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Will Fukushima Radiation Poison California?

This week marked the three-year anniversary of the massive Tohoku earthquake off the Japanese coast. This 9.0 Richter scale tectonic event and the 100-foot tsunami that it triggered killed six times more people than the 9/11 attacks. It also resulted in the meltdown of three reactor cores at the Fukushima-Daiichi nuclear plant. 

Radioactive isotopes released during the meltdown have drifted along the Pacific currents and are now approaching the US Pacific Coast. Should Californians worry about this? Not at all. Fukushima radiation levels in seawater will be so low that you could drink gallons of ocean water every day and be at no health risk -- except dehydration and vomiting. 

Here’s why. 

Fukushima released three radioactive isotopes into the ocean, each with a different half-life. Half-life is the amount of time for the total amount of radioactive material to drop by 50%. Radiation is 94% lower after four lengths of this time, and 99.2% reduced after seven. 

Iodine-131 has a half-life of just eight days; all released I-131 vanished long ago. Cesium-134 has a half-life of two years, so exactly half of it remains. Cesium-137 is mostly still intact with a half-life of just over 30 years. 

Roughly 11.3 kg (25 lb.) of Cs-137 was released into the Pacific Ocean and 95% of it (24 lb.) remains. Similarly, roughly 729 grams (26 oz.) of Cs-134 were released and 365 grams (13 oz.) remain. 

The Pacific Ocean has a total weight of around 6.6x10^20 kg. That’s more than 1.4 million trillion pounds. 

The point of these mind-blowing numbers is that the concentration of leaked cesium in the ocean is unimaginably small. So small, that the amount of Cs in the water is far below the amount deemed harmful to humans. Even if they were drinking it. 

Scientific models have predicted the worst-case concentration of Cs-137 in ocean water reaching the US West coast. They find this level to between 0.002 and 0.03 Bq/L (becquerels per liter of water). How many Bq/L is safe? 

Japan certifies water with up to 200 Bq/L safe to drink. The US FDA considers it safe to consume a liter of water with up to 1200 Bq, so long as you don’t do it often. The US EPA has a stricter limit (7.4 Bq/kg), but this is based upon the idea that such water is consumed every day for 70 years. 

The bottom line about cesium radiation on California beaches: the water will likely contain hundreds to millions of times less radiation than safe drinking water. Bathing is even less risky, as skin exposure limits are much higher still. Dental X-rays, air travel, tube-televisions and even bananas are more worrisome than Fukushima isotope levels in our seawater.

Tom Hartsfield is a physics Ph.D. candidate at the University of Texas.


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