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Cesar Jung-Harada 🌏
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Radioactive Sediment Micro Trawler

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We have collected 33 sediment samples from riverbeds and the seabed as close as 1.5km away from the Fukushima Daiichi Nuclear Power Plant (FDNPP) in Japan — see video above.

The invention: most ocean floor sediment sampling uses an Ekman grab. There are multiple issues with an Ekman grab:

  1. the Ekman grab digs deep and mixes old (deep) and new (on top) sediments -> the micro trawler only "shaves" the surface, the most recent sediment, effectively taking a "snapshot" of the most recent sediments.
  2. the the Ekman grab tends to leak the finest elements as it is brought back to the surface, which is an issue since the finest the sediment, the more exposed surface area per weight (often synonymous with toxicity) -> the micro trawler mainly collects the fine sediment and that can be adjusted with the size of the mesh. As the micro trawler is hoisted back to the surface, the "mouth" is up and the sediments are secured down in the sock, avoiding leakage.
  3. typically you need to stop to deploy the Ekman grab -> the micro trawler can be deployed at moderate speed, not slowing down the transect
    1. the micro trawler is more compact, cheaper to fabricate and has less moving parts than the Ekman grab

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The locations: Dr Olivier Evrard’s team demonstrated that radioactivity levels “move” seasonally, mostly depending on precipitation (rain). After a rainy season, the radioactive particles gets “washed” from the mountain tops, down into the rivers and into the ocean (video of our approximate analog simulation). We collected samples from the most affected rivers and at sea in the immediate vicinity of the crippled, leaking nuclear power plant.

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The time: the video was taken on October 9, between Typhoon 4 Phanfone(Oct 7th over Tohoku) and Typhoon 5 Vong Fong (Oct 14th). RT reports“Radiation levels at Fukushima rise to record highs after typhoon”:

“Samples from October 9 indicate that there are 150,000 becquerels of tritium per liter in the groundwater near Fukushima, according to Japan’s JIJI agency. Compared to levels recorded last week, that’s an increase of more than 10 times.”

We were “lucky” in that our predictions of the best time and place to collect the samples was accurate. The map on the right represents the levels of Cs-134 along the northeastern coast of Japan in October 2014 on the seabed.

The original blog posts are:

Special thanks to