September 30, 2010 Three-time Tour de France winner Alberto Contador has tested positive to the steroid clenbuterol, a banned substance. Contador, who won his third yellow jersey at the end of July's three-week epic, announced the news through his personal press officer but blamed the positive test on food contamination. "Alberto Contador is affected by a doping control at the last Tour de France on July 21, where the substance clenbuterol was found," the message read. The UCI confirmed in a statement that only a "very small concentration" of the drug had been found and that the case warranted "further scientific investigation" because the Cologne laboratory which detected the substance is known to be able to detect the tiniest traces of drugs. "The concentration found by the laboratory was estimated at 50 picograms which is 400 times less than what the antidoping laboratories accredited by WADA (World Anti Doping Agency) must be able to detect," the statement read. There are a trillion picograms in a gram. "In view of this very small concentration and in consultation with WADA, the UCI immediately had the proper results management proceedings conducted, including the analysis of B sample that confirmed the first result." "The rider, who had already put an end to his cycling season before the result was known, was nevertheless formally and provisionally suspended as is prescribed by the World Anti-Doping Code. "This case required further scientific investigation before any conclusion could be drawn." Contador is the second cyclist this season to blame a positive test for clenbuterol on food contamination. China's Li Fuyu, who rode for the RadioShack team of seven-time Tour de France winner Lance Armstrong, tested positive for the banned substance earlier this season and blamed food contamination. Used to treat breathing disorders such as asthma, clenbuterol is an organic compound that has short-term effects similar to the stimulant ephedrine, as it increases heart rate, temperature, perspiration and blood pressure. It has also been used as a "fat burning" weight loss drug, although scientific studies have not conclusively proven the drug's qualities in this domain.