Fukushima’s impact on the Pacific

OUR ENVIRONMENT Fukushima’s impact on the Pacific

Understanding the impact of radioactive caesium release

The incident at the Fukushima Daiichi nuclear power plant in March 2011 released the largest ever single-event deposition of radioactive caesium into a marine ecosystem — effectively launching a multi-decade study which spans the Pacific Ocean as far as Australia.

The research is important as Pacific rim governments, fishing industries, and the science community have grappled with the question of the environmental consequences of this unprecedented event.

Previous data from the Chernobyl accident was helpful in predicting contamination on the land surface. However, most of the Fukushima radioactive releases were deposited into the waters of the ecologically-rich North Pacific. Five years later, important findings have emerged while other questions remain to be answered.

Where is the caesium today? Recent data shows model predictions of the large-scale movement of the element have generally proven true. The radioactive caesium is circulating within the North Pacific Gyre and small amounts have arrived at the western coast of North America within 3–5 years as expected.

The models also predicted that highlydiluted caesium from Fukushima would eventually cross the equator and enter into Australian waters via the Indonesian Throughflow (the southward currents off the north-western coast of Australia). While the caesium contamination is expected to be highly diluted, real-world monitoring is needed to address basic concerns about fisheries and ecosystems.

In 2015 ANSTO worked with the Australian Radiation Protection and Nuclear Safety Agency to collect water samples and fish from Western Australian coastal waters to test for Fukushima influence. Preliminary results did not find the presence of the 134Cs isotope that would indicate Fukushima contamination. But the data has provided a valuable baseline important for a range of ocean circulation, marine water chemistry and ecological health concerns.

In some cases, trace contaminants may become mobile not by ocean currents, but by migratory wildlife. Using ANSTO’s specialised bioanalytics capabilities, investigations into migratory birds for the presence of isotopes released from Fukushima are ongoing. Rare collections of eggshells from uninhabited islands close to and remote from Fukushima sampled before and after the Tōhoku earthquake are beginning to provide unique data about the dispersion of the relevant radioisotopes and the effect of ocean currents, such as the Kuroshio current and counter-current.

Within these currents, across much of the Pacific Ocean, fish now carry isotopic signatures from the incident. ANSTO joined with researchers from Japan and other International Atomic Energy Agency member states to evaluate potential impacts on fisheries, including those of eastern Japan where fisheries were closed and carefully regulated after the accident. Six years on, most fisheries are open, with only the caesium levels in some fish nearest to the plant remaining elevated. This persistence was not predicted by early models and it was somewhat surprising when 740,000 Bq kg-1 of radioactive caesium was found in a hexagrammos otakii (greenling) in 2013. This highest recorded value represents an increase of more than one million times over the pre-event levels, and more than 7000 times the limit for consumption of fish in Japan.

The highest levels were found in areas closed to fishing in proximity to the stricken power plant, but were not limited to one fish, or one species. Measurements exceeding 100,000 Bq kg-1 of 134 , 137Cs were recorded in more than 100 fish from 10 species sampled in 2013 from Fukushima.

This persistence and its possible causes (food chain transfer from contaminated sediments among other sources) were highlighted in ANSTO-led research, the main finding of which was that although the accumulation in the fish nearest to the plant was relatively high, the levels decreased rapidly with distance away from the plant. Fukushima-released isotopes have been detected in fish across the North Pacific, but at levels that do not pose a dose risk to the fish, nor consumers of the fish.

These assessments were performed under International Atomic Energy Agency programmes in collaboration with researchers from Japan, the US and other countries. Australia performed a role as an independent third party and provided training to staff from International Atomic Energy Agency member states from Asia.

Contact

mathew.johansen@ansto.gov.au

COLLABORATORS

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ANSTO

RESEARCH FACILITY / TECHNIQUE

Bioanalytics laboratories Centre for Accelerator Science (CAS) Isotopic tracing techniques RESEARCHER TEAM

Dr Mathew JOHANSEN Prof Richard BANATI

Nicholas HOWELL

David CHILD

Dr Michael HOTCHKIS

Jennifer HARRISON

PUBLICATIONS

Environmental Science and Technology 2015

Fukushima

Tokyo

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NUCLEAR FUEL CYCLE Nuclear fuel cycle

Although ANSTO does not produce nuclear power, our researchers are working internationally to find ways of reducing the volume of nuclear waste produced by power reactors, and the amount of radiation damage caused during the nuclear energy production process.