#Radioactive Tea from Chiba, This Year's First Pick: Max 14 Bq/kg of Cesium, Brewed, Exceeding the Safety Limit

This is the first case in Japan of this year's green tea exceeding the new safety limit of 10 Bq/kg of brewed tea.

14 Bq/kg of radioactive cesium in brewed tea could translate into the maximum 1,400 Bq/kg of radioactive cesium in the dried leaves, with the possible range between 800 to 1,400 Bq/kg, far exceeding even the provisional safety limit (500 Bq/kg) that was in place until April 1, 2012. For more on the old and new test methods for green tea, see my previous post. (If you read Japanese, here's a comprehensible togetter (string of tweets) on the subject compiled by @Kontan_Bigcat, titled "Standard for radioactive cesium in green tea was stricter last year, and here's why".)

Chiba Prefecture's test result (using only the new way of measuring brewed tea) of total 16 samples from 5 municipalities shows some samples close to the new safety limit of 10 Bq/kg of radioactive cesium in brewed tea. 2 samples exceeded the new safety limit.

Chiba Prefecture's page says the samples are prepared in this way, following the guideline from the Ministry of Health and Welfare dated March 15, 2012:

荒茶又は製茶10g以上を30倍量の重量の熱水（90℃）で60秒間浸出し、40メッシュ相当のふるい等でろ過した浸出液

Use "ara-cha" (bulk tea) or "sei-cha" (blend tea), more than 10 grams, add hot water (90 degrees Celsius) 30 times the weight of the tea, brew for 60 seconds, strain the liquid using a strainer (40 mesh)

(I put in the English labels)

No.	栽培地 Location	品目 Item	栽培状況	採取日	放射性セシウム
					セシウム134	セシウム137	合計 注3
1	成田市 Narita	茶（一番茶飲用）Tea, First pick	露地 grown outdoors	5月14日	1.91	3.21	5.1
2		茶（一番茶飲用）	露地	5月14日	2.08	3.45	5.5
3		茶（一番茶飲用）	露地	5月14日	5.45	8.72	14
4		茶（一番茶飲用）	露地	5月14日	5.17	7.33	13
5	勝浦市 Katsuura	茶（一番茶飲用）	露地	5月15日	1.55	4.02	5.6
6		茶（一番茶飲用）	露地	5月15日	1.98	3.61	5.6
7		茶（一番茶飲用）	露地	5月15日	1.61	3.09	4.7
8	多古町 Tako	茶（一番茶飲用）	露地	5月14日	2.60	4.52	7.1
9		茶（一番茶飲用）	露地	5月14日	2.06	3.32	5.4
10	八街市 Yachimata	茶（一番茶飲用）	露地	5月16日	1.89	2.91	4.8
11		茶（一番茶飲用）	露地	5月16日	2.83	3.50	6.3
12		茶（一番茶飲用）	露地	5月16日	1.69	2.99	4.7
13		茶（一番茶飲用）	露地	5月16日	3.43	4.53	8.0
14		茶（一番茶飲用）	露地	5月16日	2.33	3.41	5.7
15	芝山町 Shibayama	茶（一番茶飲用）	露地	5月16日	1.99	2.49	4.5
16		茶（一番茶飲用）	露地	5月16日	1.33	2.19	3.5

Based on the above result, the shipping ban on the teas in Tako-machi and Shibayama-machi has been lifted. Other municipalities (except for Narita City) will soon follow.

Last year, green tea (dry leaves) from Chiba Prefecture was found with radioactive cesium ranging from slightly over 200 Bq/kg to 2,300 Bq/kg. Even the fresh leaves were found with 260 to 980 Bq/kg of cesium, according to the excel sheet data from the prefecture.

For those who are still wondering what "Becquerel" means, Chiba Prefecture's page has the definition for you, too:

ベクレル：放射能の強さを表す単位で、単位時間（1秒間）内に原子核が崩壊する数を表す。

Becquerel: Unit of radioactivity. It indicates the number of nuclei decaying in a unit time (1 second).

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