This map shows the location of seawater samples taken by scientists and citizen scientists that were analyzed at the Woods Hole Oceanographic Institution for radioactive cesium as part of Our Radioactive Ocean. Cesium-137 is found throughout the Pacific Ocean and was detectable in all samples collected, while cesium-134 (yellow/orange dots), an indicator of contamination from Fukushima, has been observed offshore and in select coastal areas. Credit: Figure by Jessica Drysdale, Woods Hole Oceanographic Institution
Scientists monitoring the spread of radiation in the ocean from the Fukushima nuclear accident report finding an increased number of contaminated sites off the US West Coast, along with the highest detection level to date, from a sample collected about 1,600 miles west of SF. The level of cesium in the sample is 50% higher than other samples collected, but is still >500X lower than US government safety limits.
“These new data are important for 2 reasons,” said Buesseler, a marine radiochemist with the Woods Hole Oceanographic Institution (WHOI). “First, despite the fact that the levels of contamination off our shores remain well below government-established safety limits for human health or to marine life, the changing values underscore the need to more closely monitor contamination levels across the Pacific. Second, these long-lived radioisotopes will serve as markers for years to come for scientists studying ocean currents and mixing in coastal and offshore waters.”
The recent findings reported by Buesseler agree with those reported by scientists who are part of the group Kelp Watch and by the team of Canadian scientists working under the InFORM umbrella. While Buesseler’s work focuses on ocean chemistry and does not involve sampling of biological organisms, the InFORM scientists have done sampling of fish and have not seen any Fukushima cesium in fish collected in British Columbia.
Almost any seawater sample from the Pacific will show traces of cesium-137, an isotope of cesium with a 30-year half-life, some of which is left over from nuclear weapons testing carried out in the 1950s to 1970s. The isotope cesium-134 is the “fingerprint” of Fukushima, but, with a 2-year half-life, it decays much quicker than cesium-137. Scientists back calculate traces of cesium-134 to determine how much was actually released from Fukushima in 2011 and add to it an equal amount of cesium-137 that would have been released at the same time.
Working with Japanese colleagues, Buesseler also continues to independently monitor the ongoing leaks from Fukushima Dai-ichi by collecting samples from as close as 1km away from the nuclear power plants. During his most recent trip this October they collected samples of ocean water, marine organisms, seafloor sediment and groundwater along the coast near the reactors. Buesseler says the levels of radioactivity off Fukushima remain elevated – some 10 – 100 times higher than off the US West Coast today, and he is working with colleagues at WHOI to try to determine how much radioactive material is still being released to the ocean each day.
“Levels today off Japan are thousands of times lower than during the peak releases in 2011. That said, finding values that are still elevated off Fukushima confirms that there is continued release from the plant,” said Buesseler.
http://www.whoi.edu/news-release/fukushima-higher-levels-offshore
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