My guess is that barium sulfate is not toxic because it hardly dissolves at all in water and therefore doesnt easily access the bloodstream. (Ksp value: 1.1*10-10)
On the other hand, a lot of barium...
a general answer is that if it is a cation the ion is smaller than the atom due to loosing one or more electrons which would decrease the size of the radius anions are larger because they are gaining...