Dietmar Weiss. Contamination of water, sediments and biota of the Northern Pacific coastal area in the vicinity of the Fukushima Daiichi NPP

Transcription

1 Dietmar Weiss Contamination of water, sediments and biota of the Northern Pacific coastal area in the vicinity of the Fukushima Daiichi NPP

2 Content Introduction Progress of contamination of the sea environment Sea water Artificial radionuclides in sea water of other origin Bottom sediments Marine organisms Radionuclide accumulation processes in aquatic organisms Radiological consequences Conclusions

3 Introduction Immediately after the occurance of the nuclear accident at Fukushima Daiichi NPP the GRS established an emergency center for the evaluation of the nuclear safety of the BPP and of the local and regional radiological situation in Japan The evaluated data and information were delivered to the BMU, mass media and the public For this, the results of radioactivity measurements in marine environment carried out by the plant owner TEPCO, by Japanese authorities and NGOs were registered, evaluated and spread via GRS website to the public

4 Contamination of coastal waters (1)

5 Contamination of coastal waters (2) J-131 in coastal waters (TEPCO data) Following strong fluctuations in activity concentration the maximum of at 180,000 Bq/l was detected on 30th March, 330 m south of discharge chanal The I-131 activity concentrations exponentially decreased while being permanently lower than the authorized limit of 40 Bq/l since late April Since 10th May the activity concentration has been lower than the detection limit of about 6 Bq/l

6 Contamination of coastal waters (3) Cs134 and Cs137 in coastal waters (TEPCO data) Following strong fluctuations in activity concentration the maximum of at 47,000 Bq/l of each Cs-isotope was detected also on 30th March, 330 m south of discharge chanal The Cs134 and Cs137 activity concentrations exponentially decreased while being permanently lower than the authorized limit of 60 Bq/l (Cs 134) and 90 Bq/l (Cs-137), resp. since beginning of May Since second decade of May the activity concentration has been lower than the detection limit of about 6 Bq/l

7 Contamination of coastal waters (4)

8 Contamination of coastal waters (5)

9 Contamination of coastal waters (6)

10 Contamination of coastal waters (7)

11 Contamination of coastal waters (8)

12 Contamination of offshore waters (1) Measurements of sea water contamination at distances of 35 through 60 km from the shore were carried out by MEXT since 23th May The I-131 maximum concentrations of 35 Bq/l through 160 Bq/l were detected at three sampling points 35 km through 40 km east from the Fukushima Daiichi NPP on 15 th April The latest detectable Cs-activity concentrations were measured on 5 th May with 9 Bq/l and 11 Bq/l, resp. at the same sampling points as for I-131 In near bottom waters the maximum concentrations of 9 Bq/l for both Cs-isotopes and of 11 Bq/l for I-131 were detected on 28 th May The I-131 concentrations became lower than the detection limit since mid-april while those of Cs-isotopes were indicated in early May

13 Sampling stations in the vicinity of Fukushima NPP and in distances from the coastline between 20 km and 50 km Contamination of offshore waters (2)

14 Contamination of offshore waters (3)

15 Contamination of offshore waters (4)

16 Artificial radionuclides in sea water of other origin (1) In the past artificial radionuclides, e.g. Cs-isotopes were mainly introduced into the marine environment by fallout resulting from Atmospheric nuclear weapon tests (Cs-137 only) Reactor accident at Chernobyl NPP (initial Cs-134/Cs137 ratio of 0.5) Recently, the Cs-137 activity concentrations resulting from global fallout are between Bq/l and 0.01 Bq/l in seas of the northern hemisphere The maximum Cs-137 concentrations of about 1 Bq/l was measured in Spring 1986 in the northern Baltic Sea due to the Chernobyl fallout

17 Artificial radionuclides in sea water of other origin (2) Liquid discharges into the marine environment result mainly from fuel reprocessing plants The maximum Cs- 137 discharges from Sellafield reprocessing plant amounted to about 5,000 TBq/yr (mid 1970th to early 1980th)

18 Contamination of bottom sediments (1) The Maximum Cs-137 activity concentration of 210 Bq/kg was detected on 24th May (water depth 126 m) at the same point were the highest water contamination was measured. The I-131 activity concentration was lower than the detection limit since mid-may due to the short physical halflife of 8 days While at some sampling points the Cs-activity is slowly decreasing till now at other points it wass still increasing until late summer A further increase of Cs-activity can not be expected due to the strong decrese of water contamination and the sandy nature of the sediments

19 Contamination of bottom sediments (2) The Maximum Cs-137 activity concentration in sediments is very low compared to the contamination of soil where up to 40,00 Bq/kg Cs-137 (Sukagawa) and 140,000 Bq/kg (Itate) were measured. For comparison, the maximum Cs-137 activity concentration in silty sediments of the western Baltic Sea amouterd to about 200 Bq/kg resulting from fallout of Chernobyl NPP accident

20 Contamination of bottom sediments (3)

21 Contamination of bottom sediments (4)

22 Contamination of bottom sediments (5)

23 Contamination of bottom sediments (6)

24 Contamination of sea weed (1) Seaweed are in highly appreciated as food in Japan Seaweed acumulates Iodine by a factor from 100 (Nori, red algae) to 10,000 (Kombu), brown algae) The intake of I-131 follows the same process as for stable iodine. Consequently, it would amounts at most to the 10,000 fold of I-131 concentration in sea water Also the decrease in I-131 concentration in algae follows with a short time delay the concentration trend for I-131 in sea water, and I-131 in algae is being exchanged by stable iodine Nevertheless, the mesasured I-131 activity concentrations were much lower than expecxted. The maximum I-131 concentration was detected in Hijiki with 2,200 Bq/kg

25 Contamination of sea weed (2) Tribe Species Content of iodine Enrichment (Japanese name) [mg/100 g dry mass] factor (at 50 mg/m 3 iodine in sea water) Red algae Nori Dulse Green algae Sea lattice Brown algae (Tang) Wakame Hijiki Arame Kombu

26 Contamination of shellfish, shrimps, mussels, snails and, calamary (1) The measured concentrations of Cs-isotopes in Mussels, grabs, snails and shrimps from coastal water in front of Fukushima NPP were enhanced but only in few cases the authorized limit of 500 Bq/kg (total Cs) was exceeded 820 Bq/kg in mediterranean mussel 940 Bq/kg in surf clam 1,190 Bq/kg in Japanese midden crab

27 o Sandlance Contamination of fish (1)

28 Contamination of fish (2) Sandlances often occurs in the coastal waters off Fukushima It is a demanded edible fish in Japan and it constitutes fodder e.g. for cod, pollock and seabirds Due to ist way of life and eating habits (small crustaceans) it strongly accumulates radionuclides Thus, up to 14,400 Bq/kg radioactive cesium and 12,000 Bq/kg I-131 were measured in sandlances from the coastal area off Fukushima in mid-april Whereas I-131 has not been detected for Cs activity was still measured up to 400 Bq/kg in late September, 2011

29 Contamination of fish (3) o Flatfish Flatfish living on the sea bottom accumulate like sandlances radionuclides, in particular that of cesium, due to their way of life and eating habits The cesium concentrations arose with a major delay in time as compared to thaqt of the seawater and in late May amouted up to 250 Bq/kg Cs remaining at this level till now The maximum cesium activity of 1,610 Bq/kg was detected with 1,600 Bq/kg on 10th September.

30 o Pelagic fish Contamination of fish (4) Species Cs activity (Bq/kg) Mar - Apr May - Jun Jul - Aug Sep - Oct Max. Cod < < < (25.06.) Pollock < < < < (15.05.) Seabass < (15.09.) Mackerel < < < < (06.07.) Anchovy < < (05.08.) Sardine < < (16.07.) Tuna < < < < (03.10.) Cesium activity concentrations in edible fish from Northern Pacific fishing grounds (data from Fishery Agency of Japan)

31 Contamination of fish (5)

32 Contamination of fish (6)

33 Calculation of Cesium activity concentrations in aquatic organisms (1)

34 Calculation of Cesium activity concentrations in aquatic organisms (2) fishing grounds (data from FA /3/)

35 Calculation of Cesium activity concentrations in aquatic organisms (3) fishing grounds (data from FA /3/)

36 Radiation doses Stay at or in water About 100 µsv/hr until midmay, decreasing to 1 µsv/hr at beginning of May High enrichment of I 131 in sea weed (and in less degree of Cs isotopes) Between 2.2 msv/100g (red algea) and 220 msv/100g (Kombu) until mid-april; decreasing to 0.02 msv/100g to 2 msv/100g at beginning of May Timely delayed Cs accumulation in fish The dose resulting from fish consumption (except for fish from the restricted 30 km zone) is estimated to some 10 µsv/yr also by means of the Japanese consumption rate of 60 kg fish per year

37 Conclusions It can be stated that no danger for peaple arises from consumption of seafood from the large Pacific fishing grounds, also under consideration of a consumption rate of 60 kg fish per year Only in few cases Cs-activities which exceed the autorized limit of 500 Bq/kg were measured in seafood out of the 30 km zone around Nevertheless, the sea area around Fukushima Daiichi is restricted for fishing

38 Thank you for your attention!