Section 4.58 - Environmental Contaminants and Substances of Human Use(1) Environmental contaminants are either endogenous to the horse or can arise from plants traditionally grazed or harvested as equine feed or are present in equine feed because of contamination during the cultivation, processing, treatment, storage or transportation phases.(2) Substances of human use and addiction may be found in the horse due to its close association with humans.(3) If the preponderance of evidence presented in the hearing shows that a positive test is the result of environmental contamination, including inadvertent exposure due to human drug use, or dietary intake, or is endogenous to the horse, those factors should be considered in mitigation of any disciplinary action taken against the affected trainer. Disciplinary action shall only be taken if test sample results exceed the regulatory thresholds in the most recent version of the ARCI Endogenous, Dietary, or Environmental Substances Schedule.(4) The identification and adoption of these uniform thresholds for certain substances shall not preclude an individual jurisdiction from maintaining thresholds for substances not on this list which predate the adoption of 205 CMR 4.00 in such jurisdiction.Adopted by Mass Register Issue 1356, eff. 6/9/2017.