Elements whose nuclei undergo spontaneous disintegration with the emission of subatomic particles, alpha and beta particles, or electromagnetic rays such as X-rays and gamma rays. Naturally occurring radioelements including potassium-40, uranium, thorium, and radium are present at trace levels in soils, water, and consequently in foods, contributing to background dietary exposure. Artificial radioelements from nuclear activities are monitored far more strictly because of their health significance at elevated levels. Food-safety programs measure radioelements in vulnerable commodities after contamination events, compare results against regulatory limits, and restrict the sale of foods exceeding them.