72
1
Introduction
On March 11, 2011, a massive earthquake and
tsunami occurred in northeastern Japan. The
Fukushima Daiichi Nuclear Power Plant (FNPP)
lost power as a result of the tsunami, and a subsequent explosion within the building released a
large quantity of radioactive material into the
atmosphere and sea ( Honda et al. 2012 ; Wakeford
2011 ; Akahane et al. 2012 ; Chino et al. 2012 ;
Aoyama et al. 2013 ). According to previous
reports (TEPCO 2012 ; Estournel et al. 2012 ), the
total amount of radioactive
137 Cs released into the
ocean was 3.6 × 10
15 Bq.
Radioactive Cs levels exceeding the Japanese
limit for human consumption (100 Bq/kg) were
detected in various fi sh species caught in coastal
Fukushima (Watabe 2012 ). Until September
2013, fi shing in Fukushima Prefecture was
banned, while the Fisheries Agency of Japan and
authorities in Fukushima Prefecture measured
radioactive Cs concentrations in marine organisms after the accident. These analytical data
have been published by Wada et al. ( 2013 ).
Concentrations of radioactive Cs in octopus species ( Enteroctopus dofl eini and Octopus conispadiceus ) and gastropods ( Buccinum isaotakii )
decreased rapidly. Two hundred days after the
accident, radioactive Cs was not detected in these
organisms. Concentrations of radioactive Cs in
anchovy larvae ( Engraulis japonicus ), the bivalve
Pseudocardium sachalinense , and the seaweed
Eisenia bicyclis decreased with time. However,
concentrations of radioactive Cs in coastal
demersal fi sh, such as Microstomus achne ,
Sebastes cheni , and Okamejei kenojei , decreased
slowly, with levels in excess of 100 Bq/kg
recorded in 2012.
The reasons for these differences in the rate of
decrease in radioactive cesium among the sampled species may include local or large migrations, nutritional physiology, digestive processes,
and mode of excretion. To clarify how radioactive material is dispersed within the marine ecosystem and how levels in organisms may vary in
the future, cesium concentrations near FNPP
were monitored.
This ongoing project involved the assessment
and measurement of (1) diffusion via the food
web, (2) diffusion via migration/ranging, and
(3) a long-term study of the biological half-life of
radioactive Cs within the fi sh body (Fig. 1 ). This
report contains a brief outline and some preliminary key results from the study.
2
Materials and Method
This study measured the spatial and temporal
changes in radioactive Cs concentrations in
coastal
organisms
near
the
damaged
FNPP. Sampling locations were selected at
Yotsukura (35 km south of FNPP; depth,
0.5–1 m), Ena (50 km south of FNPP; depth,
5–6 m), and Souma (50 km north of FNPP; depth,
5–6 m) (Fig. 2 ).
Immediately after the accident, released
radioactive material fl owed south due to the
ultrasonic pinger was used to investigate the ranging behavior of the rockfi sh Sebastes cheni in an area contaminated with high concentrations of
cesium. Immediately after the accident at FNPP, very high levels of radioactive cesium were recorded in coastal marine organisms, but these
decreased with time. At present, the concentrations found in demersal
coastal fi sh are higher than in pelagic species. The ranging behavior of
rockfi sh, contaminated at comparatively high levels, was very limited,
with the fi sh remaining within a small territorial area and thus limiting
the diffusion of radioactive cesium. It is 3 years since the Fukushima
accident; however, continuous monitoring of radioactive cesium concentrations in benthic and coastal fi sh is still required to implement suitable
management policies.
H. Arakawa et al.
1
Introduction
On March 11, 2011, a massive earthquake and
tsunami occurred in northeastern Japan. The
Fukushima Daiichi Nuclear Power Plant (FNPP)
lost power as a result of the tsunami, and a subsequent explosion within the building released a
large quantity of radioactive material into the
atmosphere and sea ( Honda et al. 2012 ; Wakeford
2011 ; Akahane et al. 2012 ; Chino et al. 2012 ;
Aoyama et al. 2013 ). According to previous
reports (TEPCO 2012 ; Estournel et al. 2012 ), the
total amount of radioactive
137 Cs released into the
ocean was 3.6 × 10
15 Bq.
Radioactive Cs levels exceeding the Japanese
limit for human consumption (100 Bq/kg) were
detected in various fi sh species caught in coastal
Fukushima (Watabe 2012 ). Until September
2013, fi shing in Fukushima Prefecture was
banned, while the Fisheries Agency of Japan and
authorities in Fukushima Prefecture measured
radioactive Cs concentrations in marine organisms after the accident. These analytical data
have been published by Wada et al. ( 2013 ).
Concentrations of radioactive Cs in octopus species ( Enteroctopus dofl eini and Octopus conispadiceus ) and gastropods ( Buccinum isaotakii )
decreased rapidly. Two hundred days after the
accident, radioactive Cs was not detected in these
organisms. Concentrations of radioactive Cs in
anchovy larvae ( Engraulis japonicus ), the bivalve
Pseudocardium sachalinense , and the seaweed
Eisenia bicyclis decreased with time. However,
concentrations of radioactive Cs in coastal
demersal fi sh, such as Microstomus achne ,
Sebastes cheni , and Okamejei kenojei , decreased
slowly, with levels in excess of 100 Bq/kg
recorded in 2012.
The reasons for these differences in the rate of
decrease in radioactive cesium among the sampled species may include local or large migrations, nutritional physiology, digestive processes,
and mode of excretion. To clarify how radioactive material is dispersed within the marine ecosystem and how levels in organisms may vary in
the future, cesium concentrations near FNPP
were monitored.
This ongoing project involved the assessment
and measurement of (1) diffusion via the food
web, (2) diffusion via migration/ranging, and
(3) a long-term study of the biological half-life of
radioactive Cs within the fi sh body (Fig. 1 ). This
report contains a brief outline and some preliminary key results from the study.
2
Materials and Method
This study measured the spatial and temporal
changes in radioactive Cs concentrations in
coastal
organisms
near
the
damaged
FNPP. Sampling locations were selected at
Yotsukura (35 km south of FNPP; depth,
0.5–1 m), Ena (50 km south of FNPP; depth,
5–6 m), and Souma (50 km north of FNPP; depth,
5–6 m) (Fig. 2 ).
Immediately after the accident, released
radioactive material fl owed south due to the
ultrasonic pinger was used to investigate the ranging behavior of the rockfi sh Sebastes cheni in an area contaminated with high concentrations of
cesium. Immediately after the accident at FNPP, very high levels of radioactive cesium were recorded in coastal marine organisms, but these
decreased with time. At present, the concentrations found in demersal
coastal fi sh are higher than in pelagic species. The ranging behavior of
rockfi sh, contaminated at comparatively high levels, was very limited,
with the fi sh remaining within a small territorial area and thus limiting
the diffusion of radioactive cesium. It is 3 years since the Fukushima
accident; however, continuous monitoring of radioactive cesium concentrations in benthic and coastal fi sh is still required to implement suitable
management policies.
H. Arakawa et al.