The primary hazard associated with actinides is their radioactivity, though they may also cause heavy metal poisoning if absorbed into the bloodstream. Generally, ingested insoluble actinide compounds, such as uranium dioxide and mixed oxide (MOX) fuel, will pass through the digestive tract with little effect since they have long half-lives, and cannot dissolve and be absorbed into the bloodstream. Inhaled actinide compounds, however, will be more damaging as they remain in the lungs and irradiate lung tissue.