In the first post I started giving some background information on radiation danger on the event of the 30th anniversary of Chernobyl. Most people accept the dangers of high doses of radiation. The disagreement is over whether constant small doses of radiation are bad for you. This area is confusing with lots of polemical websites putting opposite points of view. To add to the murk even for someone who has worked with radiation in the lab the units used are confusing. A couple more background points (no pun intended) I need to made before we move on. The first is that we are constantly exposed to radiation all the time. The sources are from space (cosmic rays) and from naturally occurring radioisotopes in our bodies and environment. Even this background dose seems to be disputed with some people saying its about 6millisieverts/year, others putting it lower at 1-3. It is said to have risen due to bomb tests and civil nuclear power. The second point is that radiation damage occurs by what is regarded as ionising radiation (that mentioned in the first post) forming free radicals. These are shortlived atom(s) with unusual and unstable number of unpaired electrons. They interact rapidly with chemicals in our body such as DNA damaging them. This can lead to cancers but also other effects such cardiovascular disease.
There are several areas of uncertainty when it comes to low doses. The first as was made plain in the letter given in the link above is where and how the dose is received. The unit dose for gamma rays and alpha particles could be the same but the alpha emitter must be swallowed or on the skin. Hence the dose could be delivered in a concentrated manner to one particular organ. The same dose of gamma over the whole body would likely not be as damaging. As an example of this I went to dentist today. He would not give me an X-ray since it was too soon after the last one. The dose would have been 0.1millisieverts which is not much in whole body terms, but of course I would be getting it on one small part of jaw.
The second area of uncertainty arises from if you were living close to Chernobyl what particular isotope you ingested. I worked with Iodine-125 (the number refers to its atomic mass). This is a potent gamma emitter and is produced in nuclear reactors. Its leaked from reactors such as Calder Hall in the past. However the turnover of iodine in the thyroid gland is very high. We had a stock of iodine tablets, if you were irradiated you take some some of these and pee the radiation out. Radioactive sodium or elements chemically similar to it would be the same. The problem arises where the turnover is slow or almost non-existent. Radioactive carbon is one example and strontium which is similar enough to calcium to end up in the bone marrow is another.
Another area of uncertainty is that the idea of a cumulative dose is hard to measure at low levels and hard to work with scientifically.
The last problem is due to the ethics of exposing people to low levels of radiation. This tends to automatically limit the studies. Theses (such as they are) have used Japanese bomb survivors, Chernobyl cleanup workers, people living around nuclear plants and astronauts (the dose they receive cannot really be described as low though).
The evidence stacks up as follows. There do seem to be more cancers in Nagasaki survivors who received low doses (see http://www.nap.edu/read/11340/chapter/2). There has been one very large study on Chernobyl clean up workers which claims a significant increase in Leukaemia rates. There have been some studies that have found Leukaemia rate increases around nuclear power plants. To the best of my knowledge there have been no major increases in cancer rates in astronauts.
I would ask the following questions about the above. How did scientists determine the Nagasaki survivors dose retrospectively and know it was low? On the Chernobyl workers as we wrote in our book its hard in the ex-Soviet Union to determine whether someone has died of other causes due to the low life expectancy and very unhealthy lifestyles (its also difficult to get hold of such data in Russia). On the childhood Leukaemia rates the data does not always prove a link (in fact in this table only one study does show a significant rate). The problem with these latter studies as you will see is that the numbers are so small. A small number of outliers can skew the stats.
Looking into this from what I have found I don’t think the low level radiation dose theory is proven. However that does not mean I would want to live in the Chernobyl exclusion zone or think the scientific logic is flawed. Essentially at an individual level you are looking a random event. It takes changes to 3 or 4 genes to trigger cancer. Radiation could be the trigger for all or none of these, it depends where you are are and what you are in contact with. There is though a precautionary principle and many effects in biology are exponential i.e. a small trigger has a huge effect. There is no good reason to build more nuclear power stations for a variety of reasons -this is just another one. We may have to rely on space research to look for an answer here.
PS Incidentally I heard a epidemiologist on the 5pm news last night who confirmed my points on the Chernobyl workers it looks like there was an effect buts its hard to prove.