Thorium is a chemical element (atomic number 90). Although it is radioactive, the alpha-particles it emits cannot penetrate the skin and cannot cause radiation sickness from external exposure. However, it can lead to an increased incidence of cancer if ingested in a purified form. It has a limited number of commercial uses and exposure is usually occupational. It is ubiquitous in the environment and humans naturally ingest a small but safe dose of it on a daily basis. Thorium at Wikipedia
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