It all depends on quantities and how it dilutes and disperses once in the ground. During the raining season the dilution will take care of potentially local high concentrations. During dry spells, that's all your roots are going to get. It may be poisonous to them.
Starsan working solution is acidic. Phosphoric acid with some other stuff in it, something that breaks the surface tension, like soap. Probably OK.
Used PBW is sodium carbonate and sodium metasilicate, it is alkaline. It may break down, but many trees and shrubs don't like alkaline soil.