Like most fathers, Yoji Fujimoto frets about the health of his young children. In addition to normal parental concerns about the food they eat, the air they breathe and the environment they will inherit, however, he must add one more: the radioactive fallout from a nuclear disaster.
Three days after meltdown began at the Fukushima Daiichi nuclear plant on 11 March 2011, Mr Fujimoto moved his two daughters, then aged four and three, to safety hundreds of kilometres away. Last December, the eldest of the two was diagnosed with adenoidal cysts, the prelude to a type of cancer that often strikes the salivary glands. "I was told by the doctor that it's very rare," he says.
Although Mr Fujimoto and his family were in Chiba Prefecture, over 60 miles (100km) from the plant and in the opposite direction from the worst of the fallout, he believes his daughter inhaled enough radiation to cause her illness. "I'm convinced this is because of the Fukushima accident."
The United Nations said last week it did not expect to see elevated rates of cancer from Fukushima, but recommended continued monitoring. The report by the UN Scientific Committee on the Effects of Atomic Radiation said prompt evacuation meant the dose inhaled by most people was low. Tokyo Electric Power Co, operator of the Daiichi plant, estimates the final tally for escaped radiation at 900,000 terabecquerels, about one-fifth the amount released by the Chernobyl accident in 1986. Most was vented in the first three weeks.
The precise impact of this radiation is bitterly contested, but at least one finding from Chernobyl seems consistent – elevated rates of thyroid cancer in children. The Chernobyl Forum, a 2003-05 UN-led study, cited close to 5,000 cases of thyroid cancers among those exposed under the age of 18 in the most affected areas, probably from drinking contaminated milk. Many scientists believe it takes four to five years for the cancers to develop.
Although rumours of a spike in cancers, birth defects and abnormalities have swirled in the quarter of a century since Chernobyl, the UN found "no clearly demonstrated" rise in other cancers among affected populations. But that assessment has been questioned. "There is extensive documentation of other effects," says Steve Wing, an epidemiologist at the University of North Carolina.
Dr Wing accepts that estimating the number of Chernobyl-induced cancers with any precision is not possible, "in large part because of a lack of monitoring of the radiation doses to downwind populations", and because cancer estimates are largely based on "highly flawed" studies of A-bomb survivors.
But he says that parents like Mr Fujimoto do have reason to worry. "We know that doses to populations are both unquantified by the official agencies, that evidence suggests relatively high doses, and that children and women are more vulnerable to radiation. So the questions and deep concerns for the people in Fukushima will continue for the rest of their lives."
That assessment is backed by Dr Alexey Yablokov, a Russian biologist who published Chernobyl: Consequences of the Catastrophe for People and the Environment, probably the most controversial assessment of the disaster. He was in Japan last week to promote the Japanese translation of the book, which insists that the health impact of Chernobyl has been seriously underestimated. He didn't soften his message for his audience in Tokyo. "I expect a growth in the numbers of thyroid cancers in Japan from next year," he said. Critics say one problem with Chernobyl research is that the then Soviet government initially tried to play down the disaster, skewing the statistics. The government of Fukushima Prefecture has promised lifelong health checks for 360,000 people who were under 18 at the time of the disaster.
In February, the government said it had found just three cases of thyroid cancer after checking 38,000 people, a figure Shinichi Suzuki, professor of thyroid surgery at Fukushima Medical University, said was statistically insignificant. "It's difficult to imagine that there is a relationship between the cancer and the nuclear accident," he said, to widespread scorn from parents.
Kanako Nishitaka, a single mother of two, says many have no faith in government surveys. She was born and raised in Fukushima city, about 40 miles from the nuclear plant, but moved away in May 2011 after doctors found caesium in her daughter, Fuu's, body. "I was told it was about the same amount as people exposed to nuclear bomb tests," she recalls. "The scientists who do these surveys tell us to move back home, but I wonder if they would take their own children to Fukushima?"
Many parents point to a recent finding that more than 40 per cent of nearly 95,000 children checked by Dr Suzuki's team had thyroid ultrasound "abnormalities". About 35 per cent had nodules or cysts on their thyroids. Most of the children lived in the most contaminated zone around Daiichi plant.
The cysts and nodules are not cancers but they point to an inevitable spike in future health problems, says Mr Fujimoto – a view contested by the government. "I have absolutely no faith in what the Fukushima government is saying," he retorts. "They want people to go back and live there so they clearly want to keep a lid on the impact of the disaster."
Parents accuse government scientists of making their minds up before the survey began – Professor Suzuki's team said last July that their aim was "to calm the anxiety of the population".
The debate has hardened into two sides: people such as Mr Fujimoto who say the authorities are playing down or even covering up the disaster, and the increasingly vocal official view that their worries are overblown. Those who stray too far from the official line risk being accused of fear-mongering.
Whatever the scientists say, Mr Fujimoto insists he won't be persuaded by government reassurances that it is safe to return to Fukushima. "There is so much information not getting out at the moment. It will be too late for my children when it is eventually released."