EDTA turns up near the bottom of the ingredient lists of lots of different personal care products. You also see disodium EDTA and tetrasodium EDTA. For all intents and purposes these are the same – they are just different ways of delivering the same thing.
The official name EDTA avoids having to use its full name, ethylenediamine tetraacetic acid. This is handy for typesetters but spoils it for chemists who appreciate the rather beautiful symmetry of this molecule, and who can see from it how it works. Basically it has 4 arms, each with a negative charge at the end. This enables it to wrap itself around positive charges, such as are found on dissolved metals like iron, copper, manganese and so on.
This is useful because these impurities can cause some issues in certain circumstances. The main ones are catalysing reactions and so speeding up the break down of the product. They can also provide nutrition to spoilage organisms. That at any rate is the story. I have never found including EDTA in formulations to have any particular benefit. I think this might simply reflect the fact that the water in use in the cosmetics industry today is purified and doesn’t have anything in that the EDTA might work on. I have stopped using it and never regretted it.
But it continues to be popular and there is probably a good case for using it in particular circumstances. Use levels are tiny – typically about 0.01% and sometimes even lower. There is no question of it being toxic. In fact EDTA is a counter toxin. If you somehow end up swallowing something unpleasant, the chances are you’ll be given EDTA to deactivate it.
So there is no conceivable problem for the user with the tiny traces of EDTA in the product. The question is what effect it might have later on when it gets into water courses. This is where it gets controversial. Inactivating metal ions is quite likely to have an impact on a biological system. Metals are key nutrients, so if you make a proportion of them unavailable this is going to cause problems. You could refer to this as eco toxicity. I think this is a bad term though. It sort of implies that a material only has a harmful effect. Life is never that simple.
So we have a theoretical risk that EDTA can disrupt aquatic environments by interfering with nutrient uptake. Is there any evidence? One of the most cited reviews of the literature reveals that lab work has indicated the risk is a real one, but it hasn’t really been confirmed by observations in the field. That review is from 1997 so possibly more has to come to light since. I did a quick search and found a recent paper that indicated there was no problem with waste water from an industrial plant in Finland.
EDTA has many uses besides its use in cosmetics. Most of what is getting into water will be coming from industrial processes rather than household use. Even in the household, laundry products will be a much bigger source than creams and shampoos. I haven’t seen any evidence that links any specific environmental problem to the presence of EDTA . But it has one quality that I think we should always be uncomfortable with. It is a very stable molecule and so persists for a long time. This means if it turns out to have some unexpected issues we haven’t yet identified we can’t get rid of it at all easily. It also means that the level in the environment is likely to increase over time. So if there is some problem that only kicks in once a certain level is reached, we might be storing up problems for the future. I’d much prefer it if some clever chemist somewhere could come up with a biodegradable alternative.
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Review of the fate of EDTA and similar compounds in the environment
Finnish study of industrial waste waters