Solubility question i encounter on my lab?

patients requiring stomach X-rays, sometimes must drink a thick, chalky emulsion of barium sulfate known as a "barium milkshake." The presence of this substance highlight s the digestive tract in the X-ray. Barium ions are known to be extremely toxic. However, given that the Ksp of barium sulfate has a value of 1.5 x 10^-9, why does this procedure no pose a health risk for the patient?