The IAEA is monitoring contamination in the marine environment near Fukushima from the damaged nuclear power plant. Japanese authorities are sampling seawater at various distances from the discharge points, including along transects 30 km and newly 15 km offshore. The highest contamination levels are near the coast at 30 m, 330 m, and 10 km from the plant, but concentrations 30 km offshore are generally decreasing over time due to dilution and ocean currents. The IAEA advised Japanese authorities on improving marine sampling and measurements.

1. Marine Environment MonitoringAssessment of IAEA Environment Laboratories on Data provided by JapanUpdate 7 AprilIAEA Environment Laboratories, Monaco

2. General commentsThe contamination of the marine environment has occurred both through atmospheric fallout or washout with precipitation, and through discharges of contaminated water into the sea

3. Authorised discharge of low level contaminated water (4 April)

4. 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 two North-South transects situated 15 and 30 km off-shoreSeawater sampling offshore Fukushima carried out by Japanese Authorities Seawater sampling locations of Japanese AuthoritiesTransect about 30 km offshore, sampling points separated by 10 kilometres, surface and bottom seawater sampled

5. Additional sampling stations at 10 and 20 km offshore, for which both surface and bottom seawater are sampled (M9-M10)

6. New transect 15 km offshore

7. Mainly surface water was collected and analysed, but meanwhile also some analyses for deep water samples were carried outMap 1

8. Concentrations in sea water near discharge point of Unit 1-4

9. Concentrations in sea water near discharge point of Unit 5 and 6

10. I-131 concentration in sea water

11. Cs-137 concentration in sea water

12. ConclusionsThe highest levels are still measured close to the coast, namely 30 m, 330 m and 10 km near-shore.

13. Concentration data from about 30 km off-shore show a generally decreasing time trend

14. It can be expected that, if no additional releases occur, the levels measured at the stations 30 km off-shore will continue to decrease significantly by dilution into deeper layers and dispersion by ocean currentsConclusionsThe number of marine sampling points has been increased with a new North-South transect 15 km offshore One marine expert from IAEA Environmental Laboratories, Monaco has been in Japan to review and advise on marine sampling and measurements (back yesterday night) .