Environmental radioactivity monitoring – Fukushima Daiichi

The Fukushima Daiichi nuclear accident in March 2011 resulted in significant initial releases of radioactive material to the atmosphere and ocean. There have been further releases of radioactive material to the ocean although at significantly lower levels than in March 2011.

  • There is no evidence of radioactive contamination to the New Zealand environment as a result of this accident.
  • Atmospheric dispersion has been largely restricted to the northern hemisphere although small traces were detected at Darwin for several days in April 2011. The only nuclide detected that was attributable to Fukushima Daiichi was Xe-133 at a level that would result in a radiation dose 100 million times smaller than the annual natural background radiation routinely received by members of the public.
  • Marine monitoring off Japan’s east coast shows that contaminated waters have been diluted and dispersed while being carried eastwards towards the centre of the North Pacific.
  • In 2015 radioactive material from Fukushima was detected for the first time along the North American shoreline.  The amount detected was extremely low – the testing organisation at the time confirmed that swimming in the water every day for a year would result in a radiation dose 1,000 times smaller than a single dental x-ray.
  • Deep, slow moving currents will eventually carry radioactive material across the equator. International dispersion models predict that such materials will reach New Zealand between 2026 and 2031.
  • Radioactive material continues to undergo radioactive decay with half-lives of 30 years (caesium-137), 2 years (caesium-134) and 8 days (iodine-131). By 2026, caesium-137 will have reduced to 70%, caesium-134 to 0.5% and iodine-131 to effectively 0% of the activities initially released into the ocean. This, combined with significant further dilution, means that the material is expected to be well below detection levels when it reaches New Zealand’s coastal waters and well short of levels that could cause health concern.
  • The Ministry of Health has checked selected goods imported from Japan for radioactive contamination. Initial testing was conducted off shore before ships entered New Zealand ports. Later testing was conducted on shore at reduced frequencies. There have been no positive readings, and the programme has concluded.

The Ministry for Primary Industries (MPI) oversaw food imports and imposed strict border controls from the date of the accident until July 2012.  By July 2012, MPI was satisfied that the Japanese had put strict testing and controls in place on food produced in Japan and lifted the New Zealand controls, but testing continued. The results (76.7 Bq/kg for caesium-137 and 57.4 Bq/kg for caesium-134) were well within applicable Codex limits of 1000 Bq/kg.

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