With toxins, dose matters. Within a certain dosage range, to add 10% to the dose is to increase the effect by about 10%. Of course, above a limit, adding dosage doesn’t have much effect. After all, dead is dead. This could be summarized as more dose, more bad, less dose, less bad. So even a tiny dose causes a tiny bit of bad.
It turns out that this is not quite true. For many items, a very small dose actually strengthens the organism. The term J-curve comes from plotting the relation of harm against dosage.
None of this is new, but it occurs to me that it is important, as it becomes very hard to predict the behavior of nonlinear systems.