First of all, we've been living in Yokohama and my teenager has had more than 6 hamburgers worth of some sort of unidentified beef since 3.11.
As far as I know, no reports say exactly what shops or restaurants the beef in issue was distributed to.
And yes, what I always hear/read is the likes of "eating one portion will probably not have too adverse of health implications." Of course, I would yell to myself, "What about two then?"
But all in all, since 3.11 we've all been learning that the problem with contaminated food happens mainly when it piles up on you. Specialists do say that it would be risky to "keep eating" contaminated food for a long period of time, but that it most likely will not affect you just because you accidentally ate it a few times.
Whatever, it's no use looking back. On the other hand, specialists keep saying that balanced meals will help you keep yourself healthy, and that makes sense to me. For example, I heard that some of the radioactive substance is similar to nutritious substances such as kalium or calcium. That means, the specialists say, that if you are taking enough natural kalium/calcium, your body won't try to absorb the radioactive substance instead. These are mere examples. Either way, natural nutrition is supposed to build a strong body that can fight against any kind of risks, not just radiation.
The other thing is stress. By reading books on mental stress, I feel that mental stress can make you as unhealthy as radiation. So by trying not to worry, you can maintain a body that can fight against any disease that radiation may cause.
Now, if you need to find that man's article, all you have to do is to go to a library and look for archives on the Japan Times. But I think you did right by refusing to do so then. Some people try to give you scary information thinking it's for the best. Others say it's wrong to shut your ears against that kind of information.
But I don't think so. There is a time when a person is ready to hear information and there is a time when the person is not. One has the responsibitily to chose the right time for yourself.
I can say one thing, though. The government is not at all "hush hush" about the fact that the radiation level on the ground is much higher than that in the air. However, I'm not sure where the "500 times" is coming from, but I'll get to that later.
Anyway, Japan has been monitoring radiation in the air for years, and this is mainly due to the Chernobyl crisis as well as our domestic nuclear power plants. To watch out for these things, it was important to monitor the air. However, the Fukushima plant accident had affected our ground, and the ground had not been officially monitored until this new crisis.
So the government has indeed started to encourage the monitoring of the ground or the areas close to it, and they have been reporting the measurements on their official websites.
For example, click 全国大学等の協力による空間放射線量測定結果 on the following Ministry's site.http://www.mext.go.jp/a_menu/saigaijohou/syousai/1303723.htm
According to this, for example, our city of Yokohama shows 0.08μSv/h today at 1.0 meter above ground, while it is 0.027μSv/h at 23 meters above ground on the same day.http://www.city.yokohama.lg.jp/kankyo/saigai/
But hmm, 500 times? I still don't get it. For example, before 3.11 Yokohama was always like 0.023μSv/h. And 0.02 x 500 is 10, so that's as high as the plant itself. Even the critical Namie-cho, Fukushima-ken is 8.8 right now. I did a quick Google search on 地浮ﾌ放射煤@500倍 (meaning "radiation on ground surface 500 times") and even the rumors only gave me information on things like "they say that the radiation leak from Fukushima's accident seems to be 500 times the leak from the A Bomb of Hiroshima."
Besides, TV has been showing ordinary people walking around on their own with measuring tools in their hands, and even those don't show anything even close to 500 times.
But the reading is, of course, higher on the ground, because due to the explosion in mid March (15th, was it?) the radioactive substances had piled on the ground a bit. That is why schools in Fukushima have shoveled out the surface soil of their schoolgrounds, and that is why contamination in Kanagawa was found from new tea leaves after all these weeks.
But generally speaking, most people aren't worried about it unless you're literally licking the ground (which some toddlers indeed do, so that's something to be concerned about). Reasonable adults can wash your vegetables, wash your hands, and you can eat/breath anything in Yokohama area or further. You can also see that most of the ground is still safe, as no other crop has been reported contaminated in Kanagawa.
I regret that I'm too busy today to post any more sources, but you can refer to other threads on this forum for more details. You can also ask again if there is anything still unclear to you. I'll try to come back.
By the way, try to talk to your friends. I mean, not by text but by voice. This may decrease your stress.