The radioactive leaks from the Fukushima Daiichi plant make up the largest recorded accidental release of radiation to the ocean, according to a new article in Oceanus Magazine from the Woods Hole Oceanographic Institute. The level of radioactive isotopes in Japan’s coastal waters — of which cesium-137 has the longest half-life — were among the world’s lowest levels before the Fukushima disaster.
“Most of the cesium from Fukushima came from the millions of gallons of water poured onto the reactors during efforts to cool them, which subsequently flowed into the ocean as runoff or via groundwater,” writes author David Pacchioli.
However, Dr. Ken Buesseler, a marine chemist at Woods Hole Oceanographic Institution, says the majority of the leaks were plugged in early April 2011, causing cesium levels close to shore to fall dramatically. Today the contamination levels are below the U.S. Environmental Protection Agency’s limit for drinking water, which indicates coastal waters off Fukushima are safe for both marine life and human exposure.
“It’s not direct exposure we have to worry about, but possible incorporation into the food chain,” said Buesseler.
In June 2011, Buesseler led a research expedition to determine the path and severity of the radioactive seawater contamination from the Fukushima disaster. The Kuroshio current, which is the Pacific Ocean’s equivalent of the Atlantic Ocean’s Gulf Stream, was an area of particular concern to Buesseler and his team.
“The first thing we noticed was that when we got to the Kuroshio, we lost the cesium-134 signal…That confirmed that the Fukushima radioactive fallout from the atmosphere did not reach these more southern latitudes,” he says.
Scientists have since created multiple models for the spread of contamination in the Pacific, but it remains to be seen how cesium mixes into deeper layers of the ocean, how it accumulates in particles and what lasting effects it exposure have on marine life.
Read the full story in Oceanus Magazine.