As one of the readers noted in the other post, the radiation contamination in Tochigi and Gunma Prefectures (northern Kanto) has been little noted.
The highest official measurement for wild mushrooms was last year, when 28,000 Bq/kg of radioactive cesium was found in wild mushrooms in Fukushima Prefecture.
The reason for the quotation marks for the word "official" in the blog post title is that there were unofficial measurements done last year by private entities with much higher numbers. One of them was done by NHK when the crew, including Dr. Shinzo Kimura, went to Fukushima soon after the accident and started measuring radiation levels and warning residents who still remained in the high-radiation areas. They found 420,000 becquerels/kg of radioactive cesium in mushrooms harvested in Akougi District of Namie-machi on March 28, 2011. (For snapshots of the NHK Documentary aired on May 18, 2011, go here. In Japanese.)
From Nikkei Shinbun quoting Kyodo (8/6/2012):
Highest level of cesium detected in wild mushroom
Tochigi Prefecture announced on August 6 that 31,000 Bq/kg of radioactive cesium was detected in wild "Lactarius volemus" (tawny milkcap mushroom) harvested in Nikko City, far exceeding the national safety standard (100 Bq/kg). Shipment of wild mushrooms from the city have been already restricted, and the prefectural government is advising citizens not to harvest and eat the wild mushrooms.
According to the Ministry of Health and Welfare, it is the highest level exceeding the amount detected in "Lactarius volemus" harvested in Tanakura-machi in Fukushima Prefecture in September last year, which measured 28,000 Bq/kg. The Tochigi prefectural government says, "We believe the cesium absorption was largely from the soil, but radioactive materials from the surrounding trees may also have affected it."
If you think by now, 17 months after the accident and at least one full year since it became widely known that certain food items were more contaminated than others (mushrooms are on the top of the list), people do not harvest, not to mention eat wild mushrooms or any mushrooms, you're very wrong.
On a separate piece of news at Asahi Shinbun medical news section, WBC (Whole Body Counter) testing revealed that a 70-year-old man in Fukushima Prefecture had 20,000 becquerels/body radioactive cesium as of July 2012. It turned out that he and his wife had been eating mushrooms, vegetables (including wild mountain vegetables) and fruits every day that they or people nearby grew or they harvested from the wild. They didn't even think that they were contaminated, and those food items were never tested. The medical doctor who wrote the article, Dr. Masaharu Tsubokura, says it is the highest that he has ever seen since he started helping people in Fukushima after the nuclear accident, and that it is the level often seen in Belarus.
As to the highly radioactive mushrooms in Nikko City, shipment is "restricted" (i.e. banned) but there is no one enforcing it. Besides, what the prefectural governments do is only to tell the producer not to ship outside the prefecture. There is nothing they do (or are willing to do) to stop these food items from being consumed or distributed inside the prefecture.
Nikko City is circled in red on the map by MEXT, from the revised 8/30/2011 map. The highest contamination of the soil, according to MEXT, is 100,000 to 300,000 becquerels/square meter for radioactive cesium (134+137):
Nikko by the way is a popular destination for summer schools for elementary schools and junior high schools in Kanto Region, as it always has been for decades.