How much Radioactivity is entering, has entered, the Pacific Ocean
The initial release of radiation was much greater than the ongoing release of radiation. That is, initially the accident was pretty horrific and released lots of radiation. Since then TEPCO finally admitted there is an ongoing release of radioactive groundwater into the Ocean. Available figures suggest this is adding some radioactive contamination to the Ocean, but not as much as the initial release.
- 16.2 Peta Bq (10^15 Bq) (see True facts about Ocean Radiation and the Fukushima Disaster)
- 20-40 trillion Bq of Tritium released since the disaster where the initial release was 5,000 to 15,000 trillion becquerels of radioactive substances (see Fukushima's radioactive ocean plume due to reach US waters in 2014)
- 0.3 Tera Bq per month (10^12 Bq) which has added another 9.6 Tera Bq of radiation into the sea at most. (see True facts about Ocean Radiation and the Fukushima Disaster)
For some context:
Background radiation levels in the Oceans around the world as measured in 1990 (source http://www.whoi.edu/page.do?pid=83397&tid=3622&cid=94989). The two hotspots are in the Baltic Sea and Black Sea. The Baltic comes from nuclear testing on Nova Zemyla (Russia), and the Black Sea contamination comes from the Chernobyl accident.
Apparently the current releases, ground water escaping into the ocean, is primarily Tritium and Strontium because the Cesium is binding to the ground. (see Fukushima's radioactive ocean plume due to reach US waters in 2014)
How much dilution -> effect elsewhere in the Pacific beyond the Japanese Coast
The Pacific Ocean is the largest Ocean on this planet. It saw much nuclear bomb testing a few decades ago, and is therefore radiation risks are not unknown here.
Based on models developed by scientists, they believe
- Cs-137 concentration 1-20 Bq / cubic meter of seawater on the West Coast US - 10x the previous levels, or not terribly high (see True facts about Ocean Radiation and the Fukushima Disaster) ... or perhaps a bit more (see Fukushima's radioactive ocean plume due to reach US waters in 2014)
A large portion of the radiation won't even reach the US West Coast, but instead stay in the middle of the Ocean in the North Pacific Gyre (a.k.a. the Great Pacific Garbage Patch). That area is formed by ocean currents that circle the center of the ocean, without interacting much with the rest of the Ocean. (see Fukushima's radioactive ocean plume due to reach US waters in 2014)
How much is "safe"?
I've been looking for information on the health effects of being exposed to radiation. Unfortunately it seems there isn't a direct correlation of NNN Bq's of radiation causes this condition. That's because of the nature of exposure to radiation, and that what's important is how much gets ingested into the body and what gets done afterward.
Radioactivity is a measure of how many atoms are disintegrating over time.
- 1 Becquerel (Bq) = 1 atomic disintegration per second
- 1 Curie (Ci) = 37 Billon atomic disintegrations per second
- Potassium-40 = 71 ten millionths Curies per gram
- Cesium-137 = 88 Curies per gram
- Strontium-90 = 140 Curies per gram
Research done by Dr. Yuri Bandazhevsky, and his colleagues and students, in Belarus during the period 1991 through 1999, correlated whole body radiation levels of 10 to 30 Becquerels per kilogram of whole body weight with abnormal heart rhythms and levels of 50 Becquerels per kilogram of body weight with irreversible damage to the tissues of the heart and other vital organs.
One of the key discoveries made by Bandazhevsky was that Cesium-137 bioconcentrates in the endocrine and heart tissues, as well as the pancreas, kidneys and intestines. This goes completely against one of the primary assumptions used by the ICRP to calculate “effective dose” as measured by milliseiverts: that Cesium-137 is uniformly distributed in human tissues.
Let me restate that. The current ICRP methodology is to assume that the absorbed dose is uniformly distributed in human tissues. This is, in fact, not the case…It was never previously translated in large part because shortly after Dr. Bandazhevsky presented it to the Parliament and the President of Belarus, he was summarily arrested and imprisoned.
The previous came from: http://whatisradiation.com/nuclear-fallout/effects-of-cesium-137.html
Comparing the Fukushima incident to Chernobyl
The Chernobyl incident gives us some data with which to judge what will happen with the Fukushima incident.
Radioactivity in the Baltic Sea - http://www.stuk.fi/sateily-ymparistossa/itameri/en_GB/_print/
The map above shows two hotspots in the world, the Black Sea and the Baltic Sea. Both came about because of Russian nuclear testing and the Chernobyl incident.
This map shows the distribution of radiation in the Baltic Sea. It's unevenly distributed, obviously.
One thing which occurred is that radioactive decay made the effects less than they had been at the time of the Chernobyl incident.
The chart may be a little small to read, but it shows a spike to nearly 1000 Bq / cubic meter of Cs-137 initially, but which has fallen off rapidly and is currently at 20ish Bq / cubic meter, or more, depending on the location measured.
Secondary radioactive contamination of the Black Sea after Chernobyl accident: recent levels, pathways and trends. - October 2013 - http://www.ncbi.nlm.nih.gov/pubmed/23639695
The recent radionuclide measurements have showed that concentrations of the Chernobyl-derived (137)Cs and (90)Sr in the surface Black Sea waters are still relatively high, reaching 56 and 32 Bq m(-3), respectively. This is comparable or even exceeds the pre-Chernobyl levels (∼16 Bq (137)Cs and 22 Bq (90)Sr per m(3) as the basin-wide average values). The measurements have revealed that the Black Sea continues to receive Chernobyl radionuclides, particularly (90)Sr, by the runoff from the Dnieper River. An additional source of (90)Sr and (137)Cs was found in the area adjacent to the Kerch Strait that connects the Black Sea and the Sea of Azov. This may be caused by the inflow of the contaminated Dnieper waters, which come to this area through the North-Crimean Canal. The long-term monitoring of (137)Cs and (90)Sr concentration in the Black Sea surface waters and in the benthic brown seaweed Cystoseira sp., in comparison with the earlier published sediment records of the radionuclides, have showed signs of a secondary radioactive contamination, which has started to increase since the late 1990's. This may be the result of the combined effect of a higher input of radionuclides from the rivers in 1995-1999 due to an increased runoff; and a slow transport of the particulate bound radionuclides from the watersheds followed by their desorption in seawater from the riverine suspended matter and remobilization from the sediments adjacent to the river mouths.
Key data - In the Black Sea, they're still seeing Cs-137 at 56 Bq / cubic meter, and Sr-90 at 32 Bq / cubic meter. It's higher than pre-Chernobyl levels. The issue is a continuous inflow of water into the Black sea from Chernobyl.