Total quantity of caesium radioisotopes in fish in the Fukushima-Ken Exclusive Economic Zone , Japan , in November 2012

The Tokyo Electric Power Company Fukushima Dai-ichi nuclear power plant in Fukushima-Ken (Prefecture), Japan, was destroyed in March 2011 due to a massive earthquake (magnitude 9) centred offshore to the northeast of Honshu Island and the subsequent historic tsunami on 11 March 2011. Due to nuclear meltdown, damage to the buildings housing the reactors by hydrogen explosions, and the contamination of cooling water from the reactor cores, huge quantities of radioisotopes were emitted to the atmosphere and to the adjacent seawater. Fishing is currently prohibited off the coast of Fukushima-Ken because intermittent surveys have found that the majority of fishery products still contain radioisotope levels exceeding the Japanese Standard Value. However, the total amount of caesium radioisotopes in fish biomass in the Fukushima-Ken Exclusive Economic Zone (EEZ) has not yet been reported. The Tokyo University of Marine Science and Technology has measured radioisotope levels in fishery species off Iwaki-Shi (City), Fukushima-Ken (located south of the destroyed nuclear power plant), and these data can be used to estimate the total fish biomass and the quantity of caesium radioisotopes in fish in the Fukushima-Ken EEZ. On 22 to 23 November 2012, the estimated total fish biomass in the Fukushima-Ken EEZ was 91,150,218.79 kg and the estimated total quantities of Cs-134 and Cs-137 in fish were 4,879,259,657 Bq and 8,381,002,727 Bq, respectively.


INTRODUCTION
The Tokyo Electric Power Company Fukushima Dai-ichi nuclear power plant, located in Futaba-Gun (County), Fukushima-Ken (Prefecture), Japan, was destroyed in March 2011 due to a massive earthquake (magnitude 9) centred offshore to the northeast of Honshu Island and the subsequent historic tsunami on 11 March, 2011.Due to the resulting nuclear meltdown, damage to the buildings housing the reactors by hydrogen explosions, and the contamination of cooling water from the reactor cores, huge quantities of radioisotopes were emitted to the atmosphere and to the adjacent seawater.Fishing is currently prohibited off the coast of Fukushima-Ken because intermittent surveys have found that the majority of fishery products still contain radioisotope levels exceeding the Japanese Standard Value.Therefore, the Japanese government has measured radioisotope levels in fishery species not only offshore near the destroyed reactors but also throughout the E-mail: hi@katsura.dk.Tel: +81-467-54-5869; Fax: +81-467-54-1383.
Japanese Exclusive Economic Zone (EEZ).The Japanese government has regularly released a subset of these measurements to the public, for example, via the internet (Japanese Governmental Off.Bull.On-Line, 2012;Ministry of Education, C., S., S. & T., 2011;NEMOTO et al., 2012;Ohnishi, 2012).To date, however, the total quantity of fishery resources and the estimated total quantity of caesium radioisotopes in fish biomass in the Fukushima-Ken EEZ after 11 March, 2011 have not been reported (Wan et al., 2012).This information is important not only to Japanese residents but also to residents of other countries.These data would make it possible to calculate overall contamination levels and to predict future trends.On 22 to 23 November, 2012, the Tokyo University of Marine Science and Technology performed an independent sampling measure radioisotope levels in fishery species off Iwaki-Shi (City), Fukushima-Ken (located south of the destroyed nuclear power plant).These data included detailed measurements of individual fish, such as weight, sex, length, and collection locality.Thus, this information could be used to estimate the fish biomass and the total quantity of caesium radioisotopes in fish in the Fukushima-Ken EEZ during November 2012.These estimates are reported here.

MATERIALS AND METHODS
Trawl (dragnet) fishing was performed on 22 November, 2012 off Yotsukura and Ena, Iwaki-Shi, Fukushima-Ken, Japan to sample the fish in the region.The total fishing areas were 9,450 and 9,775 square meter off Yotsukura and Ena, respectively (Atkins and Warren, 1953).Gill-net fishing was performed on 22 to 23 November, 2012 in the same locations.The total fishing areas were 28,900 and 50,141 square meter off Yotsukura and Ena, respectively (Buscaino et al., 2009).Subsequently, the edible portions of the fish were minced, and U-8 containers (100 mL) were filled with the minced fish flesh.The concentrations of the radioisotopes Cs-134 and Cs-137 in the fish biomass were measured by IDEA Consultants Inc. (Tokyo, Japan) using a germanium semiconductor detector (Seiko EG&G Co. model GEM20-70) (Inazu et al., 2011;Minatani et al., 2012).
The total area of the Fukushima-Ken EEZ is 33,300,000,000 square meter.
(33,300,000,000 / 98,266) = 338,876.1118Thus, the estimated biomass of all fish species in the Fukushima-Ken EEZ in November 2012 can be calculated by multiplying 338,876.1118times the total weight of the collected fish, and the total quantity of caesium radioisotopes  in the fish biomass can be estimated using the following equations: [ETFW] = Estimated total fish weight in the Fukushima-Ken EEZ [kg] [ACS134] = Average Cs-134 level in fish biomass in the Fukushima-Ken EEZ in November 2012  in Fish] = Estimated total quantity of Cs-134 in fish biomass in the Fukushima-Ken EEZ in November 2012 [Bq] [ACS137] = Average Cs-137 level in fish biomass in the Fukushima-Ken EEZ in November 2012 [Bq/kg] [Estimated Total Cs-137 in Fish] = Estimated total quantity of Cs-137 in fish biomass in the Fukushima-Ken EEZ in November 2012 Table 2 shows the resulting estimates.The estimated total fish weight in the Fukushima-Ken EEZ on 22 to 23 November, 2012 was 91,150,218.79 kg; the estimated total quantity of Cs-134 in all fish in the Fukushima-Ken EEZ was 4,879,259,657 Bq; and the estimated total quantity of Cs-137 in all fish in the Fukushima-Ken EEZ was 8,381,002,727 Bq.
[2] Some scholars and other professionals do not agree with this estimation method because the range of a particular fish species depends on environmental conditions, and they believe that it is not meaningful to extrapolate from fish sampled off the coast of Fukushima-Ken to the total area of the Fukushima-Ken EEZ.On the other hand, not only Japanese residents but also residents of other countries, especially those living in Pacific coastal areas, are strongly interested in the total quantity of radioisotopes in fish biomass in the Fukushima-Ken EEZ.This information is critical to an overall perspective and future prediction of radioactive contamination in Pacific fisheries.One way to address this contradiction is to examine historical accidents at nuclear power plants, such as those at the Three Mile Island Nuclear Generating Station in Pennsylvania, U.S.A. (1979) and at the Chernobyl Nuclear Power Plant in Ukraine, former U.S.S.R. (1986) (Macdonald et al., 1987;Asmolov et al. 1987).However, these accidents did not occur along marine coastlines.On the other hand, governments conducted frequent atmospheric nuclear tests prior to the effective date of the Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space and Under Water [often abbreviated as the Partial Test Ban Treaty (PTBT), Limited Test Ban Treaty (LTBT), or Nuclear Test Ban Treaty (NTBT)] in October 1963 (Scherb and Voigt, 2011;Lown and Pastore, 1985).Some atmospheric nuclear tests were conducted in the ocean, and reported estimates of the total Amounts  quantity of radioisotopes in fish biomass cover broad ranges extending from offshore to the boundaries of designated areas, such as EEZs (Moiseev and Kardashev, 1964).

Conclusion
(1) The estimated total fish biomass in the Fukushima-Ken EEZ on 22 to 23 November, 2012 was 91,150,218.79 kg.
(2) The estimated total quantities of Cs-134 and Cs-137 in all fish in the Fukushima-Ken EEZ on 22 to 22 November, 2012 were 4,879,259,657 Bq and 8,381,002,727 Bq, respectively.

Table 2 .
Amount of fishery resources and the estimated total amount of cesium radioisotopes in fish bodies in offshore Fukushima-Ken, Japan in November 2012.