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New Study: Over a Trillion becquerels of Fukushima radiocesium fell on Hawaii

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University of Hawai’i at Mānoa, Oct 31, 2017
Fukushima-derived radiocesium fallout in Hawaiian soils… This study estimated the magnitude of cesium deposition in soil, collected in 2015-2016, resulting from atmospheric fallout… Detectable, Fukushima-derived 134Cs inventories ranged from 30 to 630 Bq m-2 and 137Cs inventories ranged from 20 to 2200 Bq m-2… This research confirmed and quantified the presence of Fukushima-derived fallout in the state of Hawai’i in amounts higher than predicted by models and observed in the United States mainland…
The Hawaiian Islands were expected to get minimal, below 10 Bq m-2 or lower, of Fukushima-derived fallout…
Fukushima-derived soil radiocesium concentrations, were greater than anticipated based on model-predicted Pacific atmospheric dispersion rates…
Maximum estimated values of 134Cs fallout on the islands of Hawaii and O’ahu constrained by precipitation and data from sites with less than 70% canopy cover were obtained by linear interpolation of all measured soil cesium concentrations, resulting in 134Cs fallout ranging from < 60 to 1000 Bq m-2 [According to this study, “The Fukushima-derived fallout… 134Cs to 137Cs ratio was 1:1” — therefore 137Cs fallout from Fukushima was also 60 to 1000 Bq m-2, making the total radiocesium 120 to 2000 Bq m-2. Compare this to the study’s previous statement that “The Hawaiian Islands were expected to get minimal, below 10 Bq m-2 or lower, of Fukushima-derived fallout”]…
Using the conservative values and integrating over the whole area with rainfall above 200 mm, we estimate that the island of Hawaii received 1.50 x 10^12 Bq [1.5 Trillion Bq] of 134Cs and 137Cs, each isotope contributing 50%, between March 19 and April 4, 2011…
Atmospheric dispersion models predicted the majority of the plume to travel a more northern route over the Aleutian Islands… however, suggesting that the Fukushima-derived aerosol plume may have taken an alternative southern path. Our radiocesium fallout inventories are comparatively higher than those estimated and measured in North America. Previous research that used whole-water wet deposition to predict ‘its fallout in North America estimated up to 180 Bq m -2 in Alaska, 46 Bq m -2 in California, and 29 Bq m -2 in Washington State…
This is the first study to our knowledge studying Fukushima-derived fallout in the Pacific Islands…
Fukushima-derived radiocesium fallout in Hawaiian soils
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November 28, 2017 Posted by | Fukushima 2017 | , , | 1 Comment

Geology graduates investigate Fukushima-derived radioactivity in Hawaii

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Trista McKenzie in the lab

On March 11, 2011, following the Tohoku earthquake and tsunami, several reactors at the Fukushima Dai-ichi Nuclear Power Plant suffered damage and released radioactive chemicals into the atmosphere and contaminated wastewater into the nearby Pacific Ocean. Hannah Azouz and Trista McKenzie, two recent graduates from the University of Hawaiʻi at Mānoa School of Ocean and Earth Science and Technology (SOEST) bachelor of science in geology program, assessed the extent to which the soil of Hawaiʻi and locally purchased fish have been impacted by radioactivity from this event.

The students’ mentor, Henrietta Dulai, associate professor of geology, explained the motivation for this work, “My research team has been monitoring Fukushima-derived cesium in the Pacific Ocean since 2011 and we concluded that the Hawaiian Islands were spared from a direct hit of radionuclide plume spread by ocean currents. Yet, fish migrate and so even fish caught locally may accumulate some cesium in waters north of Hawaiʻi. Further, only one week after the disaster, the Department of Health identified Fukushima-derived radionuclides in the air, milk and precipitation over Hawaiʻi Island. We wanted to determine how much cesium was deposited from the atmosphere to the islands.”

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Fresh-caught Ahi tuna

Locally-purchased fish

To investigate the impact on locally-purchased fish, Azouz measured Fukushima-derived cesium isotopes in thirteen types of fish that are most commonly consumed in Hawaiʻi.

The FDA-accepted intervention limit for cesium isotope intake is 300 Bq/kg for fish. All fish tested were significantly below intervention limits—the highest cesium concentration in the examined species was in the Ahi tuna, carrying less than 1 Bq/kg.

“These data are informative to the community and they reassure me about the safety of the food we consume,” said Azouz. “The activities of the radionuclides were gratefully low—a person consuming the annual average amount of fish would receive the same dose of radioactivity as if they consumed one banana.”

“I did not know how passionate I would become about earth sciences,” said Azouz, who grew up in California but now calls Kailua home. “The most rewarding thing about this project is providing honest relief and real answers to the public. I can’t wait to publish this study and get it out onto the internet for the rest of the community to see!”

Azouz’s work was funded by the Undergraduate Research Opportunities Program (UROP) at UH Mānoa, with support from the Honors Program and SOEST.

“I recommend the University’s Honors Program as a great way to jump start a future career in your favored field. The research opportunities are endless,” said Azouz.

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Soil and mushrooms

To estimate the atmospheric fallout of Fukushima-derived cesium and iodine onto Hawaiʻi, McKenzie analyzed mushroom and soil samples from Oʻahu and Hawaiʻi Island from areas with various average rainfall.

McKenzie’s research confirmed and quantified the presence of Fukushima-derived fallout in Hawaiʻi—the radioactive elements were present in both mushrooms and soil. However, the activities detected were much lower than fallout associated with the nuclear weapons testing in the Pacific. Additionally, they found that Fukushima-derived cesium in soils was correlated with precipitation—the more rainfall, the more cesium.

The levels of cesium activity (factoring both historical and Fukushima-derived fallout) in mushrooms were more than 12 times under the Derived Intervention Limit. For soils, there is no specific safety limit for radiocesium, but McKenzie found cesium inventories were not high—up to 1,200 Bq/m2 cesium in Hawaiʻi soils compared to 200,000 Bq/m2 in forest soils found near the Fukushima Power Plant.

McKenzie’s fieldwork was funded by UROP at UH Mānoa, as was a trip to Vienna, Austria, to present her research at the European Geosciences Union (EGU) General Assembly. Subsequent to her presentation in Vienna, McKenzie also won the American Geophysical Union Multi-Society Undergraduate Spring 2016 Virtual Poster Showcase.

“I chose this project for my undergraduate research because it offered me a chance to investigate a really important question,” said McKenzie. “I’ve enjoyed both the field and lab work, and as a result of attending the EGU, I was able to meet geologists from all over the world and gain valuable presentation experience,” said McKenzie.

Both Azouz and McKenzie will continue working with Dulai in the fall—this time as graduate students.

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Hannah Azouz sharing research findings at the 2015 SOEST Open House

Geology graduates investigate Fukushima-derived radioactivity in Hawaiʻi

 

June 4, 2016 Posted by | Fukushima 2016 | , , , , | Leave a comment