Friday, January 23, 2015

BC州野生きのこのセシウム What are BC Wild mushrooms telling you?

Looking For Fukushima Contamination in Mushrooms and Soil of Western North America


DECEMBER 16, 2014By Jay T. Cullen

The purpose of this diary is to report results from a recently published, peer reviewed study (behind paywall) examining the degree of Fukushima contamination in fungi and soil of western North America. The diary is the most recent contribution to an ongoing series which aims to provide evidence from scientific studies assessing the impact of the Fukushima Daiichi disaster on the environment and the health of residents of North America. Trappe and colleagues measured the activity of cesium isotopes (134-Cs half life ~ 2 years; 137-Cs half life ~30 years) in wild mushrooms, soil and leaf litter of the west coast from California up to Vancouver Island. The conclusions of the study were as follows:
この記事は、北米西部のきのこ類と土壌の福島からの汚染の程度を調査した最近発表された査読研究の結果を報告するためのものであり、北米の環境と住民の健康に福島原発事故が与えた影響を査定する科学的研究に基づく証拠を示すため継続して報告している記事のうちもっとも新しいものである。この研究者たちはカリフォルニアからバンクーバー島までの野生きのこ、土壌、そして落ち葉のセシウム(セシウム134 半減期2年、セシウム137 半減期30年)を測定した。その結論は以下のとおり。
  1. No activity measurements exceeded levels thought to impact human health
  2. 137-Cs activity increased in fungi and soil towards the north
  3. 134-Cs increased to the south in leaf litter
  4. Chanterelles did not significantly bioconcentrate Cs isotopes
  5. 137-Cs and 134-Cs activities were highly variable from sample to sample
  6. 137-Cs levels largely reflected non-Fukushima sources from either atmospheric weapons tests in the last century or the Chernobyl disaster in 1986
Chanterelles アンズダケ
  1. すべての結果は人間の健康に影響を与えるレベルを超えていない。
  2. きのこと土壌のセシウム137のレベルは北上するほど上昇した。
  3. 落ち葉のセシウム134は南下するほど上昇した。
  4. アンズダケはセシウム核種を生物濃縮していなかった。
  5. セシウム137と134のレベルはサンプルによりかなり多様だった。
  6. セシウム137のレベルのほとんどが福島由来ではない前世紀の大気核実験か1986年のチェルノブイリ事故からのものであることを反映していた。

The study by Trappe et al. (2014) was published in the Canadian Journal of Forest Research in August 2014 and can be found here. The authors began with the following hypotheses which motivated the research:

  1. activity levels of Cs isotopes in wild edible mushrooms were below the U.S. Food and Drug Administration derived intervention limits of 1200 becquerels per kilogram (Bq kg–1)
  2. Cs activity would be higher in samples farther north due to jet stream influenced precipitation patterns as most deposition of radioisotopes is associated with rain that predominant jet stream patterns bring to the Pacific northwest rather than to California 
  3. Chanterelles would bioaccumulate Cs isotopes at levels above those of their substrates (transfer factor > 1.0)
  1. 食用きのこのセシウムのレベルはアメリカ食品医薬品局(FDA)の規制値1キロ当たり1200ベクレルを下回っていた。
  2. 放射性核種の沈着は降雨と関連し、ジェットストリームはカリフォルニアより太平洋北西に流れるものが優勢のため、サンプルのセシウムのレベルは北のサンプルほど高くなるであろう。
  3. アンズダケはきのこの基質よりも高いレベルのセシウムを生態蓄積していくであろう。(移行因数>1.0)

To test these hypotheses they collected samples of fungi, soil and leaf litter from a variety of sites up and down the west coast of North American approximately 6–10 months after the Fukushima accident. These samples were subsequently analyzed for Cs isotopes at the Oregon State University Radiation Center using high purity germanium detectors that quantify gamma radiation spectra. All activities were decay corrected to April 1, 2011 and reported as Bq kg-1.

Results were as follows.

Hypothesis #1activity levels of Cs isotopes in wild edible mushrooms were below the U.S. Food and Drug Administration derived intervention limits of 1200 becquerels per kilogram (Bq kg–1)
The following figure summarizes measurements made in Chanterelle mushrooms, soil and leaf litter.

Mean activity levels of 137-Cs and 134-Cs for sampled materials (chanterelles, mineral soil, deciduous litter, and needle litter). This chart omits the 157 Bq·kg–1 chanterelle collection from Bamfield due to its outlier influence on the Y axis. Lowercase letters indicate mean values that were not statistically different. 
セシウム137と134の平均値(アンズダケ、土壌、落葉樹の落ち葉、針葉樹の落ち葉) この図にはバムフィールドで採取したアンズダケの1キロあたり157ベクレルはY軸を大幅にはみ出すために省いている。小文字で書かれているのは平均値が統計的に相違ないということを示しいる。
In all cases the summed activities of 134-Cs (which because of its short half life is a fingerprint for Fukushima fallout) and 137-Cs were well below the US Food and Drug Administration intervention level of 1200 Bq kg-1. One Chanterelle sample collected in Bamfield, British Columbia was a significant outlier at 157 Bq kg-1. Including this outlier the average 137-Cs activity for Chanterelles was 12.3 Bq kg-1 with mean activities higher in the Pacific north west (15.1 Bq kg-1) compared to California (0.4 Bq kg-1). The authors hypothesis holds in this case.

Hypothesis #2Cs activity would be higher in samples farther north due to jet stream influenced precipitation patterns as most deposition of radioisotopes is associated with rain that predominant jet stream patterns bring to the Pacific northwest rather than to California
The authors found that 137-Cs activity tended to increase towards the north as the following figures showing the 137-Cs content of soil and Chanterelles with latitude demonstrate.

137-Cs in soil samples (Bq·kg–1) with latitude (°N) of collection site (p = 0.01, adj. R2 = 0.27) 

Regression of 137-Cs in chanterelle mushroom samples (Bq·kg–1) with latitude (°N) (p = 0.01, adj. R2 < 0.39).   

Unlike 137-Cs, 134-Cs activities were comparably lower than 137-Cs and were highest in the south and decreased towards the north or showed little trend with latitude. The following figure demonstrates this trend in leaf litter samples.


Regression of 134-Cs in surface litter samples (Bq·kg–1) with latitude (°N) of collection site (p = 0.006, adj. R2 = 0.22). 

These trends and relative activities give us important information. Firstly, given that the cesium isotopes were released to the atmosphere in roughly a 1:1 ratio (134-Cs/137-Cs = 1) in March and April 2011 the low decay corrected activity ratio of 134-Cs/137-Cs in mushrooms, soil and leaf litter in the study suggest that significant amounts of 137-Cs did not come from Fukushima. This 137-Cs is likely present from atmospheric weapons testing in the 20th century or the Chernobyl disaster in 1986 which both released much larger amounts of 13-Cs to the environment.

The trend towards higher activities of 134-Cs in the south refutes the authors hypothesis that Fukushima fallout would be higher in the north given average precipitation patterns. However, at the time the main Fukushima plume arrived at the North American west coast March 17-20, 2011, the jet stream was positioned much farther to the south than average and brought 4.4 cm of rain to San Francisco (maps can be accessed here). During that same period Corvallis, Oregon, reported only 1.9 cm and here where I live in Victoria, British Columbia only 1.2 cm of rain fell. The anomalous path of the jet stream during the plumes arrival is thus consistent with the observations that 134-Cs levels and Fukushima fallout were slightly higher in California than in the Pacific north west in 2011.

Position of the jet stream on March 18, 2011 taken from 

Hypothesis #3Chanterelles would bioaccumulate Cs isotopes at levels above those of their substrates 

Little evidence was found that Chanterelle mushroom species were bioaccumulating either 134-Cs or 137-Cs higher than levels in the soil in which they grew. The average concentration factor (mushroom activity/soil activity) for 137-Cs was 1.0 while the median was 0.4. For 134-Cs the concentration factor was on average 1.4 with a median of 0.7. Some samples had high concentration factors for both isotopes (6.0-6.5) however the majority of samples were below 1.0. This data suggests that Hypothesis #3 does not hold.

The activities of Cs isotopes in mushrooms, soil and litter from before and after the Fukushima disaster began are compared in the following table.

Cesium isotope measurements (Bq·kg–1 dry mass) in comparable samples collected before and after the Fukushima accident. 
The authors conclude from this comparison that the much of the activity they detected in their study predated the Fukushima disaster. This is in keeping with measurements which suggest that the levels of fallout from the Fukushima disaster in western North America was about a factor of 10 lower than from the Chernobyl disaster and many orders of magnitude less significant than weapons testing fallout in the 20th century.


What is unexpected was Cs134 detections from Pre-Fukushima samples..... 

~BC sample results from this study~

Samples were collected in the fall and (or) winter season of 2011–2012, approximately 6–10 months after the Fukushima accident.

samples of 100 g dry mass of each material type is requested; however, some samples were smaller.

Fungal samples were cleaned of most of the adhering soil and debris, air dried at 60 °C for 12–24 h, and ground to a uniform powder. Each sample was then weighed,...and the volume was determined to the nearest 10 mL.
きのこのサンプルは付着した土などを落とし、60 °Cで12-24時間乾燥させ、粉砕した。それぞれの重量が測定され、体積は10mlほどと定められた。

For your reference....

検体名 Sample Name: 
乾燥まつたけ Dry Pine Mushroom 

採種年月 Collection date: 
2014 年 11月 (November, 2014)

採取場所 Collection Place: 
BC, Canada
測定日時 Date Tested: 
2014 年12月9日 (December 9,2014)

測定時間 Duration
2400 秒(seconds) 

重量 Weight: 44 g
乾燥前 Before Dehaidration: 400g (Dehydrated at 52 °C for about 10 hours)

試料容器 Container:
1Lマリ ネリ容器(Marinelli)

検査機器 Detector: φ5×4inch NaI

...When it was FRESH, the level of Cs137 would be 116.391 bq/kg.

In comparison...

福島・南相馬市産のマツタケから10万2900ベクレルのセシウム検出 Nov.8, 2014
Pine Mushroom Collected in Minami-Soma, Fukushima : 102,900 bq/kg. (Cs134+137)

Reported by Fukushima Prefecture

November, 2014  reported by Ministry of Agriculture, Forestry and Fisheries 農林水産省

長野県 Nagano
7.9~81 bq/kg
岩手県   Iwate
9.5~67 bq/kg
山梨県  Yamanashi
3.2~49 bq/kg


  1. Good work Vancouver Food Radiation Monitoring! Thank you for your very important information.

  2. Thank you for your comment. I'm planning to do the cross check with GE detector for BC pine mushroom sample.