Radiation and Food Safety: Is Food from Japan safe to eat?

We remember Japan on the one month Anniversary of the great Japan Quake and Tsunami

A lot of people have been avoiding Japanese food because of the fear of radiation in the food.   As a result, restaurants have been reporting sales dropping by as much as 50% to 60%.  Not only are the local restaurants affected, the suppliers are similarly affected.  As consumers, food safety is of paramount concern of course.  But we need to make informed decisions rather than to rely on hearsay.

I feel that part of the reason for the fear of eating Japanese food is the lack of clarity on the subject matter.   So I hope that this concise article will give you a birdseye view of what is happening so that you can make an informed decision to eat or not to eat at your favourite Japanese restaurant.

Realtime radiation map of Japan

Types of Radiation

As you know, there has been radiation leakage following the damage at the Fukushima Nuclear Plant, but exactly what kind of radiation are we dealing with?

There are essentially two forms of radiation.  Ionizing radiation is a form of energy emitted from the damaged nuclear plant which can cause immediate effects like radiation sickness (vomiting, burns etc)  These forms of radiation exist as a form of energy (like light or electromagnetic energy) and are either Xrays or gamma rays.  Exposure to high levels of Xrays can cause damage to body tissues.  But we still do Xrays and CT scans because the amount of radiation exposure is so little that it will not cause any long term harm.  Ionizing radiation can travel very far and in the case of the Fukushima blast, the government of Japan had to increase the safety zone from 10km to 20km which show just how far this form of radiation can spread.  But bear in mind that 20km represents only 0.625% of the entire length of Japan (3200km), so the area affected is still very small.

Radiation contamination in foods is a different matter altogether.  Here we are referring to radioactive nucleotides which you can think of as some sort of radioactive dust particle that can either get into the air or water and spread over a large region to affect vegetables and seafood.  There are two types of radioactive particles we often hear about viz Iodine 131 and Caesium 134/137.

When these radioactive particles are ingested, they can travel to different parts of the body and over time, they can accumulate and cause cancer.  For example, Iodine is normally taken up by the thyroid gland in order to make thyroid hormones.  So if a person accidentally ingests radioactive Iodine , these radioactive form of Iodine will be taken up by the thyroid gland and over time, it may lead to thyroid cancer.

The radiation map above shows the regions of Japan that are affected by radiation.  (This is done by individuals taking radioactive readings and reporting them online) As you can see, the purple regions of Fukushima and Miyagi are the affected areas and there is some detectable radiation in Ibaraki (brown), just south of Fukushima.  The region represents less than 10% of the whole of Japan.  The rest of Japan (the green zones) do not have detectable radiation.

Here is a useful map to view the different regions of Japan

Radiation in Vegetables and Seafood

On 19th Mar, news broke out that there were detectable levels of radiation in spinach and milk which were located more than 90 miles from the nuclear plant.  The milk was from Fukushima (7) prefecture while the spinach was from Ibaraki (8) prefecture.  This has led to our AVA to ban all produce from these areas.  Subsequently, the AVA has banned produce from Tochigi (9), Gunma (10), Saitama (11), Chiba (12), Tokyo (13),  Kanagawa (14), Shizuoka (22) and Hyogo (28).  Except for Hyogo (28), and Shizuoka (22), most of the prefectures lie in the Kanto region which is very close to Fukushima itself.  Although they have detected radiation in the outlying regions, they are at this point unable to tell if the radiation actually came from Fukushima or other sources.  However, to put this into pespective, the AVA has banned foods coming from 9 out of 43 prefectures in Japan.  That means that food from the other three quarters of Japan is still radiation free.

Our AVA has set a very strict standard of 100 bq/kg  for Iodine 131 and 1000 bq/kg for Caecium 134/137.  But what do these levels mean? According to AVA website, these are set at very "Kiasu" (my words - lit scared of losing out) levels. The AVA has issued blanket bans on regions where imported vegetables were found to have levels exceeding 100 bq/kg.  However, according to the AVA, these levels still pose only a tiny risk such that if an adult ate 3.5kg of these vegetables, he would receive a similar level of radiation exposure of one X-ray and he would need to consume 184 kg of these vegetables to receive an exposure level equivalent ot the normal background radiation a person is exposed to in a year.  That means that even if you are a good boy/girl and ate all the veggies in your next Japanese meal and they all happen to have escaped the AVA's radiation detection, you would still get much less radiation from eating that than from one single X-ray.

In terms of Seafood products, fish from Ibaraki (8) region was found to contain radiation, so as a result, fishing co-operatives in that region have stopped all fishing activity there.  The contamination of seafood is presumably due to the leakage of radioactive water into the ocean from Fukushima nuclear plant.  According to Marine chemistry expert Ken Buesseler of the Woods Hole Oceanographic Institution, "the levels of radioactive iodine and cesium drop a thousand-fold from the coast adjacent to the plant to about 19 miles (30km) offshore." ie there is very little radiation in the seawater 30km from the plant.  But as a safety measure, fishing off the coast of Fukushima (7), and neighbouring Miyagi (4) and Iwate (3) regions have been halted to stop any chance of contaminated fish reaching the markets.

Radioactive Iodine does accumulate in seafood but its half life is very short, only 8 days, which means that in one month the radioactive Iodine ingested by the fish is gone. However, the problem of radioactive Caesium is still unclear.  Since the half life of radioactive Caesium is 30 years, this might accumulate in the fish.  Some fish from the Chiba prefecture was found to contain radioactive Caesium but at levels far below safety levels.  There has been a study that shows that Caesium only stays in the fish for 50 days and passes out through the urine, but we will need more evidence before we know for sure what is really happening.   Whatever the case may be, the Japanese govt has said that they will set up systems to prevent contaminated fish from reaching the markets and our AVA is conducting surveilance on each shipment of seafood coming to Singapore.  Soso far no radiation has been detected in any shipments of seafood coming from Japan.

As you can see from the map of Japan that there are still many coastal regions of Japan that are unaffected by radiation and some so far away from Fukushima that the seafood is still very safe to eat.  So if you are given some Hokkaido (1) scallop or Kanpachi/Hamachi which are harvested from the fish farms in Kagoshima (46), you can be assured that they are still very safe.

How Radiation is Measured

One of the confusing things about the whole issue is the various units of measurements use to describe radioactivity.  The reports often use Becquerals, Grays and Sieverts to describe the amount of radiation which can cause some confusion.

In a nutshell, the simplest unit of measurement is the Becqueral.  This unit simply measures the amount of radiation eminating from anything.  When the AVA measures the amount of radiation found in food, this is the unit of measurement used.  To measure the amount of radiation in a fish for example, they would take a sample of the fish, put it into a machine (all this takes place at SGH) and measure the amount of radiation in the sample. 

The Gray measures the amount of radiation that is actually absorbed.  Because there are different types of radiation sources, each type may have the same amount of radiation but cause different levels of damage.  So Xrays and radioactive Iodine might have the same radiation levels but how much of it is actually absorbed by a person may be different.  So if you take Bequerals as the number of words that your wife is saying, Grays is the number of words you actually heard. Know what I mean?

The most complicated unit of measurement is the Sievert.  This unit of measurement takes into account the cumulative dosage of radiation and its effect on the human being.  You can say that the the person was exposed to 8 Grays of radiation, but that does not tell you how much harm has been done.  Whereas with the Sievert, you can say that a person who has received 8 Sievarts would probably not survive the exposue.  So if Grays is the number of words you heard your wife say, Sieverts is the number of words that would eventually get you off your butt and go get the TV fixed.

Here is the excellent BBC article which explains these terms clearly.

Radiation Chart click here

The above Radiation chart gives you a fascinating perspective on the effect of radiation exposure expressed in Sieverts.  For instance, 10 minutes of exposure to the Chernobyl reactor after meltdown gives you an exposure 50 Sv, (8 Sv is fatal).  Each day, you are exposed to 10 microSv of radiation just by living on planet earth, one Chest Xray exposes you to 20 microSv (same as eating 3.5kg of the radioactive spinach from Japan) whereas a Chest CT scan is worth 5.8 mSv of radiation.  The lowest dose that has been shown to increase cancer risk is 100mSv.  Since 1000 microSv = 1 mSv, that means you would need at least 5000 Xrays or eat 17500kg of spinach to develop cancer.

In other words, the current levels of radiation found in the veggies from Japan are really so small that they are unlikely to cause cancer even if they are ingested.  However, since we want to be even more Kiasu, the AVA won't even let them come to Singapore.  In fact, they won't even let any other veggies from the same area of Japan come in once one such veggie has been tested positive for radiation.  That is how Kiasu they are which is good, 'cos its better to be Kiasu than to actually "su" (lose).  Or should I say its better to be Kiasee (scared of dying) than to actually "see" (die).

So, I hope this little post will put everything in proper perspective.

If you have enjoyed Japanese food in the past, there is no reason why you should stop going to your favourite Japanese restaurants now.  Yes, we should all pray for Japan, but there are some very practical (and enjoyable) things that you can do after you have prayed and that is to eat their food and in so doing support their rebuilding efforts!

Continue to read Part II here

AVA website here
WHO FAQs on the Japan Nuclear concerns here.
Japan Ministry of Health, Labour and Welfare Earthquake site here
Japan Ministry of Agriculture, Forestry and Fisheries here
BBC guide to life, the universe, everything: Radioactivity here
Newscientist:  Nuclear Crisis: How safe is Japan's food and water here
Healthcare news: Radiation and Food, are you what you eat? here

Update 16 May
AVA has lifted bans on produce from Shizuoka and Hyogo


reychen said...

I would categorize this as a comprehensive "report analysis!"

Thanks for the time and effort you've put in, Leslie.

Anonymous said...

Thank you very much for this writeup. =) I love Japanese food, and will continue to patronize the Japanese restaurants here.

I do like to point to news articles that have somewhat of a different conclusion from yours regarding radiation though, just so people can have a more "informed" perspective, whatever that means.



Joao said...

Very informative and educational! Will spread this around.

Anonymous said...

Hi Dr Tay,

Thank you for a great concise and appreciate your effort in allaying fears! Will definitely share with my friends and family.

I can feel the pain of the people dealing with Japanese food, even the sushi and makis are not moving in the supermarket.

Fresh Fry aka 福星 said...

bravo! kudos to your effort to educate us!

Holy Drummer said...

This post is timely in addressing any preconceived notions we may have on the effects of radiation.

Personally, I don't see any compelling cause or reason to fear - actually maybe because I just love Japanese food too much to care LOL. For me I just wonder if prices are going to maintain or drop haha! So would eating at Japanese restaurants be even cheaper now as a result of the greater dip in demand despite the shorter supply? It'd be a bonus for consumers like me =p

Think AVA safeguards are already firmly in place to ensure that the strictest food safety standards are adhered to, notwithstanding the radiation crisis. Situation seems to be under control in SG.

Hope the article clears the air hurhur =p

Lee Lee said...

Thanks Dr Tay for helping us understand what is the actual scenario as well as educating us on the limits one needs to be infected or affected before the onset of cancer.

ieat said...

Many thanks for all your comments. I am glad you all find it useful!

cactuskit said...

Thks for putting all together in this post. Read bits here and there but this directly allay the concerns.

Anonymous said...

Hi Leslie,

I have been a fervent follower of your food blog for the last 4 years, and I read your most recent post with interest. While I find it heartwarming that you have taken the effort to re-instill trust in Japan's products, I also share your view that the consumer should be informed with the facts before making their choices.

I have complete faith that you did your homework on this topic. However, as with all academic analysis, let there be questions on this one too. In particular, I am concerned that you have mentioned that "radioactive caesium does not accumulate in fish". This statement was backed by an FAQ from a Japanese fishery.

Firstly, it is not certain that radioactive caesium does not accumulate in fish. Caesium is known to accumulate in the soft tissues and muscle mass of humans. (http://www.epa.gov/rpdweb00/radionuclides/cesium.html#body ) Although it may be hypothetically possible that fishes retain less of it due to them being submerged in an aquatic environment, this is not backed up with any extensive study or empirical results (I did a quick search on the literature regarding cesium). The notion that fishes do not retain caesium is based mostly on intuition and extrapolation of limited data.

Secondly, the amount of caesium in fishes also depends on how high they are in the food chain. Predatory (large) fishes are likely to contain larger amounts of caesium than a small fish, primarily due to 2 factors: 1) diet consist of caesium-laden fishes and 2) lower surface area to volume ratio, thus leading to less effective removal from body. As such, even if small fishes from Japan, say a baby tuna, does not carry significant sources of caesium, it does not mean that all fishes from Japan would have the same level of caesium. In particular, fishing laws have mandated that fishes must be of adult sizes so as to ensure sustainability. This suggests that the fishes caught in the nets are of the larger fish variety.

Thirdly, there have been independent reports of caesium being detected in fishes found in Japan. (http://www.abc.net.au/news/stories/2011/04/06/3183332.htm?section=justin) While it is true that the Japanese government has taken steps to stop fishing around the area of the nuclear plant, the fact that radioactive material have been discovered across the Pacific suggests that the diffusion of caesium in the water body is not to be underestimated. Thus, it is not certain that fishes from other areas of Japan are not affected by the nuclear waste.

Fourthly, the Tokyo Daiichi plant, until last week, had been dumping low-level contaminated water from the plant into the sea. While I understand the necessity of the action, it also means that the fishes in the pacific continue to face radioactive waste.

Finally, the fact that the supporting information for the statement that "radioactive caesium does not accumulate in fish" comes from a Japanese fishery isn't very comforting.

Admittedly, there are many unknowns involved with little empirical results to support any theory on the safety of Japan's fishes currently. Still, it is my wish, just as yours, for consumers to have as much information as possibly available before they make their choices.

That said, may Japan tide through these trying times.


ieat said...

Thanks for your comments Anonymous. Yes more research is required and I am certainly no expert in radiation medicine.

This is a platform for discussion, so we welcome all your comments. Do remember to sign off with a name so that we can address you in our replies.

I will continue to monitor the situation and news on caesium and update the post accordingly.

Ivy said...
This comment has been removed by the author.
Ivy said...

IMO, seafood is still okay for the general public. However, the pregnant and young children should stay away from seafood. Especially with the recent case of high levels of radiation detected in seafood after Japan's dumping of the water from the nuclear plant into the sea.

Jessica Tan said...

Thanks for the detailed update. At a time like this, Japan needs our support and as a believer, I believe God's healing hands are all over the nation and I will continue to support Japan and have chosen not to dwell on the what ifs (what if the fishes are contaminated etc.,). God Bless

Anonymous said...

How about the Japanese sweet potato? I do like it.

Maria said...

Dear Leslie,

Hi, another year has passed, and wondering with all the new information about the radioactive leakage from Fukushima plants (e.g. Some reports claim 300 tons a day has been leaked out? And radioactive traces has been found across the other side of the Pacific Ocean) are the food products (esp. Seafood) from Japan still safe to eat? And how is AVA in Singapore monitoring the food now?

Many thanks,would like to hear your view on this.



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