Dartmouth researchers discovered that harmless levels of radioactive materials are present in Hanover as a result of the Japanese nuclear reactor explosions that occurred after the March 11 earthquake almost 10,000 miles from campus, according to earth sciences professor Joshua Landis. The team did not set out to study the reactor explosions' effects, but instead made the observation while doing routine tests of soil and stream sediments on campus in March, Landis said.
"It just so happened that we had started an experiment just before the earthquake where we were measuring [radioactive isotope] beryllium-7 in the rainwater," graduate students John Gartner said.
The research team comprised of Landis, Gartner and Nathan Hamm, earth sciences professor Carl Renshaw and geography professor Frank Magilligan regularly collects radiation data from soil and stream sediments in Hanover, according to Landis. The researchers collected soil and rainwater samples from Shattuck Observatory and stream sediment samples from Mink Brook, according to Landis.
"Typically, about half of the radiation that we're exposed to [comes] from natural sources and the other half [comes from] man-made sources like X-rays," Renshaw said.
The group measures levels of beryllium-7, a natural source of radiation with a short half-life, according to Renshaw. By comparing the discovered beryllim levels and decay rates, researchers can study sediment transport and trace the movement of particles across the Earth's surface, Landis said.
The equipment that the research team used to measure beryllium-7 also picked up other sources of gamma ray radiation, including iodine-131 released into the atmosphere by the nuclear reactor explosion in Japan, Landis said.
"We first saw traces of the iodine on the 18th of March," Landis said, "It makes sense that we saw it approximately 10 days after the explosions based on the distance and precipitation cycles."
After weekly measurements, the team found deposits of 6,000 atoms of iodine per square centimeter, a "really small" number of atoms, according to Landis. While long-term consumption of high levels of iodine can lead to thyroid cancer and thyroid diseases, the iodine discovered was never at levels dangerous to humans, he said.
"If you were to consume all of the iodine that came down with rainwater on a square meter of ground, it would be on par with the radiation levels of an X-Ray," Landis said.
Because the iodine levels were undetectable after mixing with ground water, there were also no potentially dangerous environmental effects, Landis said.
Team members were relieved to find no evidence of cesium-137, another byproduct of the explosion that has a half-life of 30 years, Renshaw said. Because the body treats cesium like potassium, it easily spreads to all tissues and bones rather than just the thyroid if ingested, greatly increasing the chance of health problems, according to Renshaw.
"It's definitely going to be a huge problem in Japan," said Hamm. "That's why they have a 10-mile radius around the reactor that people aren't supposed to live in."
While the team has finished collecting data from Hanover all of the iodine is virtually gone due to its short half-life they will continue to analyze and process the information gathered, Gartner said.
"From a purely scientific point of view, it's been a really interesting tweak on what we already do," he said. "But it came from the tragedy of Fukushima."
There is "no new risk from this point onward" and Hanover residents have no reason to be concerned about radiation, Gartner said.