(UPDATE) From TEPCO's Kashiwazaki-Kariwa Nuke Plant website (in Japanese only), I've learned that they test radiations in soil, water, food, etc. once every quarter in the area within 5 kilometers from the plant. The latest measurement data on the website is from 2009.
It is a minute amount, but at least TEPCO's Matsumoto, who announced the news of the detection, didn't say "there is no effect on health" like its regulatory agency in the government or the government's cabinet secretary.
The milk samples were taken on May 12.
Niigata Prefecture is on the Japan Sea side. Kashiwazaki City, where radioactive cesium was detected from the milk, has Kashiwazaki-Kariwa Nuclear Power Plant, but TEPCO says cesium was from Fukushima I Nuke Plant.
Well, the prevailing wind has switched, and now the plume from Fukushima I is often going inland, and sometimes all the way across to the Japan Sea. It is no surprise that radioactive cesium has been detected in Niigata. There is no escaping the radioactive particles.
(Picture shows the Nagatori railroad station. Nagatori is one of the two locations where cesium was detected from milk.)
From Mainichi Shinbun Japanese (9:10PM JST 6/14/2011):
東京電力は１４日、新潟県柏崎市内で採取した牛乳から微量の放射性セシウムを検出したと発表した。検出量は原乳１リットルあたり最大０．０４６ベク レルで、内閣府原子力安全委員会の指針が定める摂取制限の約４０００分の１の値という。柏崎刈羽原発からは放射性物質の漏えいはなく、東電は福島第１原発 から飛散したものとみている。
TEPCO announced on June 14 that a minute amount of radioactive cesium was detected in the raw milk produced in Kashiwazaki City in Niigata Prefecture. The amount was maximum 0.046 becquerel/liter, about 1/4000 of the limit set by the Nuclear Safety Commission. There has been no radioactive materials leak from Kashiwazaki-Kariwa Nuclear Power Plant, and TEPCO believes cesium came airborne from Fukushima I Nuclear Power Plant.
The milk samples taken in Nagatori and Kitajo districts of Kashiwazaki City on May 12 were tested. Cesium-134 was detected at 0 to 0.025 becquerel/liter, and cesium-137 was detected at 0.021 to 0.025 becquerel/liter. TEPCO conducts regular surveys of radioactive materials in the area around Kashiwazaki-Kariwa Nuclear Power Plant, according to the agreement with the local municipalities.
TEPCO's Junichi Matsumoto said, "We again recognize the enormity of this accident. We will consider testing the other agricultural crops [in Niigata?] and testing [the milk?] in Fukushima Prefecture."