All three cities present liabilities and IOC members voting on Saturday may settle for the place with the fewest question marks. Tokyo is expected to be a slight favourite, but the race is considered too close to call.
Tokyo tried to deflect concerns about a leak of radioactive water at the crippled Fukushima nuclear plant in northern Japan.
Istanbul also faced hard questioning about a string of doping cases that have embarrassed Turkish officials. And Madrid was quizzed about doping and the 27-per cent unemployment rate in one of Europe's largest economies.
Tokyo bid leader Tsunekazu Takeda said the water and food in Tokyo are as safe as they are in New York, Paris, London or Buenos Aires.
"The radiation level in Tokyo is the same as London, New York and Paris," said Takeda, an IOC member and president of the Japanese Olympic committee. "It's absolutely safe, 35 million people living there in very normal conditions. We have no worries."
Five of the seven questions for Takeda in a news conference dealt with the Fukushima leak.
Takeda answered all but one question in English, switching to Japanese near the end to add emphasis.
"Not one person has been affected by the radiation issue," he said through a translator. "Fukushima and Tokyo are 250 kilometres (150 miles) apart. Since we are quite remote you don't need to be concerned about this issue."
Tokyo calls its bid "a pair of safe hands," emphasizing Japanese technology and its ability to deliver on time. This could attract IOC members who are worried about delays in building venues for the 2016 Rio de Janeiro Olympics. Controversy has also surrounded the 2014 Winter Olympics in Sochi, Russia.
Tokyo scored the highest in the IOC's technical report, but IOC members often vote along regional, political or friendship lines that have little to do with logistic or engineering appraisals.
Tokyo's presentation included a demonstration of the country's technology in robotics, featuring a robot named Mirata who simulated fencing with two-time Olympic silver-medallist Yuki Ota.
Turkish Olympic committee president Ugur Erdener faced repeated questions about doping. Several dozen Turkish athletes tested positive before the recent world athletics championships, setting off alarm bells.
Istanbul has also tried to explain away massive anti-government demonstrations in June, and a civil war and chemical attack in bordering Syria.
"Turkey now has a very aggressive anti-doping policy, and we have a well-organized and totally independent national anti-doping agency," Erdener said. "Our policy is very clear: zero-tolerance in doping. Of course we understand there is no gain without pain. As a result of our zero-tolerance policy, especially in the last five or six months, we have a number of cases and sanctions. ... We want a clean sport everywhere in our nation."
Erdener was also asked about air pollution in Istanbul.
"We don't have an air pollution problem now," he said.
He also said building venues and infrastructures for the games would not result "in any extra kind of taxes for our people."
Madrid bid leader Alejandro Blanco emphasized that Spain passed a new doping law several months ago — a response to perceived past laxness in tackling doping.
"We have been, and are, a reference in the fight against doping," Blanco said. "We have a problem which everybody knows about, the Operation Puerto. ... That operation affected the image of Madrid," he said of the doping investigation that started in 2006 and implicated several cyclists and other Spanish sportspeople.
"We are in the frontline of the fight against doping," Blanco added, saying — like Turkey — Spain has a "zero tolerance" policy.
Madrid Mayor Ana Botella and Ignacio Gonzalez, the head of the Madrid regional government, said the local economy had final begun to improve, though only marginally.
Blanco declined to confirm a report in the Spanish daily El Mundo saying Madrid would receive about 50 votes on the first ballot — half of the approximately 100 IOC votes.
"We do not make individual assessments, we do not give opinions regarding the number of votes we have," Blanco said. "We simply value what we have come here for ... to get the majority of votes."
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