A citizens' group in Tokyo has found elevated levels of radioactivity at sporting facilities that will be used in the 2020 Olympic Games and is warning that competitors and the hundreds of thousands of people expected to flock to the city for the event will be putting themselves in danger. The Citizens' Group for Measuring Radioactive Environment at Facilities for the 2020 Tokyo Olympics claims wind-borne radiation from the four crippled reactors at the Fukushima nuclear plant has contaminated a number of future venues. We found caesium-137 at almost every place we carried out tests, and there was no caesium here before the accident at Fukushima Activist Mitsuo Tanaka Measurements were taken at 39 sporting venues that have been earmarked to stage events in seven years' time, including the Kasumigaseki Country Club, which will host the golf tournament, the Asaka shooting range and the site of the planned National Stadium, which will stage the opening and closing ceremonies and a number of other events. The tests were also carried out at the planned site of the Olympic Village and the media centre, with the highest radiation reading - 0.484 microsieverts per hour - detected in undergrowth close to Yumenoshima Stadium, where the equestrian events will be held. Soil samples collected at the site had 3,040 becquerels of caesium per kilogram. Some experts point out that the context in which the tests were carried out is crucial. "It is difficult to have this debate unless we know for sure whether this radiation is from Fukushima or whether it is naturally occurring background radiation," said Pieter Franken, founder of the Japan office of the environmental monitoring organisation Safecast. While the readings do not pose an immediate threat to human health, members of the group say they are still significantly higher than the level of 0.23 microsieverts per hour set by the government as the standard for decontamination work going on in the exclusion zone around the nuclear plant. "We found caesium-137 at almost every place we carried out tests, and there was no caesium here before the accident at Fukushima," Mitsuo Tanaka, a member of the group, told the South China Morning Post . In July, the group wrote to Jacques Rogge, the then president of the International Olympic Committee, and members of its evaluation committee and urged them not to select Tokyo as the host of the 2020 Games. Tanaka's group received a brief e-mail message to confirm that their letter had been received by the IOC - but it clearly had limited impact, as Rogge announced on September 7 that Tokyo had beaten off competition from Madrid and Istanbul for the right to host the Games. A similar message was sent to the committee behind Tokyo's bid to host the Games, but Tanaka's group received no reply. In response to a request from the Post , a spokesman for Toyko 2020 insisted: "Radiation levels in the air and water of Tokyo are safe. "Measures have been taken even before the 2011 nuclear accident in Fukushima, and they show that radiation levels in Tokyo are absolutely safe and normal - comparable with levels in other major cities, like London, New York and Paris," the spokesman said. "The Tokyo Metropolitan Institute of Public Health is constantly measuring radiation levels and will continue to do so," he added. However, the organisers' confidence has done little to reassure Tanaka. "We believe the money spent on having the Games in Tokyo should have been spent on helping the 80,000 people who have had to leave their homes close to the Fukushima plant," he said.