How do we know if a particular chemical is safe to use?
Well, there are a number of things we can look at: but it must be borne in mind that in some cases all we can do is make an educated guess.
You see, there are literally billions of chemicals, and they simply cannot all be tested. They are being invented at a greater rate than they can be tested, and unfortunately it is a simple fact of life that testing regimes cannot keep up.
This is why it takes so long for new drugs to be approved. For anything that is going inside the human body, very strict testing protocols must be adhered to and this takes some time. But the good thing about that is that if you were going to take a drug that had been approved for sale, you could be confident that it had been properly tested.
But other chemicals are simply not exposed to such rigourous testing. Suppose, for example, that a new process of making plastic dashboards in your car was developed, with a new type of plasticiser that was resistant to damage by UV radiation (sunlight).
Such a chemical may well be tested for acute toxicity, but not chronic toxicity. That is, it could well be that it had no immediate effect on you, but over 10 or 20 years, it may – perhaps causing cancer. Please note, this is just an example – I’m not saying that plasticisers in the plastics in your cars are damaging your health.
In this kind of situation, data for toxicity would generally come from examining the available data for similar chemicals, as often the chemical behaviour will be about the same.
As and example of this, if petrol ever comes into contact with groundwater, the biggest concern are the so-called BTEX chemicals – benzene, toluene, ethylbenzene, and xylene. If you compare the structures of these chemicals, they look pretty similar, and so their properties are pretty similar.
The other problem with predicting the effect of a chemical on the human body is that the chemistry of the human body is unbelievably complex and it’s very hard often to pinpoint reaction pathways and mechanisms.
There are a number of categories that chemicals may fall into in terms of their toxicity. Mostly, there are three areas that we must concern ourselves with.
Firstly there is acute toxicity. Secondly there is chronic toxicity. And thirdly there are chemicals that are carcinogenic/ mutagenic/ teratogenic.
We will look at these over coming days, and how to find and interpret the relevant safety data.