quite low; 0.5ppm/ 8 hours in British Columbia and Ontario, 1ppm/ 8 hours by OHSA (USA) and 0.1ppm by NIOSH according to this webpage.

According to this if you can smell it, you are being exposed to 61 ppm, if I understood that table correctly.

I know the realities of working in a lab; people constantly pour out acetonitrile and methanol and other, more toxic solvents, on open benches (x30 chemists x 8 hours/day x 260?days/year X… it adds up!) and not all labs were designed with enough fume hoods/strong enough ventilation, or even supply enough gloves (I was expected to resuse mine in my undergraduate research lab!) or any respiratory protection, and people are hesitant to use them because “it won’t happen to me” and so on. But the longer I worked in that environment, the more worried I got about what kind of crap I was being exposed to. I tend to take lab safety pretty seriously (and safety as a whole, regardless of environment).

Anyways, you know your job, and can better evaluate your exposure and risk, but still… just consider the fact that there is a risk. Cancer is the chemist’s disease and all that!

Sorry for the hijack, I didn’t intend to say so much, but now that it’s typed out, I’m posting it anyways!

I took Christopher’s “there’s nothing to worry about” not as “don’t worry about benzene” but more of a “don’t worry about the minute amount of benzene in diet soft drinks” considering it took years of people handling the stuff in a cavalier manner before anyone figured out that it really should be locked up.

Yes, there’s a risk. There’s also a risk from the acrylates in your french fries. The only way not to be exposed to potential carcinogens is to not eat, breathe, or refuel your vehicle.

I did note that, but the rest of the abstract deals with a survey of foods containing benzene. I tried to get the reference to see if the quoted line cites another study, but we don’t have that journal here.
I think I’m getting smidge too focused on this now…but not focused enough to visit Pitt’s library. Yet.

I’m not cavalier about anything I work with in the lab. Benzene is carcinogenic, and when another solvent will do the same thing I will use it. On the other hand, when you consider the way chemists used benzene for years before they knew about its problems, you would expect that older chemists would be dropping like flies from cancer if you trust the way the media portrays it. People encounter much more potent carcinogens in their daily lives, and they don’t even know about it. Worrying about a couple ppb in your soft drink is loony.

Perhaps, but it is an entirely avoidable thing. There’s not much reason to drink something that may contain up to 14 or 15 times the levels permitted in drinking water when you have other acceptable choices. There’re plenty of soft drinks that don’t have the ingredients associated w/ benzene.