The string of Mexican boxers testing positive for the banned substance clenbuterol has included superstar Canelo Alvarez, Luis Nery, Francisco Vargas and, in recent days, Rey Vargas and Julio Cesar Martinez.

On Thursday, the WBC announced that it will begin acknowledging the increased allowable threshold for the drug established earlier this year by the World Anti-Doping Association, meaning those fighters' positive tests, as conducted by the Voluntary Anti-Doping Association in conjunction with the WBC's Clean Boxing Program, would no longer have been considered a failed test because the amount found in their system was so small. Clenbuterol remains banned under WADA code, and drug tests found to have an amount that exceeds the new threshold would still count as a failed test and result in punishment.

Junior featherweight world titlist Vargas and top flyweight contender Martinez both recently tested positive for trace amounts of the drug in random sample collections. Those results were announced by the WBC earlier this week, with the WBC saying that the amounts were "so small that no further action is being taken."

Alvarez had two positive tests for clenbuterol in the lead-up to his middleweight world title rematch with Gennadiy Golovkin that was supposed to take place in May 2018. However, because of the test results, Alvarez was suspended for six months by the Nevada State Athletic Commission and the bout was eventually rescheduled for September. But Golovkin was livid over Alvarez's test results and accused him of cheating, causing a rift between the two that remains to this day. Alvarez's reputation, meanwhile, took a big hit, with many outraged fans referring to him derisively as "Clenelo."

Alvarez, as well as the other boxers, claimed the trace amounts were caused by ingesting contaminated beef, which has been a long-standing issue with athletes in Mexico, where farmers often include the substance in cattle feed because it helps reduce fat and increase lean muscle mass. The WBC now accepts that as a reason for the adverse findings in the tests as long as the amount is below the new WADA threshold.

"This is a confirmation of the innocence of fighters like Saul 'Canelo' Alvarez and Francisco Vargas, who once were in the middle of controversy, when Clean Boxing Program tests performed by VADA found clenbuterol in their examination," the WBC said in a statement. "The WBC has received additional reports from VADA in which two Mexican fighters (Vargas and Martinez) showed atypical findings of clenbuterol, which are well below the new WADA standard. All fighters will receive proper nutrition education from the WBC Clean Boxing Program and weight management program. WBC champion Rey Vargas and WBC (mandatory) challenger Julio Cesar Martinez are at no fault with regards to their VADA atypical finding."

Effective June 1, WADA established a new threshold for the amount of clenbuterol allowed in an athlete's system in part to take into account the possibility of food contamination.

"That will prevent athletes from being penalized for an anti-doping rule violation as a result of consuming contaminated meat," the WBC said. "The levels of clenbuterol and related substances found in WBC CBP cases to date -- Canelo Alvarez, Francisco Vargas and Luis Nery -- have been significantly lower than the new WADA standard. Even before the new WADA standard, the WBC has consistently treated those cases accordingly. Thus, after an extensive investigation, the WBC did not penalize the affected athletes."