#Radiation in Japan: Spiders in Iitate-mura Concentrating Radioactive Silver 1,000 Times

Dr. Bin Mori is a professor emeritus at University of Tokyo, Faculty of Agriculture. Since the beginning of the Fukushima nuclear crisis on March 11, the professor has been writing his blog focusing on the effect of radiation in plants and remediation of agricultural land.

I have featured his autoradiographs of dandelion and horsetail on my blog before.

In his post on October 30, Professor Mori wrote about his discovery, probably the world first, he made in spiders (Nephila clavata) he caught in Iitate-mura, Fukushima Prefecture, where the villagers were forced to evacuate after being designated as "planned evacuation zone". The spiders, he found, had radioactive silver (Ag-110m) at 1,000 times the concentration in the environment.

The following is my translation of Dr. Mori's October 30 blog post, with his express permission:

飯舘村で雨の降る中での植物の採取は困難であったので、竹藪や杉林の中で、網を張っているジョロウグモ(Nephila clavata)を捕獲してきました。

Since it was difficult to collect plants in the rain in Iitate-mura, I caught instead "nephila clavatas" in the bamboo groves and cedar forest.

クモは直接土を食べるかどうかわからないが、網にかかった蝶やアブやカナブンなどを食べて林の中の食物連鎖の上位に位し、放射性セシウムを濃縮しているだろうと考えたからです。

I don't know whether the spiders eat dirt itself, but I thought they may have concentrated radioactive cesium in their bodies as they were at the top of the food chain in the forest, eating butterflies, horseflies, and drone beetles that they caught in their webs.

(Picture 1: Nephila Clavata)

ジョロウグモを４匹一緒にしてＧｅ半導体で、放射性セシウム (Cs-137とCs-134) を分析しました（図１）。すると、Cs-137のエネルギーピークである661.7keVの隣の657.8keVの位置にほぼ等量の未知のエネルギーピークを見いだしました（図２）。

I put 4 nephila cravatas together in the germanium semiconductor detector, and analyzed radioactive cesium (Cs-137 and Cs-134) (Picture 1). Then I noticed an unknown energy peak at 657.8keV, right next to the energy peak of Cs-137 at 661.7keV (Chart 2).

(Chart 2: Ag-110m peak detected next to Cs-137)

これを同定するとAg-110m（銀の核異性体：半減期249.5日）の放出する４つのガンマ線の１つのピークであることがわかりました。他の３つのピークも検出されました(図３）。

When I identified this peak, it turned out to be one of the 4 gamma-ray peaks from Ag-110m (nuclear isomer of silver, half life 249.5 days). The other 3 peaks were also detected (Chart 3).

(Chart 3: 4 peaks of Ag-110m identified)

したがって、ジョロウグモが東電福島原発由来の放射性降下物である超微量の放射性銀（Ag-110m）を濃縮していることがわかりました。

So, the conclusion is that nephila clavatas have concentrated a minute amount of radioactive silver (Ag-110m), which is one of the radioactive fallout materials from Fukushima I Nuclear Power Plant.

クモの放射能の濃度は　

Cs-134(2.9Bq/4匹 )＋Cs-137(3.9Bq/4匹) = 3656Bq /kg生体重
に対して
Ag-110m (2.6Bq/4匹)＝1397Bq /kg生体重
でした。

The densities of the radioactive materials in the spiders were:

Radioactive cesium:
Cs-134 (2.9 Bq/4 spiders) + Cs-137 (3.9 Bq/4 spiders) = 3,656 Bq/kg live weight　

versus

Radioactive silver:
Ag-110m (2.6 Bq/4 spiders) = 1,397 Bq/kg live weight

この林の汚染土壌のCs(137+134)とAg-110mの存在比は、約2500:1 でしたので、上記の数値を用いて計算すると、ジョロウグモは約1000倍にまで土壌の放射性銀を生体濃縮していたことになります。

In the forest where the spiders were caught, the ratio of radioactive cesium (134+137) to Ag-110m was about 2,500 to 1. Using the above numbers, I calculated that nephila clavatas bio-concentrated the radioactive silver in the soil to about 1,000 times.　　　

昆虫が銀を高濃度濃縮するという知見はこれが世界で最初の発見です。また、すでに林内で放射能の生物濃縮が始まっているということが明らかです。

This is the first discovery in the world that an insect highly concentrates silver. Also, it is evident that bio-concentration of radioactivity in the forest has already started.

　この研究の詳細は１１月２６日（土）日本土壌肥料学会関東支部会（松戸の千葉大園芸学部）で発表します。乞御来聴。

I will present the details of my research on Saturday November 26 at the Japanese Society of Science and Plant Nutrition's Kanto Branch meeting (Faculty of Horticulture at Chiba University in Matsudo City, Chiba). Please come.　　

付記：計測に際しては、東京大学大学院農学生命科学研究科・田野井慶太朗助教のお世話になりました。

Appendix: I'd like to thank Keitaro Tanoi of University of Tokyo Graduate School of Agricultural and Life Sciences for the measurement.

追記１：ここで用いた生体濃縮の定義は、セシウムに対する比率で計算したものです。詳しくは論じませんが、放射性セシウムの生体濃縮の定義によっては、ジョロウグモの銀の濃縮度は、これよりもけた違いに高くなる可能性があります。

PS: The definition of bio-concentration used here is calculated from the ratio to radioactive cesium. I won't discuss it in details here, but depending on how bio-concentration of radioactive cesium is defined, the concentration ratio of radioactive silver by nephila clavata may be even higher.

In the very last sentence, Professor Mori is literally saying "higher by a digit". But I am not exactly sure whether he means literally or figuratively, or whether he means higher by single digit or more. (I'm asking the professor for clarification.)

Professor Mori says he is planning to write up the paper on the subject in English and submit it, but he says that's secondary. The most important thing, he says, is to disseminate information as wide as possible when it comes to radiation contamination, and he uses his blog to post his own unique discovery like this even before he writes it up as a scientific paper.

(What a difference between him and certain researchers who withhold critical information about radiation contamination in Japan so that their papers get accepted by prestigious foreign papers.)

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