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.”
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.
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.
—By Marcie Grabowski