IAAF scientific expert Jordi Segura said metenolone could be taken either orally or by injection, and the substance can be eliminated from the system within four to five days, the IOC said.
It's the second Olympic doping scandal here for Belarus. The team had earlier sent home hammer thrower Ivan Tsikhan after retests of his samples from the 2004 Athens Olympics, where he won silver, came back positive.
Besides Ostapchuk, only one athlete tested positive for a banned substance after competing in London. U.S. judo fighter Nick Delpopolo was cited for traces of marijuana in his urine sample.
"This is the eighth athlete to have been caught by our extensive in-games testing but many more were kept away from the games by the pre-games program," Adams said. "And keeping samples for eight years means that we can continue to test long after the competition is over."
Three Beijing events were tainted by drug scandals during the 2008 Games, and two more medals were changed months later when a new test for the blood-booster CERA was introduced. The signature men's 1,500-meter gold medal was stripped retroactively from Rashid Ramzi of Bahrain.
AP Sports Writers Chris Lehourites and Rob Harris in London and Associated Press Writer Leonid Chizov in Moscow contributed to this report.
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