​Poison scheduling provides a means of classifying poisons to identify the degree of control to exercise over their availability to the public. Many people think that the "S" schedule indicates an increasing level of toxicity. Although toxicity is one of the factors considered, and is itself a complex of factors, the decision to include a substance in a particular Schedule also takes into account many other criteria such as the proposed use, potential for abuse, safety in use and the need for the substance.
AgVet Chemicals Information Sheet - Poisons Schedules (116Kb)