By March of 2014 a strongly diluted plume of ocean water containing radionuclides from the 2011 Fukushima nuclear incident in Japan will reach the west coast of North America, according to a new study published in the journal Deep-Sea Research 1.
However, the plume, which contains cesium-137, is so diluted it will be harmless, according to the report, which cites the power of two energetic currents off the Japan coast -- the Kuroshio Current and the Kurushio Extension -- as the primary drivers for the accelerated dilution of the radioactive plume.
According to the study's authors, the Japanese currents diluted the cesium-137, which has a half-life of 30 years, so effectively that the plume dropped below the World Health Organization's safety levels within four months of the Fukushima incident, which occurred March 11, 2011 after a crippling earthquake and tsunami combination overcame the Fukushima Daiichi nuclear power station on Japan's northern Pacific coast.
Study co-author Erik van Sebille, an oceanographer at the University of New South Wales in Sydney, said that a measurable increase in radioactive material will be observable on the west coast of the United States by the three-year anniversary of the Fukushima nuclear incident.
"However, people on those coastlines should not be concerned as the concentration of radioactive material quickly drops below World Health Organization safety levels as soon as it leaves Japanese waters," he said in a news release.
While the the North American Pacific coast may not have much to worry about, Japan's Pacific coast remains another issue.
Recent news reports from Fukushima have indicated that radioactive water continues to leak from the beleaguered nuclear campus and an untold amount is still flowing into the Pacific Ocean.
The news was a blow to Japanese fishermen. While there is no commercial fishing along most of Fukushima's coast, once radionuclides are in the water there is no way to corral them and the Japanese public is highly concerned about food safety. The environmental impacts of Fukushima radiation on marine life along the Japanese coast remain unclear. But in a survey of 170 types of fish caught off the Japan coast, 42 fish species tested were labeled as too radioactive for consumption, while another 15 species showed little or no signs of contamination, according to a report by The Associated Press. Few, if any, of the fish sampled showed detectable levels of cesium, the AP reported.
However, in March of this year a bottom-dwelling fish caught close to the Fukushima plant was found to have levels of cesium 7,400 times the government limit for safe human consumption. The US Environmental Protection Agency has outlined health and environmental impacts of cesium here.
Other than cesium, another concern is strontium and tritium, both of which are toxic. Strontium can accumulate in bones and officials are keen to watch out for it, especially in recent weeks where spikes in strontium levels have been detected around Fukushima, the AP said.
Oceanographer van Sebille said over time "the great majority of the radioactive material will stay in the North Pacific, with very little crossing south of the Equator in the first decade. Eventually over a number of decades, a measurable but otherwise harmless signature of the radiation will spread into other ocean basins, particularly the Indian and South Pacific oceans."
"Australia and other countries in the Southern Hemisphere will see little if any radioactive material in their coastal waters and certainly not at levels to cause concern," van Sebille said. He added that his team has created a website that allows users to track the movement of radiation and other ocean pollution.
Editor's note: A NOAA image depicting tsunami wave heights generated by the March 2011 disaster was initially used when this story was published on Aug. 29, 2013. Although the image was clearly captioned, some readers said the graphic was misleading. An updated image was added to this story on Aug. 30, 2013.
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