News earlier this month that scores of soccer players at the Under-17 World Cup in Mexico tested positive for traces of clenbuterol — and the decision by WADA and FIFA to not pursue any of the cases — reveals just how inconsistent sports justice has been in applying rules in clenbuterol cases.

Clenbuterol positives have drawn a wide variety of sanctions (see list below), with some athletes serving full, two-year bans in first offenses while others are being cleared entirely.

With Alberto Contador facing a possible two-year ban and the loss of his 2010 Tour de France crown after testing positive for traces of clenbuterol, that question of consistency will be under the microscope.

When Contador’s case first made headlines, some laughed at the suggestion that eating meat could trigger a “false positive,” but the argument has been gaining legitimacy within the corridors of both the World Anti-Doping Agency and other sports federations.

Following a string of high-profile clenbuterol cases, the issue has become so serious that WADA issued a warning earlier this month when it revealed it would not follow up on appeals involving clenbuterol cases coming out of Mexico.

On October 17, WADA gave its strongest message yet on the clenbuterol issue, saying it would not appeal a case involving five Mexican footballers who tested positive after eating meat in a training camp ahead of the CONCACAF Gold Cup in June.

“WADA has subsequently received compelling evidence from a FIFA study at the U17 World Cup in Mexico that indicates a serious health problem in Mexico with regards to meat contaminated with clenbuterol,” WADA stated in a release. “This is a public health issue that is now being addressed urgently by the Mexican Government.”

FIFA – soccer’s governing body – also studied the clenbuterol issue involving Mexico when scores of Under-17 soccer players tested positive.

FIFA revealed that players from 19 of 24 teams competing in an Under-17 World Cup in Mexico this summer had traces of clenbuterol in their systems, with 109 of 208 samples coming back positive. Both FIFA and WADA declined to prosecute the cases, citing possible food contamination as the culprit.

“It’s extremely serious for WADA,” Olivier Niggli, WADA’s legal director, said in a conference call to journalists. “Now it’s known it’s an issue, warnings are going to be sent.”

The Mexican cases come on the heels of other clenbuterol positives coming out of China.

Fuyu Li, a Chinese rider on RadioShack, tested positive for clenbuterol in 2010 after returning to Europe from his home in China. Fuyu Li, however, did not challenge his case and is currently serving a two-year ban.

Riders at the recent Tour of Beijing were so scared of testing positive for clenbuterol that nearly the entire peloton refused to eat beef or pork during their week-long trip.

“We haven’t eaten any meat at all during our time here, because we don’t want to take a risk,” Rabobank’s Theo Bos said. “I have lost 3kg because all we’re eating is salad and soup. Everyone is worried about it.”

While the issue is now at the forefront of the debate, it will be interesting to see if the Court of Arbitration for Sport takes issue with the origin of the beef when it hears Contador’s case November 21-24.

Contador has argued that traces of clenbuterol found in his system came after eating contaminated steaks brought to France from nearby Spain. The Spanish cycling federation cleared Contador in February and he’s since been cleared to race.

While many cases have come out of Mexico and China, Contador’s clenbuterol positive is the lone case from Europe. The drug – which is used illicitly to make beef leaner ahead of slaughter – has been banned for use in livestock in Europe since the mid-1990s.

Niggli, speaking to reporters in a conference call earlier this month, refused to make comparisons between different clenbuterol cases or distinguish between the location of the cases.

“I don’t think we can generalize from what is happening in one specific country,” Niggli said. “It is an illusion to say Mexico is the only country, but definitely there is a big difference depending where you are coming from.”

Samples involving the Mexican soccer cases were tested in the same WADA-accredited lab in Cologne, Germany, that reviewed the Contador controls from the 2010 Tour.

Contador’s sample was 50 picograms per milliliter while samples from the U-17 cases that were not prosecuted by WADA revealed that most were between 50 and 300 pg/ml. Some samples were as high as 1,300 picograms, FIFA officials said.

Contador’s lawyers will certainly use these latest decisions by WADA to not pursue sanctions as part of their defense for the Spanish rider.

Different cases, different sanctions

Jessica Hardy: The American swimmer tested positive during the U.S. Olympic trials in 2008 and received a one-year ban. WADA initially tried to extend the ban to two years, but lost in CAS. Hardy claims her positive came from a tainted nutritional supplement.

Josephine Onyia: The Nigerian-born Spanish track and field athlete won a gold medal in the 100m hurdles during the 2008 world athletics final, yet tested positive for both clenbuterol and methylhexaneamine in 2008. The Spanish federation initially cleared her, but WADA challenged it to CAS, which handed down a two-year ban.

Fuyu Li: The Chinese cyclist on RadioShack is serving a two-year ban after testing positive in a control in Belgium in April 2010, just days after returning to Europe from China. Speaking to VeloNews, Li said that he was sure that meat triggered his positive, but Chinese officials decided to wait to see what happens in Contador’s case. That might be too late for Li, whose ban runs through early next year.

Zhou Mi: Hong Kong-based badminton star is serving a two-year ban after testing positive for clenbuterol in 2010. Now pregnant, Zhou Mi missed a deadline to appeal her case to CAS. She claims her positive came from eating tainted pork in China.

Dimitrij Ovtcharov: The Ukrainian-born German table tennis player tested positive for clenbuterol in September, 2010, after a trip to China. He later provided hair samples, which helped his defense. German and international table tennis officials dropped the case and WADA did not challenge it to CAS.

Alessandro Colo: The Italian cyclist tested positive for clenbuterol during the 2010 Vuelta a Mexico. Despite supporting evidence that the positive could have come from a possible food contamination, the Italian anti-doping agency still gave him a one-year ban, citing rules that outline “strict liability” of what’s found inside an athlete’s system.

Philip Nielsen: The Danish cyclist also tested positive during the 2010 Tour of Mexico and was acquitted by a Danish sports tribunal. Earlier this month, WADA withdrew its appeal before CAS.

Mexican footballers: Five Mexico footballers tested positive for clenbuterol in June 2011 and, just a day before the Nielsen case, WADA dropped its appeal before CAS to challenge the Mexican Football Federation’s decision to clear the players of doping.

U-17 World Cup: FIFA revealed that players from 19 of 24 teams competing in an Under-17 World Cup in Mexico this summer had traces of clenbuterol in their systems, with 109 of 208 samples coming back positive. Both FIFA and WADA declined to prosecute the cases, citing possible food contamination as the culprit.