The World Anti-Doping Agency has asked China for information on the use of steroids in raising cattle after some athletes blamed their positive doping tests on tainted beef.

"There seems to be some evidence that some beef in China may have been stimulated in their growth by the use of steroids," WADA director general David Howman commented on Tuesday. "We have written to the Chinese minister to ask for a full explanation of what happens in the industry in China. We're waiting for a response."

A recent study by a WADA-accredited lab in Cologne, Germany, found that 22 of 28 travelers returning from China tested positive for low levels of clenbuterol, probably from food contamination. The lab warned athletes traveling to China about the risks of inadvertent clenbuterol ingestion.

Clenbuterol is on WADA's list of banned substances as an anabolic agent that builds muscle and burns fat. It is also used by farmers to bulk up livestock.

Athletes testing positive for the drug can face bans of up two years.

Three-time Tour de France champion Alberto Contador was cleared by the Spanish cycling federation last week after he blamed his positive clenbuterol test on contaminated meat from Spain.

Howman said WADA is waiting to see whether the International Cycling Union appeals the Contador ruling before deciding on a possible appeal of its own to the Court of Arbitration for Sport.

"We are not even at the stage of having to make a decision," Howman said after a meeting of the EU Sport Forum, where officials discussed the EU Commission's new sports strategy.

German table tennis player Dimitrij Ovtcharov was cleared after blaming contaminated Chinese meat for his positive clenbuterol test. WADA dropped an appeal in that case.

"We looked at the evidence in the table tennis case and we were satisfied that the tribunal made the proper decision based on the evidence that it had received," said Howman, who rejected the idea that the Ovtcharov ruling could be considered a precedent for Contador's case.

Howman also said there were bigger profits in the trafficking of sports drugs like steroids, EPO and growth hormones than in heroin trafficking.

"There is more money to be made because in many countries it is legal," Howman continued, adding that WADA was asking countries to pass laws that would help stop their sale. "These substances are bad for our youth, for our elite athletes and for anyone who happens to buy them."

The substances are unsafe because they are being made without any regulatory supervision and in unsanitary conditions, Howman added.

"The markup can be anywhere from 10 to 100 times - you spend a dollar and you make $100," Howman continued and concluded "That's a pretty good investment. They buy the raw materials and then they put them together in a kitchen laboratory."