Yes, such substitutions are indeed possible and can possibly happen.
This being the case, is it possible to substitute one important element from an object or system, for instance the calcium in our bones, with another element from its respective column, such as strontium.
There are some strontium based supplements on the market (strontium citrate, ranelate etc.) that are being touted as potential treatment for diseases like osteoporosis, and such like, however, evidence supporting their efficacy is tenuous at best. It is chemically similar enough to calcium to compete with calcium uptake.
Strontium-90, is a radioisotope of strontium that is described as a bone seeker ( an element that tends to accumulate in the bones of humans and other animals when it is introduced into the body).
It is typically a product of nuclear fission, and is found in spent nuclear fuel and radioactive wastes. It does have some industrial and medical applications.
There is some dispute over its half-life in the human body, primarily because of its complex metabolism in the human body. The elimination rate of strontium from the human body shows variance between individuals, based on age, and sex.
As strontium has an affinity to the calcium-sensing receptor of parathyroid cells that is similar to that of calcium, the increased risk of liquidators of the Chernobyl power plant to suffer from primary hyperparathyroidism could be explained by binding of strontium-90.