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, 113 (14), 3838-43

Risk Assessment of Radioisotope Contamination for Aquatic Living Resources in and Around Japan

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Risk Assessment of Radioisotope Contamination for Aquatic Living Resources in and Around Japan

Hiroshi Okamura et al. Proc Natl Acad Sci U S A.

Abstract

Food contamination caused by radioisotopes released from the Fukushima Dai-ichi nuclear power plant is of great public concern. The contamination risk for food items should be estimated depending on the characteristics and geographic environments of each item. However, evaluating current and future risk for food items is generally difficult because of small sample sizes, high detection limits, and insufficient survey periods. We evaluated the risk for aquatic food items exceeding a threshold of the radioactive cesium in each species and location using a statistical model. Here we show that the overall contamination risk for aquatic food items is very low. Some freshwater biota, however, are still highly contaminated, particularly in Fukushima. Highly contaminated fish generally tend to have large body size and high trophic levels.

Keywords: Weibull distribution; detection limit; radiocesium; random effects; statistical risk assessment.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. S1.
Fig. S1.
Linear regression of the difference between log(Cs137) and log(Cs134) against the cumulative days from 1 April 2011 for the observed data above detection limits.
Fig. 1.
Fig. 1.
Temporal risk changes for freshwater and marine species in Fukushima prefecture. Risks are evaluated by Pr(Cs134+Cs137>D) for freshwater species [freshwater fish, diadromous fish, freshwater crustaceans, and freshwater molluscs: (A) D=20, (B) D=50, and (C) D=100] and marine species [demersal fish, pelagic fish, marine crustaceans, and marine molluscs: (D) D=20, (E) D=50, and (F) D=100] from 1 April 2011 to 1 September 2015. Red lines are (unweighted) medians, and dashed lines are 90% CIs for the risks.
Fig. S2.
Fig. S2.
Temporal risk changes for freshwater and marine species for prefectures to the north of Fukushima (Aomori, Iwate, and Miyagi). Risks are evaluated by Pr(134Cs+137Cs > D) for freshwater species [freshwater fish, diadromous fish, freshwater crustaceans, and freshwater molluscs; (A) D = 20, (B) D = 50, (C) D = 100] and marine species [demersal fish, pelagic fish, marine crustaceans, and marine molluscs; (D) D = 20, (E) D = 50, (F) D = 100] from April 1, 2011 to September 1, 2015. Red lines are (unweighted) medians and dashed lines are 90% CIs for the risks.
Fig. S3.
Fig. S3.
Temporal risk changes for freshwater and marine species for prefectures to the south of Fukushima (Gunma, Saitama, Tochigi, Ibaraki, and Chiba). Risks are evaluated by Pr(134Cs+137Cs > D) for freshwater species [freshwater fish, diadromous fish, freshwater crustaceans, and freshwater molluscs; (A) D = 20, (B) D = 50, (C) D = 100] and marine species [demersal fish, pelagic fish, marine crustaceans, and marine molluscs; (D) D = 20, (E) D = 50, (F) D = 100] from April 1, 2011 to September 1, 2015. Red lines are (unweighted) medians and dashed lines are 90% CIs for the risks.
Fig. 2.
Fig. 2.
Spatial radioisotope contamination risks for species groups and prefecture groups around Fukushima. Risk is evaluated by Pr(Cs134+Cs137>100Bq/kg)>106.
Fig. 3.
Fig. 3.
The relationship between the Weibull distribution parameters, trophic level, and log(Lmax) [(A) TL vs. log(Lmax), (B) log(m) vs. TL, (C) ρ vs. log(Lmax), and (D) log(k) vs. TL]. Red lines are predicted trends for TL or log(Lmax). Neither TL nor log(Lmax) for log(m) was selected by AIC.

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