Why is osmium tetroxide very expensive and highly toxic?
Osmium tetroxide is expensive because osmium is a rare element.
Osmium is one of the rarest elements in the Earth's crust.
Osmium is obtained as a by-product from nickel and copper processing. It has to be separated from Ru, Rh, and Ir and then converted to OsO₄. This all costs money.
The US production of Os is probably only about 75 kg/year.
Osmium tetroxide is highly toxic, but its mechanism of action is unknown.
OsO₄ can enter the body by ingestion or by inhalation of its vapor or aerosol.
It is a severe irritant of the eyes, skin, and respiratory tract.
Skin burns result in blisters or skin discoloration.
Ingestion can lead to burning sensation, cramps, collapse, or shock.