China's judo Olympic winner Tong Wen was found positive for banned steroid clenbuterol, which she blamed food contamination.

Also blaming food containing the weight-loss and muscle-building clenbuterol was three-time Tour de France winner Alberto Contador of Spain, who tested on July 21 and the analysis of that sample revealed traces of the banned steroid.

The World Anti-Doping Agency (WADA) rejected Contador's claims that his positive test was caused by contaminated meat bought in Spain. WADA even cited a European Union study from 2008 in which experts tested 300,000 meat samples but found evidence of the possible use of clenbuterol in only one of those.

In the meanwhile, American cyclist Floyd Landis, stripped of his 2006 Tour de France title for doping, told media that the use of clenbuterol is widespread in cycling, in one of his many striking remarks which included his attacks on seven-time Tour de France winner Lance Armstrong.

Landis previously alleged that Armstrong and members of their former U.S. Postal team systematically doped and Armstrong has always denied doping.

Many and explosive as the positive cases were, anti-doping experts considered it a proof of their effective work.

"I want to reiterate that zero tolerance does not mean zero positive case. On the contrary, positive cases prove that the system is working since drug cheats will always exist," said China Anti-Doping Agency deputy head Zhao Jian.

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