Question

Barium sulfate is used as a radio‐opaque material for patients receiving CAT scans and upper GI series. Barium ion is highly toxic. Reconcile these two statements. Hint: common ion effect.

Answer 1

Barium sulfate is used as a contrast material during Ct scans. Barium sulfate is a highly insoluble substance. So it is used only as a suspension and not as a solution in CT scan studies. Barium sulfate powder is usually suspended in a drink to get a suspension having the consistency of milk or a very thin milk-shake.

It is the Barium ion Ba++ which is highly toxic and not BaSO4.The amount of Ba++ ions in BaSO4 suspension will be well- within the toxic limit of concern.

Any sulfate ion present in the suspension will further suppress the dissociation of BaSO4 into Ba++ and SO4-- ions by common ion effect.