We are all familiar with the Fukushima Dachaii Nuclear Power Plant (FDNPP) disaster that was the result of the earthquake and subsequent tsunami on March 12, 2011. We have read countless reports on the status of the power plant and the spread of radionuclides as a result of the explosions in the reactors. A quick recap is necessary though. On March 11, 2011 a magnitude 9.0 earthquake struck just off the Pacific coast of Japan triggering a massive tsunami which destroyed everything in its path. The tsunami caused massive flooding which killed the backup power at the plant and caused the reactor cooling systems to fail. The failure of the cooling system led to a meltdown and several hydrogen explosions which released radionuclides into the environment. The three nuclides of greatest concern are iodine-131 (half-life: 8 days), cesium-134 (half-life: 2.1 yrs) and cesium-137 (half-life: 30.2 yrs). Other radionuclides, such as iodine-129, were also released, however they have not been the subject of much study...yet.
The big fear in North America was: will these three radionuclides, all of which can be absorbed into our bodies, reach us, and will there be enough present to cause harm? A recent article by a group from the USGS and the University of Illinois tackles this problem and presents one of the first summaries of radiation monitoring data that I have seen to date. The article presents data from several sources but the primary ones are the US National Atmospheric Deposition Program (NADP), which primarily samples rains and chemical particulates in rain. The other main source was the US EPA National Air and Radiation Environmental Laboratory (RadNet) which operates radiation air monitors across the US. Some samples from the Canadian Air and Precipitation Monitoring Network (CAPMoN) were also used. A comparison to the Chernobyl disaster is also included.
131I - Background and Results
Iodine-131 is a radioactive isotope of iodine that has an eight day half life. It is definitely a dangerous isotope to humans and releases a substantial amount of radiation in the form of both beta and gamma rays. The specific activity of 131I is 4.81x10^15 Bq/g. Its risk to human health is further exacerbated by the fact that our bodies love to absorb iodine from the environment around us and that iodine is an extremely mobile element. In fact, iodine can exist as a gas, a solid or dissolved in water and it can transfer between these three states very readily depending on the conditions of the environment around it. Furthermore, iodine is attracted to organic molecules making it even more mobile. It is also en essential nutrient of life. In fact, all salt has iodine added to it so that we do not become iodine deficient. In the case of salt, however, the isotope added is iodine-127 and is not radioactive. If our bodies absorb too much 131I we are being subjected to a high dose of radiation from within us. Iodine concentrates in the thyroid gland so exposure to 131I will greatly increase the risk of cancer particularly thyroid cancer. The maximum dose of 131I that is allowed is 4 Bequerels per litre (Bq/L) for drinking water and 3.7 Bq/L for air according to the US-EPA. According to the Canadian Nuclear Safety Commission (CNSC) the maximum acceptable concentration for drinking water is 6 Bq/L and is 0.2 Bq/m^3 for air.
As a result of the releases from Fukushima both RadNet and the NADP sampling network showed hits of 131I in their precipitation and bulk air samples. The data presented for the detected levels for 131I ranged from 0.1-40 Bq/L for all North American rain samples and from 60-5100 Bq/m^2 for deposition from air. Obviously the highest value for water is ten times the allowable limit of 131I in drinking water. It is important to note that due to the short half life of 131I many of the samples were measured after too much time had passed to detect 131I, causing it to appear less ubiquitous than perhaps it was. Also, the paper points out that concentrations of 131I decreased from west to east due to decay, deposition of the 131I and dilution of the plume over time.
This suggests that geographical distance played an important role, as the sites that were further away from Fukushima had smaller deposition of radioactive material. The comparison of this data to that from sites around the globe after the Chernobyl disaster shows that levels measured in North America were within the range of data from the Fukushima fallout. However, samples collected from sites closer to the Chernobyl disaster are far higher for 131I in air.
134Cs - Background and Results
Cesium-134 is another isotope that was released from Fukushima. It has a 2.1 year half life and also is quite radioactive and has a specific activity of 4.81x10^13 Bq/g. It emits both beta and gamma radiation. Cesium differs from iodine primarily by its different behaviour in the environment, as it is much less mobile and often sticks to soils. It can still be found dissolved in water and stuck to particles carried in the atmosphere. Cesium can enter our bodies in food, drinking water or through inhalation, giving it the triple threat of exposure pathways. Furthermore, once in our bodies cesium behaves like potassium, which is not surprising given they are both alkali metals. Finally, once in our bodies cesium tends to concentrate in the muscles. The silver lining here however, is that once cesium is in our bodies it does not reside there for long. It has a biological half life of ~110 days meaning half of what is absorbed will be secreted within 110 days. The maximum acceptable concentrations for 134Cs in water are eluding me on both the EPA and CNSC websites, but if anyone does know them or stumbles across them please comment below. I was successful in finding a maximum allowable concentration in air though from the CNSC, which is 0.2 Bq/m^3.
The results from the measurement of 134Cs in water range from 0.01-2.0 Bq/L for both RadNet and NADP samples and for deposition from air the values range between 0.47-180 Bq/m^2.
137Cs - Background and Results
The overall behaviour, risks, and absorption pathways of cesium-137 are the same as 134Cs. The main difference is that 137Cs has a much longer half life of 30 years and emits only beta radiation. It has a specific activity of 3.26x10^12 Bq/g, slightly less than that of 134Cs, which makes sense given the slightly longer half life. However, 137Cs decays into Barium-137 which emits both beta and gamma radiation and has a specific activity of 2.0x10^19, making it extremely dangerous due to its very short half life of 2.6 minutes. The CNSC drinking water limit for cesium-137 is 10 Bq/L and the EPA limit is still impossible to find (this is really annoying!). The CNSC also have a limit for 137Cs in air which is 2.6 Bq/m^3.
The concentrations of 137Cs that were measured by the radiation survey fell between 0.03-1.4 Bq/L for both RadNet and NADP samples in water and 0.78-240 Bq/m^2 for deposition from air. Once again the levels for both cesium isotopes are far less than those recorded after Chernobyl.
Overall the conclusions of the paper were that fairly high levels of radionuclides were transported from Fukushima. However, these levels are far less than those generated in the US during nuclear weapons testing and the radionuclides released from Chernobyl. This paper also demonstrates the sensitivity and effectiveness of radionuclide monitoring in North America and is proof that a rapid response to a nuclear disaster can be executed. I would add that despite some exceedance of maximum allowable standards by the measured values of radionuclides there was no health threat to people in North America from Fukushima. I would really encourage people to comment and share their opinions on this paper and the impact of the Fukushima disaster.
CNSC Standards: http://www.nuclearsafety.gc.ca/eng/mediacentre/updates/2011/japan-earthquake/march-28-2011-japan-earthquake-safe-concentrations-of-radionuclides-air-water.cfm
Iodine Fact Sheet: http://www.evs.anl.gov/pub/doc/Iodine.pdf
Cesium Fact Sheet: http://www.evs.anl.gov/pub/doc/Cesium.pdf
Wetherbee, G. A., Gay, D. A., Debey, T. M., Lehmann, C. M. B., & Nilles, M. A. (2012). Wet Depostion of Fission Product Isotopes to North America Released from the Fukushima Dai-ichi Incident, March 2011 Environmental Science and Technology
Thursday, March 22, 2012
Wednesday, March 14, 2012
This post will be a brief departure from the usual stuff I write about. Basically, I am hoping to spread the word that I need some help with my summer sampling this year. I feel a bit weird about asking you, my readers, for help, but I am getting desperate to find someone so I thought I might as well give this a shot.
For the past two years I have been sampling major and minor watersheds in the Yukon and Northwest Territories looking for radioactive iodine-129. The results so far have shown that substantial quantities of 129I released from nuclear fuel reprocessing have been transported to the Arctic via a combination of direct atmospheric transport or volatilization from the ocean and subsequent atmospheric transport. The iodine then deposits on the landscape through precipitation or settling of particulate matter and is then transported via runoff or groundwater to the rivers where I sample it. The results from the summer of 2011 showed a sharp increase in the fallout of 129I leading us to surmise that Fukushima had released some 129I that had then made its way into the Arctic. However, more work is needed to confirm this, and this summer we are going to look at a time series of data as opposed to a single sample representing the entire summer. Essentially we want to look at the entire cycle of iodine and radioactive 129I in and out of a given watershed for an entire summer.
To this end I am soliciting the internet and the readers of my blog to spread the word that I am looking for someone who is in the Yukon and northwest NWT for the summer to take weekly water and rain samples for me over the course of the whole summer. So if you know anyone who might be able to help me out please let me know and spread the word!
Thanks everyone for your help.
|North Klondike River. Tombstone Territorial Park. Yukon (May 2010)|
Wednesday, March 7, 2012
One of the problems of grad student life is that sometimes things in the lab just don't work. You can read all the papers, copy and execute all the procedures, yet sometimes things just don't pan out the way you want them to. Unfortunately, this happened in our lab a few weeks ago when we were trying to extract iodine from mudstone samples. Ideally, the final result would have been a bright yellow powder composed of silver iodide (AgI). However, in the case of our mudstone samples, the iodine was getting lost somewhere in the extraction process, and we could not figure out where. This was an obvious problem and one that we needed to resolve. To do this we decided to try using the brand new scanning electron microscope (SEM) that a professor in the department just purchased. SEM works by shooting a sample with a beam of electrons and then analyzing the energy emitted from the sample which is dependant on the shape, composition and conductivity. This allows us to obtain a very high magnification image as well as gather information about the sample composition. I am not going to go into a detailed description of SEM now...perhaps in a future post. This post is more about looking at the cool photos we took to try and figure out why our extraction procedure was unreliable...we are still working on finding an answer.
|Sorry no scale. This one is mostly sodium hydroxide.|
|No idea what this is??|
|The "Fortress of Solitude" for a very tiny Superman. The scale bar is 1mm. Also not sure what this is besides it being silica rich.|
|The "fortress" a little bit closer|
|The "fortress" really zoomed in.|
Hope you liked looking at these photos. Hopefully I'll have more to post in the near future. All of these photos were taken using a JEOL 6610LV SEM for any who are interested.
|The sample chamber. The round thing is a pewter beer stein being analyzed for lead. I have no idea if any was found.|
Here is the current website for the lab: https://sites.google.com/site/probelab2/home