WHY USE A RADIOISOTOPE?

When researchers contemplate using a radioactive compound there are several things they have to consider. First and foremost, they must ask the questions: is a radioisotope necessary, is there another way to achieve our objectives? The reason for this is that radioisotope use is governed by very strict legislation. The rules are based on the premise that radioactivity is potentially unsafe (if handled incorrectly) and should therefore only be used if there are no alternatives. Then, once it is decided that there is no alternative, the safest way of carrying out the work needs to be planned. Essentially this means using the safest isotope and the smallest amount possible.

But why do we use radioisotopes in the first place? There are very good reasons; here are some of them. Firstly, it is possible to detect radioactivity with exquisite sensitivity. This means that, for example, the progress of a chemical through a metabolic pathway or in the body of a plant or animal can be followed relatively easily. In short, much less of the chemical is needed, and the detection methods are simple. Secondly, it is possible to follow what happens in time. Imagine a metabolic pathway such as carbon dioxide fixation (the Calvin cycle). All the metabolites in the cycle are present simultaneously so a good way to establish the order of the metabolism is to add a radioactive molecule (e.g. 14C-labelled sodium bicarbonate) and see what happens to it.