Barium toxicity also disturbs the sodium-potassium ion pump capability -- another key feature in an MS profile. Ms could pivot upon a common disruption of the sulphate signaling systems in the body. Toxic levels of barium appear to disrupt this signaling system. Most of the health risks are caused by breathing in air that contains barium sulphate or barium carbonate.
Here is the description in Mirena:
"The polyethylene of the T-body is compounded with barium sulfate, which makes it radiopaque."