This ToxTutor link from the NIH describes routes of exposure in greater detail, particularly as it relates to types of injection.
This in-depth CDC training module focuses on the importance of route of exposure in toxicology.
In “Toxicology: The learning curve,” reporter Dan Fagin reports on the hypothesis some researchers have regarding unexpected dose response effects, such as a dramatic effect from a small dose.
For a detailed explanation of different types of dose response curves, particularly of endocrine disruptors, this 2012 overview from Endocrine Reviews provides an in-depth look: “Hormones and Endocrine-Disrupting Chemicals: Low-Dose Effects and Nonmonotonic Dose Responses.”