Fukushima Hot Particles are contaminating portions of northern Japan and US
- uploaded: Dec 10, 2011
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My name is Barry Levy and together with Dr. Carol Allen, we have organized the session. Unfortunately Dr. Allen will will have to leave shortly after her own presentation to help lead a workshop on cultural diversity for the public health nursing section. We have 6 presentations this morning. We hope to have time for at least one, maybe more questions after each of the presentations, one at a time. We are starting 5 mins late so we will end about 10:05.
The first presentation is entitled, Radiation Exposure to the Population of Japan after the Earthquake by Marco Kaltofen. Marco Kaltofen is a registered professional civil engineer and PhD student with the Dept. of Civil and Environmental Engineering at Worcester Polytechnic Institute in Worcester, Mass. He works as a consulting engineer for the Boston Chemical Data Corporation. His employment and research interest is in the tracking of nuclear and chemical waste in the environment and the subject of his PhD dissertation is on the tracks of radioactive dust and it's affect on human health; Marco Kaltofen.
Thank you very much. Good morning; thank you for having me here. My research work is on not so much radiation, but on the things that carry the radiation to people. So what I have been studying has been what happens to dust after it becomes contaminated, and how that dust carries radiation to the human body. I have to say that I have no personal financial relationships with commercial interests relevant to this presentation during the past 12 months.
In doing this research, I have a few people I would like to thank. In particular, I would like to thank the volunteers of Safecast. Safecast is a group of both technical and non-technical volunteers in Japan who have been working since the March 11 earthquake, tsunami and radiation release, to try and document some of the radiation exposures people are experiencing in northern Japan. The central theme of my work is that the dust contaminated with fallout from the Fukushima accidents, is the source of human exposure to radiation. If you are seeing some of the media coverage of radiation exposure in Japan, you have probably heard a lot of different ways that people have talked about how we are exposed to radiation and how it compares to our daily lives.
Now I am actually going to ask for a show of hands. Am I allowed to do this? (Sure)
Has anyone heard the radiation in Japan being compared to say taking a flight from Los Angeles to Washington D.C.? O.K. How about to eating a banana? Has anyone heard this one? Bananas have potassium, potassium has a natural radioactive isotope so we get a certain amount of low level radiation from that exposure. The last question, has anyone heard that a little bit of low level radiation might actually be good for you? This is a hypothesis by Dr. Ed Calgaries that a very small amount of radiation may actually cause what amounts to something analogous to immunological response. Sorry, I am a civil engineer, I cannot say those medical words. That response is actually a net positive at very, very low levels. So what we are talking about here is a slightly different kind of radiation, where we are looking at a lot of concentrated radiation in a very small particle.
So the total amount of radiation we are exposed to might in fact be low, but because we are exposing only a small number of tissues, for instance, for a respirable dust particle, we inhale the dust particle that is radioactive. It actually is about the same scale of size as a cell in the human body. So that radioactive particle is adjacent to a cell that is going to stay there because it has a long residence time. And so to that particular cell, that is not a very low dose. In fact, that is a high dose, it is actually even a lethal dose to that cell, although overall it is a very low level of exposure to the entire human body.
So lets look at some of the things that were released by the reactors at Fukushima. Radioiodine, Iodine 131: this is a short lived gas; it tends to decay by about half every 8 days. Cesium 134 and cesium 137: these have half lives of about two years or 30 years respectively. By the way have people heard the story of half lives? talked about radioisotopes? Thank you. Cobalt 60 has a half life of about 5 years. A whole zoo of what are called fission wastes and neutron activation products; these are the materials that poison nuclear fuels when they are in the reactor. And then of course the original uranium and plutonium fuels that are in the reactor and other transuranics heavier than uranium isotopes like Americium and Neptunium which are very specific to that uranium.
For how people are exposed to this radiation, there are several different ways these dusts will actually get into the human body. Number 1 is going to be the inhalation of airborne particles. Followed by the inhalation of re-suspended dusts. The difference being early on in the accidents, we have a lot of material emitted into the air. It is washed out by rain. It falls out as a settled dust. And then over time, the atmosphere clears but sometimes those dusts when they collect in a certain place, are going to re-suspend and the air will become contaminated again after a short downtime.
People also ingest contaminated foods. The list I have put here, these are foods that have already been found to be contaminated with unacceptable levels of radiation. Things like seaweed, shellfish, beef, milk, spinach, eggs, tea, finfish. I should add mushrooms and other things that are grown not just in the immediate area of the reactors but sometimes as much as a couple of hundred miles away.
And if any of you are used to working with juvenile health issues, and you are familiar with contamination from lead paint in dusts in homes, we also tend to, especially as children, ingest a good deal of soils and dusts. The EPA tells us that the average child is ingesting about a tenth of a gram of dust every day. I do not know about you, but I remember my kids when they were little. They say sometimes it might be as much as a gram or even a gram and a half of dust a day. That is an important way people are exposed to contaminated soils. And lastly, there is dermal contact, getting this material on the outside.
So we tried to take a look at certain samples that would tell us a little bit about how dusts are moving through the environment in Japan. So we looked at automobile air filters. We tried this as a qualitative means of trying to capture a large number of radioactive particles, so we could learn about how those particles are in terms of their size, how they might dissolve in human body fluids, to capture enough particles that we could statistically analyze how they would behave in the environment and in the body. As it turns out, the way the average Japanese driver uses their car, the amount of air consumed by a car engine, is actually on the same order of magnitude as the amount of air that people use day to day. So a car versus a healthy worker, will use anywhere between 10 - 30 cubic meters of air a day on average, for the car at least to burn fuel.
To follow up on that, we also used a number of quantitative air filters. These are small metered filters running with air pumps that are taking an exact known amount of air and cutting off the specific particle size with a known amount. We cannot get as many particles with this method, but we can use it to calibrate what the actual concentration is of hot particles in the atmosphere. We looked at home air filters, from people's homes in Japan and in the U.S.
We also looked at children's shoes. Children track in a lot of material on their shoes. Children play very hard in outdoor soils and their shoes tend to pick up any contaminants that are in the soil.
We also looked at settled dust in the homes, surface soils and foods and plants in Japan and the U.S. Our air sampling stations were set up in multiple locations. The first sampling station was the one I set up in Massachusetts about two hours after we learned of the reactor accidents, because we would look at the map and see that we were at the same latitude as these reactors in Massachusetts. So that over time, we are likely to see some of that material make it's way in the atmosphere to us. We also set up facilities in Seattle, San Francisco, Boulder, Hawaii and multiple facilities in Japan. Just two of them are here on the map.
The primary radioisotopes we detected, the things we actually found in our dust samples, the cesium 134 and the cesium 137. Iodine 131, which as you know is a thyroid seeker, but with a short half-life. We only saw Iodine 131 back in April, and even the samples we had in storage, you could see the iodine slowly decaying off.
Cobalt 60, which is another activation product from deep inside the reactor. The Cobalt 60 is formed from steels in the reactor that are exposed to radiation. So obviously, somehow the steel in the center of the reactor must have come in contact with the atmosphere and then other fission products as well.
This is a quick map. I do not know if anyone has seen this before. This is a general map, taken by the aircraft over Fukushima Prefecture that shows pretty much where most of the plume has gone. So if you will notice, we have evacuation radii. We have a 20 kilometer zone around which people have been evacuated from near reactors.
But in fact, because of the weather and the geography, you can see how most of this material has moved to the northwest. The permissible radiation dose, I am not going to focus on this for very long.
Let me just say that the permissible radiation doses in Fukushima Prefecture were raised by a factor of 20. There is obviously a lot more to this decision than I could ever get into in 50 minutes.
Our sampling team experienced a few difficulties in getting the materials they need. Probably the biggest one is in working with our volunteers teaching them how to how to collect these samples safely, get them safely and lawfully to the United States to be analyzed.
And here is some of the data. One of the first things we did, was we took our automobile air filters from different locations. We opened them up and we laid the filter paper inside these air filters on a piece of x-ray film and developed them. On the far left we have an automobile air filter that operated during March, April and May in Seattle, Washington. It looks clear, if your eyes are really good, you can see one tiny little dot near the center. We have an automobile air filter from Tokyo and you can see that each one of these black spots represents a radioactive particle that was trapped on the filter paper and exposed the x-ray film. And also we have Fukushima's which is about 65 kilometers away from the site. This automobile air filter is actually hazardous. My university is annoyed with me because we have to contract to have this filter disposed of as radioactive waste. Unfortunately, you can just imagine what this means to the people in Fukushima City which is not evacuated, and even for the (automobile) mechanics who are changing these air filters.
Here is a look at one of the particles. We are using a standing electron microscope to actually see the particle itself. This is a hot radioactive particle. It is about 10 microns across, meaning it is a respirable size particle. This is one of the very few particles where we found Americium, which is a byproduct of plutonium decay.
Quick comparison: This is the total radiation in children's shoes from Koniyamo (Kanayama?), which is in Fukushima Prefecture. This city is actually featured in today's Wall Street Journal. You can see that the total radiation levels in the shoes from Fukushima are higher for these children than in the U.S.
And here we have the total amount of cesium, radiocesium, which is probably the most problematic isotope people are exposed to there. And you can see that the cesium levels are more than 166 times higher in the shoes from Fukushima. So these are actually shoes worn by children in schools and brought home. We are finding that the laces and the soles are probably the two key contaminated areas on the shoes. The soles have contact with soils. It is possible that the laces are actually contaminated from contact with fingers.
Since the accidents about 8 months ago, the airborne levels have dropped. The soil levels still remain high in places, but the food chain radiation we are still finding increasing. This radiation is not uniform. There are hot spots, particularly in Fukushima Prefecture where we might have zones that are relatively radiation free now that they experience net increases, as some of the radiation from hot spots tends to build up. And for an air filter that was run in Noda City, just north of Tokyo, 150 kilometers from the accident site, an indoor home air filter showed 230 picocuries of radiation. I should just say that the U.S. limits radiation in soils to about 5 picocuries.