It started with an impromptu taxi ride in 2013. It led to one of those serendipitous “aha” moments that make science such an adventure.
Ken Buesseler, Senior Scientist at the Woods Hole Oceanographic Institution, had just gotten off a research vessel on the eastern Japanese coastline with a team of scientists. They had been patrolling the waters around the Fukushima Daiichi Nuclear Power Plant, measuring the concentration of radioactive contaminants, especially the long-lived cesium 137 isotope, still spewing from the reactors that had melted down two years prior.
WATCH: Miles talks to Buesseler and others when he went to Fukushima in 2014 for the PBS NewsHour.
On a whim, Matthew Charette, one of Buesseler’s colleagues who focuses on coastal groundwater research, proposed the team pile into taxis and go to a local beach to collect some groundwater samples.
“We stuck pipes into the ground and people asked us, ‘What are you doing?’” remembers Buesseler. “We said, ‘We’re taking groundwater samples.’”
They were miles south of the melted down nuclear plant, and the seawater there had much a lower radioisotope concentration than around Fukushima. It was supposed to be more of an exercise than anything.
And yet: “The groundwater kept coming back with the highest readings of cesium,” says Buesseler.
The team was stunned. Nobody had thought to look into the groundwater right near the shoreline and see if it was contaminated.
The scientists came back eight more times, sampling groundwater on beaches along the Japanese coastline. Even more than 60 miles south of Fukushima, the groundwater showed elevated levels of cesium. They also discovered that this radioactive material is leaching back out into the ocean.
Buesseler and colleagues published these findings Monday in the journal Proceedings of the National Academy of Sciences. The study concludes that the groundwater leaching of cesium is “of similar magnitude” to the other two main sources: water flowing out to the ocean through the Fukushima plant itself and rivers in the area washing leftover radioactive particles in the soil out to sea.
The exact mechanics of why this is happening is still being worked out, but the team has proposed a theory. Radioactive particles drifted southward on the ocean currents following the 2011 accident and were washed ashore by waves. That’s where the likes of cesium could seep through the sand and get trapped in the fresh groundwater.
Cesium behaves differently in saltwater and freshwater. “In freshwater, it likes to attach to soil and clay, and in the ocean it is soluble,” says Buesseler. When the tides come in and more saltwater mingles in the brackish interstitial zone between ocean and groundwater, some cesium is dislodged and enters the ocean. “You can stand in the surf zone and see the cesium going up and down with the tides,” says Buesseler.
Don’t worry, Buesseler says there isn’t at much of a risk from standing in that water. Swimming is safe, as long as you don’t drink the water (why would you?). In fact, he says the radioactivity you would experience there is hundreds of times less than the amount of radioactivity in a dental x-ray.
Nevertheless, when you add up all of the beaches affected, the rate of radiation release is similar to the other large sources that are known.
“This study really highlights our lack of understanding of the issue,” says Buesseler. “We didn’t even think to look here.”
This type of research is important if we want to understand how nuclear facilities interact with their environment. About half of the 440 nuclear power plants in the world sit on or near a coastline. Yet, funding for this kind of research is hard to find, says Buesseler. The Woods Hole team had to go to private funders and other governments because the U.S. agencies would not support their project.
If you would like to participate in and support this type of work directly, Buesseler encourages you join him and his colleagues at www.OurRadioactiveOcean.org.