USADA CEO Travis Tygart wrote:
Tygart ... said that USADA is trying to effect change with WADA that would see positive tests in very specific circumstances — extremely low levels of a substance that could be found in contaminated meat, water, supplements, or medication — trigger an investigation, rather than an automatic ban. In May 2019, WADA adopted that policy for clenbuterol, but Tygart says he would like to see it extended to a handful of other substances.
Lawson’s case would fit this criteria. Trenbolone, because of its use in the US beef industry, is one of the substances that would be included in Tygart’s proposal. ...
Under Tygart’s proposal, once an investigation begins for a violation such as this, where the level of the substance is minute ..., it could potentially proceed in one of two ways: 1) the burden remains on the athlete to prove that they ingested the substance unintentionally, but they would face only a six-month ban as opposed to four years; or 2) the ban remains four years, but the burden of proof shifts to the anti-doping agency, which would have to provide more evidence of intentional cheating beyond an extremely low-level positive.
In both situations, the goal is the same: ensure that genuine inadvertent positive tests are not unfairly punishing clean athletes.
"We firmly believe the system has to treat innocent, inadvertent positives with fairness," Tygart says. "And we should be very strict, and obviously firm against intentional cheats. But a single drug test of a very, very low level for a substance that can be found in meat for example, or we know is coming through supplements or we know is coming through water or prescription medication contamination, to treat them, based on one fact — a low-level positive — the same as an intentional cheat that you have a bunch of evidence on and a scheme to beat the system, that system is just, in our opinion, not a fair one and is not one that can be sustained in the long term. And we really see it as an athlete’s rights issue."
Tygart doesn’t believe that all low-level positives are necessarily indicative of inadvertent use; they could also represent the tail end of intentional use. But a single test is just one snapshot, and if that is the only evidence in a case, it can be impossible to differentiate between the two scenarios.