News from Tokyo that radiation in the water supply is twice the level considered safe for infants is yet another worry for the citizens of Japan. The authorities there have recommended that people in the city do not allow babies under one to drink tap water. So how much risk is there?

As many people have pointed out, and has been mentioned here before, we are all exposed to radiation all the time, from the environment and from medical procedures like x-rays. The Health Protection Agency says the average dose per year in the UK is around 2.7 millisieverts (mSv), but is higher for people in some parts of the country. In Cornwall, the average annual radioactive radon dose to people is 7.8 mSv.

So what about Japan? There were reports that Tokyo's tap water contained, at one point, 210 becquerels of radioactive iodine per litre. That is twice the recommended limit of 100 becquerels for infants although below the 300 limit for adults. Becquerels is a measure of radiation emmitted whereas millisieverts is a measure of dosage on the body (there are many handy guides to these terms on the web).

Professor Richard Wakeford from the Dalton Nuclear Institute and visiting Professor of Epidemiology at Manchester University said the health effects would be extremely small. He calculated that drinking water for a year at the Japanese limit would give an infant a dose of 0.4mSv, so you would need to double that to get the effect of drinking water at the higher level of radiation for a year. Professor Wakeford said "in theory, there would be a very small additional risk of cancer, but in practice nothing more than you could expect to get from normal background levels of radiation".

So the extra risk from drinking tap water in Tokyo for a year would be far less than that of someone moving, say, from London to Cornwall for a year.

As several scientists have pointed out, the alert about drinking water in Tokyo is simply a sensible precautionary measure, based on the principle that if you can easily avoid risk, you should do so.

Dr Jim Smith, Reader in Environmental Physics at the University of Portsmouth said: "It should be emphasised that the limit is set at a low level to ensure that consumption at that level is safe over a fairly long period of time. This means that consumption of small amounts of tap water - a few litres, say - at twice the recommended limit would not present a significant health risk. I would expect that the recommendation not to drink tap water would also extend to women who are pregnant or breastfeeding."

Prof Wakeford added: "The primary objective is to limit the radiation dose to the thyroid gland of infants and young children, because it is well established that infants and young children are at the greatest risk from the accumulation of radioactive iodine in the thyroid. The contamination limits keep the resultant doses to tolerable levels."

Nonetheless, one bit of newswire copy said that the tap water alert in Tokyo was sending "anxiety levels soaring over the nation's food and water supply". Residents in Tokyo are reportedly clearing the supermarket shelves of tap water. On Sunday, milk, spinach and other vegetables from areas near the Fukushima plant were found to have radiation levels higher than regulated standards, but the Japanese authorities said it did not pose an immediate risk to health.

I do not mean to underplay the issue of the Fukushima nuclear leak. But the dangers from Tokyo tapwater do not bear any comparison with the earthquake and tsunami where there are currently nearly 9,500 confirmed dead and more than 14,700 people still missing.

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?

"The situation is definitely more serious". That is how the government's Chief Scientist has summed up the rapidly developing crisis at Fukushima. Professor John Beddington altered his assessment of the situation because of the loss of water covering spent fuel rods stored in ponds close to the reactors.

In this rapidly developing crisis, this is causing "considerable concern" according to Professor Beddington, speaking in a TV interview. American, French and British nuclear experts who are monitoring the situation believe that the pond in Reactor 4 is all but gone.

He explained that the worst case scenario is that the fuel rods could start to burn and emit substantial amounts of nuclear material into the atmosphere. Professor Beddington said he was also "extremely worried" that the fuel tanks in Reactors 5 and 6 are leaking and if open to the air might emit significant amounts of radiation which would undermine the ability of the Japanese emergency workers to continue their efforts to control the situation.

So what does this mean for the potential health risks? Up to now Professor Beddington had supported the line taken by the Japanese authorities, that any danger was confined to within a 30 kilometre (18 mile) radius of the reactors.

Now he believes: "The situation is definitely more serious both within the area and further afield". The Scientific Advice Group for Emergencies (SAGE) which advises the government, have looked at "plausible worst case scenarios". For days that has been a potential meltdown of some of the reactor nuclear material but now a potential fire and release of radioactive material from the fuel rods has to be added in. Professor Beddington said if both these things happened and there were unfavourable winds, then radioactive material could affect Tokyo.

But he added this caveat: "Even in that situation we think the level of radiation that would come into the Tokyo area would be such that you could mitigate against it with relatively straightforward and simple measures - such as staying indoors with the windows closed."

British nationals are being advised to stay at least 80 kilometres (50 miles) from the nuclear plant, and to consider leaving Tokyo.

update 1530

"We are right to be worried by need to put the risks in context" said Gerry Thomas, Professor of Medical Pathology at Imperial College London. She is concerned that the dangers to human health are being exaggerated by some in the international media and could cause "psychological damage" to the Japanese.

She said that, even in the worst-case scenario, with a large release of radioactive material from Fukushima, the health dangers would be minimal.

"The Japanese are doing the right things - giving people iodine tablets, setting up an exclusion zone and asking people to stay indoors". Even if radiation from Fukushima reached Tokyo she believes the long-term health risks would be minimal.

Gerry Thomas is an expert in the health effects of radiation and has been studying tissue samples from many of the cancer patients affected by the Chernobyl disaster. Like other experts she said Fukushima was in no way as serious as Chernobyl and she urged those reporting the situation not to overplay the situation.

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?

Images of helicopters dropping sea-water on the Fukushima nuclear power station, and of some worried residents leaving Tokyo, present a startling and unsettling picture. Watching the news and reading the papers it would be easy to be left with the impression that the health risks from the nuclear leak are rapidly escalating and spreading far beyond the exclusion zone.

The latest advice from the British Foreign Office may also add to the sense of unease:

"Due to the evolving situation at the Fukushima nuclear facility and potential disruptions to the supply of goods, transport, communications, power and other infrastructure, British nationals currently in Tokyo and to the north of Tokyo should consider leaving the area."

But if you read on, the travel advisory from the FCO is more reassuring:

"The most recent advice from the UK's Chief Scientific Adviser (Sir John Beddington) remains that for those outside the exclusion zone set up by the Japanese authorities there is no real human health issue that people should be concerned about. This advice is kept under constant review."

The exclusion zone is 20 kilometres (12 miles) around the plant. Those living between 20-30 kilometres away (12-18 miles) are being advised to stay indoors.

Sir John Beddington spoke by phone two days ago to British Embassy staff in Tokyo and a transcription of his comments is, I think, worth setting out in detail. He said:

"....do we have any concerns now in terms of human health? Well the answer is yes we do, but only in the immediate vicinity of the reactors. So the 20 kilometre exclusion zone the Japanese have actually imposed is sensible and proportionate. If they extended out a little bit more to 30 kms, that is well within the sort of parameters that we would think are extremely safe."

Of course, everyone is concerned about what might happen if the situation at Fukushima gets worse. Sir John went on to talk about the worse case scenario - a meltdown at the plant. He did not think this was likely, but what would be the result if it did?

"In this reasonable worst case you get an explosion. You get some radioactive material going up to about 500m up into the air. Now, that's really serious, but it's serious again for the local area....The problems are within 30 km of the reactor. And to give you a flavour for that, when Chernobyl had a massive fire at the graphite core, material was going up not just 500m but to 30,000 feet (9,144m) . It was lasting not for the odd hour or so but lasted months, and that was putting nuclear radioactive material up into the upper atmosphere for a very long period of time. But even in the case of Chernobyl, the exclusion zone that they had was about 30km. And in that exclusion zone, outside that, there is no evidence whatsoever to indicate people had problems from the radiation. The problems with Chernobyl were people were continuing to drink the water, continuing to eat vegetables and so on and that was where the problems came from. That's not going to be the case here. So what I would really re-emphasise is that this is very problematic for the area and the immediate vicinity and one has to have concerns for the people working there. Beyond that 20-30km, it's really not an issue for health".

Sir John is not alone in his assessment of the health risks. It is similar to comments I have heard by many other scientists.

On Today on BBC Radio 4, Professor Laurence Williams, former UK chief inspector of nuclear installations, stressed that Fukushima was not another Chernobyl and made it clear if he was living in Tokyo he would not leave:

"....I wouldn't be concerned. This is not a Chernobyl. We are not going to see high levels of radioactivity being put up high into the atmosphere and distributed on the winds. If we do get to the worse situation where the fuel in those reactors slumps because it doesn't have any structural integrity because of over-heating, then there will be a release of caesium and iodine (although the iodine is decaying all the time) and there will be strontium and ruthenium and other things that will come out....my guess is it is a low-level release and very localised it will not be like Chernobyl. People living in Tokyo are 150 miles (241km) away, so I would not be worried."

So even in the worst-case scenario, the risks to human health beyond the exclusion zone appear to be low. The main immediate threat to health is to the emergency workers trying to stabilise the plant. Radiation levels at the plant have fluctuated and we don't know exactly what materials are leaking out, nor in what quantity, nor over what time period.

Finally a note on potassium iodide tablets. Radioactive iodine from a nuclear leak can pollute the air and contaminate the food chain. Potassium iodide tablets can block radioactive iodine from being taken into the thyroid. The Japanese authorities have distributed these to people in the vicinity of Fukushima as a precautionary measure. But sales of iodide tablets have also soared in the US, thousands of miles away. It is not proportionate or sensible, but an indication of the level of unease that a nuclear accident can cause.

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?