Endocrine Disruptors – What Are They?
Endocrine disruptors are a bit of a tough subject, so before starting this post I went for a walk to think it over. After a disappointing summer the god responsible for the weather had given us the consolation prize of some balmy warm days in late August. It was mild and I could cross the fields by the light of a harvest moon. It often happens at this time of year that the full moon rises just as the sun sets, so this was traditionally handy for farmers busy getting the crops in. But it was handy for a mind clearing walk too.
It reminded me of a bit from Flaubert’s novel Salammbo. The novel is set in ancient Carthage, and in one scene there is a moonlit procession of white linen clad priestesses through pomegranate groves to the temple of Tanit, the goddess of the moon and of fertility. I don’t know how much of that scene came from Flaubert’s imagination. I read somewhere that he did extensive research, so it might well have been literally true. But whatever, there would be a good scientific basis for the pomegranate being sacred to a fertility goddess.
Pomegranates contain phytoestrogens which could promote fertility in the right circumstances. Phytoestrogens are similar to estrogen itself, which is a key part of the endocrine system. Materials that mimic estrogen can act as endocrine disruptors.
Pomegranate seed oil has been investigated, inconclusively, as a treatment for menopausal symptoms. I haven’t found any studies that show it actually increasing fertility, but I find it easy to believe it might. Other plants certainly can affect the fertility of animals. Red clover for example has been shown to produce an endocrine disruptor that limits the fertility of the sheep grazing on it. It has also been suggested that similar chemicals in soy have harmful effects on humans consuming them, possibly lowering the age of onset of puberty.
Are Endocrine Disruptors A Problem?
Estrogen is a powerful hormone that has lots of significant effects on the body, and so molecules that mimic it have the potential to be very damaging. And they can have this effect at very small levels, particularly when we are talking about developing bodies such as foetuses and small children. It is in the nature of this kind of thing that is hard to unpick cause and effect, so it is an area of public health where caution is paramount.
The only really hard science available in this field is that the ability of a given chemical to mimic estrogen can be measured in the lab. It turns out that there are lots of estrogen mimics out there. The activity is a function of how similar in shape the molecule is to the receptors of estrogen. Many naturally occurring and many synthetic molecules show estrogen like behaviour in the lab and so potentially could be endocrine disruptors.
Endocrine Disruptors Are Everywhere
Given that we are exposed to estrogen mimics all the time, how do we manage to survive? The answer is to be found in the book that started the green movement back in 1963. Rachel Carson’s Silent Spring. She argued eloquently that chemicals introduced into the environment can accumulate through the food chain. She was talking mainly about materials like DDT. DDT in fact is not particularly toxic. When the debate about DDT was going on one of its advocates took to publicly eating high doses of it to prove this point. He came to no harm, as anyone who understood the issue would have expected. It is a shame that an opponent didn’t do exactly the same thing to prove that they realised that that really wasn’t the point.
The problem was that DDT was being used at levels where it should have been perfectly safe. But to everyone’s surprise, it was killing large numbers of birds. The explanation was that birds were eating insects with DDT in them and so concentrating it beyond safe levels. This happened because DDT is soluble in body fat and is very persistent. Rachel Carson was not an opponent of pesticides in general. She states this explicitly in Silent Spring. Her issue was with ones that were harmful to the environment because of their oil solubility and chemical stability.
This was all new and rather surprising in the sixties and seventies, but is now something that is well understood. When you are looking at the possible risks a chemical poses we now know that you need to look at more than simply the toxicity. In fact, toxicity is not even the major consideration. Remember, DDT is not very toxic. Its problems arise from its being very stable and easy to store, so insects could accumulate large amounts of it while still looking attractive as snacks to passing birds.
This lesson can be applied to endocrine disruptors. They may be common, and they may be able to work at very low levels. But to pose a risk they also have to have the right chemical properties to hang around long enough in your body. It is a real enough risk, but it is one that people have been on the look out for for a long time. In fact the first warning of this issue I know about is from Silent Spring itself, about fifty years ago. Since then, no evidence has ever come to light of actual endocrine disruption in humans occurring. But it remains a theoretical possibility. It certainly isn’t something to be dismissed. And it has affected sea birds. The culprit in that case was PCBs (polychlorinated biphenols) and the effect was thinning of egg shells.
Why D4 and D5 Should Be Banned
So it is with all this in mind that I turn to the now rather old story about Health Canada taking action to limit a couple of silicones known as D4 and D5. The precise chemistry isn’t important. The problem with these two materials is that they are stable and can accumulate in the food chain. This is more than just a theoretical possibility. A study has shown them having a harmful effect on aquatic species. I think that Health Canada have got this about right. They have been rightly cautious. Much like adding milk to a cup of coffee, you can’t get it back if you go too far.
I doubt very much that D4 or D5 would pose any direct risk to a consumer using a product containing them. But we need to take a broader view than that. Just because the cosmetics we use are safe for us doesn’t mean we shouldn’t take care about what they do to the planet we live on.
Endocr Res. 2010 Jan;35(1):1-16. Pomegranate (Punica granatum) seed linolenic acid isomers: concentration-dependent modulation of estrogen receptor activity. Tran HN, Bae SY, Song BH, Lee BH, Bae YS, Kim YH, Lansky EP, Newman RA.
I have just realised the link the sheep and clover study is broken. Apologies for any inconvenience.
Silent Spring came out on the 27th September 1962 – exactly fifty years before this post. It remains worth a read.