"..and then he looked right through me as if I wasn't there."
-- Killing Me Softly
My research is incomplete, but I'm not convinced that there is a such thing as radioactive fish. Let me tell you why.
Ionizing radiation does not work like a poison, it doesn't stay. It is actually kinetic energy of electromagnetic particles. The best way to think of how radiation kills you is to think of a million tiny water needles running through your body over a period of exposure. They are so small that you don't feel them, but they leave a trail of dead cells in their wake. Depending on what cells they hit, they do different kinds of damage. In red blood cells they do lots of damage, they just bounce off of bones. Once these 'water needles' run out of their kinetic energy, they disappear, or melt away like water. The point is that they don't leave any trace of themselves behind, that is, if they are the tiny ones like electrons or gamma rays.
Neutron radiation is different. Neutrons are big enough to knock atoms out of balance and kick out another neutron and destabilize them. Neutron radiation is the key to why nuclear power works. One neutron hits another neutron sometimes with enough energy to kick out some electrons and more than one neutron. In elements like Uranium where there are big huge numbers of neutrons, you could create a chain reaction. That's all nuclear fission is, like a bowling ally infinite loop that creates bowling balls. Collisions and collisions.
How long can an unstable atom spit out more neutrons and energy? That's it's half life and it depends on the atom. It's like certain atoms carry a grudge if they get hit by a neutron. They have long half lives. Cesium is like that. Iodine is like that. Obviously Uranium is like that. Water, on the other hand is not like that. In the first place, it doesn't have a lot of neutrons. That's why when the Japanese nuke plants got out of hand, they doped the water with Boron. Boron is neutron greedy and it doesn't get unstable. But normally neutrons don't do much to water.
Something that is irradiated doesn't necessarily become radioactive itself. It depends on if it gets hit by neutrons or not, and then if it does get hit by neutrons is it the stuff that carries a neutron grudge. And this is where you have to make the distinction when it comes to fish. So far as I know fish are made of materials whose atoms don't have long half-lives. I mean if they did, how could the fish live?
In a nuclear reactor, the worrisome part are heavy elements that are radioactive. In Japan, some of these heavier elements which I believe to have been present in the feul cores escaped after the explosions. What is not clear to me is how the reactor containments have not been breached (as I keep hearing) and yet these more heavy elements escaped. Some logical clarity and less dumbed down reporting would be helpful. At any rate, it's suff like that, carried away in particulate matter (smoke) that lands on fruits and vegetables that cause the radioactivity 'of' food. It's not the radiation, it's the contamination by heavy radioactive material. In other words, toxic waste.
So we get more to the question of fish, and in particular the role of seawater in this ecology. The engineers generally use and reuse purified water to cool the reactor core and drive the turbines. That's a closed loop system for the most part, but still, the water does not stay radioactive even though it is exposed to neutron activation. The half life of water is about 7 days, and as far as I can tell it doesn't get very radioactive. Perhaps not at all. But the thing is that for the emergency, the engineers have used seawater to cool the reactors. To the extent that seawater contains various salts and trace elements with longer half-lives than water itself, this is the 'poison'. Sulfur, for example has a half life of 88 days. But in average seawater, sulfur is about .091%. Magnesium, on the other hand has a half life about 10 minutes, but there's more magnesium in seawater than sulfur. .129% So now you're beginning to see the start of a math problem.
If you have 10,000 tons of seawater exposed to x amount of neutron radiation (as a fraction of the total ionizing radiation given off by the nuclear core) what fraction of that will be absorbed by the trace salts in that seawater when dumped into the ocean? And by dumped into the ocean that means 10,000 tons of seawater in an area roughly the size of the region fished for your sushi flavor of choice. I can't imagine that a generic fishing boat is going to be within 10 miles of shore, and 10 miles of ocean can contain how many tons of water? So then you have that whole dispersal question and how many drops carry out into the fisheries. So you have some fraction of radioactive mineral salts and their half-lives to account for and guess how much of that gets into fish...
You should clearly see that even when the seawater pumped out of Fukishima is seven million times what it 'should' be, there are a lot of factors dispersing that radioactivity, including the fact that radioactive material itself degrades.
On the whole as a class of environmental disaster, this is, in my view, two orders of magnitude smaller than the blown oilwell from last year in the Gulf of Mexico. It's the radioactive smoke from an explosion, not largely contaminated seawater that's the problem, and the cesium and iodine on the fruits and veggies (particularly spinach) is the most dangerous stuff, not the seawater.
So eat your fish.
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