Thorium: Thorium. A radioactive element of the actinide series of metals. It has an atomic symbol Th, atomic number 90, and atomic weight 232.04. It is used as fuel in nuclear reactors to produce fissionable uranium isotopes. Because of its radioopacity, various thorium compounds are used to facilitate visualization in roentgenography.Thorium Dioxide: Thorium oxide (ThO2). A radiographic contrast agent that was used in the early 1930s through about 1954. High rates of mortality have been linked to its use and it has been shown to cause liver cancer.Thorium Compounds: Inorganic compounds that contain thorium as an integral part of the molecule.Uranium: Uranium. A radioactive element of the actinide series of metals. It has an atomic symbol U, atomic number 92, and atomic weight 238.03. U-235 is used as the fissionable fuel in nuclear weapons and as fuel in nuclear power reactors.Scenedesmus: A genus of GREEN ALGAE in the family Scenedesmaceae. It forms colonies of usually four or eight cylindrical cells that are widely distributed in freshwater and SOIL.Soil Pollutants, Radioactive: Pollutants, present in soil, which exhibit radioactivity.Actinoid Series Elements: A series of radioactive elements from ACTINIUM, atomic number 89, to and including LAWRENCIUM, atomic number 103.Water Pollutants, Radioactive: Pollutants, present in water or bodies of water, which exhibit radioactivity.Oxyquinoline: An antiseptic with mild fungistatic, bacteriostatic, anthelmintic, and amebicidal action. It is also used as a reagent and metal chelator, as a carrier for radio-indium for diagnostic purposes, and its halogenated derivatives are used in addition as topical anti-infective agents and oral antiamebics.Microalgae: A non-taxonomic term for unicellular microscopic algae which are found in both freshwater and marine environments. Some authors consider DIATOMS; CYANOBACTERIA; HAPTOPHYTA; and DINOFLAGELLATES as part of microalgae, even though they are not algae.Americium: Americium. A completely man-made radioactive actinide with atomic symbol Am, atomic number 95, and atomic weight 243. Its valence can range from +3 to +6. Because of its nonmagnetic ground state, it is an excellent superconductor. It is also used in bone mineral analysis and as a radiation source for radiotherapy.Air Pollutants, Radioactive: Pollutants, present in air, which exhibit radioactivity.Background Radiation: Radiation from sources other than the source of interest. It is due to cosmic rays and natural radioactivity in the environment.