Hazards of thorium or its compounds may generally be classed into three types, namely, radiological, chemical and combustion.
The radiological hazards of thorium are connected essentially with the radioactivity of the isotopes in the decay chain from thorium-232 to lead-208. In the body the thorium-type isotopes generally tend to concentrate in the liver, kidneys, spleen and bone marrow.
Ordinary chemical toxicity of thorium or its compounds by means of introduction into the body is generally considered low. However, intravenous injections of thorium compounds, on the other hand, are more toxic leading to serious perturbations or even death.
Some alloys of thorium pyrophoric and may, even in massive form, ignite or rapidly disintegrate on exposure to air. The greatest danger of fire and explosion from the metal and alloys is when they are in powder form. For all these reasons, thorium and its alloys should be handled with extreme care and with adequate utensils and cloathing.