1. Marine Environment Monitoring Assessment of IAEA Environment Laboratories on Data provided by Japan IAEA Environment Laboratories, Monaco

2. General comments The contamination of the marine environment has occurred both through atmospheric fallout or washout with precipitation, and through discharges of contaminated water into the sea Japanese institutes continue to perform measurements in seawater at 30 m and 330 m off the discharge points of Dai-ichi NPP, as well at 10 km and 20 km off-shore and along a North-South transect situated 30 km off-shore

3. Seawater sampling offshore Fukushima carried out by Japanese Authorities (23 - 30 March 2011) Seawater sampling locations of Japanese Authorities Transect about 30 km offshore, sample locations separated by 10 kilometres, surface seawater sampled Additional sampling stations at 10 and 20 km offshore, for which both surface and bottom seawater are sampled

4. General Comments Higher levels are measured 30 m, 330 m and 10 km near-shore relative to those measured 30 km off-shore Concentration data off-shore reported for the past week show a quite heterogeneous distribution, as expected, both on the surface and deep layers, with general decreasing time trend It can be expected that, in the absence of additional releases, the levels measured at the stations 30 km off-shore will continue to decrease significantly by dilution into deeper layers and dispersion by ocean currents

5. Bathymetry and main ocean currents Credit: SIROCCO Credit: NOAA

6. I-131 concentrations in seawater at 10 - 30 km off-shore FukushimaData submitted by Japanese authorities

7. Cs-137 concentrations in seawater at 10-30 km off-shoreData submitted by Japanese authorities

9. 30 km offshore surface water concentrations were up to 3-4 orders of magnitude higher than the values measured in 2005

10. 330 m East of Fukushima Dai-ichi concentrations were up to 3 orders of magnitude higher than the values measured offshore, this showing the high dilution capacity of the marine environment1 106 103 102 101 108 104 105 107 1 106 103 102 101 108 104 105 107 Bq.m-3 Bq.m-3 [1 – 101] [103– 104] [105– 107] Cs-137 Bq.m-3 April 2005 30 km 24, 27 March 2011

11. I-131 and Cs-137concentrations in seawater at the common discharge point of Units 1-4Data submitted by Japanese authorities

12. I-131 and Cs-137concentrations in seawater at the common discharge point of Units 5-6Data submitted by Japanese authorities

13. Conclusions Measurements of seawater are carried out by Japanese authorities since 23 March and data are reported to the IAEA for information and assessment. I-131 and Cs-137 were detected with highest activity concentrations of about 80 Bq/L and 25 Bq/L in surface water, respectively, on 23 March. Data reported for 30 March show generally lower values below 10 Bq/L for both I-131 and Cs-137. A higher value of 80 Bq/l was measured at the point situated 10 km offshore for I-131, while Cs-137 at this station remains low at 8 Bq/l.

14. Conclusions Levels at 30 m and 330 m from the discharge points showed increasing concentrations up to 130 000 Bq/L for I-131 and 32 000 Bq/L for Cs-137 Modelling of the dispersion of radionuclides was initiated by the SIROCCO group of the Observatoire Midi-Pyrenees, University of Toulouse, and first results indicating the general pattern of dispersion are available. The results show an initial transport into north-east direction and fast dispersion along the Kuroshio curent. One marine expert from IAEA Environmental Laboratories, Monaco currently in Japan to review and advise on marine sampling and measurements