The amount of iodine-131 in the seawater is to be less than 30 becquerels/liter, and radioactive cesium is to be less than 50 becquerels/liter (I assume it is the total of cesium-134 and -137) in order for the local municipalities to open their beaches.
The Ministry felt, no doubt, that it could set the limits very low because the tests done by the local governments showed there was no radioactive materials detected in the ocean water at the beaches, except one in Fukushima that detected 13 becquerels/liter of radioactive cesium.
These limits are lower than the legal density limits for radioactive materials in the exhaust water out of a nuclear power plant in a normal operation:
- Iodine-131: 40 becquerels/liter
- Cesium-134: 60 becquerels/liter
- Cesium-137: 90 becquerels/liter
They are also lower than the provisional limit for drinking water and milk for babies. By the way, did you know that the provisional standards for radioactive materials in water and milk for babies are HIGHER than those for the exhaust water from a nuclear plant?:
- Iodine-131: 100 becquerels/liter
- Cesium total: 100 becquerels/liter
Not to mention they are much lower than the provisional limits for drinking water and milk for the rest of the population:
- Iodine-131: 300 becquerels/liter
- Cesium (total): 200 becquerels/liter
The reasoning? Read the article I translated below, and be puzzled.
From Fukui Shinbun (6/23/2011):
環境省は２３日、全国の海水浴場など海や湖沼、河川にある遊泳場所（水浴場）を安全に利用できる目安とし て、放射性セシウム濃度は水１リットル当たり５０ベクレル以下、放射性ヨウ素は３０ベクレル以下とする指針値を策定した。適用は今夏限り。２４日に全都道 府県に通知する。
The Ministry of the Environment announced its guideline on June 23 regarding the safe use of bathing facilities at the ocean, lakes and rivers in Japan, setting the limits of radioactive materials in the water at 50 becquerels/liter for radioactive cesium and 30 becquerels/liter for radioactive iodine. This guidance will apply to this summer only. The Ministry will formally notify the prefectural governments on June 24.
...指針値は、放射性セシウムで１リットル当たり２００ベクレルという飲料水の暫定基準値より厳しい設定とな る。理由について環境省は「日常生活に不可欠な飲料水などと違い、海水浴などのレジャーは余暇を楽しむ選択的行為だから、被ばくは可能な限り小さく抑える のが望ましい」と説明している。
The guideline numbers are lower than the provisional safety limits on drinking water. The Ministry of the Environment explained the reasoning as "Unlike drinking water which is indispensable for daily life, the ocean bathing is a recreational activity that people choose to do. So, it is desirable to make the radiation exposure as small as possible."
同省は水浴場開設の判断を自治体に委ねる考えだが、岩手、宮城両県は今夏、県内すべての水浴場開設を見送り、福島県は勿来を含め海水浴場を開設しない方針という。The Ministry will leave the decision of whether to open the beaches to the local municipalities. Already, Iwate and Miyagi Prefectures have decided not to open any beaches at all within the prefectures, and Fukushima Prefecture is not going to open any ocean beaches.
Well, WHAT ABOUT THE BEACH SAND? Has anyone measured the beach sand, with the equipment that can measure alpha, beta and gamma rays? People will sit on the beach, lie down on the beach for sun bathing. Bare feet and near-naked bodies. Hello? AND OCEAN SOIL?
Maybe it is safe to swim, but I wouldn't sun-bathe on the beach unless I hear someone actually tested the sand.