Fifth Fukushima Daiichi Meltdown Anniversary: Food Contamination Risks

Summary: Food contamination risks are low overall for marine species, but high for some freshwater species, on the fifth Fukushima Daiichi meltdown anniversary.

aerial view of Fukushima explosions, with Unit 3 still evaporating, taken by global Hawk drone, Tuesday, March 15, 2011: naturalflow, CC BY SA 2.0 Generic, via Flickr

Food contamination risks are low overall for marine species on the fifth Fukushima Daiichi meltdown anniversary, according to research Feb. 29, 2016, in the Proceedings of the National Academy of Sciences.

Two researchers at the Fisheries Research Agency in Kanagawa and two at The Institute of Statistical Mathematics in Tokyo base their findings upon levels of radiocesiums. They consider that “The [current and the future] contamination risk for food items should be estimated depending on the characteristics and geographic environments of each item.” They deem that “evaluating current and future risk for food items is generally difficult because of small sample sizes, high detection limits, and insufficient survey periods.” Their models expose low overall contamination risk for aquatic food items despite some “still highly contaminated” freshwater species.

The fifth Fukushima Daiichi meltdown anniversary finds the government of Japan still having y-emitting radioisotopes monitored for food contamination risks and against “highly contaminated” food consumption.

Officials and scientists give two radiocesiums (cesium isotopes) as targets that warrant monitoring because of radioactive leakages by Fukushima Daiichi’s damaged drains since March 11, 2011. Cesium (Cs) 134 and Cesium (Cs) 137, the main radioisotopes released from the nuclear meltdowns, have respectively long half-lives of 2.0652 years and of 30.167 years. The report of monthly inspections of radioisotope contamination since the meltdowns is quantified at the database of the Ministry of Health, Labor, and Welfare in Tokyo.

The four researchers judge the 1,646 combinations of prefectures and species as more straightforward in collection than in data analysis.

Data from April 1, 2011, date of peak ocean discharges after the Tōhoku earthquake and tsunami, to March 31, 2015, keep many “N.D.” (not detected) results. The non-detection designation leads to the conclusion that the prefecture and the species in question are contamination-free or that they have radiocesium concentrations below detection limits.

Researchers Morita and Okamura in Kanagawa and Eguchi and Ikeda in Tokyo make up for undetectable results by comparing similar prefectures and species at similar times. They note that, when comparisons have similarly undetectable results, “the minimum detection limit is treated as if it was the observed value (not the detection limit).”

Results of the study’s statistical model offer high and low food contamination risks on the fifth Fukushima Daiichi meltdown anniversary.

Statistical risk analysis prompts the co-researchers’ conclusion that “The risk of cesium contamination in Fukushima has steadily decreased from 1 April 2011 to 1 September 2015.”

Marine species qualify for smaller contamination risks since “freshwater fish have longer biological half-lives of radiocesium because of differences in osmoregulation systems” for controlling water content. Food contamination risks remain higher for demersal (seabed-hovering), diadromous (freshwater and saltwater-dwelling) and freshwater fish; for freshwater crustaceans; and for Fukushima and prefectures in southern Japan.

Market and restaurant operators usually serve freshwater fish whose radiocesium concentration tends to fall below recreational fishery and tourism industry limits of 100 becquerels per kilogram.

The researchers think larger samples, longer times, lower limits communicate food contamination risks on the fifth Fukushima Daiichi meltdown anniversary.

The risk of cesium contamination generally is greater in freshwater species than in marine species: PNAS @PNASNews, via Twitter Feb. 29, 2016

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

aerial view of Fukushima explosions, with Unit 3 still evaporating, taken by global Hawk drone, Tuesday, March 15, 2011: naturalflow, CC BY SA 2.0 Generic, via Flickr @ https://www.flickr.com/photos/vizpix/5529038135

The risk of cesium contamination generally is greater in freshwater species than in marine species: PNAS @PNASNews, via Twitter Feb. 29, 2016, @ https://twitter.com/PNASNews/status/704428702592077825

For further information:

Harvey, Chelsea. 29 February 2016. “With Fukushima’s Fifth Anniversary Approaching, We Can Probably Start to Relax out Radioactive Seafood.” The Washington Post > Energy and Environment.
Available @ https://www.washingtonpost.com/news/energy-environment/wp/2016/02/29/with-fukushimas-fifth-anniversary-approaching-we-can-probably-start-to-relax-about-radioactive-seafood/

Marriner, Derdriu. 9 November 2015. "Fukushima Contaminated Water at West Coastlines of the Americas." Earth and Space News. Monday.
Available @ https://earth-and-space-news.blogspot.com/2015/11/fukushima-contaminated-water-at-west.html

Marriner, Derdriu. 30 November 2015. "Fukushima Is Afflicting the Pale Grass Blue Butterfly Zizeeria maha." Earth and Space News. Monday.
Available @ https://earth-and-space-news.blogspot.com/2015/11/fukushima-is-afflicting-pale-grass-blue.html

Marriner, Derdriu. 7 December 2015. "North American West Coast Radioactive Plumes From Fukushima 2011." Earth and Space News. Monday.
Available @ https://earth-and-space-news.blogspot.com/2015/12/north-american-west-coast-radioactive.html

Okamura, Hiroshi; Ikeda, Shiro; Morita, Takami; and Eguchi, Shinto. “Risk Assessment of Radioisotope Contamination for Aquatic Living Resources in and around Japan.” 29 February 2016. Proceedings of the National Academy of Sciences of the United States of America. DOI: 10.1073/pnas.1519792113
Available @ http://www.pnas.org/content/early/2016/02/23/1519792113
Available @ http://www.pnas.org/content/113/14/3838.full

PNAS @PNASNews. 29 February 2016. "Food safety risk from Fukushima accident." Twitter.
Available @ https://twitter.com/PNASNews/status/704428702592077825