Here is what you need to know about the radioactive water leaking from Japan’s Fukushima nuclear plant into the Pacific Ocean.
Scientists on both sides of the Pacific have measured changing levels of radioactivity in fish and other ocean life since the March 2011 earthquake and tsunami triggered a nuclear meltdown at Japan’s Fukushima Daiichi nuclear plant. On Aug. 2, 2013, when Japan’s Tokyo Electric Power Co. (TEPCO) gave its first estimate of how much radioactive water from the nuclear plant has flowed into the ocean since the disaster, the company was finally facing up to what scientists have recognized for years.
"As an oceanographer looking at the reactor, we've known this since 2011," said Ken Buesseler, a marine chemist at the Woods Hole Oceanographic Institute in Woods Hole, Mass. "The news is TEPCO is finally admitting this."
TEPCO estimated that between 20 trillion and 40 trillion becquerels (units of radioactivity representing decay per second) of radioactive tritium have leaked into the ocean since the disaster, according to the Japanese newspaper Asahi Shimbun. The Fukushima plant is still leaking about 300 tons of radioactive water into the ocean every day, according to Japanese government officials. [Infographic: Inside Japan's Nuclear Reactors]
Japan is haunted by two lingering questions from this aftermath of the disaster: First, how the radioactivity might seriously contaminate ocean life that represents a source of seafood for humans; second, whether it can stop the leaks of radioactive water from the Fukushima plant.
Radioactivity is not created equal
The Fukushima plant is leaking much less contaminated water today compared with the immediate aftermath of the nuclear meltdown in June 2011 — a period when scientists measured 5,000 to 15,000 trillion becquerels of radioactive substances reaching the ocean. Even if radioactivity levels in the groundwater have spiked recently, as reported by Japanese news sources, Buesseler expects the overall amount to remain lower than during the June 2011 period.
"The amount of increase is still much smaller today than it was in 2011," Buesseler told LiveScience. "I'm not as concerned about the immediate health threat of human exposure, but I am worried about contamination of marine life in the long run."
The biggest threat in the contaminated water that flowed directly from Fukushima's reactors into the sea in June 2011 was huge quantities of the radionuclide called cesium. But the danger has changed over time as groundwater became the main source for leaks into the ocean. Soil can naturally absorb the cesium in groundwater, but other radionuclides, such as strontium and tritium, flow more freely through the soil into the ocean. (TEPCO is still coming up with estimates for how much strontium has reached the ocean.)
Tritium represents the lowest radioactive threat to ocean life and humans compared with cesium and strontium. Cesium’s radioactive energy is greater than tritium, but both it and tritium flow in and out of human and fish bodies relatively quickly. By comparison, strontium poses a greater danger because it replaces the calcium in bones and stays for much longer in the body.