Bang Goes The Theory: Series 5, Episode 8

For an answer to my question: 'Nuclear Radiation 06 Oct. 2011' I contacted MARINET, the Friends of the Earth Marine Network www.marinet.org.uk. and received this reply, I share it in that it may prove informative to others:

I too saw the programme and thought it of good quality, except for the lady from London University who tried to persuade us that more people die from driving cars than from exposure to radiation - a very dodgy piece of science, and I'll explain why in a moment.

First, let me answer your question about whether the sea is made radioactive. The answer is that the water and the other chemical compounds in the sea are not made radioactive, but the sea does become radioactively contaminated if radioactive material is discharged into it. Thus the H2O still remains normal, but if water goes through a reactor the hydrogen and oxygen atoms can be made unstable (radioactive) and thus this water becomes radioactive and, if discharged into the sea, will contaminate the sea. Obviously there is a dilution effect, and exposure depends on how much material is discharged and how near you are to the point of discharge (dilution will be greater the further you are distant from the point of input).

Radioactive discharges contain not just unstable (radioactive) hydrogen and oxygen atoms. Any element can be made unstable, and if the element has been through a reactor it will become radioactive and, if discharged to sea, will contaminate the sea. Thus discharges from Sellafield, for example, which handles nuclear waste and makes discharges to sea will deposit in the sea a wide range of radioactive elements. Nuclear power stations will behave in a similar manner, but at a less intensive level than Sellafield.

The fate of these discharged unstable (radioactive) elements depends on how they react in water i.e. is the element soluble or insoluble. If it is soluble (e.g. caesium) it will become widely dispersed in the sea water, and the level of contamination of the sea water will depend of the scale and constancy of the discharge. Also, if it is soluble, it is very likely to be absorbed by fish.

If the unstable element is insoluble, it will remain in the water column until such time as a process occurs to remove it. Such a process may be biological e.g. plants (such as seaweed) and animals (fish and shellfish) use elements in the construction of their bodies and tissues (like we need iron, sodium and so forth) and so if the sea water contains radioactive versions (isotopes) of these elements they may become absorbed by the plant or animal's body. If this is so, then the animal or plant experiences internal exposure to radiation.

Insoluble elements can also be trapped in the physical, geological structure of the marine environment e.g. between the grains of sand. However it is muddy sediments on the sea bed and in river estuaries that generally become the most radioactively contaminated (if discharges are made) because mud is very glutinous and thus particles which come into contact with it adhere to it. Muddy marine sediments can become major pockets of radioactivity if discharges of contaminated material is made to sea. The muddy marine sediments around Sellafield, for example, display this characteristic.

It should also be borne in mind that naturally occurring unstable (radioactive) atoms exist all around us - what is termed "natural background radiation" - and the sea will naturally contain a degree of radioactivity. However, when discussing discharges, we are essentially talking about radioactivity created by man, and thus levels of radiation that are elevated above natural background levels.

If you want to see what the levels of radioactivity are around the coasts of the UK, you should consult the following publication Radioactivity in Food and the Environment (RIFE) published annually by the Environment Agency http://www.environment-agency.gov.uk/homeandleisure/110353.aspx

With regards to the degree of danger posed by exposure to radiation, all radiation (radioactivity) is dangerous. What matters is the type of radiation you are exposed to (alpha, beta, gamma, x-ray, neutron), whether the exposure is internal or external to the body, and the level (amount) of exposure. As you will appreciate, there are a number of variables here.

However the essential point is that when exposed to radiation either a particle from the unstable atom or energy emitted from the unstable atom passes through the cell(s) of the body. Each cell contains DNA (which it uses for its replication) and if radiation passes through a cell and damages its DNA then a problem can potentially arise. If the DNA is badly damaged, the cell will not replicate and simply dies and the body will generally dispose of the dead cell without any problem. However if the DNA is only slightly damaged the cell may still retain the capacity to replicate, but in a distorted manner - that is when problems can arise. The body has the capacity to remove cells that are malformed, but if the exposure of cells is prolonged (because the radiation has become lodged in the body) then the continuous production of malformed cells may become too much for natural body processes to handle. That is when and how a radiation induced illness can be generated.

Unless exposure to radiation is very intense (i.e. causes massive cell death), the body can usually "tolerate" exposure to radiation in the short to medium term, but over the longer term things become more problematic. Indeed, the "ageing process" is thought to be heavily influenced by exposure to natural background levels of radiation. A radiation induced illness usually has an incubation period, measured in months and years.

Thus when so called experts come forward and say that only a handful of people died from Chernobyl compared to tens of people who die on the roads everyday, they are totally distorting the nature of the event. What is important about exposure to radiation is that the ill effect is delayed, often taking a long time to emerge and kick into effect. Thus, when assessing death or illness rates due to radiation exposure, one has to try to determine whether naturally ocurring diseases and illness are either "brought forward" (i.e. occur earlier in one's life than might other wise have been the case) or are made more likely ( i.e. whether there in an increased incidence in the general population over time). Many medical studies purporting to assess the effects of radiation do neither of these epridemiological tests (probably because they are difficult to trace and very costly to conduct, which is rather "convenient" for advocates of nuclear energy who want to downplay the adverse effect of their technology).

Given that exposure to natural radiation is a significant causal factor in the ageing process, exposure to additional radiation due to man-made radioactivity will likely accelerate the ageing process i.e. bring forward or trigger biological/physiological events in one's life. Thus to compare exposure to radioactivity with a short term, immediate event like a car crash is very misleading. Intense exposure to radiation will kill, but exposure to less intense, lower levels will impact in the medium to long term, rather than the short term. This is an essential difference.

When it comes to whether nuclear power is safe or unsafe (both during the operation of the plant and in the management of its waste materials) why run all the risks described above when you can have renewable energy which has virtually none of these risks at all . . . .

I hope this has addressed your enquiry. If you have additional thoughts, simply let me know.

www.marinet.org.uk

Dear Charlotte,

Thanks for your question. I’ll do my best to answer some of the points you raise, although I must say right from the start that of course I do not know anything about your mother’s particular case. I’ll start by talking about the effects that radiation can have on people.

As was stated in the programme, radiation damages cells, most often by damaging the DNA at the centre of the cell and therefore affecting the way it reproduces. Scientists distinguish two different types of effects due to radiation; the first is the case where there is a large dose of radiation to all or part of the body. This is done deliberately in radiotherapy and has the effect of killing the cells – exactly what you want to do to a tumour. As you saw in the programme the modern radiotherapy machines are designed to target the tumour tissue to kill it and to spare as much of the normal tissue as possible. This is hard when the tumour is deep in the body but modern radiotherapy machines are getting better and better at doing it. This means that the damage to healthy tissues, and therefore the side effects, are as low as possible. Other than from radiotherapy, this kind of damage is very rare – there were cases amongst the firemen at Chernobyl who experienced huge doses when they entered the reactor. Another famous case was the Russian who was poisoned by polonium-210 a few years ago. These kinds of effects are known by scientists as ‘deterministic effects’ and the severity of the effect depends on the dose of radiation given in a way that is well understood.

The second kind of effect was also mentioned in the programme – it is the case where a much smaller dose of radiation leads to a slightly increased risk of developing cancer. Because everyone’s risk of getting cancer at some time in their life is pretty high (about 1 in 3) it’s hard to work out how much extra risk is due to radiation. Data obtained from Hiroshima survivors who received quite high doses has been used to work out a figure based on the dose received but the result is only ever a probability. You can only say things like ‘because of the radiation dose you received you have an extra chance of 1 in 1000 of developing cancer at a later date’; you can never say which of 1000 people will be the extra one who actually develops cancer. (Remember that about 333 of 1000 people are going to develop it anyway.) These kinds of effects usually take many years – the figure usually quoted is something like 20 years.

To turn to your mother’s case, you say she received some radiotherapy after surgery for a skin cancer. Usually the radiation used for treating skin cancers is comparatively low energy X-rays and these do not penetrate very far into the body. This means that the dose in the region of the cancer should have been large enough to kill the cells but the dose elsewhere should have been very low. It is a very effective treatment for several types of skin cancer. Given that you say that the new cancers that developed were of the same type as the original cancer, I would have thought that they have developed from that and are not a result of the radiation treatment, but obviously I cannot comment in more detail.

Perhaps I should add that radiotherapy, where the tumour is accurately targeted, is very different from the situations where people receive a dose over the whole body in nuclear accidents. There continues to be a large amount of research effort going into finding out more about how radiation damages cells – both cancerous and normal - and to working out the best way to deliver radiotherapy. It remains a very effective treatment for many forms of cancer.

Best wishes

Liz Parvin
Senior Lecturer in Physics