Not sure that is how the cookie crumbles, rather: it will be decided that chemical X is harmful at a certain dose, which leads to some permissible concentration

Not sure that is how the cookie crumbles, rather: it will be decided that chemical X is harmful at a certain dose, which leads to some permissible concentration Y of X, and that Y can then be used for regulation of disposing X. A place that needs to dispose a certain volume of X with concentration >Y then pays a sort of a mixologist to dilute X to a concentration <=Y before dumping it all anyway (unless it would be less expensive and more practical to react X away).