I propose the following experiment:

A large enclosure, capable of housing at least perhaps a million fo mice or more, seeded with several hundred of various strains of mice.

The mice are taken care of normally, but their food is laced with increasingly higher concentrations of cadmium, so that it always causes significant, but not total mortality. (or perhaps just enough to sufficiently reduce the capacity to breed)

Prediction: the mice evolve resistance and better general health and we end up with extremely healthy and long lived super-mice.