Radiation health expert Shunichi Yamashita in his office at Fukushima Medical University in November 2012. Credit: Geoff Brumfiel

After two turbulent years on the job, the head of Fukushima prefecture's massive survey to understand the health effects of the 2011 Japanese nuclear accident is stepping down. Shunichi Yamashita, a radiation health expert from Nagasaki University, told Nature by e-mail that he will leave his post at the end of March.

The Fukushima Health Management Survey is an ambitious project to chronicle any adverse health effects arising from the three meltdowns at the Fukushima Daiichi nuclear plant, caused by the tsunami and magnitude-9 earthquake off the coast of Japan on 11 March 2011. The survey's goals include estimating the dose received by the prefecture's 2.05 million residents, thyroid screening of tens of thousands of children who may have been exposed to radioactive iodine-131, and understanding the mental-health consequences of the accident.

Yamashita, whose mother is a survivor of the atomic bomb at Nagasaki, is considered to be one of Japan's leading authorities on radiation health. Before coming to Fukushima, he was involved in studies of both the Japanese atomic bomb survivors and victims of the 1986 nuclear accident at Chernobyl in the Ukraine.

Mixed messages

But Yamashita's tenure as head of the health survey has been marked by controversy. "He had a difficult start in Fukushima from the very first days," says Wolfgang Weiss, a German physicist and member of the United Nations Scientific Committee on the Effects of Atomic Radiation. Even as the Japanese government evacuated many areas in Fukushima, Yamashita insisted that radiation levels presented little risk, creating confusion.

He also made public gaffes, including telling Fukushima residents to smile and be happy, says Azby Brown, a member of Safecast, a Tokyo-based non-profit organization that monitors radiation in Fukushima prefecture. "He was seen as being flippant and dismissive," Brown says. "He did a great job of running the actual study and a bad job of managing expectations and communicating to the public."

Yamashita denies that his decision to step down was influenced by public pressure. Instead, he says, he is simply not going to renew his two-year contract with the study. In addition, he explains, authorities in Fukushima prefecture were worried about his dual role as head of both the survey board and the executive body carrying out many of the measurements. Yamashita says that he will keep working part-time at Fukushima Medical University to help coordinate work with Nagasaki University, adding that he will "support Fukushima continuously" after stepping down.

The latest results from the health survey were released on 13 February. So far, roughly 38,000 children have been surveyed, revealing three confirmed cases of juvenile thyroid cancer and seven cases of suspected cancer. Yamashita cautions that it is impossible to tell whether the cancers are a result of the accident, or if increased screening by the health survey turned up cases that might have otherwise gone undetected. Control studies are now under way in parts of the country that were not affected by the nuclear accident.