In order to better understand the impact of the Fukushima Daiichi Nuclear Power
Plant (FDNPP) accident on a commercial marine species, neon flying squid
(
The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, which was caused
by the combined effect of the March 2011 earthquake and subsequent tsunami,
resulted in increased levels of artificial radioactivity in the marine
environment to the east of Japan (IAEA, 2015). The radioactive releases,
dominated by radiocesium, were transported eastwards in surface water across
the midlatitude North Pacific at a speed of 3–7 km day
A large amount of research has been conducted to determine the level of artificial radionuclides in biota samples and to assess the relevant radiological impact on both human and marine species. However, most studies have focused on the concentration of radiocesium in fish (Johansen et al., 2015; Wada et al., 2016), and only a few publications have reported on radionuclides in other marine species (Buesseler et al., 2012; Yu et al., 2015). Few data are available for open-ocean locations as compared to coastal areas, especially from 2011. Filling these data gaps will improve and expand understanding of the dynamics of cesium in the early months following the accident.
This study assessed samples of
Thirteen composite samples of
Squid samples were dissected, after thawing, into muscle and gut tissues (other soft
tissues including the digestive tract, gills, heart, gonads, and associated glands),
dried at 50
At each station, 60 L surface seawater samples, were collected with a submersible pump,
stored in polyethylene barrels with acidification to pH
Map of sampling sites.
The ERICA Assessment Tool (version 1.2; Brown et al., 2008) was used with
Tier 2 assessment to evaluate the radiological risk to squid from the study
areas in 2011. The ERICA tool has the capability to specify organism sizes,
and in this study average mass (1.3 kg) and dimensions (ellipsoid equivalent
of 0.3, 0.1, and 0.085 m for length, width, and height, respectively) from
the specimens were used to calculate dose rates. The dimensions of the
average
Committed effective doses (sievert, Sv) for human consumers of squid were estimated using
standard exposure-to-dose conversion factors (DCFs) for ingestion from the International
Commission on Radiological Protection (ICRP) Compendium of Dose Coefficients based on
ICRP Publication 60 (ICRP, 1999). Key DCFs are
The water-to-organism whole-body concentration ratio
(CR
In total, 98 specimens were obtained from six stations. The mass of the specimens ranged from 118 to 2551 g, with an average of 1347 g. Sixty percent of the specimens weighed 701 to 1700 g. The trunk length of the specimens ranged from 115 to 440 mm (on average 333 mm). Seventy-five percent of the specimens had a length greater than 290 mm (adult size), suggesting that the majority of the specimens hatched in the winter of 2010 or spring of 2011 and had been living for 8 to 11 months (Wang and Chen, 2005). Combining the estimated age of the squid, and assuming residence in the general region east of Fukushima Prefecture, it can be inferred that most specimens had been accumulating radionuclides since the FDNPP accident. However, a minor proportion (the small size category) may have hatched after the accident and had shorter exposure times.
The activity levels of radionuclides in Table 1 indicate that all
Although this estimate contains large uncertainties because of using MDA of
Ag-110m as the water concentration, these Ag data provide new insights for
international researchers. Additionally, they fill a gap because the relevant
international database (Wildlife Transfer Parameter Database;
The mean CR
The results also showed that both Cs-134 and Cs-137 were concentrated mainly in the muscle of the squid (Fig. 2a). Cesium behaves similarly to potassium in biota and tends to be distributed to the muscle tissue. These results for the open-ocean real-world conditions are consistent with previous laboratory results of more than 80 % accumulation in the muscle and head of cuttlefish after only 8 h of exposure to water (Bustamante et al., 2004, 2006). In contrast, for Ag, the open-ocean squid had 95 % Ag in the gut versus muscle (Fig. 2b). This result was also consistent with the laboratory cuttlefish, which had 98 % Ag in the gut following a single spiked feeding and 29 days depuration (Bustamante et al., 2004). From the same study, within the gut, accumulation of Ag is dominant in the digestive gland.
The smallest squid samples had the highest concentration factors for Cs-134,
Cs-137, Ag-110m, and U-238 (Fig. 2). Despite their inferred shorter exposure
times (shorter life span), the higher accumulation occurred in the smaller
size class compared to the larger size class. These results are consistent
with observed Cs depuration rates in juvenile cephalopods (
The levels of activity for
Activity concentrations of Cs-134
Radionuclide levels in composite samples (Bq kg
Tissues: M – muscle, G – gut, WB – whole-body. ND: level was below the minimum detectable activity.
Most nonhuman biota radiation-dose-assessing models focus on estimation of
dose rates using the
The whole-body to muscle and whole-body to gut concentration ratios for radionuclides in squid samples are listed in Table 2. For many radionuclides, the tissue-specific concentrations for the small squids tend to be higher than those for large squids. The uncertainty in the whole-body to gut CRs for Cs-137 and Cs-134 are relatively high because of the comparatively low level and large activity range of radiocesium in gut samples. The CRs presented here are calculated for the nonequilibrium conditions following the accident. This issue is somewhat compensated for by using the average activity concentrations that have accumulated over time, albeit over the relatively short life spans of the squid. Equilibrium conditions are generally not achieved in natural systems, and in our results all CRs should be considered in context. Further research is necessary to obtain a better estimation of the biokinetics of uptake in squid and of the whole-body to gut CRs for Cs-137 and Cs-134.
Concentration ratios for radionuclides in 2011 following the accident (see text).
Ingestion dose estimates for human consumers of the squid in this
study (Sv yr
The internal radiological dose rates in squid from artificial radionuclides
(
Dose rates (
From the radionuclides measured in edible squid tissue (muscle), a committed
effective ingestion dose of 0.010 mSv (median; minimum
Elevated levels of Cs-134 and Ag-110m from the FDNPP accident were found in the squid
(
The data related to this paper are provided in the Supplement and will be submitted to the International Atomic Energy Agency's Marine Information System (MARiS) database.
The supplement related to this article is available online at:
WY contributed to data analysis and modeling of dose to biota; MPJ contributed to the modelling of dose to biota and human consumers, and data interpretation; WY and MPJ wrote the manuscript with support from LL; JH helped supervise the project; WM contributed to sample collection. All authors discussed the results and contributed to the final manuscript.
The authors declare that they have no conflict of interest.
This study was partially supported by the Scientific Research Foundation of the Third Institute of Oceanography, SOA (2015010), the Northwestern Pacific Marine Environmental Monitoring Project, the Coordinated Research Project (CRP K41017), and Regional Cooperative Agreement Project (IAEA/RCA RAS7028) of the International Atomic Energy Agency (IAEA), the National Key Scientific Instrument and Equipment Development Project (2016YFF0103905), the International Organizations and Conferences Project of the State Oceanic Administration of China, and the Public Science and Technology Research Project of the Ocean (201505005-1). Edited by: Manmohan Sarin Reviewed by: four anonymous referees