Details on Levels of Radioactivity in The Tokyo Water Supply
April 3rd, 2011
|
| Share |
The Tokyo Water Supply:
On March 23, Japanese officials announced that tests on water samples taken the previous day from one Tokyo’s water treatment plants showed iodine-131 levels of 210 becquerels per kilogram. Tests on previous days had only indicated much lower traces of iodine-131. Recent rainfall may have contributed to the spike in levels or it may have been a fluke in the sampling program. These levels were not detected across the board in the water supply of Tokyo, but only in one of the samples collected.
210 becquerels per kilogram is an extremely low level of activity, but the standards for iodine-131 tend to be very conservative. It is possible to set such extremely conservative limits because iodine-131 is not normally present in the enviornment in any significant quantity. With a half-life of only eight days, any iodine from nuclear weapons tests or releases from Chernobyl has long decayed away, leaving the enviornment essentially free of the isotope, except for a tiny amount excreted by thyroid cancer patients.
The standards for I-131 in tap water vary from place to place. The general international standard for safe water is 3000 Bq/Kg. Although this level is extremely conservative, Japan has much tighter standards for permitted iodine-131 concentrations. In Japan the recommended safety standards are 300 Bq/Kg for the general population and 100 Bq/Kg for infants.
The fact that the water concentrations, at least in one circumstance exceeded this lead to a run on bottled water and panic among citizens of Tokyo, especially those with young children. There was confusion as to whether it was safe to even bathe children in the tap water. Those who did not have young children were still concerned that the levels might be high enough to pose a danger, even if they were bellow the official designation for adult drinking water.
In reality, even if an infant were given large amounts of water containing 210 Bq/Kg of iodine-131, it is highly unlikely that any health effects would result. Not only is the Japanese level extremely conservative, but such standards tend to be based on the presumption that a population would be continuously drinking water at such a level, as might be the case in a continuously leaking nuclear reactor or other source of contamination.
In fact, the levels in the Tokyo water supply dropped rapidly. It would be expected that the levels would be reduced by 50% every eight days based on half-life alone, but they actually dropped much more rapidly than this. Within less than a week, the levels were too low to be reliably measured. This further suggests that the level was never actually as high as reported in the general water supply, but represented a single isolated high reading.
If you live in the Tokyo area, there is no reason for concern about the water supply. You should feel free to use the water for drinking, bathing and other purposes, even if you have an infant.
Sources:
House of Japan: Tokyo tap water to normal
Nikkei: Radiation Levels In Tokyo Tap Water Return To Normal Range
The Japan Times: Iodine-131 level falls in Iitate, IAEA says
Sify News: Radioactivity levels in Tokyo’s tap water declared safe for infants
Time: Fukushima’s Radiation Round-Up: How Bad Is It?
WKRC: Tokyo tap water not safe for infants
Metro Magazine: Tokyo Tap Water Information
This entry was posted on Sunday, April 3rd, 2011 at 9:34 am and is filed under Bad Science, Enviornment, Nuclear, Politics. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
View blog reactions
April 3rd, 2011 at 10:51 am
The rapid reduction in the level of I-131 detected in the water treatment centre was probably due to wash-through where water with higher levels of contamination was passed through the system and replaced with fresh, less contaminated water. The short half-life of I-131 is a factor that limits the amount of new contamination being added from upstream deposits; as long as more releases from the reactor cores and fuel cooling ponds at the plant at Fukushima can be avoided it’s unlikely there will be a recurrence of such levels in the Tokyo/Kanto area.
Quote Comment
April 3rd, 2011 at 11:08 am
Lawrence Solomon: Dams are worse
http://opinion.financialpost.com/2011/04/01/lawrence-solomon-dams-are-worse/
A forgotten 1975 Chinese disaster killed 230,000 people
“Japan’s ongoing disaster at the Fukushima nuclear plant, now in its agonizing third week, has led many to conclude that nuclear is the most dangerous way to generate electricity. Not so. Nuclear is not the most dangerous, not by a long shot. That distinction unambiguously belongs to large hydroelectric dams.
The most catastrophic dam failure in history occurred in China in 1975, with the near-simultaneous failures of the Banqiao and Shimantan dams. The “August 1975 disaster,” as the Chinese call the horrors associated with the dams’ collapse, drowned 26,000 people, according to the Chinese government. Another 200,000 lives were lost in its aftermath. Records from the days following the dams’ collapse describe the chaos.”
Quote Comment
April 3rd, 2011 at 2:36 pm
Well unless you name is Chris Busby you will shake some arbitrary preschool mathematics around and claim that 100 Bq of I-131 will cause cancer 100% of the time according to ECCR (his own organisation which have very little authority about anything)…
But 3000 Bq/kg would give 2,3 mSv/year, if you could keep the intake up for that long and assume 100% uptake.
Quote Comment
April 4th, 2011 at 3:33 am
DV82XL said:
No, this is rubish. That’s the biggest single accident with a power plant(which also doubled as an irrigation and flood protection system).
Nothing beats coal power in deaths per TWh; hydro isn’t even close. 200 000 deaths? *Pfeh* I say, coal power does that every 6 months or so in China, not to mention the number who are made chronically ill. If you include the rural people who burn coal for heating and cooking it’s every few months.
Quote Comment
April 4th, 2011 at 3:51 am
Brian Wang on deaths per TWh:
http://nextbigfuture.com/2011/03/lifetime-deaths-per-twh-from-energy.html
The trend is clear: all chemical fuels combustion, even biomass, is dangerous, whereas the things that don’t burn fuel are safe. Hydro, wind, solar, nuclear all very safe, with nuclear even slightly safer than solar PV (though note that this solar death figure is based on assumptions).
We should reduce all fuels including biomass and replace with non-combustion energy sources.
Quote Comment
April 4th, 2011 at 7:38 am
I’m not sure where Tokyo gets its water from, but typically cities get water from aquafers with refresh rates between 25 years to thousands of years. Unless the water source was less than 3 weeks old it couldn’t have come from the accident at the plants. My guess is poor counting techniques or contaminated sample collectors. Or they’re drinking snow melt.
Quote Comment
April 4th, 2011 at 7:58 am
Mike P said:
Like pretty much all of urban Japan, Tokyo gets its water supply from rivers. The *average* rainfall for Japan is about 60 inches a year, or to put it American terms twice as much rainfall as Seattle gets. Up in the mountains which feed those rivers it can be as high as 120 inches a year. There’s a reason Japan grows water-dependent rice rather than arid plains wheat as a staple grain crop.
Many densely populated areas of America are located in near-desert terrain requiring deep-well depletion of underground aquifers to keep all those golf courses nice and green. This is not common in other civilised countries.
Quote Comment
April 4th, 2011 at 10:09 am
Robert Sneddon said:
I would not go that far. The US does have some cities that use deep wells or long aquifers to get water, but many of the largest do not.
The New York City area gets its water through a series of aqueducts that go up to Catskills where there are reservoirs that are replenished by rain and snow melt. Most of the Eastern Seaboard gets water from either sallow wells to the water table or surface reservoirs. The Eastern US has plenty of fresh water.
The midwest gets most water from the Great Lakes watershed. Chicago draws its water right off of Lake Michigan.
But then there are the desert cities, like Phoenix, Scottsdale, Albuquerque etc which do require deep aquifers or long aqueducts. A few do use rivers and lakes, however. Las Vegas, for example, gets water from Lake Powell.
Quote Comment
April 5th, 2011 at 11:59 pm
While we’re on this topic, I haven’t seen enough people pointing out that this common claim (that rain water in the U.S. has become dangerously radioactive because it exceeds the EPA standard for drinking water) is a heaping load of bulshytt.
First, the supposedly-intolerable levels of I-131 are found in rainwater and will be diluted in drinking water. Second, the limit is for an average over a year. That will be much less than the peak amount when you recall that I-131 has a half life of only 8 days. Three, it’s based on an idiotic standard. The EPA standard is 0.1% of the radioactivity of bananas.
Quote Comment
April 6th, 2011 at 12:44 am
“Las Vegas, for example, gets water from Lake Powell”
I think you mean Lake Mead, in back of Hoover Dam.
Quote Comment
April 6th, 2011 at 8:11 am
atomikrabbit said:
oops. My bad. Yeah. Lake Mead
Quote Comment
April 6th, 2011 at 4:58 pm
Joseph Hertzlinger said:
Yes, the EPA standard is completely without scientific basis.
What is interesting is that every other thing we eat or drink is regulated by the FDA. And the FDA limit is 170 Bq/kg, which applies to bottled water. If you convert 170 Bq/kg to pCi/l you get almost 4600 pCi/l.
So the radioactivity in bottled water can legally be more than 1500 times higher than the radioactivity in tap water.
Quote Comment
April 6th, 2011 at 5:29 pm
Regulation is the art of making up numbers and making them sound important.
Quote Comment
April 6th, 2011 at 6:03 pm
I saw the EPA limit listed as 3 Bq/l. I’m assuming it’s set so low because there shouldn’t be ANY I-131. Any detectable I-131 means there is something very wrong going on somewhere, not that the water is unsafe. Of course this type of limit is useless right now since we know where the I-131 is coming from.
Quote Comment
April 6th, 2011 at 7:48 pm
The thing that makes me laugh over this spasm of concern over I-131, is that everyone gets enough iodine in the salt we eat. Currently about 70% of the households in the world use iodized salt, according to Unicef, and usage approaches 100% in Western nations. Thus the potential for a significant uptake of the I-131 isotope from the trace amounts found in these water samples is very, very low. The potential of acquiring a radiotoxic, or carcinogenic, dose approaches zero.
But then again facts, logic, and commonsense have little impact on radiophobia.
Quote Comment
April 6th, 2011 at 11:42 pm
Apparently not satisfied that reports of iodine-131 in migratory tuna is enough to scare us, the (American) media seem to think it necessary to report on the presence of cesium-137 in addition. I see Cs-137 has a half-life of a tad over 30 years–does that mean its level of radiation is low enough (i.e., it’s sufficiently stable), that even if fish do ingest some it’s not radioactive enough to do damagwe? Just asking.
Quote Comment
April 7th, 2011 at 4:15 am
Cs-137 is a concern but as you say with the 30 year half life you need an awful lot to give a significant dose. Also the biological half life of cesium is 70 days. So in about 700 days all the cesium is eliminated from you body. Doing a decay equation shows that only about 4% of the cesium that is absorbed will decay within your body before it is excreted.
Now of course if you keep eating food with elevated levels of Cs-137 it will be replenished and the internal levels will build up. But you would need a lot to matter. And since it acts like potassium it is relatively evenly distributed through the body so the exposure is not concentrated in a single organ like it is with I-131.
Quote Comment