Barium

All water or acid soluble barium compounds are extremely poisonous. At low doses, barium acts as a muscle stimulant, while higher doses affect the nervous system, causing cardiac irregularities, tremors, weakness, anxiety, dyspnea and paralysis. Dust containing barium can also cause a condition called baritosis where it accumulates in the lungs.

Highly insoluble barium compounds, such as barium sulfate, can be taken orally because it is eliminated from the digestive tract.

High levels of barium are often found in smokers.

Metallic barium has limited industrial use, but has been historically used to remove remaining air from vacuum tubes. It is also used in fireworks, rubber production, oil well drilling, and in its purer, more insoluble form, in imaging the gastrointestinal tract using X-rays.