I was asked recently why there is flame retardant in soft drinks - specifically, Mountain Dew.
This is the sort of question, as a chemist, I have trouble answering. My first response was the facetious comment that all of our drinks - soft drinks, coffee, tea, wine, beer, milk - contain flame retardant. What can you expect?
After all, water is a chemical compound and a flame retardant.
It is used by fire fighters all over the world. It is often used to prevent flames from spreading.
And everything we drink is based on water.
But water wasn't really the subject of the question. The question was actually about the presence of brominated vegetable oil which are compounds with names like 9,10,12,13-tetrabromolinoleic acid and 9,10-dibromooleic acids. These are the fatty acid residues found in brominated triglycerides.
It is much easier is to just call all of these compounds brominated vegetable oil or BVO but that is part of the issue in discussing these compounds. Using initials or a broad categorical term hides the chemicals in a way which makes them sound more sinister and yet using the chemical names is equally perplexing for most consumers.
It is a no-win situation.
It is important to remember, though, that these compounds are vegetable oils such as soy bean or corn oil. They are naturally occurring compounds in their non-brominated forms.
Molecular bromine itself does not occur as a chemical substance.
It is an oxidant and is converted to the bromide ion in an aqueous environment.
This reaction is why bromine and the other halogens (chlorine and iodine) can be used as bleaching agents and disinfectants.
In any case, molecular bromine is not present in brominated vegetable oils and neither are bromide ions. There is a third way bromine can be found. It is in the form of covalently-bonded molecules.
The bromine atoms are covalently bonded to carbon atoms in these oils.
(The fact that bromine atoms bear the same name as molecular bromine is often confusing and can lead to misinformation.)
A covalent bond makes it very difficult for bromine atoms to be released upon digestion. It is the ionic bromide ions which are linked to the symptoms associated with bromism. Indeed, bromism was a common problem 100 years ago when over-the-counter medicines, such as bromo-seltzer, routinely used bromide salts.
Doctors would even prescribe lithium bromide as a calming agent. It has neurological effects. But an overdose can lead to a long list of symptoms ranging from restlessness and irritability to psychosis, stupor and even coma.
It has been estimated that somewhere between five per cent and 10 per cent of admissions to psychiatric hospitals at the time might have been due to excess consumption of bromides.
Further, acute effects include nausea and vomiting while chronic abuse can lead to anorexia and constipation. Too much bromide can even result in dermatological effects.
Needless to say, better sedatives without these side effects are now available and bromide salts are no longer prescribed.
But that doesn't really answer the question of what brominated vegetable oil is doing in soda pop.
In this case, the vegetable oil is acting as an emulsifier.
Many soda pops - including Mountain Dew - contain flavour molecules which are oils. Oil and water don't mix and if left on their own, the oils would separate from the water and float on the surface of the soft drink. In essence, the oils would rise like the cream in milk or the bubbles in beer.
What an emulsifier does is act as a soaping agent. It contains a non-polar chain which is attracted to the oil and a polar head group capable of interacting with water.
The result is a cloudy dispersion of tiny drops of oil throughout the soft drink.
However, the flavour oils are also less dense than water - typically 0.97 g/mL - which means they would still float to the surface over time. But brominating vegetable oils makes it denser - typically 1.33 g/mL - and the resulting emulsified droplets composed of flavour and vegetable oil match the density of water.
In other words, the flavour oils want to float but the brominated vegetable oils weigh the droplets down.
Of course, brominated organic compounds are used as flame retardants and there is a great deal of concern about their safety.
Certainly when over-consumed, they can lead to the symptoms of bromism.
One patient who drank between two and four litres of soft drink per day had bromide levels that eventually resulted in paralysis below the waist. In his case, removing the soft drink from his diet and using dialysis to extract the bromide from his blood eliminated his symptoms. But the high dose of brominated organic compounds could have other lasting effects.
More concerning though is our massive consumption of soda pop, period.
But as for brominated vegetable oils, they are being phased out of soda pop.
